Vol 17, No 5 (2010)
Case Reports
Published online: 2010-09-23

open access

Page views 1066
Article views/downloads 5488
Get Citation

Connect on Social Media

Connect on Social Media

Diphenhydramine induced QT prolongation and torsade de pointes: An uncommon effect of a common drug

Zehra Husain, Khursheed Hussain, Rajiv Nair, Russell Steinman
Cardiol J 2010;17(5):509-511.


The histamine I receptor antagonist diphenhydramine is a freely available, over the counter medication for sleep and the most frequently used antihistamine drug. It inhibits the fast sodium channels and, at higher concentrations, the repolarising potassium channels, particularly Ikr which leads to prolongation of the action potential and the QT interval. The toxicity of diphenhydramine is dose-dependent, with a critical dose limit of 1.0 g. We report a case of a young woman who consumed more than 3 g of diphenhydramine in the setting of alcohol intoxication and developed QTc prolongation with nonsustained polymorphic ventricular tachycardia. These changes reverted to normal with supportive treatment. An overdose of diphenhydramine with concomitant alcohol use can induce torsade de pointes in an otherwise normal heart. (Cardiol J 2010; 17, 5: 509-511)

Article available in PDF format

View PDF Download PDF file