Case of polymorphic ventricular tachycardia in diphenhydramine poisoning.

This is the first reported case of torsades de pointes attributable to diphenhydramine, a drug with weak I(Kr) effects. A 26-year-old, healthy man was admitted to intensive care after a diphenhydramine overdose. Results of physical examination, ECG, and electrolytes were normal at admission. Despite supportive care, he developed typical, sustained, torsades de pointes with a markedly prolonged QT interval requiring cardioversion. Drugs with weak I(Kr)-blocking effects may cause lethal proarrhythmia in susceptible individuals when delivered in high concentrations. This case illustrates the variation in repolarization reserve that exists in a free-standing population.