Valacyclovir

Pronunciation: pronunciation varies by local usage.

Generic name: valacyclovir
Brand names: VALTREX
Drug class: Oral antiviral prodrug of acyclovir
Form: Film-coated tablet
Route: Oral
Legal status: Prescription medicine in the United States per the reviewed label; specific legal/supply classification wording is unresolved from the reviewed source.

Availability and supply rules vary by country

Trade names by country: United States · Canada

What valacyclovir is and how it works

Valacyclovir is an oral antiviral medicine. It is a prodrug of acyclovir and is active against herpes simplex virus types 1 and 2 (the viruses that cause cold sores and genital herpes), varicella-zoster virus (shingles and chickenpox). It is available as a brand-name prescription tablet (VALTREX). (1)

Approved uses and ages differ by country. In the United States, VALTREX is approved for adults for cold sores, initial and recurrent genital herpes, suppressive therapy to reduce genital herpes recurrences, herpes zoster (shingles), and — when used as suppressive therapy together with safer sex practices — reduction of the risk of transmitting genital herpes to a heterosexual partner. For children, it is approved for cold sores (age 12 and older) and chickenpox (ages 2 to under 18). Dosing depends on the specific indication, kidney function, and age. Adequate hydration is needed during treatment to help protect the kidneys.

Mechanism of action: how valacyclovir works

Valacyclovir is a prodrug of acyclovir. Detailed conversion and mechanism-of-action pharmacology beyond this is unresolved from the reviewed source. (1)

What valacyclovir is used for

Cold sores (herpes labialis)

Approved for treatment of cold sores in adults and in children 12 years of age and older. The recommended adult and pediatric dose is 2 grams every 12 hours for 1 day. (1)

Genital herpes – initial episode

Approved for treatment of an initial episode of genital herpes in adults. The recommended dose is 1 gram twice daily for 10 days. (1)

Genital herpes – recurrent episodes

Approved for treatment of recurrent genital herpes in adults. The recommended dose is 500 mg twice daily for 3 days. (1)

Genital herpes – chronic suppressive therapy

Approved for chronic suppression of recurrent genital herpes in adults. The recommended dose is 1 gram once daily in immunocompetent patients, or 500 mg once daily in patients with fewer than 10 recurrences per year. In HIV-infected patients, the dose is 500 mg twice daily. (1)

Reduction of heterosexual transmission of genital herpes

Approved for reducing the risk of heterosexual transmission of genital herpes when used as suppressive therapy and combined with safer sex practices. The recommended dose for the source partner is 500 mg once daily. (1)

Herpes zoster (shingles)

Approved for treatment of herpes zoster in adults. The recommended dose is 1 gram three times daily for 7 days. (1)

Chickenpox (varicella) in pediatric patients

Approved for treatment of chickenpox in children 2 years to less than 18 years of age. The recommended dose is 20 mg/kg (up to a maximum of 1 gram) three times daily for 5 days. (1)

Before taking valacyclovir

Do not take / not appropriate for

If you have ever had a severe hypersensitivity reaction (e.g., anaphylaxis, Stevens-Johnson syndrome, toxic epidermal necrolysis, acute generalized exanthematous pustulosis, or drug reaction with eosinophilia and systemic symptoms) to valacyclovir, acyclovir, or any ingredient in this product, tell your prescriber before starting treatment — this medicine should not be taken without your prescriber's guidance if this applies to you. (all products) (1)

Tell your clinician about

If you have kidney problems or are at risk of dehydration (kidney function and hydration will influence dosing).
If you have a history of any serious allergic reaction to valacyclovir, acyclovir, or any ingredient in the product.
All prescription and over‑the‑counter medicines, vitamins, and herbal supplements you take, especially any medicines that can affect the kidneys.
If you are pregnant, plan to become pregnant, or are breastfeeding.
If you have a condition that weakens your immune system (for example, advanced HIV infection) or have had a bone marrow or kidney transplant, because of a risk of a rare blood clotting disorder with high doses.
If you are older than 65 years, because you may be at increased risk of kidney or nervous system side effects.

(1)

How to take valacyclovir

Take valacyclovir exactly as prescribed by your healthcare provider. The dose and duration depend on your medical condition, kidney function, and age.
Drink plenty of fluids during treatment to stay well hydrated and reduce the risk of kidney problems.
For genital herpes suppressive therapy used to reduce transmission risk, this is combined with safer sex practices as directed by your prescriber; valacyclovir reduces but does not eliminate the risk of transmission.
Do not change your dose or stop the medicine early on your own; let your prescriber advise on any change to dose or treatment duration.
If you have kidney problems, your dose will be lowered; follow the schedule exactly and report any new symptoms.

(1)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1)

Missed dose

A specific missed-dose regimen is not established in the reviewed label. Contact your prescriber or pharmacist for individual instructions if you miss a dose, rather than adjusting your own dosing schedule.

Overdose

Specific overdose management is unresolved from the reviewed label. If an overdose is suspected, contact emergency services or a poison-control/poison-information service immediately, or go to the nearest emergency department, rather than relying on self-management.

Side effects

Valacyclovir can cause side effects. Staying well hydrated helps reduce the risk of kidney-related side effects. Elderly patients and those with kidney problems are more likely to experience nervous system side effects.

Headache

What to notice: A headache that is new or worsening.

What to do: Usually mild; inform your healthcare provider if it persists or becomes severe. (1)

Nausea

What to notice: Feeling sick to your stomach.

What to do: If nausea is severe or continues, talk to your prescriber. (1)

Abdominal pain

What to notice: Discomfort or pain in the stomach area.

What to do: Report persistent or severe abdominal pain to your healthcare provider. (1)

Signs of kidney problems (acute renal failure)

What to notice: Decreased urination.

What to do: Contact your healthcare provider right away. Adequate hydration and dose adjustment may be needed. Risk is higher in older adults, people with existing kidney disease, those taking other medicines that can affect the kidneys, and those who are not adequately hydrated. (1)

Nervous system effects (CNS effects)

What to notice: Agitation, confusion, hallucinations, delirium, seizures, or encephalopathy.

What to do: Reported predominantly in older adults and/or people with kidney impairment receiving higher-than-recommended doses. Seek medical attention promptly if these occur. (1)

Serious skin reactions (SCARs)

What to notice: A painful rash with mucosal (mouth, eye, or genital) involvement, or a progressive severe rash.

What to do: Seek immediate medical evaluation. Do not decide on your own whether to keep taking valacyclovir — let the treating clinician advise on whether to continue or stop it, since these reactions can be life-threatening. (1)

Blood clotting disorder (TTP/HUS)

What to notice: This is a rare but sometimes fatal condition reported in high-risk groups; the exact patient-recognizable symptom pattern is unresolved from the reviewed label.

What to do: This has occurred in patients with advanced HIV-1 disease and in allogeneic bone marrow transplant or kidney transplant recipients receiving high-dose valacyclovir (8 g/day) in clinical trials. Seek prompt medical evaluation for any unexplained bruising, bleeding, or unusual symptoms, and let your clinician know you are taking valacyclovir. (1)

Serious warnings

Acute renal failure — emergency

Symptoms: Markedly reduced urination.

Action: Seek emergency medical attention. Risk is higher in older adults, people with existing kidney disease, those on other kidney-affecting medicines, and those without adequate hydration. Ensure adequate hydration during treatment, and report any change in urination immediately. (1)

Thrombotic thrombocytopenic purpura / hemolytic uremic syndrome (TTP/HUS) — emergency

Symptoms: A rare but sometimes fatal blood disorder; the exact patient-recognizable symptom pattern is unresolved from the reviewed label.

Action: Reported in patients with advanced HIV-1 disease and in allogeneic bone marrow transplant or kidney transplant recipients receiving high-dose valacyclovir (8 g/day) in clinical trials. If unexplained bruising, bleeding, or unusual symptoms develop, seek emergency care immediately and tell the doctor you are taking valacyclovir. (1)

Central nervous system toxicity — emergency

Symptoms: Hallucinations, agitation, confusion, delirium, or seizures.

Action: Reported predominantly in older adults and/or people with kidney impairment receiving higher-than-recommended doses. Seek immediate medical attention. (1)

Severe cutaneous adverse reactions (SCARs) — emergency

Symptoms: A painful rash with mucosal (mouth, eye, or genital) involvement, or a progressive severe rash.

Action: Seek immediate medical attention and mention that you are taking valacyclovir. Let the treating clinician advise on whether to continue or stop the medicine — these reactions can be life-threatening. (1)

Interactions

Medicine or test	Effect	Action
No clinically significant drug‑drug or drug‑food interactions are known.	The US prescribing information states that valacyclovir has no known clinically significant interactions.	Nevertheless, always give your healthcare provider and pharmacist a complete list of all medicines you take, including over‑the‑counter products. (1)

Pregnancy, breastfeeding, kidney/liver function, age

Patients with kidney impairment

Dose reduction is required when creatinine clearance is below 50 mL/min. The exact reduced dose and frequency depend on the condition being treated and the degree of impairment; a clinician must use the full prescribing information to determine the correct regimen. Maintain adequate hydration and report any symptoms of worsening kidney function. (1)

Elderly patients (over 65 years)

Elderly patients are more likely to have reduced kidney function and may be at greater risk for nervous system side effects (confusion, hallucinations) and acute renal failure. Dose adjustment based on kidney function is recommended. Adequate hydration is especially important. (1)

Immunocompromised patients (advanced HIV, transplant recipients)

In clinical trials, high‑dose valacyclovir (8 grams per day) was associated with TTP/HUS in patients with advanced HIV‑1 disease and in allogeneic bone marrow transplant and renal transplant recipients. The doses used for approved indications are lower, but caution is warranted. The specific patient-recognizable symptom pattern for TTP/HUS is (1)

Pregnancy

Decades of clinical experience with valacyclovir/acyclovir have not identified a drug‑associated increased risk of birth defects. Data are insufficient to assess miscarriage risk. Animal studies at up to 7 times the maximum recommended human dose showed no adverse developmental effects. Discuss the benefits and risks with your healthcare provider. (1)

Breastfeeding

Acyclovir, the active metabolite, passes into breast milk. After a maternal dose of 500 mg twice daily, the nursing infant would be exposed to an estimated acyclovir dose of about 0.6 mg/kg/day. This is a small fraction of the typical pediatric dose. Consult your healthcare provider before breastfeeding while taking valacyclovir. (1)

Pediatric patients

Valacyclovir is approved for cold sores in children 12 years and older and for chickenpox in children 2 to under 18 years. Dosing is based on age and weight for chickenpox (20 mg/kg three times daily, maximum 1 gram per dose). The safety and efficacy for other indications or in younger children have not been established. (1)

Monitoring

Before starting

Assess kidney function (creatinine clearance) to determine the appropriate dose, especially in the elderly, those with known kidney disease, or patients taking nephrotoxic drugs.
Review any history of hypersensitivity to valacyclovir, acyclovir, or any product component.
Discuss adequate hydration and the importance of starting therapy at the earliest symptom for cold sores, shingles, and chickenpox.

During treatment

Ensure adequate hydration to minimize the risk of acute renal failure.
Monitor for signs of nervous system toxicity, particularly in the elderly or those with renal impairment: agitation, confusion, hallucinations, delirium, seizures, or encephalopathy.
Monitor for any skin rash; if a painful rash with mucosal (mouth, eye, or genital) involvement, or a progressive severe rash, appears, arrange urgent clinical evaluation — the evaluating clinician determines whether treatment should continue or be discontinued.

(1)

Storage

Specific storage conditions are unresolved from the reviewed label. Follow the storage instructions on your prescription label and packaging.

Professional information

Clinician‑facing context only. Use the current local prescribing information for exact dosing, especially the renal‑adjustment table, and consult relevant clinical guidelines.

United States (FDA DailyMed label)

Indication: All indications

Dose summary: Adult dosing: cold sores — 2 g q12h x 1 day; genital herpes initial — 1 g BID x 10 days; recurrent — 500 mg BID x 3 days; suppression immunocompetent — 1 g QD (or 500 mg QD if <10 recurrences/yr); suppression HIV+ — 500 mg BID; transmission reduction — 500 mg QD (source partner); herpes zoster — 1 g TID x 7 days. Pediatric dosing: cold sores ≥12 years — 2 g q12h x 1 day; chickenpox 2 to <18 yrs — 20 mg/kg TID x 5 days (max 1 g/dose). Renal impairment: dose/frequency reduction required when CrCl <50 mL/min; consult full label for specific adjustment per indication.

Renal context: Dose reduction is qualitative — the exact mg/frequency per CrCl band is not itemized here; use the full prescribing information. Adequate hydration is essential. (1)

Mechanism of action

Hepatic guidance

Hepatic-impairment dosing guidance is unresolved from the reviewed label; consult the current full prescribing information.

Overdose note

Specific overdose management is unresolved from the reviewed label. Refer a suspected overdose to emergency services or a poison-information service for current management guidance. (1)

Frequently asked questions

What is valacyclovir used for?

It is used to treat infections caused by herpes viruses, including cold sores (herpes labialis), genital herpes outbreaks, shingles (herpes zoster), and chickenpox. It can also be taken daily to suppress recurrent genital herpes and to reduce the risk of passing genital herpes to a heterosexual partner. (1)

Can I take valacyclovir if I have kidney problems?

Yes, but your dose will need to be lowered because the drug is cleared by the kidneys. Your prescriber will calculate your kidney function (creatinine clearance) and adjust the dose accordingly. Maintain adequate hydration during treatment to help protect your kidneys. (1)

Is valacyclovir safe during pregnancy?

Decades of clinical experience with valacyclovir and acyclovir have not identified a drug-associated increased risk of birth defects, though data are insufficient to assess miscarriage risk. You should discuss the potential benefits and risks with your healthcare provider if you are pregnant or planning a pregnancy. (1)

Can I breastfeed while taking valacyclovir?

Acyclovir, the active form of valacyclovir, passes into breast milk in small amounts. The estimated infant dose is low compared with typical pediatric treatment doses. Still, you should consult your healthcare provider before breastfeeding on this medicine. (1)

How quickly should I start valacyclovir for a cold sore or shingles?

For best results, treatment should be started at the earliest sign—for cold sores, when you feel tingling or itching before the blister appears; for shingles, as soon as possible after the rash appears. Follow your prescriber’s instructions exactly. (1)

What is the mechanism of action of valacyclovir?