Absorption of Diazepam in Man Following Rectal and Parenteral Administration

Abstract

Serum concentrations of diazepam and N-desmethyldiazepam [often used for pre-anesthesia] were measured in 6 adult patients after administration of 10 mg diazepam in solution by the rectal, i.v. and i.m. routes. Maximum serum concentrations of 121-200 ng/ml were recorded from 10-20 min after the rectal instillation, but after injection the levels rose slowly and irregularly, reaching a maximum (62-186 ng/ml) in 1-24 h. The bioavailability of diazepam given by rectal instillation was 50 .+-. 17% (mean .+-. S.D.) as compared with the i.v. administration. The possible reasons for the low bioavailability were discussed. Apparently, administration by rectal tube provides a useful alternative to the tablets (and i.m. injections) when a rapid onset of effect of the drug is wanted and when i.v. administration is not applicable or practical.