Phentermine-Topiramate Er

Drug overview for PHENTERMINE-TOPIRAMATE ER (phentermine hcl/topiramate):

Generic name: PHENTERMINE HCL/TOPIRAMATE (FEN-ter-meen/toe-PYRE-a-mate)
Drug class: Amphetamines/Anorexiants/Stimulants
Therapeutic class: Weight Loss/Gain Agents

Phentermine hydrochloride and topiramate (phentermine/topiramate) is a fixed-combination anorexigenic agent; phentermine is a sympathomimetic amine and topiramate is an anticonvulsant agent.

No enhanced Uses information available for this drug.

DRUG IMAGES

PHENTERMINE-TOPIR ER 15-92 MG
PHENTERMINE-TOPIR ER 7.5-46 MG
PHENTERMINE-TOPIR ER 11.25-69
PHENTERMINE-TOPIR ER 3.75-23MG

The following indications for PHENTERMINE-TOPIRAMATE ER (phentermine hcl/topiramate) have been approved by the FDA:

Indications:
Weight loss management for obese patient (body mass index 30 or greater)
Weight loss management for overweight patient with bmi 27 to 29 and weight-related comorbidity

Professional Synonyms:
None.

The following dosing information is available for PHENTERMINE-TOPIRAMATE ER (phentermine hcl/topiramate):

Dosing
Administration
PHENTERMINE-TOPIRAMATE ER
PHENTERMINE-TOPIRAMATE ER

Phentermine/topiramate is commercially available as capsules containing immediate-release phentermine hydrochloride and extended-release topiramate in various fixed-dose combinations. Dosage is expressed in terms of the dose of phentermine (as the free base) and dose of topiramate.

Phentermine/topiramate is administered orally as capsules once daily in the morning with or without food. (See Description.) Administration in the evening is not recommended to avoid insomnia. Patients receiving phentermine/topiramate should be monitored for possible worsening of depression, suicidality, or unusual changes in behavior during therapy. (See Suicidality Risk under Cautions: Warnings/Precautions.)

Dosing information for PHENTERMINE-TOPIRAMATE ER
DRUG LABEL	DOSING TYPE	DOSING INSTRUCTIONS
PHENTERMINE-TOPIR ER 11.25-69	Maintenance	Adults take 1 capsule by oral route once daily in the morning for 14 days
PHENTERMINE-TOPIR ER 15-92 MG	Maintenance	Adults take 1 capsule by oral route once daily in the morning
PHENTERMINE-TOPIR ER 7.5-46 MG	Maintenance	Adults take 1 capsule by oral route once daily in the morning
PHENTERMINE-TOPIR ER 3.75-23MG	Maintenance	Adults take 1 capsule by oral route once daily in the morning for 14 days

Generic dosing information for PHENTERMINE-TOPIRAMATE ER
DRUG LABEL	DOSING TYPE	DOSING INSTRUCTIONS
PHENTERMINE-TOPIR ER 11.25-69	Maintenance	Adults take 1 capsule by oral route once daily in the morning for 14 days
PHENTERMINE-TOPIR ER 15-92 MG	Maintenance	Adults take 1 capsule by oral route once daily in the morning
PHENTERMINE-TOPIR ER 7.5-46 MG	Maintenance	Adults take 1 capsule by oral route once daily in the morning
PHENTERMINE-TOPIR ER 3.75-23MG	Maintenance	Adults take 1 capsule by oral route once daily in the morning for 14 days

The following drug interaction information is available for PHENTERMINE-TOPIRAMATE ER (phentermine hcl/topiramate):

Contraindicated
Severe
Moderate

There are 2 contraindications. These drug combinations generally should not be dispensed or administered to the same patient. A manufacturer label warning that indicates the contraindication warrants inclusion of a drug combination in this category, regardless of clinical evidence or lack of clinical evidence to support the contraindication.

Drug Interaction	Drug Names
Mixed & Indirect Sympathomimetics; Oral Phenylephrine/MAOIs SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient. MECHANISM OF ACTION: Catecholamine stores increased by MAOIs can be released by indirect acting sympathomimetics such as ephedrine and amphetamine. MAO inhibitors also interfere with gut and liver metabolism of direct acting sympathomimetics (e.g oral phenylephrine). CLINICAL EFFECTS: Concurrent use of MAOIs may result in potentiation of sympathomimetic effects, which may result in headaches, hypertensive crisis, toxic neurological effects, and malignant hyperpyrexia. Fatalities have occurred. PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: Concurrent use of monoamine oxidase inhibitors and sympathomimetics is contraindicated. The manufacturers of sympathomimetic agents recommend waiting 14 days after discontinuation of MAO inhibitors before initiating the sympathomimetic. DISCUSSION: Indirect acting sympathomimetic amines may cause abrupt elevation of blood pressure when administered to patients taking monoamine oxidase inhibitors, resulting in a potentially fatal hypertensive crisis. Mixed (direct and indirect) acting sympathomimetics have also been shown to interact with monoamine oxidase inhibitors depending on their degree of indirect action. The direct-acting sympathomimetics have not been reported to interact. Dopamine is metabolized by monoamine oxidase, and its pressor effect is enhanced by monoamine oxidase inhibitors. Since procarbazine, an antineoplastic agent, is a weak monoamine oxidase inhibitor, hypertensive reactions may result from its concurrent use with indirect and mixed acting sympathomimetics. Furazolidone, an antibacterial with monoamine oxidase inhibitor action, has also been shown to interact with indirect acting sympathomimetics. Linezolid is another antibacterial with monoamine oxidase inhibitor properties. Metaxalone is a weak inhibitor of MAO. Foods containing large amounts of tyramine have also been implicated in this interaction. Methylene blue, when administered intravenously, has been shown to reach sufficient concentrations to be a potent inhibitor of MAO-A. At recommended dosages, rasagiline, oral selegiline, and transdermal selegiline up to 6mg/day are selective for MAO-B; however, at higher dosages they have been shown to lose their selectivity. One or more of the drug pairs linked to this monograph have been included in a list of interactions that should be considered "high-priority" for inclusion and should not be inactivated in EHR systems. This DDI subset was vetted by an expert panel commissioned by the U.S. Office of the National Coordinator (ONC) for Health Information Technology.	EMSAM, FURAZOLIDONE, MARPLAN, MATULANE, METAXALONE, METHYLENE BLUE, NARDIL, PARNATE, PHENELZINE SULFATE, PROCARBAZINE HCL, PROVAYBLUE, SELEGILINE HCL, TRANYLCYPROMINE SULFATE
Dihydroergotamine/Sympathomimetics SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient. MECHANISM OF ACTION: Concurrent use of dihydroergotamine and sympathomimetics may result in additive or synergistic effect on peripheral blood vessels.(1) CLINICAL EFFECTS: Concurrent use of dihydroergotamine and sympathomimetics may result in increased blood pressure due to peripheral vasoconstriction.(1) PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: Dihydroergotamine is contraindicated with sympathomimetics because the combination may result in additive or synergistic elevation of blood pressure.(1) DISCUSSION: Significant elevation in blood pressure has been reported in patients treated with dihydroergotamine.(1) Sympathomimetics can be expected to have additional effects on blood pressure.	DIHYDROERGOTAMINE MESYLATE, MIGRANAL, TRUDHESA

Drug Interaction

Drug Names

Mixed & Indirect Sympathomimetics; Oral Phenylephrine/MAOIs

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Catecholamine stores increased by MAOIs can be released by indirect acting sympathomimetics such as ephedrine and amphetamine. MAO inhibitors also interfere with gut and liver metabolism of direct acting sympathomimetics (e.g oral phenylephrine).

CLINICAL EFFECTS: Concurrent use of MAOIs may result in potentiation of sympathomimetic effects, which may result in headaches, hypertensive crisis, toxic neurological effects, and malignant hyperpyrexia. Fatalities have occurred.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Concurrent use of monoamine oxidase inhibitors and sympathomimetics is contraindicated. The manufacturers of sympathomimetic agents recommend waiting 14 days after discontinuation of MAO inhibitors before initiating the sympathomimetic.

DISCUSSION: Indirect acting sympathomimetic amines may cause abrupt elevation of blood pressure when administered to patients taking monoamine oxidase inhibitors, resulting in a potentially fatal hypertensive crisis. Mixed (direct and indirect) acting sympathomimetics have also been shown to interact with monoamine oxidase inhibitors depending on their degree of indirect action. The direct-acting sympathomimetics have not been reported to interact.

Dopamine is metabolized by monoamine oxidase, and its pressor effect is enhanced by monoamine oxidase inhibitors. Since procarbazine, an antineoplastic agent, is a weak monoamine oxidase inhibitor, hypertensive reactions may result from its concurrent use with indirect and mixed acting sympathomimetics. Furazolidone, an antibacterial with monoamine oxidase inhibitor action, has also been shown to interact with indirect acting sympathomimetics.

Linezolid is another antibacterial with monoamine oxidase inhibitor properties. Metaxalone is a weak inhibitor of MAO. Foods containing large amounts of tyramine have also been implicated in this interaction.

Methylene blue, when administered intravenously, has been shown to reach sufficient concentrations to be a potent inhibitor of MAO-A. At recommended dosages, rasagiline, oral selegiline, and transdermal selegiline up to 6mg/day are selective for MAO-B; however, at higher dosages they have been shown to lose their selectivity. One or more of the drug pairs linked to this monograph have been included in a list of interactions that should be considered "high-priority" for inclusion and should not be inactivated in EHR systems.

This DDI subset was vetted by an expert panel commissioned by the U.S. Office of the National Coordinator (ONC) for Health Information Technology.

EMSAM, FURAZOLIDONE, MARPLAN, MATULANE, METAXALONE, METHYLENE BLUE, NARDIL, PARNATE, PHENELZINE SULFATE, PROCARBAZINE HCL, PROVAYBLUE, SELEGILINE HCL, TRANYLCYPROMINE SULFATE

Dihydroergotamine/Sympathomimetics

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Concurrent use of dihydroergotamine and sympathomimetics may result in additive or synergistic effect on peripheral blood vessels.(1)

CLINICAL EFFECTS: Concurrent use of dihydroergotamine and sympathomimetics may result in increased blood pressure due to peripheral vasoconstriction.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Dihydroergotamine is contraindicated with sympathomimetics because the combination may result in additive or synergistic elevation of blood pressure.(1)

DISCUSSION: Significant elevation in blood pressure has been reported in patients treated with dihydroergotamine.(1) Sympathomimetics can be expected to have additional effects on blood pressure.

DIHYDROERGOTAMINE MESYLATE, MIGRANAL, TRUDHESA

There are 15 severe interactions. These drug interactions can produce serious consequences in most patients. Actions required for severe interactions include, but are not limited to, discontinuing one or both agents, adjusting dosage, altering administration scheduling, and providing additional patient monitoring. Review the full interaction monograph for more information.

Drug Interaction	Drug Names
Select Indirect-Acting Sympathomimetics/Tricyclic Compounds SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Unknown. However, it is speculated that indirect-acting sympathomimetics would have decreased activity due to tricyclic blockage of their uptake into the adrenergic neuron. CLINICAL EFFECTS: Decreased effect of indirect acting sympathomimetics. PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: Use of tricyclic compounds and indirect-acting sympathomimetics should be approached with caution. Montior patients receiving concurrent therapy for decreased sympathomimetic efficacy. DISCUSSION: The pressor effects of the indirect-acting sympathomimetic amines (e.g., amphetamines, ephedrine, and methylphenidate) are antagonized by tricyclic antidepressants.	AMITRIPTYLINE HCL, AMOXAPINE, ANAFRANIL, CHLORDIAZEPOXIDE-AMITRIPTYLINE, CLOMIPRAMINE HCL, DESIPRAMINE HCL, DOXEPIN HCL, IMIPRAMINE HCL, IMIPRAMINE PAMOATE, NORPRAMIN, NORTRIPTYLINE HCL, PAMELOR, PERPHENAZINE-AMITRIPTYLINE, PROTRIPTYLINE HCL, SILENOR, TRIMIPRAMINE MALEATE
Selected Anticonvulsants; Barbiturates/Contraceptives SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Barbiturates, hydantoins, and primidone may increase the metabolism of the contraceptives via CYP3A4 induction. CLINICAL EFFECTS: May observe reduced contraceptive effects such as breakthrough bleeding, spotting, or pregnancy. Effects may be seen several days after discontinuation of the anticonvulsant or barbiturate. In addition, topiramate has been associated with an increased risk of birth defects, including cleft palate. PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks. PATIENT MANAGEMENT: To avoid pregnancy, additional or alternative means of non-hormonal contraception should be utilized. Depo medroxyprogesterone may be an alternative, since its effectiveness is not decreased by anticonvulsants. Patients receiving perampanel at doses of 12 mg/day should use alternative contraception methods, such as an intra-uterine device or condom. Patients receiving topiramate may observe decreased contraceptive efficacy and increased breakthrough bleeding, especially at doses greater than 200 mg per day. Patients taking topiramate and estrogen containing or progestin-only contraceptives should be asked to report any change in their bleeding patterns.(20) Patients taking the combination of phentermine/topiramate for weight loss should be counseled that break-through bleeding may occur but is not expected to increase the risk of pregnancy. Instruct patients to report changes in bleeding patterns to their physician and to continue to take their hormonal contraceptive. Patients should not rely on hormonal contraceptives (other than implants or IUD) alone, but may use them in combination with a barrier contraceptive. It is necessary to use effective contraception with phentermine/topiramate, because the topiramate content of the product can cause birth defects. For emergency contraception, the UK's Medicines & Healthcare Products Regulatory Agency (MHRA) recommends that women who have used a CYP3A4 inducer in the previous 4 weeks should consider a non-hormonal emergency contraceptive (ie a copper IUD). If a non-hormonal emergency contraceptive is not an option, double the usual dose of levonorgestrel from 1.5 to 3 mg. Advise the patient to have a pregnancy test to exclude pregnancy after use and to seek medical advice if they do become pregnant. DISCUSSION: Decreased effectiveness of oral contraceptives, characterized by breakthrough bleeding and amenorrhea have been documented. Through August, 2010, Australia's Therapeutic Goods Association had received 32 reports of contraceptive failure leading to pregnancy as a result of a suspected interaction between etonogestrel implants and carbamazepine. In a randomized, open-label study in healthy women, concurrent topiramate (50 mg daily to 200 mg daily) and Ortho Novum 1/35 (ethinyl estradiol and norethindrone) resulted in no changes in levels of ethinyl estradiol or norethindrone. However, in another study, concurrent topiramate at doses of 200 mg daily, 400 mg daily, and 800 mg daily with valproic acid decreased the area-under-curve (AUC) of ethinyl estradiol by 18%, 21%, and 30%, respectively. There were no changes in norethindrone levels. The US manufacturer of topiramate states that the possibility of decreased contraceptive effectiveness should be considered. At doses of 12 mg/day, perampanel decreased the maximum concentration (Cmax) and AUC of levonorgestrel by 40% each. The Cmax of ethinyl estradiol was decreased by 18%. There were no effects on ethinyl estradiol AUC. Doses of perampanel of 4 mg/day and 8 mg/day had no effect on contraceptive levels. The combination of phentermine/topiramate (15 mg/92 mg for 15 days) increased the Cmax and AUC of norethindrone by 22% and 16%, respectively. The Cmax and AUC of ethinyl estradiol decreased 8% and 16%, respectively. Because contraceptive efficacy is primarily determined by the progestin component, no effect on contraceptive efficacy is expected, although breakthrough bleeding may occur. The effectiveness of depo medroxyprogesterone is not decreased by anticonvulsants or barbiturates.	2-METHOXYESTRADIOL, AFIRMELLE, ALTAVERA, ALYACEN, AMETHIA, AMETHYST, ANNOVERA, APRI, ARANELLE, ASHLYNA, AUBRA, AUBRA EQ, AUROVELA, AUROVELA 24 FE, AUROVELA FE, AVERI, AVIANE, AYUNA, AZURETTE, BALCOLTRA, BALZIVA, BEYAZ, BLISOVI 24 FE, BLISOVI FE, BRIELLYN, CAMILA, CAMRESE, CAMRESE LO, CAZIANT, CHARLOTTE 24 FE, CHATEAL EQ, CRYSELLE, CYRED, CYRED EQ, DASETTA, DAYSEE, DEBLITANE, DESOGESTR-ETH ESTRAD ETH ESTRA, DIETHYLSTILBESTROL, DOLISHALE, DROSPIRENONE-ETH ESTRA-LEVOMEF, DROSPIRENONE-ETHINYL ESTRADIOL, ELINEST, ELURYNG, EMZAHH, ENILLORING, ENPRESSE, ENSKYCE, ERRIN, ESTARYLLA, ESTRADIOL, ESTRADIOL BENZOATE, ESTRADIOL CYPIONATE, ESTRADIOL HEMIHYDRATE, ESTRADIOL HEMIHYDRATE MICRO, ESTRADIOL MICRONIZED, ESTRADIOL VALERATE, ESTRIOL, ESTRIOL MICRONIZED, ESTRONE, ETHINYL ESTRADIOL, ETHYNODIOL-ETHINYL ESTRADIOL, ETONOGESTREL-ETHINYL ESTRADIOL, FALMINA, FEIRZA, FEMLYV, FINZALA, GALBRIELA, GEMMILY, HAILEY, HAILEY 24 FE, HAILEY FE, HALOETTE, HEATHER, ICLEVIA, INCASSIA, INTROVALE, ISIBLOOM, JAIMIESS, JASMIEL, JENCYCLA, JOLESSA, JOYEAUX, JULEBER, JUNEL, JUNEL FE, JUNEL FE 24, KAITLIB FE, KALLIGA, KARIVA, KELNOR 1-35, KELNOR 1-50, KURVELO, LARIN, LARIN 24 FE, LARIN FE, LEENA, LESSINA, LEVONEST, LEVONORG-ETH ESTRAD ETH ESTRAD, LEVONORG-ETH ESTRAD-FE BISGLYC, LEVONORGESTREL-ETH ESTRADIOL, LEVORA-28, LO LOESTRIN FE, LO-ZUMANDIMINE, LOESTRIN, LOESTRIN FE, LOJAIMIESS, LORYNA, LOW-OGESTREL, LUTERA, LYLEQ, LYZA, MARLISSA, MELEYA, MERZEE, MIBELAS 24 FE, MICROGESTIN, MICROGESTIN FE, MILI, MINZOYA, MONO-LINYAH, NATAZIA, NECON, NEXPLANON, NEXTSTELLIS, NIKKI, NORA-BE, NORELGESTROMIN-ETH ESTRADIOL, NORETHIN-ETH ESTRA-FERROUS FUM, NORETHINDRON-ETHINYL ESTRADIOL, NORETHINDRONE, NORETHINDRONE-E.ESTRADIOL-IRON, NORGESTIMATE-ETHINYL ESTRADIOL, NORTREL, NUVARING, NYLIA, OCELLA, ORQUIDEA, ORTHO TRI-CYCLEN, ORTHO-NOVUM, PHILITH, PIMTREA, PORTIA, RECLIPSEN, RIVELSA, ROSYRAH, SAFYRAL, SETLAKIN, SHAROBEL, SIMLIYA, SIMPESSE, SLYND, SPRINTEC, SRONYX, SYEDA, TARINA 24 FE, TARINA FE, TARINA FE 1-20 EQ, TAYTULLA, TILIA FE, TRI-ESTARYLLA, TRI-LEGEST FE, TRI-LINYAH, TRI-LO-ESTARYLLA, TRI-LO-MARZIA, TRI-LO-MILI, TRI-LO-SPRINTEC, TRI-MILI, TRI-SPRINTEC, TRI-VYLIBRA, TRI-VYLIBRA LO, TULANA, TURQOZ, TWIRLA, TYBLUME, VALTYA, VELIVET, VESTURA, VIENVA, VIORELE, VOLNEA, VYFEMLA, VYLIBRA, WERA, WYMZYA FE, XARAH FE, XELRIA FE, XULANE, YASMIN 28, YAZ, ZAFEMY, ZARAH, ZOVIA 1-35, ZUMANDIMINE
Ergot Alkaloids/Sympathomimetics SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Concurrent use of ergot alkaloids and sympathomimetics may result in additive or synergistic effect on peripheral blood vessels. CLINICAL EFFECTS: Concurrent use of ergot alkaloids and sympathomimetics may result in increased blood pressure due to peripheral vasoconstriction. PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: When possible, avoid the concurrent use of ergot alkaloids and sympathomimetics. If concurrent use is warranted, monitor blood pressure and for signs of vasoconstriction. Decreasing the dose of one or both drugs may be necessary. DISCUSSION: There have been reports of severe vasoconstriction resulting in gangrene in patients receiving intravenous ergonovine with dopamine or norepinephrine.	ERGOLOID MESYLATES, ERGOMAR, ERGOTAMINE TARTRATE, ERGOTAMINE-CAFFEINE, METHYLERGONOVINE MALEATE, METHYSERGIDE MALEATE, MIGERGOT
Guanethidine/Sympathomimetics (Indirect Acting) SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Indirect-acting sympathomimetics may displace guanethidine from adrenergic neurons, thereby antagonizing the clinical effect. CLINICAL EFFECTS: Blood pressure may be increased. PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: When possible, use an alternative antihypertensive agent or sympathomimetic. DISCUSSION: This interaction has been demonstrated with concomitant administration of anorexiant-type indirect-acting sympathomimetics and guanethidine. Increased blood pressure has been reported.	GUANETHIDINE HEMISULFATE
Topiramate/Carbonic Anhydrase Inhibitors SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Topiramate is a weak carbonic anhydrase inhibitor and can induce renal bicarbonate loss, resulting in metabolic acidosis. It can also reduce urinary citrate excretion and increase urinary pH, posing a risk for nephrolithiasis. As well, carbonic anhydrase inhibitors can cause decreased sweating and elevated body temperature, predisposing patients to heat-related disorders.(1) CLINICAL EFFECTS: The concurrent use of topiramate with another carbonic anhydrase inhibitor may increase the risk of metabolic acidosis and kidney stone formation.(1) Concurrent use of topiramate with other carbonic anhydrase inhibitors may increase the incidence of oligohidrosis and hyperthermia, especially in pediatric or adolescent patients.(1-2) Overheating and dehydration can lead to brain damage and death. PREDISPOSING FACTORS: Patients with conditions that predispose to acidosis (such as renal disease, severe respiratory disorders, status epilepticus, diarrhea, and being on a ketogenic diet) may be at increased risk of experiencing adverse effects from concurrent carbonic anhydrase inhibitors.(1) Pediatric and adolescent patients and patients with dehydration may be more likely to experience heat-related disorders.(1) PATIENT MANAGEMENT: The US manufacturer of topiramate states that the concurrent use of topiramate with other carbonic anhydrase inhibitors should be avoided. Patients receiving concurrent therapy should be monitored for the appearance of or worsening of metabolic acidosis, nephrolithiasis, and hyperthermia.(1) Check serum bicarbonate at baseline and periodically during treatment. Monitor for signs and symptoms of metabolic acidosis: hyperventilation, fatigue, anorexia, arrhthymias, stupor. Monitor for signs and symptoms of heat stroke: skin feels very hot with little or no sweating, confusion, muscle cramps, rapid heartbeat, or rapid breathing. Monitor for signs and symptoms of dehydration: dry mouth, urinating less than usual, dark-colored urine, dry skin, feeling tired, dizziness, or irritability. If signs or symptoms of metabolic acidosis, dehydration, oligohidrosis, or elevated body temperature occur, a decreased dose or discontinuation of zonisamide should be considered. DISCUSSION: Topiramate is a weak carbonic anhydrase inhibitor. Carbonic anhydrase inhibitors increase urinary bicarbonate excretion, reduce urinary citrate excretion and increase urinary pH. Concurrent use of topiramate with other carbonic anhydrase inhibitors may increase the risk of metabolic acidosis and kidney stone formation and should therefore be avoided.(1) Case reports of decreased sweating and elevated temperature have been reported, especially in pediatric patients. Some cases resulted in heat stroke that required hospital treatment.(1)	ACETAZOLAMIDE, ACETAZOLAMIDE ER, ACETAZOLAMIDE SODIUM, DICHLORPHENAMIDE, KEVEYIS, METHAZOLAMIDE, ORMALVI
Selected Inhalation Anesthetic Agents/Sympathomimetics SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: The exact mechanism is unknown. The anesthetics produce conduction changes that increase impulse re-entry into the myocardial tissue.(1) The anesthetics' ability to precipitate arrhythmias is enhanced by elevated arterial blood pressure, tachycardia, hypercapnia, and/or hypoxia, events that stimulate the release of endogenous catecholamines.(1) CLINICAL EFFECTS: Concurrent use of inhalation anesthetic agents and sympathomimetics may result in ventricular arrhythmias or sudden blood pressure and heart rate increase during surgery.(2) PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: Monitor blood pressure and avoid use of sympathomimetics in patients being treated with anesthetics on the day of surgery.(2) Intravenous use of epinephrine during surgery with halothane and related halogenated general anesthetics should be strongly discouraged. When intravenous epinephrine is necessary, nitrous oxide anesthesia supplemented with ether, muscle relaxants, or opioids should be used instead of halothane.(3,4) Epinephrine may safely be used subcutaneously with the following precautions: the patient is adequately ventilated to prevent hypoxia or respiratory acidosis; the total dose of epinephrine is limited to 100 mcg/10 minute period or 300 mcg/hour in adults, 3.5 mcg/Kg in infants, 2.5 mcg/Kg in children up to two years of age, and 1.45 mcg/Kg in children over two years of age; a minimum effective concentration of anesthetic is maintained; the drugs are not co-administered in patients with hypertension or other cardiovascular disorders; and the cardiac rhythm is continuously monitored during and after injection.(3-10) If arrhythmias occur after the administration of the epinephrine, the drugs of choice are lidocaine or propranolol, depending on the type of arrhythmia.(1) DISCUSSION: Administration of epinephrine during halothane anesthesia may may lead to serious ventricular arrhythmias.(3-6,11-18) This has occurred when epinephrine was administered intravenously,(6) when it was administered with lidocaine as a dental block,(11,14) or when it was administered supraperiosteally.(5) Norepinephrine has been shown to interact with halothane in a manner similar to epinephrine.(1) In two case reports, patients were given terbutaline (0.25 to 0.35 mg) for wheezing following induction of anesthesia with halothane. One patient's heart rate increased from 68 to 100 beats/minute, and the ECG showed premature ventricular contractions and bigeminy, while the other patient developed multiple unifocal premature ventricular contractions and bigeminy. The arrhythmias resolved in both patients following lidocaine administration.(19) Although not documented, isoproterenol causes effects on the heart similar to terbutaline(20) and would probably interact with halothane in a similar manner. Other inhalation anesthetics that increase the incidence of arrhythmias with epinephrine include chloroform,(20) methoxyflurane,(20) and enflurane.(12) A similar interaction may be expected between the other inhalation anesthetics and sympathomimetics.	DESFLURANE, FORANE, ISOFLURANE, SEVOFLURANE, SUPRANE, TERRELL, ULTANE
Mixed & Indirect Sympathomimetics; Oral Phenylephrine/Selected MAOIs SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Catecholamine stores increased by MAOIs can be released by indirect acting sympathomimetics such as ephedrine and amphetamine. MAO inhibitors also interfere with gut and liver metabolism of direct acting sympathomimetics (e.g oral phenylephrine). CLINICAL EFFECTS: Concurrent use of MAOIs may result in potentiation of sympathomimetic effects, which may result in headaches, hypertensive crisis, toxic neurological effects, and malignant hyperpyrexia. Fatalities have occurred with combinations of sympathomimetics and MAO-A inhibitors. PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: Concurrent use of MAO-A inhibitors and sympathomimetics is contraindicated. The manufacturers of sympathomimetic agents recommend waiting 14 days after discontinuation of MAO inhibitors before initiating the sympathomimetic. Patients receiving indirect acting sympathomimetics should not receive linezolid unless they are monitored for potential increases in blood pressure. Initial dosages of dopamine should be reduced. At recommended dosages, oral selegiline and transdermal selegiline up to 6mg/day are selective for MAO-B; however, at higher dosages they have been shown to lose their selectivity. Patients receiving higher dosages of selegiline should be considered susceptive to this interaction. DISCUSSION: Indirect acting sympathomimetic amines may cause abrupt elevation of blood pressure when administered to patients taking monoamine oxidase inhibitors, resulting in a potentially fatal hypertensive crisis. Mixed (direct and indirect) acting sympathomimetics have also been shown to interact with monoamine oxidase inhibitors depending on their degree of indirect action. The direct-acting sympathomimetics have not been reported to interact. Dopamine is metabolized by monoamine oxidase, and its pressor effect is enhanced by monoamine oxidase inhibitors. Furazolidone, an antibacterial with monoamine oxidase inhibitor action, has also been shown to interact with indirect acting sympathomimetics. Foods containing large amounts of tyramine have also been implicated in this interaction. A significant pressor response was observed in normal subjects receiving linezolid and tyramine doses of more than 100 mg. Administration of linezolid (600 mg BID for 3 days) with pseudoephedrine (60 mg q 4 hours for 2 doses) increased blood pressure by 32 mmHg. Administration of linezolid (600 mg BID for 3 days) with phenylpropanolamine (25 mg q 4 hours for 2 doses) increased blood pressure by 38 mmHg. One or more of the drug pairs linked to this monograph have been included in a list of interactions that should be considered "high-priority" for inclusion and should not be inactivated in EHR systems. This DDI subset was vetted by an expert panel commissioned by the U.S. Office of the National Coordinator (ONC) for Health Information Technology.	EMSAM, LINEZOLID, LINEZOLID-0.9% NACL, LINEZOLID-D5W, SELEGILINE HCL, XADAGO, ZELAPAR, ZYVOX
Ioflupane I 123/Dopamine Transporter Binders SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Ioflupane binds to the dopamine transporter. Agents that also bind to this transporter may affect the results of single photon emission computed tomography (SPECT) brain imaging using ioflupane.(1) CLINICAL EFFECTS: SPECT imaging using ioflupane may not be accurate in patients taking other drugs that bind to the dopamine transporter binders.(1) PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: It is unknown if discontinuing other agents that bind to the dopamine transporter prior to a scan with ioflupane will decrease interference with the scan.(1) Make sure the radiologist interpreting the scan knows the patient is taking another agent that binds to the dopamine transporter. Alternative diagnostic tools may need to be considered. DISCUSSION: Ioflupane binds to the dopamine transporter. Agents that also bind to this transporter may affect the results of the scan. These agents include amoxapine, amphetamine, armodafinil, benztropine, bupropion, buspirone, citalopram, cocaine, dexmethylphenidate, escitalopram, fluoxetine, fluvoxamine, mazindol, methamphetamine, methylphenidate, modafinil, norephedrine, paroxetine, phentermine, phenylpropanolamine, selegiline, and sertraline.(1)	DATSCAN, IOFLUPANE I-123
Iobenguane I 123/Agents that Affect Catecholamines SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Many compounds that reduce catecholamine uptake or that deplete catecholamine stores may interfere with iobenguane uptake into cells.(1) CLINICAL EFFECTS: Compounds that reduce catecholamine uptake or that deplete catecholamine stores may interfere with imaging completed with iobenguane.(1) PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: Discuss the use of agents that affect catecholamines. Discontinue drugs that reduce catecholamine uptake or deplete catecholamine stores prior to imaging with iobenguane. Before imaging with iobenguane, discontinue agents that affect catecholamines for at least 5 biological half-lives, as clinically tolerated.(1) DISCUSSION: Many agents may reduce catecholamine uptake or deplete catecholamine stores.(1) Examples include: - CNS stimulants or amphetamines (e.g. cocaine, methylphenidate, dextroamphetamine) - norepinephrine and dopamine reuptake inhibitors (e.g. phentermine) - norepinephrine and serotonin reuptake inhibitors (e.g. tramadol) - monoamine oxidase inhibitors (e.g. phenelzine, linezolid) - central monoamine depleting drugs (e.g. reserpine) - non-select beta adrenergic blocking drugs (e.g. labetalol) - alpha agonists or alpha/beta agonists (e.g. pseudoephedrine, phenylephrine, ephedrine, phenylpropanolamine, naphazoline) - tricyclic antidepressants or norepinephrine reuptake inhibitors (e.g. amitriptyline, bupropion, duloxetine, mirtazapine, venlafaxine) - botanicals that may inhibit reuptake of norepinephrine, serotonin or dopamine (e.g. ephedra, ma huang, St. John's Wort, yohimbine)	ADREVIEW
Zonisamide/Carbonic Anhydrase Inhibitors SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Zonisamide is a carbonic anhydrase inhibitor and can induce renal bicarbonate loss, resulting in metabolic acidosis. It can also reduce urinary citrate excretion and increase urinary pH, posing a risk for nephrolithiasis. As well, carbonic anhydrase inhibitors can cause decreased sweating and elevated body temperature, predisposing patients to heat-related disorders. Concurrent use of zonisamide with other carbonic anhydrase inhibitors may result in an additive risk of all these effects.(1-2) CLINICAL EFFECTS: The concurrent use of zonisamide with another carbonic anhydrase inhibitor may increase the risk of metabolic acidosis and kidney stone formation.(1) Concurrent use of zonisamide with other carbonic anhydrase inhibitors may increase the incidence of oligohidrosis and hyperthermia, especially in pediatric or adolescent patients.(1-2) Overheating and dehydration can lead to brain damage and death. PREDISPOSING FACTORS: Patients with conditions that predispose to acidosis (such as renal disease, severe respiratory disorders, status epilepticus, diarrhea, and being on a ketogenic diet) may be at increased risk of experiencing adverse effects from concurrent carbonic anhydrase inhibitors.(1) Pediatric and adolescent patients and patients with dehydration may be more likely to experience heat-related disorders.(1) PATIENT MANAGEMENT: The UK and US manufacturers of zonisamide state that caution should be used in adults when zonisamide is prescribed with other carbonic anhydrase inhibitors.(1-2) Pediatric and adolescent patients must not take carbonic anhydrase inhibitors concurrently with zonisamide.(1) Check serum bicarbonate at baseline and periodically during treatment. Monitor for signs and symptoms of metabolic acidosis: hyperventilation, fatigue, anorexia, arrhthymias, stupor. Monitor for signs and symptoms of heat stroke: skin feels very hot with little or no sweating, confusion, muscle cramps, rapid heartbeat, or rapid breathing. Monitor for signs and symptoms of dehydration: dry mouth, urinating less than usual, dark-colored urine, dry skin, feeling tired, dizziness, or irritability. If signs or symptoms of metabolic acidosis, dehydration, oligohidrosis, or elevated body temperature occur, a decreased dose or discontinuation of zonisamide should be considered. DISCUSSION: Zonisamide is a carbonic anhydrase inhibitor. Carbonic anhydrase inhibitors increase urinary bicarbonate excretion, reduce urinary citrate excretion and increase urinary pH. Concurrent use of zonisamide with other carbonic anhydrase inhibitors may increase the risk of metabolic acidosis and kidney stone formation and should therefore be avoided.(1) Case reports of decreased sweating and elevated temperature have been reported, especially in pediatric patients. Some cases resulted in heat stroke that required hospital treatment and resulted in death.(1)	ZONEGRAN, ZONISADE, ZONISAMIDE
Ulipristal/Selected Anticonvulsants SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Eslicarbazepine, mephenytoin, oxcarbazepine, rufinamide, and topiramate may induce the metabolism of ulipristal by CYP3A4.(1,2) CLINICAL EFFECTS: Concurrent use or use of eslicarbazepine, mephenytoin, oxcarbazepine, rufinamide, or topiramate within the previous 2-3 weeks may result in decreased levels and effectiveness of ulipristal.(1,2) In addition, topiramate has been associated with an increased risk of birth defects, including cleft palate.(3) PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: The US and UK manufacturers of ulipristal states that concurrent use with CYP3A4 inducers such as eslicarbazepine, mephenytoin, oxcarbazepine, rufinamide, or topiramate is not recommended. Decreased effectiveness of ulipristal may occur even 2-3 weeks after discontinuation of these agents.(1,2) DISCUSSION: CYP3A4 inducers may decrease levels and effectiveness of ulipristal. Enzyme induction may take 2-3 weeks to wear off. Plasma levels of ulipristal may be reduced even if the CYP3A4 inducer was discontinued in the previous 2-3 weeks.(1) Concurrent administration of ulipristal 30 mg and rifampin 600 mg, another CYP3A4 inducer, for 9 days decreased the maximum concentration (Cmax) and area-under-the-curve (AUC) by 90% and 93%, respectively. The Cmax and AUC of monodemethyl-ulipristal decreased by 84% and 90%, respectively.(2)	ELLA
Atogepant/CYP3A4 Inducers SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Strong, moderate, and weak CYP3A4 inducers may increase the metabolism of atogepant by CYP3A4.(1) CLINICAL EFFECTS: The concurrent use of strong, moderate, or weak CYP3A4 inducers with atogepant may result in decreased levels and clinical effectiveness of atogepant.(1) PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks. PATIENT MANAGEMENT: The manufacturer of atogepant recommends that patients on concomitant strong, moderate, or weak CYP3A4 inducers receive atogepant 30 mg or 60 mg once daily for prevention of episodic migraines and avoid use of atogepant for prevention of chronic migraines.(1) Patients receiving concurrent therapy with CYP3A4 inducers and atogepant should be observed for decreased clinical effectiveness. DISCUSSION: In a study of healthy subjects, rifampin, a strong CYP3A4 inducer, decreased the area-under-curve (AUC) and maximum concentration (Cmax) of atogepant by 60% and 30%, respectively. Topiramate, a weak CYP3A4 inducer, decreased atogepant AUC and Cmax by 25% and 24%, respectively.(1) Strong CYP3A4 inducers linked to this monograph include: apalutamide, barbiturates, carbamazepine, enzalutamide, fosphenytoin, ivosidenib, lumacaftor, mitotane, phenobarbital, phenytoin, primidone, rifampin, rifapentine, and St. John's wort. Moderate CYP3A4 inducers linked to this monograph include: belzutifan, bosentan, cenobamate, dabrafenib, dipyrone, efavirenz, elagolix, etravirine, lesinurad, lorlatinib, mavacamten, mitapivat, modafinil, nafcillin, pacritinib, pexidartinib, repotrectinib, rifabutin, sotorasib, telotristat, thioridazine and tovorafenib. Weak CYP3A4 inducers linked to this monograph include: armodafinil, bexarotene, brigatinib, brivaracetam, clobazam, danshen, darolutamide, dexamethasone, dicloxacillin, echinacea, eslicarbazepine, floxacillin, garlic, genistein, ginseng, glycyrrhizin, methylprednisolone, mobocertinib, nevirapine, omaveloxolone, oritavancin, oxcarbazepine, pioglitazone, pitolisant, quercetin, relugolix, rufinamide, sarilumab, sulfinpyrazone, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vemurafenib, vinblastine, and zanubrutinib.(1,2)	QULIPTA
Mixed & Indirect Sympathomimetics; Oral Phenylephrine/Rasagiline SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Catecholamine stores increased by MAOIs can be released by indirect acting sympathomimetics such as ephedrine and amphetamine. MAO inhibitors also interfere with gut and liver metabolism of direct acting sympathomimetics (e.g oral phenylephrine). CLINICAL EFFECTS: Concurrent use of MAOIs may result in potentiation of sympathomimetic effects, which may result in headaches, hypertensive crisis, toxic neurological effects, and malignant hyperpyrexia. Hypertensive crisis has been reported in patients taking recommended doses of rasagiline with sympathomimetic agents. PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: At recommended dosages, rasagiline is selective for MAO-B; however, at higher dosages it has been shown to lose its selectivity. Patients receiving higher dosages of rasagiline should be considered susceptive to this interaction. Concurrent use should be approached with caution. DISCUSSION: Indirect acting sympathomimetic amines may cause abrupt elevation of blood pressure when administered to patients taking monoamine oxidase inhibitors, resulting in a potentially fatal hypertensive crisis. Mixed (direct and indirect) acting sympathomimetics have also been shown to interact with monoamine oxidase inhibitors depending on their degree of indirect action. The direct-acting sympathomimetics have not been reported to interact. Dopamine is metabolized by monoamine oxidase, and its pressor effect is enhanced by monoamine oxidase inhibitors.	AZILECT, RASAGILINE MESYLATE
Erlotinib/CYP3A4 Inducers SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Inducers of CYP3A4 may induce the metabolism of erlotinib.(1) CLINICAL EFFECTS: Concurrent or recent use of a CYP3A4 inducer may result in decreased levels and effectiveness of erlotinib.(1) PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks. PATIENT MANAGEMENT: Avoid the concurrent use of CYP3A4 inducers in patients receiving therapy with erlotinib. Consider the use of alternative agents with less enzyme induction potential.(1) Consider increasing the dosage of erlotinib by 50 mg increments as tolerated at two week intervals (to a maximum of 450 mg) while closely monitoring the patient. The highest dosage studied with concurrent rifampin is 450 mg. If the dosage of erlotinib is increased, it will need to be decreased when the inducer is discontinued.(1) DISCUSSION: Pretreatment and concurrent therapy with rifampin increased erlotinib clearance by 3-fold and decreased the erlotinib area-under-curve (AUC) by 66% to 80%. This is equivalent to a dose of about 30 mg to 50 mg in NSCLC.(1) In a study, pretreatment with rifampin for 11 days decreased the AUC of a single 450 mg dose of erlotinib to 57.6% of the AUC observed with a single 150 mg dose of erlotinib.(1) In a case report, coadministration of phenytoin (180mg daily) and erlotinib (150mg daily) increased the phenytoin concentration from 8.2mcg/ml to 24.2mcg/ml and decreased the erlotinib concentration 12-fold (from 1.77mcg/ml to 0.15mcg/ml) and increased the erlotinib clearance by 10-fold (from 3.53 L/h to 41.7 L/h).(2) In a study, concurrent use of sorafenib (400 mg twice daily) and erlotinib (150 mg daily) decreased the concentration minimum (Cmin), concentration maximum (Cmax), and AUC of erlotinib.(3) In an animal study, concurrent use of dexamethasone and erlotinib decreased the AUC of erlotinib by 0.6-fold.(4) Strong inducers of CYP3A4 include: barbiturates, encorafenib, enzalutamide, fosphenytoin, ivosidenib, mitotane, phenobarbital, phenytoin, primidone, rifampin, and rifapentine.(5,6) Moderate inducers of CYP3A4 include: belzutifan, bosentan, cenobamate, dabrafenib, dipyrone, efavirenz, elagolix, etravirine, lesinurad, lorlatinib, mavacamten, mitapivat, modafinil, nafcillin, pacritinib, pexidartinib, repotrectinib, sotorasib, telotristat, thioridazine, and tovorafenib.(5,6) Weak inducers of CYP3A4 include: amprenavir, armodafinil, bexarotene, brigatinib, brivaracetam, clobazam, danshen, darolutamide, dicloxacillin, echinacea, eslicarbazepine, flucloxacillin, garlic, genistein, ginkgo, ginseng, glycyrrhizin, mobocertinib, nevirapine, omaveloxolone, oritavancin, oxcarbazepine, pioglitazone, pitolisant, quercetin, relugolix, rufinamide, sarilumab, sulfinpyrazone, sunvozertinib, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vemurafenib, vinblastine, and zanubrutinib.(5,6)	ERLOTINIB HCL
Zuranolone/CYP3A4 Inducers SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction. MECHANISM OF ACTION: Inducers of CYP3A4 may induce the metabolism of zuranolone.(1) CLINICAL EFFECTS: Concurrent use of a CYP3A4 inducer may result in a loss of zuranolone efficacy.(1) PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks. PATIENT MANAGEMENT: Avoid the concurrent use of zuranolone with CYP3A4 inducers.(1) DISCUSSION: Coadministration of zuranolone with rifampin decreased the maximum concentration (Cmax) by 0.31-fold and area-under-curve (AUC) by 0.15-fold.(1) Strong CYP3A4 inducers linked to this monograph include: apalutamide, barbiturates, carbamazepine, encorafenib, enzalutamide, fosphenytoin, ivosidenib, lumacaftor, mitotane, phenobarbital, phenytoin, primidone, rifampin, rifapentine, and St. John's wort. Moderate CYP3A4 inducers linked to this monograph include: belzutifan, bosentan, cenobamate, dabrafenib, dipyrone, efavirenz, elagolix, etravirine, lesinurad, lorlatinib, mavacamten, mitapivat, modafinil, nafcillin, pacritinib, pexidartinib, repotrectinib, rifabutin, sotorasib, telotristat ethyl, thioridazine, and tovorafenib. Weak CYP3A4 inducers linked to this monograph include: armodafinil, bexarotene, brigatinib, brivaracetam, clobazam, danshen, darolutamide, dexamethasone, dicloxacillin, echinacea, eslicarbazepine, flucloxacillin, garlic, genistein, ginseng, glycyrrhizin, methylprednisolone, mobocertinib, nevirapine, omaveloxolone, oritavancin, oxcarbazepine, pioglitazone, pitolisant, quercetin, relugolix, rufinamide, sarilumab, sulfinpyrazone, sunvozertinib, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vemurafenib, vinblastine, and zanubrutinib.(2,3)	ZURZUVAE

There are 10 moderate interactions. The clinician should assess the patient’s characteristics and take action as needed. Actions required for moderate interactions include, but are not limited to, discontinuing one or both agents, adjusting dosage, altering administration.

Drug Interaction	Drug Names
Amphetamines; Phentermine/SSRIs; SNRIs SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed. MECHANISM OF ACTION: Amphetamines may affect serotonin release and/or reuptake, depending on their molecular structure. Ring substitution tends to increase amphetamine-induced release of endogenous serotonin. However, the effect on serotonin release may also be dose related and is more likely if the amphetamine is taken in doses greater than those approved and generally employed in treating Attention-deficit-hyperactivity-disorder, or if abused, especially over long periods of time.(1) Amphetamines, phentermine and serotonin-norepinephrine reuptake inhibitors(SNRIs) may have additive effects on blood pressure. CLINICAL EFFECTS: Concurrent use of amphetamines with agents that affect serotonin may increase the risk of serotonin syndrome. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(8) Concurrent use of amphetamines or phentermine and a SNRI may increase the risk for high blood pressure or make hypertension more difficult to control. SSRIs and SNRIs linked to this monograph are: citalopram, desvenlafaxine, duloxetine, escitalopram, fluoxetine, fluvoxamine, levomilnacipran, milnacipran, paroxetine, sertraline, venlafaxine, vilazodone and vortioxetine. PREDISPOSING FACTORS: High doses or long-term abuse of amphetamines may increase the risk of this interaction. PATIENT MANAGEMENT: The concurrent use of amphetamines with SSRIs or SNRIs should be approached with appropriate monitoring. Instruct patients receiving concurrent therapy to report any signs or symptoms of serotonin syndrome immediately. Monitor blood pressure during concurrent therapy and adjust dosage or change medication for persistent increases in blood pressure. If concurrent therapy is warranted, patients should be monitored for signs and symptoms of serotonin syndrome. Instruct patients to report muscle twitching, tremors, shivering and stiffness, fever, heavy sweating, heart palpitations, restlessness, confusion, agitation, trouble with coordination, or severe diarrhea. DISCUSSION: In a case report, a 13 year-old female experienced tachycardia when amphetamine was added to her sertraline regimen.(2) Increased side effects have also been reported in patients maintained on fluoxetine who ingested illicit amphetamines.(3) In a case report, a 22 year-old female had previously been taking phentermine and oral contraceptive agents. The patient stopped taking phentermine and, after an undetermined length of time, started taking fluoxetine (20 mg daily). The patient discontinued her fluoxetine after three months. Eight days later, she took one dose of phentermine (30 mg). Within several hours, she developed jitteriness, stomach cramps, dry eyes, palpitations, and tremors. The patient received once dose of lorazepam (1.5 mg) and her symptoms resolved over night.(4) In a case report, a 32 year-old male developed agitation, anxiety, shivering, tremors, and diaphoresis two weeks after adding venlafaxine to his dexamphetamine.(5) There have also been reports of safe and effective use of amphetamines with fluoxetine,(6) dextroamphetamine and sertraline,(6) and dextroamphetamine with fluoxetine.(7)	CELEXA, CITALOPRAM HBR, DESVENLAFAXINE ER, DESVENLAFAXINE SUCCINATE ER, DRIZALMA SPRINKLE, DULOXETINE HCL, DULOXICAINE, EFFEXOR XR, ESCITALOPRAM OXALATE, FETZIMA, FLUOXETINE DR, FLUOXETINE HCL, FLUVOXAMINE MALEATE, FLUVOXAMINE MALEATE ER, LEXAPRO, OLANZAPINE-FLUOXETINE HCL, PAROXETINE CR, PAROXETINE ER, PAROXETINE HCL, PAROXETINE MESYLATE, PAXIL, PAXIL CR, PRISTIQ, PROZAC, SAVELLA, SERTRALINE HCL, TRINTELLIX, VENLAFAXINE BESYLATE ER, VENLAFAXINE HCL, VENLAFAXINE HCL ER, VIIBRYD, VILAZODONE HCL, ZOLOFT
Valproic Acid Derivatives/Topiramate SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed. MECHANISM OF ACTION: The exact mechanism is unknown, but a pharmacokinetic interaction does not occur.(1-4) Topiramate may contribute to increased ammonia levels by inhibiting carbonic anhydrase and cerebral glutamine.(5) Concurrent use may exacerbate or unmask existing metabolism defects.(1-4) CLINICAL EFFECTS: Concurrent use of valproic acid or its derivatives and topiramate may increase the risk of hyperammonemia with or without encephalopathy. Hyperammonemic encephalopathy may present as changes in state of consciousness and/or cognitive function with lethargy and vomiting.(1-4) Concurrent use has also resulted in hypothermia.(1) PREDISPOSING FACTORS: The risk of hyperammonemia with or without encephalopathy may be increased in patients with inborn metabolism errors or decreased hepatic mitochondrial activity.(1-4) PATIENT MANAGEMENT: In patients receiving concurrent valproic acid derivatives and topiramate, monitor for unexplained lethargy, vomiting, and/ or changes in mental status. If these symptoms develop, check the patient's ammonia level.(1-4) The valproic acid derivative and/or topiramate may need to be discontinued if hyperammonemia develops.(1-3) DISCUSSION: There have been several reports of hyperammonemia with and without encephalopathy in patients receiving concurrent valproic acid derivatives and topiramate.(1-12) In many of these reports, the patients tolerated the valproic acid derivative alone, but developed hyperammonemia with or without encephalopathy following the addition of topiramate.(1-9) Two clinical trials showed no clinically significant pharmacokinetic interaction between valproic acid and topiramate.(12,13)	DEPAKOTE, DEPAKOTE ER, DEPAKOTE SPRINKLE, DIVALPROEX SODIUM, DIVALPROEX SODIUM ER, SODIUM VALPROATE, VALPROATE SODIUM, VALPROIC ACID
Exemestane/Selected Moderate-Weak CYP3A4 Inducers SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed. MECHANISM OF ACTION: CYP3A4 inducers may induce the metabolism of exemestane.(1) CLINICAL EFFECTS: Concurrent use of a CYP3A4 inducer may result in decreased levels and effectiveness of exemestane.(1) PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks. PATIENT MANAGEMENT: The US manufacturer of exemestane recommends that patients receiving concurrent therapy with a strong CYP3A4 inducer receive 50 mg of exemestane daily after a meal.(1) It may be prudent to consider a dosage increase for patients receiving weaker CYP3A4 inducers. DISCUSSION: In a study in 10 healthy postmenopausal subjects, pretreatment with rifampin (a strong CYP3A4 inducer, 600 mg daily for 14 days) decreased the area-under-curve (AUC) and maximum concentration (Cmax) of a single dose of exemestane (25 mg) by 54% and 41%, respectively.(1) Strong inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 80% or more and include: carbamazepine, enzalutamide, mitotane, phenobarbital, phenytoin, rifabutin, rifampin, and St. John's wort.(1-3) Moderate inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 50-80% and include: belzutifan, bosentan, cenobamate, dabrafenib, dipyrone, efavirenz, elagolix, etravirine, lesinurad, mavacamten, mitapivat, modafinil, nafcillin, pacritinib, pexidartinib, repotrectinib, rifabutin, sotorasib, telotristat ethyl, thioridazine, and tovorafenib.(2,3) Weak inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 20-50% and include: armodafinil, bexarotene, brigatinib, brivaracetam, clobazam, danshen, darolutamide, dexamethasone, dicloxacillin, echinacea, elafibranor, enasidenib, eslicarbazepine, floxacillin, garlic, gingko, ginseng, glycyrrhizin, lorlatinib, meropenem-vaborbactam, methylprednisolone, nevirapine, omaveloxolone, oritavancin, oxcarbazepine, pioglitazone, pitolisant, quercetin, relugolix, rufinamide, sarilumab, sulfinpyrazone, sunvozertinib, suzetrigine, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vemurafenib, vinblastine, and zanubrutinib.(2,3)	AROMASIN, EXEMESTANE
Metformin/Carbonic Anhydrase Inhibitors SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed. MECHANISM OF ACTION: Carbonic anhydrase inhibitors increase bicarbonate excretion which may cause metabolic acidosis.(1) High systemic concentrations of metformin may result in lactic acidosis.(2,3) Topiramate, a mild carbonic anhydrase inhibitor, may also increase systemic exposure to metformin.(1) CLINICAL EFFECTS: Carbonic anhydrase inhibitors may increase the risk for metformin associated lactic acidosis.(1-3) Untreated lactic acidosis may be fatal. Symptoms of lactic acidosis include malaise, myalgias, respiratory distress, low blood pH, increased anion gap and elevated blood lactate.(2) Carbonic anhydrase inhibitors linked to this monograph are acetazolamide, dichlorphenamide, methazolamide, sulthiame, topiramate, and zonisamide. PREDISPOSING FACTORS: Risk factors for metformin associated lactic acidosis include renal impairment,sepsis, dehydration, excessive alcohol intake, acute or chronic metabolic acidosis, hepatic insufficiency, acute heart failure, metformin plasma levels > 5 micrograms/mL, and conditions which may lead to tissue hypoxia. Geriatric patients may also be at higher risk due to slower metformin clearance and increased half-life in this population. The risk for metabolic acidosis is higher with increased doses of either agent. PATIENT MANAGEMENT: For patients receiving concurrent therapy, monitor renal function and assure that patient does not have risk factors for metformin associated lactic acidosis. Discontinue metformin when risk factors are present. If both drugs are given, monitor renal function and for signs and symptoms of metformin toxicity (lactic acidosis) such as malaise, myalgias, respiratory distress, increasing somnolence, and respiratory distress. Laboratory results which may signal lactic acidosis include: low pH, an increased anion gap, and increased lactate to pyruvate ratio. Manufacturer recommendations: the manufacturer of metformin recommends caution with concomitant use of carbonic anhydrase inhibitors due to an increased risk for metformin associated lactic acidosis.(2) The manufacturer of topiramate notes that topiramate can frequently cause metabolic acidosis and that metformin should not be used in patients with metabolic acidosis.(1) DISCUSSION: A literature search for lactic acidosis due solely to the combination of metformin and carbonic anhydrase inhibitors or topiramate did not reveal any case reports of symptomatic metabolic acidosis due to this combination. Never-the-less, since carbonic anhydrase inhibitors act by inhibiting the reabsorption of bicarbonate in the renal tubule, some lowering of systemic bicarbonate and pH is common and supports the plausibility of this interaction. In addition, a pharmacokinetic interaction has been described with topiramate. A study in healthy volunteers evaluated the effect of topiramate 100 mg every 12 hours on the kinetics of metformin 500 mg every 12 hours. Mean metformin exposure (area-under-curve or AUC) was increased 25%.(1)	ACTOPLUS MET, ALOGLIPTIN-METFORMIN, DAPAGLIFLOZIN-METFORMIN ER, GLIPIZIDE-METFORMIN, GLYBURIDE-METFORMIN HCL, INVOKAMET, INVOKAMET XR, JANUMET, JANUMET XR, JENTADUETO, JENTADUETO XR, KAZANO, METFORMIN ER GASTRIC, METFORMIN ER OSMOTIC, METFORMIN HCL, METFORMIN HCL ER, PIOGLITAZONE-METFORMIN, RIOMET, SAXAGLIPTIN-METFORMIN ER, SEGLUROMET, SITAGLIPTIN-METFORMIN, SITAGLIPTIN-METFORMIN ER, SYNJARDY, SYNJARDY XR, TRIJARDY XR, XIGDUO XR, ZITUVIMET, ZITUVIMET XR
Topiramate/Hydrochlorothiazide SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed. MECHANISM OF ACTION: Hydrochlorothiazide may increase levels of topiramate. Also, both agents may decrease potassium levels.(1,2) CLINICAL EFFECTS: Concurrent use of hydrochlorothiazide may result in elevated levels of topiramate and hypokalemia.(1,2) PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: Monitor serum potassium and topiramate in patients receiving concurrent therapy. The dosage of topiramate may need to be adjusted, an alternative diuretic or potassium supplement may be needed. DISCUSSION: In a study in 23 healthy subjects, concurrent hydrochlorothiazide (25 mg daily) increased the maximum concentration (Cmax) and area-under-curve (AUC) of topiramate (96 mg BID) by 27% and 29%, respectively. During concurrent therapy, 61% of patients had a serum potassium level less than 3.5 mEq/L, compared with 27% with topiramate alone and 25% with hydrochlorothiazide alone. During concurrent therapy, the mean decrease in serum potassium levels was -0.60 mEq/L, compared with -0.25 mEq/L with topiramate alone and -0.12 mEq/L with hydrochlorothiazide alone.(1)	ACCURETIC, AMILORIDE-HYDROCHLOROTHIAZIDE, AMLODIPINE-VALSARTAN-HCTZ, ATACAND HCT, AVALIDE, BENAZEPRIL-HYDROCHLOROTHIAZIDE, BENICAR HCT, BISOPROLOL-HYDROCHLOROTHIAZIDE, CANDESARTAN-HYDROCHLOROTHIAZID, CAPTOPRIL-HYDROCHLOROTHIAZIDE, DIOVAN HCT, ENALAPRIL-HYDROCHLOROTHIAZIDE, EXFORGE HCT, FOSINOPRIL-HYDROCHLOROTHIAZIDE, HYDROCHLOROTHIAZIDE, HYZAAR, INZIRQO, IRBESARTAN-HYDROCHLOROTHIAZIDE, LISINOPRIL-HYDROCHLOROTHIAZIDE, LOSARTAN-HYDROCHLOROTHIAZIDE, LOTENSIN HCT, METHYLDOPA-HYDROCHLOROTHIAZIDE, METOPROLOL-HYDROCHLOROTHIAZIDE, MICARDIS HCT, OLMESARTAN-AMLODIPINE-HCTZ, OLMESARTAN-HYDROCHLOROTHIAZIDE, PROPRANOLOL-HYDROCHLOROTHIAZID, QUINAPRIL-HYDROCHLOROTHIAZIDE, SPIRONOLACTONE-HCTZ, TELMISARTAN-HYDROCHLOROTHIAZID, TRIAMTERENE-HYDROCHLOROTHIAZID, TRIBENZOR, VALSARTAN-HYDROCHLOROTHIAZIDE, VASERETIC, ZESTORETIC
Lacosamide/Sodium Channel Blockers; Potassium Channel Blockers SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed. MECHANISM OF ACTION: Lacosamide may enhance the slow inactivation of voltage-gated sodium channels and may cause dose-dependent bradycardia, prolongation of the PR interval, atrioventricular (AV) block, or ventricular tachyarrhythmia.(1) CLINICAL EFFECTS: Concurrent use of lacosamide and agents that affect cardiac conduction (sodium channel blockers and potassium channel blockers) may increase the risk of bradycardia, prolongation of the PR interval, atrioventricular (AV) block, or ventricular tachyarrhythmia.(1) PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: Lacosamide should be used with caution in patients on concomitant medications that affect cardiac conduction, including sodium channel blockers and potassium channel blockers.(1) If concurrent use is needed, obtain an ECG before lacosamide therapy and after lacosamide dose is titrated to steady-state.(1) Patients should be monitored closely when lacosamide is given intravenously.(1) DISCUSSION: In a clinical trial in patients with partial-onset seizures, asymptomatic first-degree atrioventricular (AV) block occurred in 4/944 (0.4%) of patient who received lacosamide compared to 0/364 (0%) with placebo.(1) In a clinical trial in patients with diabetic neuropathy, asymptomatic first-degree AV block occurred in 5/1023 (0.5%) of patients who received lacosamide compared to 0/291 (0%) with placebo.(1) Second-degree and complete AV block have been reported in patients with seizures.(1) One case of profound bradycardia was observed in a patient during a 15-minute infusion of 150 mg of lacosamide.(1) A case report of a 49 year old male with refractory complex partial and generalized seizures described the development of ventricular tachycardia four months after addition of lacosamide 400 mg/day to the existing regimen of carbamazepine, lamotrigine, clonazepam, and valproate. The patient's ECG showed first-degree AV block, posterior left fascicular block, and severe widening of the QRS complex, all of which resolved upon discontinuation of lacosamide.(2)	LACOSAMIDE, MOTPOLY XR, VIMPAT
Ubrogepant/Moderate and Weak CYP3A4 Inducers SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed. MECHANISM OF ACTION: Moderate or weak CYP3A4 inducers may induce the metabolism of ubrogepant.(1) CLINICAL EFFECTS: Concurrent use of a moderate or weak CYP3A4 inducer may result in decreased levels and effectiveness of ubrogepant.(1) PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks. PATIENT MANAGEMENT: The manufacturer recommends a dosage adjustment of ubrogepant when coadministered with moderate or weak CYP3A4 inducers. Initial dose of ubrogepant should be 100 mg. If a second dose is needed, the dose of ubrogepant should be 100 mg.(1) DISCUSSION: Coadministration of ubrogepant with rifampin, a strong CYP3A4 inducer, resulted in an 80% reduction in ubrogepant exposure. No dedicated drug interaction studies were conducted to assess concomitant use with moderate or weak CYP3A4 inducers. Dose adjustment for concomitant use of ubrogepant with moderate or weak CYP3A4 inducers is recommended based on a conservative prediction of 50% reduction in exposure of ubrogepant.(1) Moderate inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 50-80% and include: belzutifan, bosentan, cenobamate, dabrafenib, dipyrone, efavirenz, elagolix, etravirine, lesinurad, lorlatinib, mavacamten, mitapivat, modafinil, nafcillin, pexidartinib, rifabutin, telotristat, thioridazine, and tovorafenib.(2,3) Weak inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 20-50% and include: armodafinil, bexarotene, brigatinib, brivaracetam, clobazam, danshen, dexamethasone, dicloxacillin, echinacea, elafibranor, enasidenib, eslicarbazepine, floxacillin, garlic, genistein, ginseng, glycyrrhizin, meropenem-vaborbactam, methylprednisolone, nevirapine, omaveloxolone, oritavancin, oxcarbazepine, pioglitazone, pitolisant, relugolix, repotrectinib, rufinamide, sarilumab, sulfinpyrazone, sunvozertinib, suzetrigine, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vemurafenib, vinblastine, and zanubrutinib.(2,3)	UBRELVY
Topiramate/Anticholinergics SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed. MECHANISM OF ACTION: Topiramate can cause decreased sweating and elevated body temperature. Agents with anticholinergic activity can predispose patients to heat-related disorders.(1-2) CLINICAL EFFECTS: Concurrent use of topiramate with agents with anticholinergic activity may increase the incidence of oligohidrosis and hyperthermia, especially in pediatric or adolescent patients.(1-2) Overheating and dehydration can lead to brain damage and death. PREDISPOSING FACTORS: Pediatric and adolescent patients and patients with dehydration may be more likely to experience heat-related disorders.(1) PATIENT MANAGEMENT: The manufacturer of topiramate states that caution should be used when topiramate is prescribed with other medicinal products that predispose to heat-related disorders, such as agents with anticholinergic activity (e.g. clomipramine, hydroxyzine, diphenhydramine, haloperidol, imipramine, and oxybutynin) concurrently with zonisamide.(1) Monitor for signs and symptoms of heat stroke: skin feels very hot with little or no sweating, confusion, muscle cramps, rapid heartbeat, or rapid breathing. Monitor for signs and symptoms of dehydration: dry mouth, urinating less than usual, dark-colored urine, dry skin, feeling tired, dizziness, or irritability. If signs or symptoms of dehydration, oligohidrosis, or elevated body temperature occur, discontinuation of zonisamide should be considered. DISCUSSION: Case reports of decreased sweating and elevated temperature have been reported, especially in pediatric patients. Some cases resulted in heat stroke that required hospital treatment.(1) A 64-year old woman developed non-exertional hyperthemia while taking multiple psychiatric medications with topiramate.(2)	ADASUVE, AMITRIPTYLINE HCL, AMOXAPINE, ANAFRANIL, ANASPAZ, ANTIVERT, ATROPEN, ATROPINE SULFATE, ATROVENT HFA, BELLADONNA, BELLADONNA LEAF POWDER, BELLADONNA-OPIUM, BENZTROPINE MESYLATE, BEVESPI AEROSPHERE, BONJESTA, BREZTRI AEROSPHERE, BROMFED DM, BROMPHENIRAMINE MALEATE, BROMPHENIRAMINE-PSEUDOEPHED-DM, CARBINOXAMINE MALEATE, CARBINOXAMINE MALEATE ER, CARBZAH, CHLORDIAZEPOXIDE-AMITRIPTYLINE, CHLORDIAZEPOXIDE-CLIDINIUM, CHLORPHENIRAMINE MALEATE, CIMETIDINE, CLEMASTINE FUMARATE, CLIDINIUM BROMIDE, CLOMIPRAMINE HCL, COBENFY, COBENFY STARTER PACK, COMBIVENT RESPIMAT, CUVPOSA, CYCLOPENTOLATE HCL, CYPROHEPTADINE HCL, DARIFENACIN ER, DARTISLA, DESIPRAMINE HCL, DEXCHLORPHENIRAMINE MALEATE, DICLEGIS, DICYCLOMINE HCL, DIMENHYDRINATE, DIPHEN, DIPHENHYDRAMINE HCL, DIPHENHYDRAMINE-0.9% NACL, DIPHENOXYLATE-ATROPINE, DONNATAL, DOXEPIN HCL, DOXYLAMINE SUCC-PYRIDOXINE HCL, DOXYLAMINE SUCCINATE, DUODOTE, ED-SPAZ, FESOTERODINE FUMARATE ER, FLAVOXATE HCL, GLYCATE, GLYCOPYRROLATE, GLYCOPYRROLATE-WATER, GLYRX-PF, HALDOL DECANOATE 100, HALOPERIDOL, HALOPERIDOL DECANOATE, HALOPERIDOL DECANOATE 100, HALOPERIDOL LACTATE, HOMATROPINE METHYLBROMIDE, HYCODAN, HYDROCODONE-CHLORPHENIRAMNE ER, HYDROCODONE-HOMATROPINE MBR, HYDROMET, HYDROXYZINE HCL, HYDROXYZINE PAMOATE, HYOSCYAMINE SULFATE, HYOSCYAMINE SULFATE ER, HYOSCYAMINE SULFATE SR, HYOSYNE, IMIPRAMINE HCL, IMIPRAMINE PAMOATE, IPRATROPIUM BROMIDE, IPRATROPIUM-ALBUTEROL, ISOPROPAMIDE IODIDE, KARBINAL ER, LEVBID, LEVSIN, LEVSIN-SL, LIBRAX, LOMOTIL, LOXAPINE, MB CAPS, ME-NAPHOS-MB-HYO 1, MECLIZINE HCL, METHSCOPOLAMINE BROMIDE, MOTOFEN, NORGESIC, NORGESIC FORTE, NORPRAMIN, NORTRIPTYLINE HCL, NULEV, ORPHENADRINE CITRATE, ORPHENADRINE CITRATE ER, ORPHENADRINE-ASPIRIN-CAFFEINE, ORPHENGESIC FORTE, OSCIMIN, OSCIMIN SL, OXCARBAZEPINE, OXCARBAZEPINE ER, OXTELLAR XR, OXYBUTYNIN CHLORIDE, OXYBUTYNIN CHLORIDE ER, OXYTROL, PAMELOR, PERPHENAZINE-AMITRIPTYLINE, PHENOBARBITAL-BELLADONNA, PHENOBARBITAL-HYOSC-ATROP-SCOP, PHENOHYTRO, PREVDUO, PROPANTHELINE BROMIDE, PROTRIPTYLINE HCL, PYRILAMINE MALEATE, RESPA A.R., ROBINUL, ROBINUL FORTE, RYCLORA, RYVENT, SCOPOLAMINE, SCOPOLAMINE HYDROBROMIDE, SCOPOLAMINE METHYL NITRATE, SILENOR, SOLIFENACIN SUCCINATE, SPIRIVA HANDIHALER, SPIRIVA RESPIMAT, STIOLTO RESPIMAT, SYMAX, SYMAX DUOTAB, SYMAX-SL, SYMAX-SR, TIOTROPIUM BROMIDE, TOLTERODINE TARTRATE, TOLTERODINE TARTRATE ER, TOVIAZ, TRANSDERM-SCOP, TRIFLUOPERAZINE HCL, TRIHEXYPHENIDYL HCL, TRILEPTAL, TRIMIPRAMINE MALEATE, TRIPROLIDINE HCL, TROPICAMIDE, TROSPIUM CHLORIDE, TROSPIUM CHLORIDE ER, TUXARIN ER, URELLE, URETRON D-S, URIBEL TABS, URIMAR-T, URNEVA, URO-MP, URO-SP, UROGESIC-BLUE, URYL, VESICARE, VESICARE LS
Tacrolimus/Moderate and Weak CYP3A4 Inducers SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed. MECHANISM OF ACTION: Moderate or weak CYP3A4 inducers may accelerate the metabolism of tacrolimus.(1) CLINICAL EFFECTS: Concurrent use of a moderate or weak CYP3A4 inducer may result in decreased levels and effectiveness of tacrolimus.(1) PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks. PATIENT MANAGEMENT: The manufacturer of tacrolimus recommends monitoring tacrolimus whole blood trough concentrations and adjusting tacrolimus dose if needed. Monitor clinical response closely.(1) DISCUSSION: A 13-year-old cystic fibrosis patient with a history of liver transplant on stable doses of tacrolimus underwent 2 separate courses of nafcillin therapy (a moderate CYP3A4 inducer). During the 1st course of nafcillin, his tacrolimus levels started to fall 3 days after starting nafcillin, became undetectable at day 8, and recovered to therapeutic levels without a change in tacrolimus dose 5 days after discontinuation of nafcillin. During the 2nd course of nafcillin, tacrolimus level became undetectable 4 days after starting nafcillin and recovered 3 days after stopping nafcillin.(2) Moderate inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 50-80% and include: belzutifan, bosentan, cenobamate, dabrafenib, dipyrone, elagolix, etravirine, lesinurad, lorlatinib, mavacamten, modafinil, nafcillin, repotrectinib, telotristat, and tovorafenib.(3,4) Weak inducers of CYP3A4 would be expected to decrease the AUC of a sensitive 3A4 substrate by 20-50% and include: armodafinil, bexarotene, brigatinib, brivaracetam, clobazam, danshen, darolutamide, dexamethasone, dicloxacillin, echinacea, elafibranor, enasidenib, eslicarbazepine, floxacillin, garlic, genistein, ginseng, glycyrrhizin, meropenem-vaborbactam, nevirapine, oritavancin, omaveloxolone, oxcarbazepine, pioglitazone, relugolix, rufinamide, sulfinpyrazone, sunvozertinib, suzetrigine, tazemetostat, tecovirimat, terbinafine, ticlopidine, topiramate, troglitazone, vinblastine, and zanubrutinib.(3,4)	ASTAGRAF XL, ENVARSUS XR, PROGRAF, TACROLIMUS, TACROLIMUS XL
Ziprasidone/Serotonergic Agents SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed. MECHANISM OF ACTION: Ziprasidone is a 5-HT1A agonist and serotonin and norepinephrine reuptake inhibitor. Concurrent administration with one or more serotonergic agents may increase serotonin effects, resulting in serotonin toxicity.(1,2) CLINICAL EFFECTS: Concurrent use of ziprasidone and other serotonergic agents may result in serotonin syndrome, a potentially life-threatening condition with symptoms including altered mental status, hypertension, restlessness, myoclonus, hyperthermia, hyperreflexia, diaphoresis, shivering, and tremor.(1) PREDISPOSING FACTORS: Serotonin syndrome risk is dose-related. Higher systemic concentrations of either drug would be predicted to increase risk for serotonin toxicity.(2) Concomitant therapy with multiple agents which increase brain serotonin concentrations may also increase risk for serotonin syndrome.(2) PATIENT MANAGEMENT: Caution patients about the risk of serotonin syndrome with the concomitant use of ziprasidone with other serotonergic drugs. Instruct patients to contact their healthcare provider, or report to the emergency room, should they experience signs or symptoms of serotonin syndrome.(1) DISCUSSION: Several cases of serotonin syndrome have been reported in patients receiving ziprasidone.(4-6)	GEODON, ZIPRASIDONE HCL, ZIPRASIDONE MESYLATE

The following contraindication information is available for PHENTERMINE-TOPIRAMATE ER (phentermine hcl/topiramate):

Overview
Contraindicated
Severe
Moderate

Drug contraindication overview.

Phentermine/topiramate is contraindicated in patients with glaucoma, hyperthyroidism, or known hypersensitivity or idiosyncrasy to sympathomimetic amines. Use of phentermine/topiramate also is contraindicated during pregnancy and also during or within 14 days after administration of a monoamine oxidase (MAO) inhibitor. (See Drug Interactions: Monoamine Oxidase Inhibitors.)

There are 4 contraindications. Absolute contraindication.

Contraindication List
Glaucoma
Hyperthyroidism
Lactation
Pregnancy

There are 12 severe contraindications. Adequate patient monitoring is recommended for safer drug use.

Severe List
Acute cognitive impairment
Alcohol use disorder
Chronic kidney disease stage 3A (moderate) GFR 45-59 ml/min
Chronic kidney disease stage 3B (moderate) GFR 30-44 ml/min
Chronic kidney disease stage 4 (severe) GFR 15-29 ml/min
Chronic kidney disease stage 5 (failure) GFr<15 ml/min
Concentration difficulty
Depression
Drug abuse
Memory impairment
Metabolic acidosis
Suicidal ideation

There are 8 moderate contraindications. Clinically significant contraindication, where the condition can be managed or treated before the drug may be given safely.

Moderate List
Arginase deficiency
Argininosuccinate lyase deficiency
Carbamoyl phosphate synthetase deficiency
Citrullinemia
Hyperammonemia associated with n-acetylglutamate synthase deficiency
Kidney disease with likely reduction in glomerular filtration rate (GFr)
Kidney stone
Ornithine carbamoyltransferase deficiency

The following adverse reaction information is available for PHENTERMINE-TOPIRAMATE ER (phentermine hcl/topiramate):

Overview
Severe
Less Severe

Adverse reaction overview.

The most common adverse effects of phentermine/topiramate (reported at an incidence of at least 5%) in clinical studies include paresthesia, dizziness, dysgeusia, insomnia, constipation, and dry mouth.

There are 45 severe adverse reactions.

More Frequent	Less Frequent
Hypertension	Allergic dermatitis Cardiac arrhythmia Infection Kidney stone Leukopenia Urticaria

Rare/Very Rare
Anemia Asthma Bullous dermatitis Cardiomyopathy Choroidal effusion Decreased sweating Drug-induced psychosis Encephalopathy Eosinophilia Erythema multiforme Hallucinations Hepatic failure Hepatitis Hyperammonemia Hypokalemia Hypotension Hypothermia Maculopathy Metabolic acidosis Myocardial ischemia Myopia Nephrocalcinosis Ocular hypertension Osteomalacia Osteopenia Osteoporosis Pancreatitis Pemphigus Pneumonia Pulmonary hypertension Retinal pigment epithelial detachment Scotomata Secondary angle-closure glaucoma Stevens-johnson syndrome Suicidal Suicidal ideation Toxic epidermal necrolysis Valvular heart disease

Rare/Very Rare

Anemia
Asthma
Bullous dermatitis
Cardiomyopathy
Choroidal effusion
Decreased sweating
Drug-induced psychosis
Encephalopathy
Eosinophilia
Erythema multiforme
Hallucinations
Hepatic failure
Hepatitis
Hyperammonemia
Hypokalemia
Hypotension
Hypothermia
Maculopathy
Metabolic acidosis
Myocardial ischemia
Myopia
Nephrocalcinosis
Ocular hypertension
Osteomalacia
Osteopenia
Osteoporosis
Pancreatitis
Pemphigus
Pneumonia
Pulmonary hypertension
Retinal pigment epithelial detachment
Scotomata
Secondary angle-closure glaucoma
Stevens-johnson syndrome
Suicidal
Suicidal ideation
Toxic epidermal necrolysis
Valvular heart disease

There are 109 less severe adverse reactions.

More Frequent	Less Frequent
Acute abdominal pain Acute cognitive impairment Anorexia Behavioral disorders Bradykinesia Concentration difficulty Diplopia Dizziness Drowsy Dysarthria Dysgeusia Dysmenorrhea Fatigue Fever Flushing General weakness Hypoesthesia Insomnia Irregular menstrual periods Mastalgia Memory impairment Nausea Nervousness Nystagmus Paresthesia Weight loss Xerostomia	Acute abdominal pain Aggressive behavior Agitation Alopecia Altered mental status Arthralgia Ataxia Back pain Blurred vision Bronchitis Chest pain Constipation Cough Depression Diarrhea Dizziness Dysgeusia Dyspepsia Dysuria Ecchymosis Edema Epistaxis Euphoria Flushing Gastroenteritis Gingivitis Headache disorder Hemorrhage Hypertonia Involuntary muscle movement Leg pain Libido changes Mood changes Palpitations Pharyngitis Premature ejaculation Purpura Rhinitis Sinusitis Skin rash Symptoms of anxiety Tachycardia Tinnitus Tremor Upper respiratory infection Urinary tract infection Viral infection Vomiting Xerostomia

More Frequent

Less Frequent

Acute abdominal pain
Acute cognitive impairment
Anorexia
Behavioral disorders
Bradykinesia
Concentration difficulty
Diplopia
Dizziness
Drowsy
Dysarthria
Dysgeusia
Dysmenorrhea
Fatigue
Fever
Flushing
General weakness
Hypoesthesia
Insomnia
Irregular menstrual periods
Mastalgia
Memory impairment
Nausea
Nervousness
Nystagmus
Paresthesia
Weight loss
Xerostomia

Acute abdominal pain
Aggressive behavior
Agitation
Alopecia
Altered mental status
Arthralgia
Ataxia
Back pain
Blurred vision
Bronchitis
Chest pain
Constipation
Cough
Depression
Diarrhea
Dizziness
Dysgeusia
Dyspepsia
Dysuria
Ecchymosis
Edema
Epistaxis
Euphoria
Flushing
Gastroenteritis
Gingivitis
Headache disorder
Hemorrhage
Hypertonia
Involuntary muscle movement
Leg pain
Libido changes
Mood changes
Palpitations
Pharyngitis
Premature ejaculation
Purpura
Rhinitis
Sinusitis
Skin rash
Symptoms of anxiety
Tachycardia
Tinnitus
Tremor
Upper respiratory infection
Urinary tract infection
Viral infection
Vomiting
Xerostomia

Rare/Very Rare
Abnormal vaginal bleeding Accidental fall Acne vulgaris Chills Conjunctivitis Cystitis Depression Dysphoric mood Dyspnea Dysuria Erectile dysfunction Flu-like symptoms Gastroesophageal reflux disease Gingival bleeding Headache disorder Hematuria Hypercalcinuria Hyperhidrosis Increased urinary frequency Myalgia Nausea Ocular pain Ocular redness Orthostatic hypotension Polydipsia Pruritus of skin Skin rash Syncope Urinary incontinence Vertigo Visual changes Visual field defect Vulvovaginal candidiasis

Rare/Very Rare

Abnormal vaginal bleeding
Accidental fall
Acne vulgaris
Chills
Conjunctivitis
Cystitis
Depression
Dysphoric mood
Dyspnea
Dysuria
Erectile dysfunction
Flu-like symptoms
Gastroesophageal reflux disease
Gingival bleeding
Headache disorder
Hematuria
Hypercalcinuria
Hyperhidrosis
Increased urinary frequency
Myalgia
Nausea
Ocular pain
Ocular redness
Orthostatic hypotension
Polydipsia
Pruritus of skin
Skin rash
Syncope
Urinary incontinence
Vertigo
Visual changes
Visual field defect
Vulvovaginal candidiasis

The following precautions are available for PHENTERMINE-TOPIRAMATE ER (phentermine hcl/topiramate):

Pediatric
Pregnant
Lactation
Geriatric

Safety and efficacy of phentermine/topiramate in pediatric patients younger than 18 years of age have not been established; use of the drug is not recommended in such patients. Serious adverse reactions reported in pediatric patients receiving topiramate, a component of phentermine/topiramate, include acute angle glaucoma, oligohidrosis and hyperthermia, metabolic acidosis, cognitive and neuropsychiatric reactions, hyperammonemia and encephalopathy, and kidney stones.

Contraindicated

None

Severe Precaution

None

Management or Monitoring Precaution

None

Phentermine/topiramate is contraindicated in pregnant women. Use of the drug can cause fetal harm and weight loss, and offers no potential benefit to a pregnant woman. If a patient becomes pregnant while taking phentermine/topiramate, the drug should be discontinued immediately and the patient should be apprised of the potential fetal hazard.

Topiramate can cause metabolic acidosis. The effect of topiramate-induced metabolic acidosis has not been specifically studied during pregnancy; however, metabolic acidosis from other causes during pregnancy can result in decreased fetal growth, decreased fetal oxygenation, and fetal death, and also may affect the ability of the fetus to tolerate labor. A pregnancy test should be performed in women of childbearing potential prior to initiating phentermine/topiramate therapy and monthly thereafter to confirm that the patient is not pregnant.

Women of childbearing potential should use effective contraception during phentermine/topiramate therapy. A Qsymia Pregnancy Surveillance Program has been established to monitor the maternal-fetal outcomes of pregnancies that occur during phentermine/topiramate therapy. Women who become pregnant while receiving phentermine/topiramate should be encouraged to report their pregnancy to the surveillance program by calling 888-998-4887.

Topiramate is distributed into human milk. Phentermine also may be present in human milk because the drug is pharmacologically and structurally similar to amphetamines, which can distribute into human milk. Because of the potential for serious adverse reactions from phentermine/topiramate in nursing infants, a decision should be made whether to discontinue nursing or the drug, taking into account the importance of the drug to the mother.

In clinical trials of phentermine/topiramate, 254 (7%) of the patients were 65 years of age and older. No overall differences in safety or effectiveness were observed between these patients and younger adults, but greater sensitivity of some older individuals cannot be ruled out. Clinical studies of phentermine/topiramate did not include sufficient numbers of patients 65 years of age and older to determine whether they respond differently from younger adults. In general, dosage selection in geriatric patients should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

The following icd codes are available for PHENTERMINE-TOPIRAMATE ER (phentermine hcl/topiramate)'s list of indications:

Weight loss management for obese patient (bmi >= 30)
E66	Overweight and obesity
E66.0	Obesity due to excess calories
E66.01	Morbid (severe) obesity due to excess calories
E66.09	Other obesity due to excess calories
E66.1	Drug-induced obesity
E66.2	Morbid (severe) obesity with alveolar hypoventilation
E66.8	Other obesity
E66.81	Obesity class
E66.811	Obesity, class 1
E66.812	Obesity, class 2
E66.813	Obesity, class 3
E66.89	Other obesity not elsewhere classified
E66.9	Obesity, unspecified
Z68.3	Body mass index [BMi] 30-39, adult
Z68.30	Body mass index [BMi] 30.0-30.9, adult
Z68.31	Body mass index [BMi] 31.0-31.9, adult
Z68.32	Body mass index [BMi] 32.0-32.9, adult
Z68.33	Body mass index [BMi] 33.0-33.9, adult
Z68.34	Body mass index [BMi] 34.0-34.9, adult
Z68.35	Body mass index [BMi] 35.0-35.9, adult
Z68.36	Body mass index [BMi] 36.0-36.9, adult
Z68.37	Body mass index [BMi] 37.0-37.9, adult
Z68.38	Body mass index [BMi] 38.0-38.9, adult
Z68.39	Body mass index [BMi] 39.0-39.9, adult
Z68.4	Body mass index [BMi] 40 or greater, adult
Z68.41	Body mass index [BMi] 40.0-44.9, adult
Z68.42	Body mass index [BMi] 45.0-49.9, adult
Z68.43	Body mass index [BMi] 50.0-59.9, adult
Z68.44	Body mass index [BMi] 60.0-69.9, adult
Z68.45	Body mass index [BMi] 70 or greater, adult
Z68.55	Body mass index [BMi] pediatric, 120% of the 95th percentile for age to less than 140% of the 95th percentile for age
Z68.56	Body mass index [BMi] pediatric, greater than or equal to 140% of the 95th percentile for age
Wt loss mgmt, pt with bmi 27-29 & wt-related comorbidity
E66.3	Overweight
Z68.27	Body mass index [BMi] 27.0-27.9, adult
Z68.28	Body mass index [BMi] 28.0-28.9, adult
Z68.29	Body mass index [BMi] 29.0-29.9, adult