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Valaciclovir
📖 About
Always check the BNF entry for Valaciclovir for the most up-to-date dosing and safety information. Valaciclovir is a prodrug of aciclovir, designed for improved oral bioavailability.
⚙️ Mode of Action
- Converted to aciclovir after absorption.
- Inhibits viral DNA polymerase → halts viral DNA replication.
- Selective action because the drug requires phosphorylation by viral thymidine kinase.
💊 Indications
- Herpes zoster (shingles).
- Herpes simplex virus (HSV) infections, including genital herpes.
- Prophylaxis/treatment of CMV post-transplant (specialist use).
📌 Dosing (check BNF for updates)
Take with food to improve absorption. Renal dose adjustment is often required.
| Indication | Dose & Duration |
|---|---|
| Herpes zoster (immunocompetent) | 1 g TDS for 7 days (PO) |
| Herpes zoster (immunocompromised) | 1 g TDS for ≥7 days, continue 2 days after crusting (PO) |
| HSV – first episode | 500 mg BD for 5–10 days (PO) |
| HSV – first episode (immunocompromised) | 500 mg BD for 5–10 days or longer (PO) |
🔀 Interactions
- Check BNF for full list.
- Notable: other nephrotoxic drugs (e.g. ciclosporin, tacrolimus) increase risk of renal impairment.
⚠️ Cautions
- Renal impairment → adjust dose to avoid accumulation and neurotoxicity.
- Elderly patients (higher risk of renal impairment).
🚫 Contraindications
- Known hypersensitivity to aciclovir/valaciclovir or excipients.
💥 Side Effects
- Generally well tolerated.
- GI: nausea, vomiting, abdominal pain.
- CNS: headache, dizziness, confusion (especially with renal impairment).
- Rare: renal impairment, thrombocytopenia, neurological toxicity.
📚 References
📝 Revisions
- Expanded with MoA, key cautions, and structured two-column dosing table (Aug 2025).
| The content on this website is provided for educational and informational purposes only to support exam preparation (e.g., MLA, MRCP, USMLE) and learning. This is NOT medical advice, diagnosis, treatment, or professional guidance. It does not replace consultation with a qualified healthcare professional, official guidelines (e.g., NICE, GMC, BNF), or supervised clinical practice. Always verify information with current, authoritative sources. Makindo and its contributors accept no liability for any reliance on this content, including errors, omissions, or any resulting harm, loss, or consequences. By using this site, you agree to these terms. |
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