Valaciclovir, the L-valyl
ester of
aciclovir (
acyclovir), is an oral
prodrug that undergoes rapid and extensive first-pass metabolism to yield
aciclovir and the
essential amino acid L-valine.
Aciclovir, the active
antiviral component of
valaciclovir, shows good in vitro activity against the herpesviruses herpes simplex virus (HSV)-1, HSV-2 and varicella zoster virus. The bioavailability of
aciclovir from oral
valaciclovir is considerably greater than that achieved after oral
aciclovir administration. Thus,
valaciclovir delivers therapeutic
aciclovir concentrations when administered in a less frequent oral dosage regimen than is required for
aciclovir.
Valaciclovir is an effective treatment for
herpes zoster in immunocompetent adults. In a large comparative study that included patients > or = 50 years of age,
valaciclovir (1000mg 3 times daily for 7 or 14 days) and oral
aciclovir (800mg 5 times daily) were equally effective in achieving resolution of cutaneous
zoster lesions. Importantly,
valaciclovir was significantly more effective than
aciclovir in reducing the duration of
zoster-associated
pain. Preliminary results of several studies indicate that
valaciclovir (500 to 1000mg twice daily for 5 to 10 days) is as effective as
aciclovir (200mg 5 times a day for 5 to 10 days) in the treatment of
genital herpes. In patients with first or recurrent episodes of
genital herpes,
valaciclovir reduced the duration of viral shedding, hastened lesion healing and decreased lesion-associated
pain.
Valaciclovir was also effective in suppressing recurrent episodes of
genital herpes and significantly prolonged the time to a recurrent episode of
infection compared with placebo.
Valaciclovir is a well tolerated
drug; in
herpes zoster and HSV studies its tolerability profile was similar to that of
aciclovir or placebo.
Valaciclovir represents and advance in antiherpes
drug therapy and is a useful treatment option for patients with
herpes zoster or
genital herpes. It is at least as effective as
aciclovir and is administered in a more convenient oral dosage regimen. Thus,
valaciclovir may ultimately succeed
aciclovir as a first-line treatment for
genital herpes or
herpes zoster.