Rectal absorption of acyclovir in rats and improvement of absorption by triglyceride base

The rectal absorption of acyclovir has been evaluated after administration of suppositories without absorption enhancers in rats. The disappearance of plasma acyclovir followed biexponential kinetics after i.v. dosing. Rectal administration of a triglyceride (Vosco S-55 and Vosco S-55 + methylcellulose) suppository gave relatively high plasma concentrations and bioavailabilities (95.3 and 83.4%, respectively) compared with Witepsol and macrogol suppositories. However, the in vitro release profiles from suppositories did not accurately reflect plasma concentrations after rectal dosing. Our results suggest that the rectal administration of acyclovir suppositories may be a promising substitute for intravenous infusion, which is at present used for the treatment.