New data presented at the 6th International Conference on Antiviral Research, held in Venice, Italy, on April 25-30, provide a comparison of the antiviral activity of the antiherpetic drugs aciclovir (Wellcome's Zovirax) and penciclovir (the active metabolite of SmithKline Beecham's prodrug famciclovir).
According to in vitro and in vivo data presented by Eddie Littler of Wellcome's Research Laboratories in the UK, penciclovir has a more limited profile of antiviral activity than aciclovir. The two compounds have similar in vitro activities against Herpes simplex virus type-1 and Varicella zoster virus, but penciclovir has inferior in vitro activity against HSV-2, human cytomegalovirus and Epstein-Barr virus, according to Dr Littler. He noted that lack of activity in EBV may lead to lack of beneficial effect in immunocompromised patients.
Explaining the difference in activity, Dr Littler postulates that unlike aciclovir, penciclovir is a poor inhibitor of the herpes virus enzyme DNA polymerase which is essential for viral replication. However, he cautioned against extrapolating this data to the clinical situation.
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