Valtrex (Valacyclovir) Tablets for Herpes
Valtrex is an oral nucleoside antiviral prodrug containing valacyclovir. It is used in adults for herpes simplex (genital, labial), herpes zoster (shingles) and prevention of cytomegalovirus disease after solid organ transplantation, with convenient dosing.
- Active ingredients
- Valacyclovir
- Manufacturer
- GlaxoSmithKline
- Dosage forms
- tablet
- Available dosages
- 500mg, 1000mg
- Category
- Antiviral Medications
What is it?
Valtrex is the original brand of valacyclovir, marketed by GlaxoSmithKline since its approval in 1995. It is supplied as oral tablets at 500mg and 1000mg. Valtrex is dispensed only on prescription and is one of the most prescribed antivirals worldwide for herpesvirus infections. Multiple authorised generics are now widely available, and the molecule is part of the World Health Organization List of Essential Medicines.
Active ingredients
Each tablet contains valacyclovir (as the hydrochloride) as the sole active ingredient at 500mg or 1000mg. Valacyclovir is the L-valyl ester prodrug of acyclovir, with much higher oral bioavailability than acyclovir, allowing less frequent dosing.
Forms and dosages
Valtrex is administered orally with or without food. According to the prescribing information, doses depend on the indication: 500mg twice daily for 3 days for recurrent genital herpes, 1000mg twice daily for 7-10 days for initial genital herpes episode, 2000mg twice on the same day for cold sores, 1000mg three times daily for 7 days for shingles, and 500mg daily for suppressive therapy. Substantial dose reduction is required in renal impairment.
Indications
Valtrex is approved in adults for the treatment of herpes simplex virus infections, including genital herpes (initial episodes, recurrent episodes and suppressive therapy), herpes labialis (single-day high-dose regimen), reduction of transmission in heterosexual immunocompetent adults, herpes zoster (shingles) and prophylaxis of cytomegalovirus disease following solid organ transplantation. According to international guidelines, valacyclovir is preferred over acyclovir when adherence is a concern.
How it works
Valacyclovir is rapidly and almost completely converted to acyclovir during first-pass intestinal and hepatic metabolism by valacyclovir hydrolase. Acyclovir is then selectively phosphorylated by viral thymidine kinase to its triphosphate form, which inhibits viral DNA polymerase and causes chain termination. The prodrug strategy substantially improves oral bioavailability over acyclovir itself, supporting less frequent dosing.
Frequently asked questions
How is Valtrex different from acyclovir? ▾
Valtrex contains valacyclovir, a prodrug of acyclovir with much higher oral bioavailability (around 55%) than acyclovir (15-30%), allowing twice or three times daily dosing instead of up to five times daily. The active drug is identical, so efficacy is comparable at equivalent acyclovir exposures. According to international guidelines, Valtrex is preferred when adherence is a concern, with the choice made by the prescriber.
Can Valtrex prevent transmission of genital herpes? ▾
Yes. Daily Valtrex 500mg has been shown in randomised trials to reduce transmission of genital herpes simplex type 2 in serodiscordant heterosexual immunocompetent couples by approximately 50%. According to the prescribing information, suppressive therapy is offered in addition to safer-sex practices, which remain essential. The prescriber should review the relative benefits and risks for each patient.
When should Valtrex be started for shingles? ▾
Valtrex is most effective for shingles when started within 72 hours of rash onset, and ideally within 48 hours. According to the prescribing information, the regimen is 1000mg three times daily for 7 days. Earlier treatment reduces severity, accelerates healing and may reduce the risk of post-herpetic neuralgia. Older patients and those with severe rash, ophthalmic involvement or immunocompromise should always be evaluated by a clinician.
Why must the dose be reduced in kidney disease? ▾
Valacyclovir is converted to acyclovir, which is excreted predominantly unchanged in urine, so renal impairment substantially increases acyclovir concentrations and the risk of adverse effects, including neurotoxicity (confusion, hallucinations) and crystalluria. According to the prescribing information, the dose is reduced based on creatinine clearance, including in patients on dialysis where supplemental doses are given after sessions. Adequate hydration is essential.
What are the main contraindications for Valtrex? ▾
Valtrex is contraindicated in known hypersensitivity to valacyclovir, acyclovir or any excipient. Caution is required in renal impairment (with mandatory dose adjustment), in older adults, in advanced HIV disease (risk of thrombotic microangiopathy at high doses), in dehydration and during pregnancy and breastfeeding. According to the prescribing information, the medical history must be reviewed by a clinician before any prescription.
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The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.