A Diphenhydramine Overdose Mimicking Encephalitis, Complicated by Acute Kidney Injury Associated with Anticholinergic Urinary Retention: A Case Report.

A 26-year-old man presented with fever, an altered consciousness, tremor, mydriasis, tachycardia, and a dry oral mucosa and was empirically treated for suspected encephalitis. A rapid neurological improvement and anticholinergic findings prompted the reconsideration of intoxication. A family assisted room search revealed empty over-the-counter medication bottles, and he later reported ingesting 2.4 g of diphenhydramine at once. Acute kidney injury developed in association with diphenhydramine-induced urinary retention, and his urine output and renal function improved after catheterization. In encephalitis-like presentations with systemic anticholinergic signs, a diphenhydramine overdose should be considered, a collateral medication history should be sought, and urinary tract obstruction should be assessed if the renal function worsens.