lthough the clinical features of diphenhydramine overdose are well known, information about dose-dependent toxicity is still scarce. This has been investigated in patients with acute diphenhydramine poisoning in retrospective and prospective studies in 232 and 50 patients respectively [19]. Mild symptoms (somnolence,
anticholinergic signs, tachycardia, nausea/vomiting) occurred in 55–64% of patients, moderate symptoms (isolated and spontaneously resolving agitation, confusion, hallucinations, and electrocardiographic disturbances) in 22–27%, and severe symptoms (delirium/psychosis, seizures, coma) in 14–18%. Moderate symptoms occurred at doses over 0.3 g. For severe symptoms the critical dose limit was 1.0 g. Coma and seizures were significantly more frequent in those who took over 1.5 g compared with those who took 1.0–1.5 g. These data showed clear dose-dependent
acute toxicity of diphenhydramine and suggested that only patients who take over 1.0 g are at risk of severe symptoms.
•
A 35-year-old woman took diphenhydramine 16 g and developed hypertension and QRS prolongation; charcoal
hemoperfusion and
hemodialysis were used successfully [20].
•
A 28-year-old died after an overdose of diphenhydramine. He developed
hyperpyrexia and tachycardia and died from a cardiac arrest [21]. Hemorrhagic
pulmonary edema and renal shock were the most prominent findings. At the time of death, the plasma concentration of diphenhydramine was 5 mg/ml and there were particularly high concentrations in the lungs (55 mg/kg) and kidneys (50 mg/kg).
