• diphenhydramine;
  • overdose;
  • QT prolongation;
  • IKr channel;
  • torsades de pointes

This is the first reported case of torsades de pointes attributable to diphenhydramine, a drug with weak IKr 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 IKr-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. (J Cardiovasc Electrophysiol, Vol. 15, pp. 591-593, May 2004)