A515U: a prodrug of acyclovir with increased oral bioavailability.

The tolerance and pharmacokinetics of A515U, a xanthine oxidase-activated prodrug of acyclovir have been investigated in healthy volunteers and in two phase-I clinical studies in immunocompromised patients. In all cases the bioavailability of acyclovir following oral administration of A515U was substantially increased over that achieved in the same subjects with oral acyclovir itself. Plasma acyclovir levels were similar to those previously attainable only with intravenous acyclovir. This increase in bioavailability may permit reductions in the frequency of administration and extend the range of herpes virus infections amenable to oral therapy. A515U was very well tolerated, with no significant clinical adverse events being attributed to the drug.