Valacyclovir

Valacyclovir is an antiviral medication that serves as a prodrug of acyclovir. It is used to treat infections caused by herpesviruses, including herpes simplex virus and varicella-zoster virus, and to reduce viral transmission in select cases. Its oral formulation generally offers higher bioavailability than acyclovir, allowing convenient dosing.

Common medical uses include treatment of acute genital herpes, orolabial herpes, shingles (herpes zoster), and, in some settings, varicella (chickenpox) in children or adults. Valacyclovir can also be prescribed as suppression therapy for frequent genital herpes outbreaks to reduce recurrences and, when appropriate, to help lower the risk of transmitting the virus to partners.

Valacyclovir works by being converted in the liver and gut to acyclovir, which inhibits viral DNA synthesis by acting on viral DNA polymerase and causing chain termination. This reduces the replication of herpesviruses and shortens episode duration and severity.

Pharmacokinetics include oral bioavailability of about 50-60%, with distribution in body fluids and tissues. It is primarily eliminated by the kidneys, and dose adjustments are needed for impaired renal function. The half-life is longer in renal impairment.

Dosing depends on indication and renal function. Typical regimens include higher-dose short courses for initial outbreaks, shorter courses for recurrences, and daily dosing for suppression. Common adverse effects are headache, nausea, and stomach upset; dehydration and kidney-related issues can increase risk, especially with high doses or dehydration. Interactions can occur with nephrotoxic drugs and with agents like probenecid. Contraindications include hypersensitivity to valacyclovir or acyclovir; use in pregnancy and breastfeeding should be based on risk-benefit assessment.