[Valaciclovir].

Abstract

Valaciclovir is an aciclovir pro-drug considerably improving its oral availability. Its antiviral activity in vivo is related to that of aciclovir, the principle target of which is the herpes virus. Following digestive absorption, valaciclovir is rapidly transformed into aciclovir. The mean absolute bioavailability of aciclovir is of 54.2% after a single oral dose of 1,000 mg of valaciclovir, i.e., a bioavailability 3 to 5-fold greater than after oral ingestion of aciclovir. The plasma pharmacokinetic profile of valaciclovir and aciclovir observed in volunteers infected by HIV is superimposable on that of healthy subjects. In elderly patients, exposure to aciclovir is enhanced, probably because of the alteration in glomerular filtration. In patients exhibiting agranulocytosis following poly-chemotherapy, the pharmacokinetic parameters are superimposable on those observed in healthy patients. In patients with hepatic failure, there appears no need to adapt the dose, since exposure to aciclovir does not appear altered. However, the dose of valaciclovir must be adapted to renal function. During the first-episode of herpes genitalis, valaciclovir, at the dose of 500 or 1,000 mg twice daily, is as effective as 200 mg of aciclovir five times per day. In recurrent herpes genitalis, 500 mg twice daily of valaciclovir is as effective as 1,000 mg twice daily or 200 mg five times a day of aciclovir. Valaciclovir prevents recurrence herpes genitalis with a dose-dependent effect, and doses of 500 and 1,000 mg/day are as effective as 400 mg twice daily of aciclovir. There are few studies on the efficacy of valaciclovir in the treatment of oro-facial herpes. In the treatment of herpes zoster in patients aged over 50, the principle benefit provided by valaciclovir at the dose of 1,000 mg twice daily, is the decrease in the percentage of patients presenting post-zoster pain and its duration. High doses of valaciclovir (8 capsules/day) provide efficient prevention of infections related to the cyto-megalo-virus (CMV) in immunodepressed patients due to HIV infection or following renal transplantation. Tolerance to valaciclovir, like its active metabolite aciclovir, is generally good. Central neurological toxicity is frequently observed with high doses, but regresses on withdrawal. The official indications in France are the curative and preventive treatment of herpes genitalis infections, the prevention of post-zoster pain and the ocular complications of ophthalmologic herpes in immunocompetent adults, and the prevention of CMV infections after organ grafting.