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Am Fam Physician. 1998;57(5):947

to the editor: We are writing in response to the article by Dr. Stott about famciclovir (Famvir).1 Several comparisons of famciclovir and acyclovir (Zovirax) were made; however, there was no mention of valacyclovir (Valtrex).

It is worth noting the following: both famciclovir and valacyclovir were available in 1995; both drugs are dosed less frequently than acyclovir; both drugs have better bioavailability than acyclovir; both are pro-drugs, and both may have effects on postherpetic neuralgia.

In addition to omitting information about valacyclovir, the article included several comments that were incorrect or were not clinically relevant.

The author implies that the intracellular pharmacokinetics of famciclovir may be responsible for its reduced dosing frequency and its effects on postherpetic neuralgia (compared with placebo) in patients with herpes zoster. Although valacyclovir has quite different intracellular pharmacokinetics, it still demonstrates an effect on postherpetic neuralgia, not only when compared with placebo, but also when compared with acyclovir. Moreover, a trial comparing famciclovir with acyclovir2 in otherwise healthy patients (one not mentioned in the article) showed no difference between famciclovir and acyclovir in terms of efficacy for postherpetic neuralgia despite the high intracellular concentrations of drug. If intracellular pharmacokinetics of antivirals were indeed clinically relevant, one would expect an improvement in efficacy; however, no additional clinical benefit seems apparent.

In addition, the author states that famciclovir has been compared with placebo in two clinical trials in immunocompromised patients with herpes zoster. To our knowledge, the trials to which the author refers were conducted in immunocompetent patients and formed the basis for the current use of famciclovir in immunocompetent patients.

editor's note: This letter was sent to the author of “Famciclovir: A New Systemic Antiviral Agent for Herpesvirus Infections,” who declined to reply.

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This series is coordinated by Kenny Lin, MD, MPH, deputy editor.

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