Drug Interaction Report

MONITOR CLOSELY: Tetrabenazine causes central dopamine depletion by binding reversibly to human vesicular monoamine transporter type 2 (VMAT2) and interfering with presynaptic monoamine storage mechanisms. Coadministration of tetrabenazine in combination with neuroleptic agents or other dopamine antagonists (e.g., metoclopramide, amisulpride) may result in severe manifestations of dopamine deficiency. Neuroleptic malignant syndrome, hyperthermia, parkinsonism, dysphagia, akathisia and other extrapyramidal disorders have been reported during tetrabenazine therapy, either alone or in combination with neuroleptic agents.

GENERALLY AVOID: Tetrabenazine as well as many neuroleptic agents (e.g., asenapine, clozapine, droperidol, haloperidol, iloperidone, paliperidone, pimozide, phenothiazines, quetiapine, risperidone, sertindole, ziprasidone) and other dopamine antagonists (e.g., domperidone, amisulpride) have been associated with dose-related prolongation of the QT interval. Theoretically, the use of these agents in combination may result in elevated risk of ventricular arrhythmias, including ventricular tachycardia and torsade de pointes, because of additive arrhythmogenic potential related to their effects on cardiac conduction. In healthy male and female subjects, a single 25 or 50 mg dose of tetrabenazine has been shown to increase QTc by an average of approximately 8 msec. Effects at higher exposures to either tetrabenazine or its metabolites have not been evaluated. In general, the risk of an individual agent or a combination of agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such as congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). In addition, the extent of drug-induced QT prolongation is dependent on the particular drugs involved and dosages of the drugs.

MANAGEMENT: The use of tetrabenazine in combination with neuroleptic agents or other dopamine antagonists should preferably be avoided. When coadministration is required, patients should be instructed to notify their physician if they experience extrapyramidal symptoms such as bradykinesia, hypertonia, rigidity, restlessness, and dysphagia. Clinicians, caregivers, and family members should be apprised of the risk of neuroleptic malignant syndrome and be alert to potential signs and symptoms such as mental status changes (e.g., mutism, catatonia, stupor, coma, agitation, confusion, hallucinations, delusions), autonomic instability, restlessness, rigidity, ataxia, myoclonus, hyperreflexia, tremors, diaphoresis, elevated creatine phosphokinase levels, and hyperpyrexia. Patients should seek medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, palpitations, or syncope.

ADJUST DOSE: The central nervous system and respiratory depressant effects of meperidine may be potentiated by concomitant use of other agents with CNS depressant effects. An increased risk of serious adverse reactions such as respiratory depression, hypotension, profound sedation, syncope, coma, and even death should be considered, particularly in elderly or debilitated patients.

MANAGEMENT: Caution and dosage adjustments are advisable when meperidine is used in combination with other narcotic analgesics, general anesthetics, phenothiazines, sedative-hypnotics, tranquilizers, tricyclic antidepressants, or other CNS depressants such as alcohol. A lower dosage of meperidine should be considered initially, then titrated carefully according to pain level and clinical response. Meperidine dosage reductions of 25% to 50% have been recommended for patients receiving phenothiazines and other tranquilizers. Patients should be advised to avoid rising abruptly from a sitting or recumbent position, and to notify their physician if they experience dizziness, lightheadedness, orthostasis, syncope, tachycardia, or excessive CNS effects that interfere with their normal activities. Patients should also avoid driving or operating hazardous machinery until they know how these medications affect them.

ADJUST DOSE: The central nervous system and respiratory depressant effects of meperidine may be potentiated by concomitant use of other agents with CNS depressant effects. An increased risk of serious adverse reactions such as respiratory depression, hypotension, profound sedation, syncope, coma, and even death should be considered, particularly in elderly or debilitated patients.

MANAGEMENT: Caution and dosage adjustments are advisable when meperidine is used in combination with other narcotic analgesics, general anesthetics, phenothiazines, sedative-hypnotics, tranquilizers, tricyclic antidepressants, or other CNS depressants such as alcohol. A lower dosage of meperidine should be considered initially, then titrated carefully according to pain level and clinical response. Meperidine dosage reductions of 25% to 50% have been recommended for patients receiving phenothiazines and other tranquilizers. Patients should be advised to avoid rising abruptly from a sitting or recumbent position, and to notify their physician if they experience dizziness, lightheadedness, orthostasis, syncope, tachycardia, or excessive CNS effects that interfere with their normal activities. Patients should also avoid driving or operating hazardous machinery until they know how these medications affect them.

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

GENERALLY AVOID: Ethanol may potentiate the central nervous system (CNS) depressant effects of opioid analgesics. Concomitant use may result in additive CNS depression and impairment of judgment, thinking, and psychomotor skills. In more severe cases, hypotension, respiratory depression, profound sedation, coma, or even death may occur.

MANAGEMENT: Concomitant use of opioid analgesics with ethanol should be avoided.

GENERALLY AVOID: Concurrent use of ethanol and phenothiazines may result in additive CNS depression and psychomotor impairment. Also, ethanol may precipitate dystonic reactions in patients who are taking phenothiazines. The two drugs probably act on different sites in the brain, although the exact mechanism of the interaction is not known.

MANAGEMENT: Patients should be advised to avoid alcohol during phenothiazine therapy.