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Prodrug Antiviral — HSV / VZV / CMV Prevention (Oral) Pregnancy: Use with caution — aciclovir registry data show no increased birth defects; valaciclovir considered safe for HSV suppression in pregnancy

Valaciclovir

Brand names: Valtrex

Adult dose

Dose: Herpes zoster (shingles): 1 g 3 times daily × 7 days; Genital herpes (first episode): 500 mg twice daily × 10 days; Recurrent genital herpes: 500 mg twice daily × 3–5 days; HSV suppression: 500 mg once daily; CMV prevention (transplant): 2 g 4 times daily × 90 days
Route: Oral
Frequency: 1–4 times daily (indication-dependent)
Max: 4 g/day (CMV prevention — high dose); 3 g/day (zoster)
Prodrug of aciclovir — L-valyl ester increases bioavailability from 15–20% (aciclovir oral) to 54–70%. Start within 72 hours of rash onset for herpes zoster — ideally within 48 hours. High-dose (2 g QDS) for CMV prevention is an unlicensed dose in most countries — used in transplant centres as alternative to valganciclovir.

Paediatric dose

Route:
Seek specialist opinion — not licensed in paediatrics; IV aciclovir preferred in children for severe HSV/VZV; some specialist centres use valaciclovir in adolescents for suppression therapy

Dose adjustments

Renal

CrCl 30–49: reduce zoster dose to 1 g BD; CrCl 10–29: 1 g OD (zoster), 500 mg OD (HSV); CrCl <10: 500 mg OD; haemodialysis: dose post-dialysis

Hepatic

No dose adjustment required

Clinical pearls

  • Zoster timing critical: start within 72 hours of rash onset (ideally <48 hours) — reduces duration of acute neuritis and risk of post-herpetic neuralgia; no benefit if started after 72 hours in immunocompetent (unless new lesions still appearing)
  • Immunocompromised patients (HIV, transplant): treat regardless of timing — disseminated zoster risk; use IV aciclovir if systemic involvement (visceral, ophthalmologic, neurological)
  • High-dose CMV prophylaxis (2 g QDS): less expensive than valganciclovir — used in some transplant centres; evidence from VALGANCICLOVIR vs high-dose valaciclovir trials (non-inferior in some studies)
  • Neurological toxicity at high doses or in renal failure: confusion, agitation, hallucinations — ensure dose reduction in renal impairment; TMA is a rare but serious complication in immunosuppressed at very high doses

Contraindications

  • Hypersensitivity to valaciclovir or aciclovir

Side effects

  • Headache
  • Nausea
  • Dizziness
  • Neurological effects (confusion, hallucinations — especially in renal failure)
  • Thrombotic microangiopathy (TMA — at high doses in immunocompromised; rare)
  • Renal impairment (high doses — ensure adequate hydration)

Interactions

  • Probenecid/cimetidine — increase aciclovir levels (reduce tubular secretion)
  • Nephrotoxic drugs — additive renal toxicity
  • Ciclosporin — additive nephrotoxicity

Monitoring

  • Renal function (especially at high doses)
  • Neurological status
  • FBC (high-dose TMA risk)
  • Clinical response (lesion healing, pain)

Reference: BNFc; BNF 90; BASHH Herpes Guidelines 2014; BHIVA HIV Guidelines; Cochrane Review: Antivirals for Herpes Zoster; PHE Shingles Treatment Guidance. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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