Valacyclovir dosage, forms, and strengths

Valacyclovir is a generic prescription drug used to treat herpes infections in adults and children. Valacyclovir does not cure herpes, but it stops the growth and spread of the virus. It belongs to a family of antiviral drugs called synthetic nucleoside analogues. Their mechanism of action is to interfere with the replication of the herpes simplex virus (HSV) and, thus, arrest the spread of the virus in the body. 

Source: FDA prescribing information, StatPearls

Valacyclovir forms and strengths

Valacyclovir is taken by mouth as an oral tablet or film-coated tablet. It’s available in two strengths:

• Tablets: 500 milligrams (mg), 1 gram (g)

For people unable to take tablets, a healthcare provider or pharmacist can prepare an oral suspension for easier administration. Valacyclovir tablets are also available under the brand name Valtrex.

Valacyclovir dosage for adults

Valacyclovir is prescribed to adults to treat cold sores, genital herpes, and shingles (herpes zoster) in immunocompetent patients, that is, adults with healthy immune systems. For genital herpes, the dosage regimen varies depending on what stage of the infection is occurring. 

Source: Epocrates, PDR 

Valacyclovir dosage for cold sores

Valacyclovir is considered the first-line treatment for cold sores (herpes labialis) in adults and children. However, to be effective, treatment has to start almost immediately after the appearance of the earliest symptoms, such as itching, tingling, or burning. Once the cold sore, lesion or blister appears, valacyclovir may not work well to reduce the duration of the cold sores.

• Standard adult dosage for cold sores: 2 g taken every 12 hours for one day 

• Maximum adult dosage for cold sores: 4 g per day

Source: FDA prescribing information, PDR

Valacyclovir dosage for shingles

The Food and Drug Administration (FDA) has approved valacyclovir as a treatment for herpes zoster (shingles) in adults with healthy immune systems. To be effective, treatment needs to start within 72 hours of the first appearance of symptoms, such as a skin rash. Treatment is most effective when started within 48 hours of the rash’s appearance. 

• Standard adult dosage for shingles: 1 g taken every eight hours for seven days

• Maximum adult dosage for shingles: 3 g per day

Source: FDA prescribing information, PDR

Valacyclovir dosage for genital herpes episodes

Valacyclovir is also FDA-approved to treat genital herpes flare-ups in adults with healthy immune systems. For an initial outbreak, doses are higher with a longer duration when compared to recurrences. Similar to treating cold sores and shingles, valacyclovir treatment needs to start within 72 hours of an initial outbreak and within 24 hours of a repeat episode to work. 

• Standard adult dosage for an initial episode: 1 g taken every 12 hours for 7–10 days 

• Standard adult dosage for recurrent episodes: 500 mg taken every 12 hours for three days 

• Maximum adult dosage for genital herpes: 3 g per day

Source: FDA prescribing information, PDR

Valacyclovir dosage for genital herpes suppressive therapy

Healthcare providers also prescribe valacyclovir in lower doses to suppress genital herpes in people with healthy immune systems or those who are infected with HIV. In these cases, the drug is used long-term. Theoretically, treatment could last for years, but it hasn’t been proven useful for longer than a year.

• Standard adult dosage for genital herpes suppression in immunocompetent patients: 500 mg to 1 g taken once daily for up to one year

• Standard adult dosage for genital herpes suppression in HIV-infected patients: 500 mg taken every 12 hours for up to six months

• Standard adult dosage to reduce genital herpes transmission in immunocompetent patients: 500 mg taken once per day for up to eight months

• Maximum adult dosage for genital herpes suppression: 3 g per day

Source: FDA prescribing information, PDR

Valacyclovir dosage for children

Adolescents age 12 years and older can take valacyclovir for cold sores just as adults do. Children ages 2 years and older with a healthy immune system can take valacyclovir for chickenpox (varicella). However, treatment must start within 24 hours of the appearance of the skin rash to work. Finally, children and teens who weigh more than 100 pounds (45 kg) are sometimes prescribed valacyclovir off-label to treat genital herpes episodes or as suppressive therapy. As with adults, valacyclovir must be started soon after the appearance of symptoms to be successful.

• Standard pediatric dosage for cold sores: 2 g taken every 12 hours for one day 

• Maximum pediatric dosage for cold sores: 4 g per day

• Standard pediatric dosage for chickenpox: 20 mg/kg every eight hours for five days 

• Maximum pediatric dosage for cold sores: 3 g per day

Source: Epocrates, PDR 

Valacyclovir dosage restrictions

Valacyclovir doses are reduced for people with renal impairment, but no adjustments are required for hepatic impairment. Dosage reductions will not necessarily involve a reduction in the dose, but they may require a change in the dosage schedule. For instance, people who would normally take a dose every eight hours will be switched to every 12 hours if there is mild kidney dysfunction (creatinine clearance of 30-39 mL/min). The same dose-specific reductions also apply to pediatric patients. Adults and children on hemodialysis will be given the normal dose right after dialysis.

Source: FDA prescribing information, Epocrates, PDR 

How to take valacyclovir

Valacyclovir is taken by mouth as a tablet. For those who can’t take tablets, a pharmacist can prepare an oral solution from valacyclovir tablets. Flavoring can be added to make the medicine more palatable.

• Your doctor will tell you how much medicine to use. Do not use more than directed.

• This medicine works best when you take it at the first sign of a herpes breakout.

• Do not stop taking valacyclovir, change the dose, or skip doses, except under the advice of a doctor.

• Valacyclovir tablets can be taken with food or on an empty stomach.

• Drink plenty of fluids while taking valacyclovir.

• If taking the oral suspension, shake well before taking it. Measure the dose with an oral syringe. Do not use kitchen measuring devices. If you don’t have an oral syringe or other appropriate dose-measuring device, ask a pharmacist.

• Missed dose: Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.

• Store the valacyclovir tablets in a closed container at room temperature, away from heat, moisture, and direct light. Store valacyclovir oral suspension in the refrigerator and discard it after 28 days.

Source: FDA prescribing information

Valacyclovir dosage FAQs

How long does it take valacyclovir to work?

Valacyclovir may start relieving symptoms within a few days, but taking the medication as directed for the full treatment duration is important.

How long does valacyclovir stay in your system?

When a dose of valacyclovir is taken, the body changes it into acyclovir, the drug that fights the herpes simplex virus. Therefore, there are two steps to eliminating a dose of valacyclovir. The first step is getting rid of valacyclovir concentrations. The half-life of valacyclovir is 30 minutes, so it’s eliminated in about three hours. The next step is getting rid of the acyclovir. The half-life of acyclovir is three hours, so it falls to undetectable levels about 15 hours after the last dose is taken.

What happens if I miss a dose of valacyclovir?

If you forget to take a dose of valacyclovir, take it when remembered. However, if it’s almost time for the next dose, then skip the missed dose. Take the next regular dose as scheduled without doubling up on the dose. 

How long can you take valacyclovir?

For most herpes infections, people take valacyclovir for only a few days. However, people with genital herpes may take valacyclovir for months or years to prevent flare-ups or spreading it to another person.

How do I stop taking valacyclovir?

Valacyclovir does not cause withdrawal symptoms when stopped. The drug can be discontinued without the need for a tapering dose.

What is the maximum dosage for valacyclovir?

Healthcare professionals usually don’t exceed the recommended dose. According to the Prescriber’s Digital Reference, the maximum dose for single-day valacyclovir therapy is 4 grams. If valacyclovir is used for several days in a row, the maximum dose is 3 grams per day. These maximum doses are frequently the recommended dose.

Can you overdose on valacyclovir?

Most people who take too much valacyclovir experience mild adverse effects, such as nausea and vomiting. However, an overdose of valacyclovir can seriously diminish renal function, even to the point of requiring dialysis. Additionally, acyclovir toxicity can cause neurological problems similar to encephalopathy. Symptoms include lethargy, clumsiness, agitation, and even hallucinations and seizures. An overdose is more likely in people with kidney problems or renal disease. 

What interacts with valacyclovir?

Like all prescription drugs, valacyclovir has several drug interactions. Most don’t cause serious problems or side effects. The one drug interaction of note is the varicella-zoster virus (VZV) vaccine, better known as the shingles vaccine or Shingrix. The vaccine won’t work as well when taken with valacyclovir or acyclovir.

What happens when you mix valacyclovir and alcohol?

The FDA does not warn people to avoid alcohol when taking valacyclovir. However, get medical advice from the prescriber before combining alcohol with any prescription drug, including valacyclovir.

Is it safe to take valacyclovir during pregnancy?

Pregnant women can take valacyclovir. There is no evidence that valacyclovir can cause birth defects in a fetus or other pregnancy problems. Women who are breastfeeding can also take valacyclovir. Acyclovir is the active version of valacyclovir. Acyclovir is present in breast milk in women who take valacyclovir, but there is no known risk to the nursing infant.

Related resources for valacyclovir dosages:

• Herpes simplex Type 1, StatPearls

• Valacyclovir, Epocrates Online

• Valacyclovir hydrochloride drug summary, Prescriber’s Digital Reference (PDR)

• Valacyclovir hydrochloride tablet FDA prescribing information, National Institutes of Health (NIH)