Valacyclovir
Generic Name: Valacyclovir Hydrochloride
Brand Names: Valtrex
Valacyclovir is an antiviral medication used to treat herpes infections including cold sores, shingles, and genital herpes.
Drug Class
Nucleoside Analogue Antiviral
Pregnancy
Category B – Animal studies show no risk; adequate human studies are lacking.
Available Forms
500 mg oral tablet, 1 g oral tablet
What It's Used For
Dosage Quick Reference
These are general dosage guidelines. Your doctor will determine the appropriate dose for your specific situation.
| Condition | Starting Dose | Typical Maintenance Dose |
|---|---|---|
| Herpes Zoster (Shingles) | 1 g three times daily for 7 days | Same as starting dose |
| Genital Herpes (Initial Episode) | 1 g twice daily for 10 days | Same as starting dose |
| Genital Herpes (Recurrent) | 500 mg twice daily for 3 days | Same as starting dose |
| Suppressive Therapy (≥9 episodes/year) | 500 mg–1 g once daily | 500 mg–1 g once daily continuously |
Side Effects
Common Side Effects:
- Headache
- Nausea
- Abdominal pain
- Dizziness
- Fatigue
Serious Side Effects:
- TTP/HUS (in immunocompromised patients)
- Acute renal failure
- CNS effects (confusion, hallucinations, encephalopathy)
- Anaphylaxis
Drug Interactions
Major Drug & Food Interactions
- Nephrotoxic agents (e.g., aminoglycosides, NSAIDs, IV contrast): Concurrent use increases the risk of acute kidney injury, especially in patients with pre-existing renal impairment.
- Cimetidine and probenecid: Both reduce renal clearance of acyclovir (the active metabolite), raising plasma levels and the potential for toxicity.
- Mycophenolate mofetil: Valacyclovir may compete for renal tubular secretion, increasing levels of both drugs.
- Zoster vaccine (live): Valacyclovir can reduce efficacy of the live varicella-zoster vaccine; discontinue at least 24 hours before vaccination and do not restart for 14 days after.
Additional Information
Valacyclovir is an antiviral prodrug of acyclovir used to treat herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections. Its enhanced oral bioavailability compared to acyclovir allows for less frequent dosing while achieving higher antiviral levels.
Mechanism of Action
Valacyclovir is converted to acyclovir, which inhibits viral DNA synthesis:
- Prodrug conversion: Rapidly converted to acyclovir by intestinal and hepatic esterases
- Viral thymidine kinase activation: Acyclovir is phosphorylated by viral thymidine kinase to acyclovir monophosphate
- Cellular kinase conversion: Host cell kinases convert to acyclovir triphosphate (active form)
- DNA polymerase inhibition: Acyclovir triphosphate competitively inhibits viral DNA polymerase
- Chain termination: Incorporation into viral DNA causes chain termination
Selective toxicity results from preferential activation in infected cells.
Available Formulations
Valacyclovir is available as tablets:
- 500 mg, 1000 mg (1 g) tablets (Valtrex)
Medical Uses
FDA-Approved Indications:
- Herpes zoster (shingles) in immunocompetent adults
- Initial and recurrent genital herpes in immunocompetent adults
- Suppression of recurrent genital herpes in immunocompetent and HIV-infected adults
- Reduction of transmission of genital herpes
- Cold sores (herpes labialis) in immunocompetent adults and pediatric patients ≥12 years
- Chickenpox in immunocompetent pediatric patients (2-18 years)
Dosing Guidelines
Herpes Zoster:
- 1 g three times daily for 7 days
- Start within 72 hours of rash onset
Genital Herpes (Initial):
- 1 g twice daily for 10 days
Genital Herpes (Recurrent):
- 500 mg twice daily for 3 days, OR
- 1 g once daily for 5 days
Genital Herpes Suppression:
- 1 g once daily (or 500 mg once daily if <9 recurrences/year)
Cold Sores:
- 2 g twice daily for 1 day (doses 12 hours apart)
Renal Impairment: Significant dose adjustments required based on CrCl.
Important Safety Information
Contraindications:
- Known hypersensitivity to valacyclovir, acyclovir, or any component
Warnings and Precautions:
- Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS): Reported in advanced HIV disease and transplant patients at high doses
- Acute renal failure: May occur, especially with pre-existing renal impairment or dehydration
- CNS adverse reactions: Confusion, hallucinations, agitation, seizures (more common in elderly or renal impairment)
Drug Interactions
- Nephrotoxic drugs: May increase risk of renal toxicity
- Probenecid, cimetidine: Reduce acyclovir clearance; monitor for toxicity
- Mycophenolate mofetil: Concurrent use may increase exposure of both drugs
- Vaccines: Avoid live vaccines during active infection
Special Populations
- Hepatic Impairment: No adjustment for mild to moderate
- Renal Impairment: Significant dose adjustments required
- Elderly: Reduce dose based on renal function; monitor for CNS effects
- Pregnancy: Category B; may be used when benefit outweighs risk
- Lactation: Acyclovir is excreted in milk; use with caution
- Pediatric: Approved for cold sores ≥12 years; chickenpox 2-18 years
Frequently Asked Questions
Questions to Ask Your Doctor
Consider discussing these topics at your next appointment:
- ✓How often am I experiencing outbreaks, and would daily suppressive therapy be appropriate?
- ✓Do I need a dose adjustment based on my current kidney function?
- ✓Are any of my other medications potentially harmful to the kidneys when combined with valacyclovir?
- ✓Should my partner be tested or treated as well?
Related Health Conditions
This medication is commonly used to treat or manage the following conditions:
Medical Disclaimer: This information is for educational purposes only and should not be considered medical advice. Always consult with your healthcare provider before starting, stopping, or changing any medication. Your doctor can provide personalized recommendations based on your specific health condition and medical history.
Related Medications
Other medications in the same category
Questions About This Medication?
Talk to your doctor or pharmacist about whether Valacyclovir is right for you.
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