title: Diphenhydramine induced QT prolongation and torsade de pointes: An uncommon effect of a common drug.
abstract: 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.
authors.affiliation: St. Joseph Mercy Oakland, Internal Medicine/Cardiology, Pontiac, Michigan 48341, USA. doczehrah@yahoo.com
authors.forename: Zehra
authors.initials: Z
authors.lastname: Husain
authors.forename: Khursheed
authors.initials: K
authors.lastname: Hussain
authors.forename: Rajiv
authors.initials: R
authors.lastname: Nair
authors.forename: Russell
authors.initials: R
authors.lastname: Steinman
mesh_terms: D000328:Adult; D000435:Alcoholic Intoxication; D004155:Diphenhydramine / Q000009:adverse effects* / Q000506:poisoning*; D062787:Drug Overdose; D004562:Electrocardiography; D005260:Female; D006634:Histamine H1 Antagonists / Q000009:adverse effects / Q000506:poisoning; D006801:Humans; D008133:Long QT Syndrome / Q000139:chemically induced* / Q000175:diagnosis; D013406:Suicide, Attempted; D016171:Torsades de Pointes / Q000139:chemically induced* / Q000175:diagnosis
chemical_list: D006634:Histamine H1 Antagonists; D004155:Diphenhydramine