Valacyclovir

• Herpes Zoster (Shingles)
• Genital Herpes
• Cold Sores
• Chickenpox

Valacyclovir (Valtrex) is an oral antiviral prodrug of acyclovir used to treat herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections. Its enhanced oral bioavailability translates to higher and more sustained acyclovir levels with simpler dosing, making it a preferred option for shingles, genital herpes, cold sores, and chickenpox. By starting promptly after symptoms begin, valacyclovir can shorten lesion duration, reduce viral shedding, lower transmission risk to partners in genital herpes, and meaningfully reduce the chance of post-herpetic neuralgia after shingles. It is widely prescribed in primary care for outpatient management of common viral skin and mucocutaneous infections.

Mechanism of Action

Valacyclovir is the L-valyl ester of acyclovir. After oral absorption it is rapidly converted to acyclovir by intestinal and hepatic first-pass esterases, raising oral bioavailability of acyclovir from approximately 15 to 20 percent (with oral acyclovir itself) to roughly 55 percent. Once present in cells infected with HSV or VZV, acyclovir is selectively phosphorylated by viral thymidine kinase to acyclovir monophosphate. Host cellular kinases then add two more phosphates to produce acyclovir triphosphate, the active species. Acyclovir triphosphate competes with deoxyguanosine triphosphate for incorporation into viral DNA by viral DNA polymerase. Because acyclovir lacks the 3-prime hydroxyl group needed for chain extension, incorporation terminates the elongating viral DNA strand. Viral DNA polymerase is also irreversibly inactivated.

This selective activation in infected cells, dependent on viral thymidine kinase, accounts for the favorable therapeutic index of acyclovir and its prodrugs. Resistance can develop in immunocompromised patients through loss of viral thymidine kinase function but is rare in immunocompetent patients. Valacyclovir is well distributed and excreted predominantly unchanged in the urine, so renal function dominates clearance. The drug does not interact with the cytochrome P450 system in clinically significant ways. The Centers for Disease Control and Prevention and the Infectious Diseases Society of America include valacyclovir among first-line antivirals for HSV and VZV infections.

Clinical Use

Valacyclovir is FDA-approved for herpes zoster in immunocompetent adults, initial and recurrent genital herpes in adults, suppression of recurrent genital herpes in immunocompetent and HIV-positive adults, reduction of transmission of genital herpes in heterosexual partners, cold sores (herpes labialis) in patients aged 12 and older, and chickenpox in immunocompetent pediatric patients aged 2 to 18. For shingles, treatment started within 72 hours of rash onset shortens the duration of pain and accelerates lesion healing. For genital herpes, prompt treatment of recurrences shortens episodes; chronic suppressive therapy reduces episode frequency by roughly 70 to 80 percent and lowers transmission risk to uninfected partners. For cold sores, a single-day high-dose regimen aborts or shortens episodes if started at the prodrome.

Alternatives include oral acyclovir, which requires more frequent dosing, and famciclovir, with comparable efficacy and dosing convenience. Topical antivirals are generally less effective than oral therapy for clinical lesions. For severe disseminated zoster, encephalitis, immunocompromised hosts, or pregnancy with primary genital herpes near term, intravenous acyclovir is preferred. Patient selection should include accurate diagnosis, often clinical for typical lesions but supported by PCR of vesicular fluid when uncertain. Pregnancy and immunosuppression status, baseline renal function, and concomitant nephrotoxic medications guide dosing. Counseling about transmission, sexual practices, and disclosure is integral to care for patients with genital herpes.

How to Take It

Valacyclovir is supplied as 500 mg and 1 g tablets. Doses vary by indication. For herpes zoster, the regimen is 1 g three times daily for 7 days, started within 72 hours of rash onset. For initial genital herpes, 1 g twice daily for 10 days. For recurrent genital herpes, 500 mg twice daily for 3 days, or 1 g daily for 5 days. For chronic suppression, 1 g daily, or 500 mg daily in patients with fewer than nine recurrences per year. For cold sores, 2 g twice daily for one day, ideally started at the prodrome of tingling or burning. Tablets can be taken with or without food. Adequate hydration during therapy reduces the risk of crystalluria and renal injury.

A missed dose should be taken as soon as remembered unless the next dose is due within a few hours; doubling up is not appropriate. Storage at room temperature in the original container is appropriate. During the first one to two days patients may notice mild headache, nausea, or fatigue. Most resolve. Patients should drink several extra glasses of water per day during high-dose courses, particularly in the warm Florida climate where insensible fluid losses are higher. Suppressive therapy is generally continued indefinitely until annual reassessment of recurrence frequency, at which point a brief therapy holiday helps reassess need.

Monitoring and Follow-Up

Baseline assessment usually includes serum creatinine and a brief medication review for nephrotoxic concomitant agents such as NSAIDs, aminoglycosides, IV contrast, and other antivirals. For chronic suppressive therapy, periodic creatinine measurement every 6 to 12 months is reasonable, more often in older patients or those with baseline renal disease. Symptom response is the primary clinical metric. For acute treatment, expected outcomes include reduced lesion duration, faster crusting and healing, and reduced pain by day 7 to 10. For chronic suppression, a meaningful response is reduction in episode frequency by at least half. Patients should keep a brief diary during the first few months of suppressive therapy to verify benefit.

Red numbers include creatinine rising more than 30 percent above baseline, decreased urine output, worsening confusion or hallucinations particularly in older patients, easy bruising, severe rash with mucosal involvement, or a new episode of zoster while on suppressive therapy for HSV (which may suggest immunocompromise warranting evaluation). For pregnant patients with recurrent genital herpes, suppressive therapy from 36 weeks until delivery reduces recurrence at term and the need for cesarean delivery; obstetric coordination is essential. The MedlinePlus consumer resource provides additional information for patients.

Special Populations

Elderly patients are more susceptible to dose-related neurologic effects including confusion, hallucinations, agitation, and somnolence, particularly when renal function is reduced; lower doses with appropriate renal adjustment minimize this risk. Renal impairment requires significant dose adjustment. For creatinine clearance 30 to 49 mL/min, doses are typically reduced; for 10 to 29 mL/min, further reductions; and for less than 10 mL/min, the dose is markedly reduced and intervals extended. Hepatic impairment does not require adjustment. Pregnancy data are reassuring; valacyclovir is commonly used in pregnancy when indicated, particularly suppressive therapy near term. Acyclovir is excreted in breast milk in low concentrations and is generally compatible with breastfeeding. Pediatric approval covers cold sores in patients 12 and older and chickenpox in those 2 to 18. Immunocompromised patients including transplant recipients and advanced HIV are at increased risk for thrombotic thrombocytopenic purpura and hemolytic uremic syndrome at high doses, requiring careful monitoring. Patients should not receive live attenuated varicella or zoster vaccines while on therapy without specific guidance.

When to Contact Your Doctor

Call the office promptly for new confusion, hallucinations, severe headache, decreased urination, dark or tea-colored urine, easy bruising or unexplained bleeding, severe rash that blisters or involves the mouth or eyes, or shingles involving the eye or tip of the nose. Worsening pain after lesions have healed may represent post-herpetic neuralgia and warrants evaluation for additional pain therapy. Severe nausea, vomiting, or inability to maintain hydration could lead to acute kidney injury and warrants same-day attention. Pregnant patients should call early in the third trimester to coordinate suppressive therapy planning. Notify the office before adding new prescription or over-the-counter medications, particularly NSAIDs.

Patients should also know that the recombinant zoster vaccine, Shingrix, is recommended for immunocompetent adults aged 50 and older as well as for immunocompromised adults aged 19 and older to reduce the risk of shingles and post-herpetic neuralgia. Vaccination is appropriate even for those who have already had shingles, since recurrence is possible. Antiviral therapy with valacyclovir treats acute episodes and reduces complications but does not eliminate the underlying latent virus, so prevention through vaccination remains an important complementary strategy. For patients with genital herpes, open communication with sexual partners, consistent use of barrier methods, and consideration of suppressive therapy in serodiscordant couples reduce transmission risk substantially. Stress, sleep deprivation, sun exposure, and hormonal cycles can trigger recurrences in susceptible individuals; identifying personal triggers and using episodic or suppressive therapy strategically is part of long-term management.

If you suspect shingles, a herpes outbreak, or have frequent recurrences interfering with life, our internal medicine team can confirm the diagnosis and prescribe appropriate antiviral therapy promptly. Contact us or schedule a visit for evaluation.