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Prodrug Antiviral — HSV / VZV / CMV Prevention (Oral)

Valaciclovir

Brand names: Valtrex

Valaciclovir is an oral prodrug of aciclovir, an antiviral used to treat herpes simplex (including genital herpes) and herpes zoster infections and to suppress recurrent HSV.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It is rapidly converted to aciclovir, which is phosphorylated by viral thymidine kinase and inhibits viral DNA polymerase, halting viral DNA replication.

Prescribing in practice

  • Ensure adequate hydration and reduce the dose in renal impairment, as accumulation can cause acute kidney injury and neurotoxicity (confusion, hallucinations), especially in older patients.
  • Its improved oral bioavailability over aciclovir allows less frequent dosing.
  • Start treatment as early as possible after symptom onset for best effect, particularly in herpes zoster.

Monitoring

Monitor renal function in patients with impaired kidneys, the elderly, or those on other nephrotoxic drugs.

Counselling the patient

  • Drink plenty of fluids while taking this medicine.
  • Begin the course at the first sign of an outbreak.
  • Report confusion, agitation or reduced urine output.

Evidence & guidelines

Valaciclovir is an established first-line oral agent for herpes simplex and zoster in line with UK and international guidance.

Reference: BASHH Herpes Guidelines 2014; BHIVA HIV Guidelines; Cochrane Review: Antivirals for Herpes Zoster; PHE Shingles Treatment Guidance; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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