Overview
Valacyclovir is an antiviral drug and a prodrug of acyclovir. It is used for the same indications—such as shingles, cold sores, and genital herpes—but offers greater bioavailability, allowing for less frequent dosing.

Mechanism of Action
After oral administration, valaciclovir is rapidly absorbed and nearly completely converted to aciclovir and L-valine by first-pass intestinal and hepatic metabolism. The active aciclovir then inhibits viral DNA replication as described previously.

Dosage and Administration
For shingles, the standard adult dose is 1000 mg three times daily for 7 days. For genital herpes, it is typically 500 mg twice daily. Its enhanced absorption makes it a more convenient option compared to oral acyclovir.

Side Effects
Side effects are similar to acyclovir and include headache, nausea, and abdominal pain. In rare instances, severe syndromes like thrombotic thrombocytopenic purpura/haemolytic uraemic syndrome (TTP/HUS) have been reported, primarily in immunocompromised patients.

Contraindications
Contraindicated in patients hypersensitive to valaciclovir or aciclovir. Strict dosage adjustment is necessary for patients with renal impairment to prevent drug accumulation and neurotoxicity.