Diphenhydramine active uptake at the blood-brain barrier and its interaction with oxycodone in vitro and in vivo.

Diphenhydramine (DPHM) and oxycodone are weak bases that are able to form cations. Both drugs show active uptake at the blood-brain barrier (BBB). There is thus a possibility for a pharmacokinetic interaction between them by competition for the same uptake transport system.