DIPHENHYDRAMINE hydrochloride (Benadryl) is an antihistamine in the class of ethanolamines derived from the phenothiazines. In the dosages usually prescribed for allergic symptoms, the only notable neurologic side effect has been drowsiness, occurring in 20% to 60% of patients. An acute extrapyramidal movement disorder developed in a child following administration of two doses of diphenhydramine hydrochloride. This movement disorder resembled that induced in some young patients by the phenothiazines—a disorder that is usually relieved by diphenhydramine.
Report of a Case
Seventeen hours before admission, diphenhydramine was prescribed for a 3-year 11-month-old boy as treatment for an allergic reaction manifested as periorbital edema and urticaria. Medical history prior to this illness and family history were unremarkable. He received one dose of diphenhydramine hydrochloride, 25 mg, and a second dose seven hours later. Two hours after the second dose bizarre posturing of the right limbs, torticollis, distortion of the mouth, slurred speech,
Lavenstein BL, Cantor FK. Acute DystoniaAn Unusual Reaction to Diphenhydramine. JAMA. 1976;236(3):291. doi:10.1001/jama.1976.03270030045029