Interactions between tagamet(cimetidine) and Terfenadine (terfenadine)
cimetidine and terfenadine (Major Drug-Drug)
GENERALLY AVOID: Cimetidine inhibits the CYP450 isoenzymes and may interfere with metabolism of the antihistamines terfenadine and astemizole. The accumulation of either of these drugs may result in a prolongation of the QT interval and could lead to the development of ventricular arrhythmias such as torsades de pointes. One case of drug-induced torsades de pointes has been reported in a patient receiving cimetidine and terfenadine. The patient was also receiving other medications including chlorpheniramine, propoxyphene and acetaminophen. Cimetidine reportedly did not affect terfenadine pharmacokinetics or EKGs in a controlled study with 6 healthy subjects.
MANAGEMENT: Until more information is available, it may be best to avoid this combination. Cetirizine, fexofenadine, or loratadine may be safer antihistamine alternatives.
