Acyclovir was the first antiviral drug for the treatment of herpes infections. Acyclovir was initially FDA-approved to treat herpes simplex infections in 1985 as the brand name drug Zovirax® and was found to be very effective for treating herpes infections. The main problem with acyclovir is that only 10%–20% of it is absorbed from the digestive tract. To make matters worse, higher doses have worse absorption than lower doses. This made it very difficult to maintain a high enough level of the drug in the blood to be effective, requiring patients to take up to five doses per day.
Valacyclovir is considered a prodrug of acyclovir, which means that it is converted into acyclovir in the body. Since valacyclovir is absorbed much better than acyclovir (54% for valacyclovir vs 10%–20% for acyclovir), it can be dosed less frequently and get equal or better results compared to acyclovir. Valacyclovir is dosed from 1 to 3 times daily, depending on what it’s being used for, whereas acyclovir is used 2 to 5 times daily depending on the indication. Valacyclovir is generally preferred by doctors and patients because it is easier to dose and may be more effective.
Once in the blood, valacyclovir starts to work almost immediately. Since it specifically attacks the DNA replication process, it will only attack herpes viruses that are reproducing; so while it starts to work on an active infection very quickly, it will not fight the virus that is inactive and hiding in the nervous system.
Nevertheless, if taken on a daily basis it may reduce the number of outbreaks a person might experience by 70%–80% and reduce the risk of transmitting herpes to a partner by about 50%. Taken at the earliest feelings that an outbreak is on the verge of occurring, valacyclovir may either abort the attack or shorten how long it will last. Remember, with valacyclovir treatment for herpes, the earlier you take it after the symptoms appear, the better.
While it goes to work within hours of taking the medication, the symptoms and sores of an actual outbreak may take days to begin to heal and the virus can stay active throughout the healing process.
Valacyclovir comes in two doses, 500 mg and 1,000 mg tablets. Although there are only two doses, there are several different ways to use the medicine for different indications. Below is a summary of how to use valacyclovir. Keep in mind that these doses may need to be changed for people with specific conditions, such as kidney problems. If you’re prescribed valacyclovir, take it according to your prescriber’s instructions.
Abort (stop) an outbreak at the earliest sign or symptom (prodrome)
It’s important to take the medicine at the first sign or symptom because there is no evidence that the medication works once lesions are visible. Most people will be able to tell when an outbreak is coming on. They may experience burning, itching, tingling, or other sensations that alert them to an imminent outbreak.
Take two tablets of valacyclovir 1,000 mg (2,000 mg total) followed by another two 1,000 mg tablets 12 hours later. Make sure to stay hydrated by drinking fluids throughout the day. For those who are HIV-infected, the recommended dose is 1 gram (1000 mg) every 12 hours for 5 to 10 days.
Treatment with suppressive therapy
Valacyclovir is not approved for suppressive therapy of oral herpes, but doctors have the discretion to prescribe it for this use if they believe that it is an appropriate course of treatment for a particular patient. This is considered off-label treatment. It is up to the medical judgment of the doctor to decide if off-label treatment is appropriate for a patient based on the patient’s unique medical history, symptoms, and preferences. Physicians who choose to prescribe valacyclovir off-label for the suppression of oral herpes may recommend 500 mg or 1,000 mg once daily.
Treatment of initial genital outbreak
To treat an initial episode of genital herpes, the FDA recommends taking valacyclovir 1 gram (1000 mg) twice a day for 10 days starting at the first sign or symptom of lesions, preferably within 48 hours of onset. The CDC recommends this same dose for 7 to 10 days; “treatment may be extended if healing is not complete after 10 days.” For HIV-infected patients, they recommend 1 gram (1000 mg) every 12 hours for 5 to 14 days.
Treatment of recurrent genital herpes, including HIV-infected patients
The FDA recommends using 500 mg of valacyclovir twice daily for 3 days starting at the first sign or symptom of lesions—preferably within 24 hours of onset. The CDC also recommends valacyclovir 500 mg twice daily for 3 days, but adds an alternative regimen of valacyclovir 1 g (1000 mg) one time a day for 5 days. Valacyclovir 1 g taken every 12 hours for 5 to 14 days is recommended by the HIV guidelines.
Treatment with suppressive therapy
People with less than 10 outbreaks per year should take valacyclovir 500 mg once daily. Valacyclovir 1,000 mg once daily is recommended for people with 10 or more outbreaks per year.
To prevent transmission to a partner
The infected partner should take valacyclovir 500 mg once a day to decrease the risk of transmission to the uninfected partner. The data are strong but refer to patients with 9 or fewer outbreaks each year.
What follows is a summary and does not include every side effect possible. Please, read the package insert for a comprehensive list of side effects
Very Common (may affect more than 1 in 10 people): headache
Common (may affect up to 1 in 10 people): feeling sick, dizziness, vomiting, diarrhea, skin reaction after exposure to sunlight (photosensitivity), rash, itching (pruritus)
Uncommon (may affect up to 1 in 100 people), feeling confused, seeing or hearing things that aren’t there (hallucinations), feeling very drowsy, tremors, feeling agitated. These nervous system side effects usually occur in people with kidney problems, the elderly or in organ transplant patients taking high doses of 8 grams or more of valacyclovir a day. They usually get better when valacyclovir is stopped or the dose reduced.
Other uncommon side effects: shortness of breath (dyspnea), stomach discomfort, rash, sometimes itchy, hive-like rash (urticaria), low back pain (kidney pain), blood in the urine (hematuria)
Uncommon side effects that may show up in blood tests: reduction in the number of blood platelets, which are cells that help blood to clot (thrombocytopenia), reduction in the number of white blood cells (leukopenia), increase in substances produced by the liver
Rare: (may affect up to 1 in 1,000 people): unsteadiness when walking and lack of coordination (ataxia), slow, slurred speech (dysarthria), fits (convulsions), altered brain function (encephalopathy), unconsciousness (coma), confused or disturbed thoughts (delirium). Like the nervous system side effects listed above, these side effects also usually occur in people with kidney problems, the elderly or in organ transplant patients taking high doses of 8 grams or more of valacyclovir a day (higher than the maximum doses used for any indication). They usually get better when valacyclovir is stopped or the dose reduced.
Other rare side effects: kidney problems where you pass little or no urine.
Important safety information
Severe allergic reactions (anaphylaxis): These are rare in people taking valacyclovir. Anaphylaxis is marked by the rapid development of flushing, itchy skin rash, swelling of the lips, face, neck, and throat—causing difficulty in breathing (angioedema), fall in blood pressure leading to collapse. If any of these occur, get emergency treatment immediately.