Drug Interactions between asenapine and terfenadine

GENERALLY AVOID: Asenapine may cause dose-related prolongation of the QT interval. Theoretically, coadministration with other agents that can prolong the QT interval may result in additive effects and increased risk of ventricular arrhythmias including torsade de pointes and sudden death. The effects of asenapine on the QT/QTc interval were evaluated in a dedicated QT study using dosages of 5 mg, 10 mg, 15 mg, and 20 mg twice daily in 151 clinically stable patients with schizophrenia. At these dosages, asenapine was associated with increases in QTc interval ranging from 2 to 5 msec compared to placebo. No patient treated with asenapine experienced QTc increases >= 60 msec from baseline measurements or a QTc >= 500 msec. In short-term clinical trials using 5 mg or 10 mg twice daily dosages, post-baseline QT prolongations exceeding 500 msec were reported at comparable rates for asenapine and placebo. There were no reports of torsade de pointes arrhythmia or any other adverse reactions associated with delayed ventricular repolarization. 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). The extent of drug-induced QT prolongation is dependent on the particular drug(s) involved and dosage(s) of the drug(s). In addition, certain agents with anticholinergic properties (e.g., sedating antihistamines; antispasmodics; neuroleptics; phenothiazines; skeletal muscle relaxants; tricyclic antidepressants; disopyramide) may have additive parasympatholytic and central nervous system-depressant effects when used in combination with asenapine. Excessive parasympatholytic effects may include paralytic ileus, hyperthermia, mydriasis, blurred vision, tachycardia, urinary retention, psychosis, and seizures.

MANAGEMENT: Coadministration of asenapine with other drugs that can prolong the QT interval should generally be avoided. Caution and clinical monitoring are recommended if concomitant use is required. Patients should have regular ECGs and be monitored for arrhythmias when QT interval is prolonged. Persistent QTc measurements exceeding 500 msec will require suspension of asenapine therapy and immediate action to correct any concomitant risk factors before resuming treatment. Patients should be advised to seek prompt medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope. In addition, if combination therapy with agents with anticholinergic properties is required, caution is advised, particularly in the elderly and those with underlying organic brain disease. Patients should be advised to notify their physician promptly if they experience potential symptoms of anticholinergic intoxication such as abdominal pain, fever, heat intolerance, blurred vision, confusion, and/or hallucinations. Ambulatory patients should be counseled to avoid activities requiring mental alertness until they know how these agents affect them. A reduction in anticholinergic dosages may be necessary if excessive adverse effects develop.

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