THIORIDAZINE HCL (thioridazine hcl)

There are 17 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
Thioridazine/Pindolol; Propranolol 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: Pindolol and propranolol may inhibit the metabolism of thioridazine at CYP3A4.(1) CLINICAL EFFECTS: Concurrent use of pindolol or propranolol with thioridazine may result in elevated levels of thioridazine and prolongation of the QTc interval, which may result in potentially life-threatening arrhythmias,(1) and elevated levels of the beta blocker. PREDISPOSING FACTORS: The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(4) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentration of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(4) PATIENT MANAGEMENT: The manufacturer of thioridazine states that concurrent use with pindolol or propranolol is contraindicated.(1) If concurrent therapy is deemed medically necessary, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. DISCUSSION: In one study, two patients receiving thioridazine (600 mg/day to 800 mg/day) developed thioridazine levels that were in the potentially toxic range following the administration of propranolol. In one patient, thioridazine levels increased 433% over 40 days of concurrent therapy. The other patient's level increased 275% after 26 days of concurrent therapy. Neither patient exhibited any signs or symptoms of thioridazine toxicity.(2) In another study, administration of pindolol (40 mg/day) to eight patients receiving thioridazine (150 mg/day) resulted in an increase in thioridazine levels by 36%, as well as increases in the levels of the thioridazine metabolites. In addition, in seven patients, pindolol levels were found to be increased when administered with thioridazine.(3)	HEMANGEOL, INDERAL LA, INDERAL XL, INNOPRAN XL, PINDOLOL, PROPRANOLOL HCL, PROPRANOLOL HCL ER, PROPRANOLOL-HYDROCHLOROTHIAZID
Pimozide/Phenothiazines 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 may possibly result in additive effects on the QTc interval.(1) CLINICAL EFFECTS: Concurrent use may result in prolongation of the QTc interval, which may result in potentially life-threatening arrhythmias.(1) PREDISPOSING FACTORS: The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(2) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.e. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(2) PATIENT MANAGEMENT: Concurrent therapy with pimozide and phenothiazines should be avoided. The manufacturer of pimozide states that concurrent therapy with agents that prolong the QTc interval is contraindicated.(1) If concurrent therapy is deemed medically necessary, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. DISCUSSION: Pimozide has been shown to prolong the QTc interval. Therefore, the manufacturer of pimozide states that concurrent therapy with agents that prolong the QTc interval is contraindicated because of the risk of additive effects on the QTc interval.(1) No other clinical documentation is available. 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.	PIMOZIDE
Thioridazine/Selected SSRIs; Duloxetine 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: Dapoxetine,(1) duloxetine,(2) fluoxetine,(3-7) and paroxetine(3,4) may inhibit the metabolism of thioridazine by CYP2D6. Fluvoxamine may inhibit the metabolism of thioridazine by CYP2C19 and/or CYP1A2.(8) CLINICAL EFFECTS: The concurrent administration of dapoxetine, duloxetine, fluoxetine, fluvoxamine, or paroxetine with thioridazine may result in elevated levels of thioridazine. Elevated levels of thioridazine may augment thioridazine-induced prolongation of the QTc interval, which may increase the risk of serious, potentially fatal, cardiac arrhythmias such as torsades de pointes.(3,4) PREDISPOSING FACTORS: Patients who are CYP2D6 ultrarapid metabolizers may be affected to a greater extent by CYP2D6 inhibitors. Patients who are CYP2D6 poor metabolizers lack CYP2D6 function and are not affected by CYP2D6 inhibition. The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(15) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. co-administration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(15) PATIENT MANAGEMENT: Use an alternative antipsychotic agent. The concurrent use of thioridazine with dapoxetine,(1) duloxetine,(2) fluoxetine,(3-5,7) fluvoxamine,(3,4,8) or paroxetine(3,4,9,10) is contraindicated. If thioridazine cannot be discontinued, use an alternative to the interacting SSRI or duloxetine and evaluate patient for predisposing risk factors for QT prolongation. Correct modifiable risk factors and monitor for QT prolongation as appropriate throughout treatment with thioridazine. If alternative treatment is not possible and concurrent therapy is deemed medically necessary, strongly consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. At least 7 days should elapse following the discontinuation of dapoxetine before thioridazine is initiated and at least 14 days should elapse following the discontinuation of thioridazine before dapoxetine is initiated.(1) At least five weeks should elapse following the discontinuation of fluoxetine before thioridazine is initiated.(5-7) DISCUSSION: In a study, pretreatment with duloxetine (60 mg twice daily) increased the area-under-curve (AUC) of a single dose of desipramine (50 mg) by 3-fold. Desipramine is metabolized by CYP2D6.(2) In a study in 10 patients, concurrent fluvoxamine (25 mg twice daily) resulted in a 3-fold increase in the levels of thioridazine and its two active metabolites, mesoridazine and sulforidazine.(11) A study in six slow and 13 rapid metabolizers of debrisoquin showed that slow metabolizers of debrisoquin had 2.4-fold and 4.5-fold higher thioridazine maximum concentration (Cmax) and AUC, respectively, than rapid metabolizers.(5,6,12) Slow metabolizers of debrisoquin have a genetic defect that results in low levels of CYP2D6.(3) A study in healthy subjects showed a thioridazine dose-related prolongation of the QTc interval.(13) A study in schizophrenic patients found no changes in thioridazine levels following the addition of citalopram.(14)	DRIZALMA SPRINKLE, DULOXETINE HCL, DULOXICAINE, FLUOXETINE DR, FLUOXETINE HCL, FLUVOXAMINE MALEATE, FLUVOXAMINE MALEATE ER, OLANZAPINE-FLUOXETINE HCL, PAROXETINE CR, PAROXETINE ER, PAROXETINE HCL, PAROXETINE MESYLATE, PAXIL, PAXIL CR, PROZAC
Ziprasidone/Pimozide; Thioridazine 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: Pimozide, thioridazine and ziprasidone have all been shown to prolong the QTc interval. The concurrent use of ziprasidone with these agents may result in additive effects on the QTc interval.(1) CLINICAL EFFECTS: The concurrent use of ziprasidone with pimozide or thioridazine may result in additive prolongation of the QTc interval and potentially life-threatening arrhythmias.(1) PREDISPOSING FACTORS: The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(2) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(2) PATIENT MANAGEMENT: The manufacturer of ziprasidone states under contraindications that ziprasidone should not be used with other drugs that prolong the QTc interval, including pimozide or thioridazine.(1) If concurrent therapy is deemed medically necessary, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. DISCUSSION: Ziprasidone has been shown to prolong the QTc interval in a dose-related fashion. Therefore, the manufacturer of ziprasidone states under contraindications that ziprasidone should not be used with other drugs that prolong the QTc interval, including pimozide or thioridazine.(1)	GEODON, ZIPRASIDONE HCL, ZIPRASIDONE MESYLATE
Droperidol/QT Prolonging Agents 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: Droperidol has been shown to prolong the QTc interval. Concurrent use with other agents that prolong the QTc interval may result in additive effects on the QTc interval.(1) CLINICAL EFFECTS: The concurrent use of droperidol with other agents that prolong the QTc interval may result in potentially life-threatening cardiac arrhythmias, including torsades de pointes.(1) PREDISPOSING FACTORS: Congestive heart failure, bradycardia, use of a diuretic, cardiac hypertrophy, hypokalemia, hypomagnesemia, age over 65 years, alcohol abuse, and the use of agents such as benzodiazepines, volatile anesthetics, and intravenous opiate may predispose patients to the development of prolonged QT syndrome.(1) Risk may also be increased in patients with other cardiovascular diseases (e.g. myocardial infarction, history of torsade de pointes, congenital long QT syndrome), hypocalcemia, or female gender.(3) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsade de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(3) PATIENT MANAGEMENT: The manufacturer of droperidol states under precautions drug interactions that drugs known to have the potential to prolong the QT interval should not be used together with droperidol.(1) DISCUSSION: Agents that are linked to this monograph may have varying degrees of potential to prolong the QTc interval. Agents linked to this monograph have been shown to prolong the QTc interval either through their mechanism of action, through studies on their effects on the QTc interval, or through reports of QTc prolongation and/or torsades de pointes in clinical trials and/or postmarketing reports.(2) 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.	DROPERIDOL
Iomeprol/Neuroleptics 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: Neuroleptics may lower seizure threshold.(1) CLINICAL EFFECTS: Use of iomeprol in a patient receiving a neuroleptic may increase the risk of seizure.(1) PREDISPOSING FACTORS: None determined. PATIENT MANAGEMENT: The manufacturer of iomeprol states that neuroleptics should be discontinued 48 hours before iomeprol use. Treatment with a neuroleptic should not be resumed until 24 hours post-procedure.(1) DISCUSSION: Because neuroleptics may lower seizure threshold, neuroleptics should be discontinued 48 hours before iomeprol use. Treatment with a neuroleptic should not be resumed until 24 hours post-procedure.(1)	IOMERON 350
Disopyramide/QT Prolonging Agents 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 disopyramide and agents known to prolong the QT interval may result in additive or synergistic effects on the QTc interval.(1) CLINICAL EFFECTS: Concurrent administration may result in prolongation of the QTc interval and life-threatening cardiac arrhythmias, including torsades de pointes. PREDISPOSING FACTORS: The risk of torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsade de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(3) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or and/or renal/hepatic dysfunction).(3) PATIENT MANAGEMENT: The Australian manufacturer of disopyramide states that concurrent use with agents liable to produce torsades de pointes, including tricyclic or tetracyclic antidepressants, erythromycin, vincamine, and sultopride, is contraindicated.(1) If alternatives are not available and concurrent therapy is deemed medically necessary, obtain serum calcium, magnesium, and potassium levels and monitor ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. DISCUSSION: Agents that are linked to this monograph may have varying degrees of potential to prolong the QTc interval. Agents linked to this monograph have been shown to prolong the QTc interval either through their mechanism of action, through studies on their effects on the QTc interval, or through reports of QTc prolongation and/or torsades de pointes in clinical trials and/or postmarketing reports.(2) 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.	DISOPYRAMIDE PHOSPHATE, NORPACE, NORPACE CR
Artemether-Lumefantrine/QT Prolonging Agents 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 artemether-lumefantrine and agents known to prolong the QT interval may result in additive or synergistic effects on the QTc interval.(1) CLINICAL EFFECTS: Concurrent administration may result in prolongation of the QTc interval and life-threatening cardiac arrhythmias, including torsades de pointes. PREDISPOSING FACTORS: The risk of QT prolongation or torsade de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsade de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(4) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsade de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, and/or renal/hepatic dysfunction).(4) PATIENT MANAGEMENT: The UK manufacturer of artemether-lumefantrine states that the use of artemether-lumefantrine in patients taking drugs that are known to prolong the QTc interval is contraindicated. These agents include class IA and III antiarrhythmics; neuroleptics; antidepressive agents; some macrolides, fluoroquinolones, imidazole and triazole antifungals; terfenadine; astemizole; and cisapride.(1) The US manufacturer of artemether-lumefantrine states that the use of artemether-lumefantrine should be avoided in patients taking drugs that are known to prolong the QTc interval. These agents include class IA and III antiarrhythmics; neuroleptics; antidepressive agents; some macrolides, fluoroquinolones, imidazole and triazole antifungals; terfenadine; astemizole; and cisapride.(2) If concurrent therapy is deemed medically necessary, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. DISCUSSION: Agents that are linked to this monograph may have varying degrees of potential to prolong the QTc interval. Agents linked to this monograph have been shown to prolong the QTc interval either through their mechanism of action, through studies on their effects on the QTc interval, or through reports of QTc prolongation and/or torsades de pointes in clinical trials and/or postmarketing reports.(3)	COARTEM
Anagrelide/QT Prolonging Agents 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 anagrelide with agents that prolong the QTc interval may result in additive effects on the QTc interval.(1-4) CLINICAL EFFECTS: The concurrent use of anagrelide with agents that prolong the QTc interval may result in potentially life-threatening cardiac arrhythmias, including torsades de pointes.(1-4) PREDISPOSING FACTORS: The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(5) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, and/or renal/hepatic dysfunction).(5) PATIENT MANAGEMENT: The US manufacturer of anagrelide states that anagrelide should not be used in patients taking medications known to prolong the QT interval.(1) The Australian, Canadian, and UK manufacturers of anagrelide state use of anagrelide should be approached with caution in patients taking medications that can prolong the QTc interval.(2-4) If concurrent therapy is deemed medically necessary, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. DISCUSSION: In a thorough QT study, dose-related QT changes were observed with anagrelide. The maximum mean change in QTcI (95% CI) in comparison to placebo was 7.0 (9.8) ms and 13.0 (15.7) msec following doses of 0.5 mg and 2.5mg, respectively.(1) Agents that are linked to this monograph may have varying degrees of potential to prolong the QTc interval. Agents linked to this monograph have been shown to prolong the QTc interval either through their mechanism of action, through studies on their effects on the QTc interval, or through reports of QTc prolongation and/or torsades de pointes in clinical trials and/or postmarketing reports.(6) 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.	AGRYLIN, ANAGRELIDE HCL
Thioridazine/Selected Strong & Moderate CYP2D6 Inhibitors that Prolong QT 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: Dronedarone, escitalopram and quinidine may inhibit the metabolism of thioridazine by CYP2D6. Dronedarone, escitalopram, and quinidine may also result in additive effects on the QTc interval.(1,2) CLINICAL EFFECTS: Concurrent use of dronedarone, escitalopram, or quinidine may result in thioridazine toxicity, including potentially life-threatening cardiac arrhythmias, including torsades de pointes.(1,2) PREDISPOSING FACTORS: Patients who are CYP2D6 ultrarapid metabolizers may be affected to a greater extent by CYP2D6 inhibitors. Patients who are CYP2D6 poor metabolizers lack CYP2D6 function and are not affected by CYP2D6 inhibition. The risk of QT prolongation or torsade de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsade de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(3) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsade de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, and/or renal/hepatic dysfunction).(3) The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(4) PATIENT MANAGEMENT: The concurrent use of thioridazine and strong or moderate CYP2D6 inhibitors such as dronedarone, escitalopram, or quinidine is contraindicated.(1,2) Consider the use of alternative antipsychotics with less QT prolongation potential, or an alternative to dronedarone, escitalopram, or quinidine containing products. If concurrent use is deemed medically necessary, consider obtaining serum calcium, magnesium, and potassium levels at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. The manufacturer of Nuedexta states that if concurrent use with QT prolonging agents cannot be avoided, ECG monitoring should be done at initiation of concurrent therapy and at 3-4 hours after the first dose.(2) DISCUSSION: Quinidine is a strong CYP2D6 inhibitor and would be expected to increase thioridazine levels by more than 5-fold. Dronedarone and escitalopram are moderate CYP2D6 inhibitors and would be excepted to increase thioridazine by 2-fold to 5-fold.(2,5-6) 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.	ESCITALOPRAM OXALATE, LEXAPRO, MULTAQ, NUEDEXTA, QUINIDINE GLUCONATE, QUINIDINE SULFATE, XOLREMDI
Thioridazine/Rolapitant 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: Rolapitant may inhibit the metabolism of thioridazine by CYP2D6.(1) Thioridazine may induce the metabolism and clearance of rolapitant via CYP3A4.(2) CLINICAL EFFECTS: The concurrent or recent administration of rolapitant with thioridazine may result in elevated levels of thioridazine. Elevated levels of thioridazine may augment thioridazine-induced prolongation of the QTc interval, increasing the risk of serious, potentially fatal, cardiac arrhythmias such as torsades de pointes.(1,3,4) Concurrent thioridazine may result in significantly decreased levels and effectiveness of rolapitant.(2) PREDISPOSING FACTORS: Patients who are CYP2D6 ultrarapid metabolizers may be affected to a greater extent by CYP2D6 inhibitors. Patients who are CYP2D6 poor metabolizers lack CYP2D6 function and are not affected by CYP2D6 inhibition. The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(5) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. co-administration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(5) The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(6) PATIENT MANAGEMENT: Use an alternative antipsychotic or antinausea agent. The concurrent use of thioridazine with rolapitant is contraindicated. Effects of rolapitant on thioridazine are expected to last for at least 28 days after administration.(1) If thioridazine cannot be discontinued, use an alternative agent for the treatment of nausea and vomiting and evaluate the patient for predisposing risk factors which increase the risk for QT prolongation. Correct modifiable risk factors (e.g. electrolyte disorders) and monitor for QT prolongation as appropriate throughout treatment with thioridazine. If alternative treatments are not possible for either agent and concurrent therapy is deemed medically necessary, strongly consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. Monitor patients for decreased rolapitant effectiveness. Thioridazine should not be initiated in patients with a QTc interval greater than 450 msec and should be discontinued in patients found to have a corrected QTc greater than 500 msec.(4) DISCUSSION: Seven days after administration, a single dose of rolapitant was found to increase exposure to dextromethorphan, a CYP2D6 substrate, by 3-fold.(1) A single dose of rolapitant increased dextromethorphan about 3-fold on days 8 and day 22 following administration. Dextromethorphan levels remained elevated by 2.3-fold on day 28 after single dose rolapitant. The inhibitory effects of rolapitant on CYP2D6 are expected to persist beyond 28 days.(1) A study in six slow and 13 rapid metabolizers of debrisoquin, a marker of CYP2D6 activity, showed that slow metabolizers of debrisoquin had 2.4-fold and 4.5-fold higher thioridazine maximum concentration (Cmax) and AUC, respectively, than rapid metabolizers.(7) A study in 9 healthy male subjects showed a thioridazine dose-related prolongation of the QTc interval. One subtherapeutic thioridazine 10 mg dose increased QTc 9 msec (range -1 to 19 msec), and a single low-therapeutic thioridazine dose of 50 mg increased QTc 22 msec (range 11 to 33 msec).(8) Rifampin (600 mg daily for 14 days), a strong CYP3A4 inducer, decreased the Cmax and AUC of a single dose of rolapitant (180 mg on Day 7) by 30% and 85%, respectively. The half-life of rolapitant decreased from 176 hours to 41 hours.(2)	VARUBI
Thioridazine/Selected Moderate CYP2D6 Inhibitors 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: Moderate inhibitors of CYP2D6 may inhibit the metabolism of thioridazine.(1-4) CLINICAL EFFECTS: The concurrent administration of moderate CYP2D6 inhibitors with thioridazine may result in elevated levels of thioridazine.(1-4) Elevated levels of thioridazine may augment thioridazine-induced prolongation of the QTc interval, increasing the risk of serious, potentially fatal, cardiac arrhythmias such as torsades de pointes.(1) PREDISPOSING FACTORS: Patients who are CYP2D6 ultrarapid metabolizers may be affected to a greater extent by CYP2D6 inhibitors. Patients who are CYP2D6 poor metabolizers lack CYP2D6 function and are not affected by CYP2D6 inhibition. The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(5) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. co-administration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(5) The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(6) PATIENT MANAGEMENT: The concurrent use of thioridazine with CYP2D6 inhibitors is contraindicated.(1) Use an alternative agent, or change to another antipsychotic agent. If the patient is on oral terbinafine for the treatment of onychomycosis, use a terbinafine formulation with a non-systemic route. If alternative treatments are not possible for either agent and concurrent therapy is deemed medically necessary, strongly consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. Thioridazine should not be initiated in patients with a QTc interval greater than 450 msec and should be discontinued in patients found to have a corrected QTc greater than 500 msec.(3) DISCUSSION: A study in six slow and 13 rapid metabolizers of debrisoquin, a marker of CYP2D6 activity, showed that slow metabolizers of debrisoquin had 2.4-fold and 4.5-fold higher thioridazine maximum concentration (Cmax) and area-under-curve (AUC), respectively, than rapid metabolizers.(4) A study in 9 healthy male subjects showed a thioridazine dose-related prolongation of the QTc interval. One subtherapeutic thioridazine 10 mg dose increased QTc 9 msec (range -1 to 19 msec), and a single low-therapeutic thioridazine dose of 50 mg increased QTc 22 msec (range 11 to 33 msec).(7) Coadministration of cinacalcet (90 mg once daily) and desipramine (50 mg), a CYP2D6 substrate, resulted in an approximate 3.6-fold increase in the exposure of desipramine in healthy subjects who were CYP2D6 extensive metabolizers.(8) In another study, cinacalcet (50 mg daily) increased AUC of single-dose dextromethorphan (30 mg), a CYP2D6 substrate, by 4.93-fold in 2D6 extensive metabolizers.(9)	CERDELGA, CINACALCET HCL, ORLADEYO, SENSIPAR, TRUQAP
Pimozide; Thioridazine/Bupropion 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: Bupropion may inhibit the metabolism of pimozide and thioridazine at CYP2D6.(1,2) These agents are also known to lower the seizure threshold.(1,3,4,6) CLINICAL EFFECTS: Concurrent use may result in prolongation of the QTc interval and potentially life-threatening ventricular arrhythmias.(1) Concurrent use may also result in extrapyramidal symptoms such as akathisia, bradykinesia, cogwheel rigidity, dystonia, hypertonia, and oculogyric crisis.(1,6) As well, concurrent use may result in additive effects on the seizure threshold, increasing the risk of seizures.(1,3,4,6) PREDISPOSING FACTORS: The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(5) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(5) The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants an anorectics; a total daily dose of bupropion greater than 450 mg or single doses greater than 150 mg; rapid escalation of bupropion dosage; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antidepressants, theophylline, systemic steroids).(3,4) The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(7) PATIENT MANAGEMENT: The concurrent use of pimozide or thioridazine with strong CYP2D6 inhibitors such as bupropion is contraindicated.(1,6) If concurrent therapy is deemed medically necessary, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. Concurrent use should be initiated with low initial bupropion dosing and small gradual dosage increases of bupropion.(3,4) Single doses of bupropion should not exceed 150 mg.(3,4) The maximum daily dose of bupropion should not exceed 300 mg for smoking cessation(3) or 450 mg for depression.(4) DISCUSSION: The interactions of pimozide and thioridazine with bupropion have not been studied. In a controlled study in healthy subjects, steady-state paroxetine (60 mg daily, another strong inhibitor of CYP2D6) increased the area-under curve (AUC) and maximum concentration (Cmax) of a single dose of pimozide (2 mg) by 151% and 62%, respectively.(1)	APLENZIN, AUVELITY, BUPROPION HCL, BUPROPION HCL SR, BUPROPION XL, CONTRAVE, FORFIVO XL, WELLBUTRIN SR, WELLBUTRIN XL
Thioridazine/Selected Strong CYP2D6 Inhibitors 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: Strong inhibitors of CYP2D6 may inhibit the metabolism of thioridazine.(1-4) CLINICAL EFFECTS: The concurrent administration of strong CYP2D6 inhibitors with thioridazine may result in elevated levels of thioridazine.(1-4) Elevated levels of thioridazine may augment thioridazine-induced prolongation of the QTc interval, increasing the risk of serious, potentially fatal, cardiac arrhythmias such as torsades de pointes.(1) PREDISPOSING FACTORS: Patients who are CYP2D6 ultrarapid metabolizers may be affected to a greater extent by CYP2D6 inhibitors. Patients who are CYP2D6 poor metabolizers lack CYP2D6 function and are not affected by CYP2D6 inhibition. The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(5) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. co-administration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(5) The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(6) PATIENT MANAGEMENT: The concurrent use of thioridazine with CYP2D6 inhibitors is contraindicated.(1) Use an alternative agent, or change to another antipsychotic agent. If alternative treatments are not possible for either agent and concurrent therapy is deemed medically necessary, strongly consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. Thioridazine should not be initiated in patients with a QTc interval greater than 450 msec and should be discontinued in patients found to have a corrected QTc greater than 500 msec.(3) DISCUSSION: A study in six slow and 13 rapid metabolizers of debrisoquin, a marker of CYP2D6 activity, showed that slow metabolizers of debrisoquin had 2.4-fold and 4.5-fold higher thioridazine maximum concentration (Cmax) and area-under-curve (AUC), respectively, than rapid metabolizers.(4) A study in 9 healthy male subjects showed a thioridazine dose-related prolongation of the QTc interval. One subtherapeutic thioridazine 10 mg dose increased QTc 9 msec (range -1 to 19 msec), and a single low-therapeutic thioridazine dose of 50 mg increased QTc 22 msec (range 11 to 33 msec).(7) Strong CYP2D6 inhibitors linked to this monograph include: dacomitinib and terbinafine.(3)	TERBINAFINE HCL, VIZIMPRO
Levoketoconazole/Slt Strong CYP3A4 Inducers that Prolong QT 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: Strong inducers of CYP3A4 that prolong the QTc interval may induce the metabolism of levoketoconazole and result in additive risk of QT prolongation.(1-3) CLINICAL EFFECTS: Concurrent use of strong CYP3A4 inducers that prolong QT may reduce the clinical effectiveness of levoketoconazole and may cause additive effects on the QTc interval, which may result in life-threatening cardiac arrhythmias including torsades de pointes.(1-3) PREDISPOSING FACTORS: The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(3) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(3) Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks. PATIENT MANAGEMENT: The US manufacturer of levoketoconazole states that levoketoconazole is contraindicated with other agents that prolong the QT interval. Avoid the use of strong CYP3A4 inducers two weeks before and during levoketoconazole treatment.(1) Levoketoconazole is also contraindicated in patients with a prolonged QTcF interval of greater than 470 msec at baseline, history of torsades de pointes, ventricular tachycardia, ventricular fibrillation, or long QT syndrome (including first-degree family history). Use caution in patients with other risk factors for QT prolongation including congestive heart failure, bradyarrhythmias, and uncorrected electrolyte abnormalities. Consider more frequent ECG monitoring. Prior to starting levoketoconazole, obtain a baseline ECG and correct hypokalemia or hypomagnesemia. If a patient develops QT prolongation with a QTc interval greater than 500 msec, temporarily discontinue levoketoconazole. After resolution of prolonged QTc interval, levoketoconazole may be resumed at a lower dose. If QTc interval prolongation recurs, permanently discontinue levoketoconazole.(1) If concurrent therapy is warranted, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting. DISCUSSION: The US manufacturer of levoketoconazole states levoketoconazole is both an inhibitor and substrate of CYP3A4.(1) During phase 1 and 2 studies, which excluded patients with baseline QTcF interval greater than 470 msec, 4 (2.4%) patients experienced QTcF > 500 msec, and 23 (14.7%) patients experienced change-from-baseline QTcF > 60 msec.(1) Agents that are linked to this monograph may have varying degrees of potential to prolong the QTc interval but are generally accepted to have a risk of causing Torsades de Pointes. Agents linked to this monograph have been shown to prolong the QTc interval either through their mechanism of action, through studies on their effects on the QTc interval, or through reports of QTc prolongation and/or Torsades de Pointes in clinical trials and/or post-marketing reports.(3) Strong CYP3A4 inducers linked to this monograph are: encorafenib, thioridazine.(3,4)	RECORLEV
Mavacamten/Moderate CYP3A4 Inducers 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: Agents that induce the CYP3A4 isoenzyme may increase the metabolism of mavacamten.(1-3) CLINICAL EFFECTS: Concurrent use of moderate CYP3A4 inducers may decrease the levels and effectiveness of mavacamten.(1-3) PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks. PATIENT MANAGEMENT: The US and Canadian manufacturers of mavacamten state concurrent use of mavacamten with moderate CYP3A4 inducers is contraindicated.(1,2) The UK manufacturer of mavacamten states that management of mavacamten during concomitant use with moderate CYP3A4 inducers is dependent on CYP2C19 phenotype. Labeling recommends: -When initiating or increasing the dose of a moderate inducer in patients who are CYP2C19 poor metabolizers, monitor patients closely and adjust mavacamten dose based on clinical response. -When discontinuing or decreasing the dose of a moderate inducer in patients who are CYP2C19 poor metabolizers, decrease the dose of mavacamten to 2.5 mg, or pause therapy if dose is 2.5 mg. -No dose adjustment is warranted with moderate inducers in patients who are CYP2C19 intermediate, normal, rapid, or ultrarapid metabolizers.(3) DISCUSSION: Concomitant use of mavacamten (a single 15 mg dose) with a strong CYP2C19 and CYP3A4 inducer (rifampin 600 mg daily dose) is predicted to decrease mavacamten area-under-curve (AUC) and maximum concentration (Cmax) by 87% and 22%, respectively, in CYP2C19 normal metabolizers, and by 69% and 4%, respectively, in CYP2C19 poor metabolizers.(1) Moderate CYP3A4 inducers linked to this monograph include: belzutifan, bosentan, cenobamate, dabrafenib, elagolix, lesinurad, modafinil, nafcillin, pexidartinib, rifabutin, sotorasib, telotristat, thioridazine, and tovorafenib.(4,5)	CAMZYOS
Lonafarnib/Moderate CYP3A4 Inducers that Prolong QT 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: Moderate CYP3A4 inducers that prolong the QTc interval may increase the metabolism of lonafarnib. Concurrent use may result in an additive risk of QT prolongation.(1) CLINICAL EFFECTS: Concurrent use of moderate CYP3A4 inducers that prolong QT may decrease the serum levels and effectiveness of lonafarnib and have additive effects on the QTc interval, which may result in potentially life-threatening arrhythmias including torsades de pointes.(1) PREDISPOSING FACTORS: The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(2) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(2) Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks. PATIENT MANAGEMENT: The use of moderate CYP3A4 inducers with lonafarnib is contraindicated. If concurrent use is warranted, monitor ECG prior to initiation, during concurrent therapy, and as clinically indicated with other agents known to prolong the QTc interval.(1) DISCUSSION: With coadministration of a single oral dose of 50 mg lonafarnib (combined with a single oral dose of 100 mg ritonavir) following 600 mg rifampin (a strong CYP3A4 inducer) for 8 days, the area-under-curve (AUC) was reduced by 98% and the maximum concentration (Cmax) was reduced by 92%.(1) In a thorough QT study, lonafarnib 200 mg twice daily for 9 consecutive days and a single 200 mg dose on day 10 increased the mean QTc interval by 19 msec (upper bound of 90% confidence interval = 27 msec) on day 10 at 48 hours after administration of the morning dose of lonafarnib 200 mg. The maximum concentration (Cmax) on Day 10 was 2233 ng/ml, which is similar to the mean Cmax of 2695 ng/ml observed in the Hutchinson-Gilford Progeria Syndrome patient population.(1) Moderate inducers of CYP3A4 that prolong QT include: efavirenz and thioridazine.(3,4)	ZOKINVY

Drug contraindication overview.

No enhanced Contraindications information available for this drug.

Adverse reaction overview.

No enhanced Common Adverse Effects information available for this drug.

No enhanced Pediatric Use information available for this drug.

Contraindicated

None

Severe Precaution

None

Management or Monitoring Precaution

None