Zimivir
Zimivir (Valacyclovir 500/1000 mg) — GSK acyclovir prodrug for genital herpes (initial + suppression), cold sores, and herpes zoster. Improved oral bioavailability allows 2-3× daily dosing.
✓ Medically reviewed by Morgan Ellis — Pharmacy Researcher · 8 years experience · Last reviewed: May 2026
Quick Answer
Zimivir — valacyclovir 500/1000 mg (GlaxoSmithKline). Acyclovir prodrug — for genital herpes (initial + suppression), herpes labialis (cold sores), herpes zoster (shingles), and prophylaxis of CMV in transplant. Preferred over acyclovir for adherence: better oral bioavailability allows 2-3× daily dosing.
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Valacyclovir is renally cleared; dehydration causes crystallisation and acute kidney injury. Maintain good fluid intake. Adjust dose for CrCl <50 mL/min. Caution in the elderly.
Dosing by indication
| Indication | Dose |
|---|---|
| Initial genital herpes (immunocompetent) | 1 g BID × 7-10 days |
| Recurrent genital herpes (start within 24 hours) | 500 mg BID × 3 days OR 1 g once daily × 5 days |
| Suppressive therapy (≥6 episodes/year) | 500 mg or 1 g once daily long-term |
| Cold sores (start at first prodrome) | 2 g BID × 1 day (single-day regimen) |
| Herpes zoster (shingles, <72 hours from rash onset) | 1 g TID × 7 days |
| Prevention of HSV transmission to partner (with safer sex practices) | 500 mg once daily long-term |
Renal dose adjustment is required for CrCl <50 mL/min. Adequate hydration during therapy reduces crystallisation risk.
Frequently Asked Questions
Valacyclovir vs acyclovir — which is better?
Same active molecule (acyclovir). Valacyclovir has 3-5× higher oral bioavailability and allows 2-3× daily dosing instead of 5×, dramatically improving adherence. Reserved for severe disease (HSV encephalitis, neonatal HSV), IV acyclovir is still preferred.
When to start treatment?
Within 24 hours of symptom onset for episodic genital herpes. Within 72 hours of rash for shingles. At first prodrome for cold sores. Earlier = shorter outbreak.
How long for suppression?
At least 6-12 months for genital herpes suppression in patients with frequent recurrences. Reassess yearly — the natural history is often improvement over years, so a trial off therapy is reasonable.
Side effects?
Generally well-tolerated: headache, nausea, fatigue, dizziness. Rare: thrombotic thrombocytopenic purpura/haemolytic uraemic syndrome (TTP/HUS) in immunocompromised patients (FDA warning), acute kidney injury (especially if dehydrated).
Pregnancy?
Valacyclovir is widely used in pregnancy (Pregnancy Category B), particularly suppressive therapy from 36 weeks in HSV-positive women to prevent neonatal HSV. Discuss with obstetric team.
Drug interactions?
Few major interactions. Avoid combination with other nephrotoxic drugs (NSAIDs chronic, aminoglycosides). Probenecid + cimetidine modestly raise levels — usually clinically insignificant.
Renal dose adjustment?
Required for CrCl <50 mL/min. Risk of accumulation, neuropsychiatric symptoms (confusion, hallucinations) in renal failure especially in elderly.
What if I miss a dose?
Take when you remember unless nearly time for the next dose. Do not double up. Missing doses in episodic therapy reduces effect; in suppression, occasional missed doses are tolerable but consistency matters for transmission prevention.
Will it cure herpes?
No — herpes infection is lifelong. Antivirals reduce viral replication during outbreaks and prevent transmission but do not eradicate latent virus. Newer cure-focused research (CRISPR, gene editing) is experimental.
What about transmission risk?
Suppressive valacyclovir in the HSV-positive partner reduces transmission to the negative partner by ~50% (Corey 2004). Combined with consistent condom use and avoiding sex during outbreaks, transmission risk drops further.
Other Antiviral Medications
- Zimivir — valacyclovir 500/1000 mg — alternative brand
- Natclovir — valacyclovir — Natco brand
- Centrex — valacyclovir 500/1000 mg — Centurion brand
- Valgan — valganciclovir 450 mg — for CMV in transplant
- Zovirax — acyclovir — older alternative
More options in HIV Medication
Ranked by recent MedsBase order volume — what other customers in this category are picking.
| Strength | 500 mg, 1000 mg |
|---|---|
| Quantity | 120 Tablet/s, 30 Tablet/s, 60 Tablet/s, 90 Tablet/s |
| Pharma Form | Tablet/s |
| Manufacturer | Glaxosmithkline |
| Treatment | Herpes labialis, Genital herpes infection, Herpes zoster |
| Generic Brand | Valacyclovir |
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