Information last reviewed: May 2026 — for educational purposes only.
Valacyclovir, sold as Valtrex, is a prescription antiviral that is the L-valyl ester (prodrug) of acyclovir. After oral administration, it is rapidly and almost completely converted to acyclovir in the gut and liver, achieving 3–5 times higher plasma concentrations than acyclovir itself — making it the preferred oral antiviral for herpes infections. It is indicated for herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), varicella-zoster virus (VZV), cold sore outbreaks, and genital herpes treatment and suppression.
What Is Valtrex Used For?
- Genital herpes (HSV-2) — initial episode: 1 g twice daily for 10 days
- Genital herpes — recurrent episodes: 500 mg twice daily for 3 days, or 1 g once daily for 5 days
- Genital herpes — chronic suppressive therapy: 500 mg or 1 g once daily (indefinite); reduces recurrence frequency and reduces transmission risk to partners by approximately 50%
- Cold sores (herpes labialis, HSV-1): 2 g twice daily for 1 day only (2 doses taken 12 hours apart at the first sign of an outbreak)
- Shingles (herpes zoster, VZV): 1 g three times daily for 7 days; most effective when started within 72 hours of rash onset; reduces pain duration and severity
- Chickenpox (varicella): 20 mg/kg three times daily for 5 days in immunocompetent patients (not a primary indication for most guidelines)
How Does Valacyclovir Work?
After conversion to acyclovir, the drug is phosphorylated by viral thymidine kinase to acyclovir triphosphate. This active metabolite competitively inhibits viral DNA polymerase, terminating the growing viral DNA chain. Crucially, viral thymidine kinase (not host cell enzymes) is required for this initial phosphorylation step, giving acyclovir high selectivity for virus-infected cells with limited toxicity to uninfected host cells.
Tablet Strengths
- 500 mg tablets (Rx) — Valtrex or generic valacyclovir; used for suppression (once daily) and recurrent cold sores/genital herpes episodic treatment
- 1 g tablets (1000 mg) (Rx) — used for shingles (thrice daily), initial genital herpes (twice daily), and cold sores (twice daily single-day regimen)
Renal Dosing Adjustment
Acyclovir is renally cleared; dose adjustments are required for patients with reduced kidney function (eGFR <50 ml/min). In patients with severe renal impairment, standard doses can cause acyclovir nephrotoxicity (crystalline nephropathy) and neurological toxicity (confusion, agitation, tremor). Prescribers should review renal function before initiating therapy in older patients or those with known renal disease.
Price of Generic Valacyclovir
Generic valacyclovir is widely available and affordable. A 30-day supply of 500 mg once-daily suppressive therapy costs approximately $15–$40 with a discount card in the US. Episodic treatment courses are even less costly. Brand-name Valtrex is significantly more expensive; most prescribers and pharmacists will dispense the generic by default.
Frequently Asked Questions
Does suppressive valacyclovir prevent transmission of herpes?
Yes, but not completely. Daily suppressive valacyclovir therapy (500 mg once daily) has been shown in clinical trials to reduce the risk of HSV-2 transmission to an uninfected partner by approximately 48%. When combined with consistent condom use, the risk reduction is greater still. However, transmission can still occur even on suppressive therapy, particularly through asymptomatic viral shedding.
Can valacyclovir cause kidney problems?
At recommended doses in patients with normal kidney function, valacyclovir/acyclovir is generally well-tolerated and renal toxicity is uncommon. However, in patients with pre-existing renal impairment, dehydration, or in those using high doses (e.g., immunocompromised patients), acyclovir can crystallise in kidney tubules. Adequate hydration during valacyclovir therapy is recommended. Renal function should be monitored in at-risk patients.
Is there a cure for herpes?
No. Valacyclovir and other antiherpetic drugs suppress active infection and reduce recurrences but do not eliminate the latent virus from sensory nerve ganglia. Herpes simplex virus establishes lifelong latency and can reactivate at any time. Research into curative gene-editing approaches targeting latent HSV is ongoing but not yet clinically available.
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