Question: how much diphenhydramine hydrochloride is lethal?
Answer: Although the serum DPH concentration was thought to have peaked about 13 h before arriving at the hospital in this case because peak serum DPH concentration is usually reached 2–3 h after ingestion, the patient's serum DPH concentration at the time of arrival was >5 μg/mL, which is considered to be a fatal dose.