Aciclovir prodrug

Valaciclovir

Brand names: Valtrex

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

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

After absorption it is converted to aciclovir, which viral thymidine kinase phosphorylates to a triphosphate that inhibits viral DNA polymerase and terminates the growing viral DNA chain.

Prescribing in practice

Maintain good hydration and adjust the dose in renal impairment to avoid crystalluria, acute kidney injury and neurotoxicity, which are more likely in the elderly and dehydrated.
Greater oral bioavailability than aciclovir permits a simpler, less frequent dosing schedule.
Treatment is most effective when started promptly after the onset of symptoms.

Monitoring

Check renal function in those with pre-existing renal impairment, advanced age, or concomitant nephrotoxic therapy.

Counselling the patient

Keep well hydrated throughout the course.
Start treatment as soon as symptoms appear, especially for shingles.
Seek advice if you become confused or notice you are passing less urine.

Evidence & guidelines

It is a well-established oral antiviral recommended for herpes simplex and zoster in current prescribing references.

Reference: NICE NG147/CKS; 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).

Curated clinical cross-links plus same-class fallbacks.

Pathways