Clinical Symptomatology of Diphenhydramine Overdose: An Evaluation of 136 Cases in 1982 to 1985

Abstract

In West Germany, the antihistaminic diphenhydramine is marketed as a non-prescription hypnotic. Results of toxicological screening in cases of drug overdose indicate that poisoning with diphenhydramine represents a substantial part (4.5%) of the total number of intoxications. A total of 136 cases of diphenhydramine poisoning in 1982-1985 were evaluated with respect to age, ingested dose, plasma level, and clinical symptomatology. All patients had taken diphenhydramine with suicidal intent. Two-thirds of the patients were aged 14-30 years. In about 50% of the cases, between 6 and 40 times a therapeutic dose was ingested. Diphenhydramine plasma levels showed a wide range (0.1-4.7 /ug/ml) due to differences in ingested dose and time between ingestion and admission to hospital. Impaired consciousness was the most common symptom. Psychotic behavior similar to catatonic stupor-often combined with anxiety-was highly specific for diphenhydramine poisoning. Further symptoms included hallucinations, mydriasis, tachycardia, and less frequently diplopia, respiratory insufficiency, and seizures. Primary treatment included gastric lavage, administration of activated charcoal and sodium sulfate. In one case, hemodialysis and ultrafiltration were performed which had only limited effect on diphenhydramine plasma elimination kinetics. This patient died of diphenhydramine overdose and extreme hypothermia. All intoxications except the one mentioned before had an uncomplicated clinical course. In vitro experiments indicate that diphenhydramine may be almost completely removed from the plasma compartment by hemoperfusion. Routine analysis of urine samples in diphenhydramine overdose led to the identification of 4 previously unknown metabolites and artifacts of diphenhydramine.