A Case of Electrocardiographic and Mental Change in a Patient with a Diphenhydramine Overdose

ABSTRACT

The antihistaminic drug diphenhydramine is mainly used as a sedative, hypnotic and antiemetic. In many countries it is available over-the-counter, very common, and generally regarded as a harmless drug. However, diphenhydramine overdose can result in cardiotoxicity due to its ability to block fast sodium channels in a manner analogous to classic Vaughan-Williams type IA antidysrhythmic agents. As such, cardiotoxicity from diphenhydramine resembles that of the tricyclic antidepressant agents. Here we report a case of a 52 year old man who ingested 2,000 mg of diphenhydramine and presented with an altered mental state and an electrocardiographic change. His electrocardiogram showed sinus tachycardia with a rate 145 beat/min, a QRS interval of 88 ms, and a QTc of 556 ms. He had a wide anion gap metabolic acidosis. He was treated with intravenous sodium bicarbonate and supportive therapy. His clinical manifestations waned and he was transferred to another hospital nearby his hometown.