Pharmacokinetic modeling of over-the-counter drug diphenhydramine self-administered in overdoses in Japanese patients admitted to hospital.

The determined plasma concentrations of diphenhydramine of around 1000 ng/mL at ~ 3 h after orally administered overdoses in cases 1 and 2 may not have been high enough to cause hepatic impairment because levels of aspartate aminotransferase and alanine aminotransferase were normal; however, there was an increase in total bilirubin in case 1. Nonetheless, high virtual liver exposures of diphenhydramine were estimated by the current PBPK model. The present results based on drug monitoring data and pharmacokinetic predictions could serve as a useful guide when setting the duration of treatment in cases of diphenhydramine overdose.