How long does valacyclovir stay in your system?

Valacyclovir (Valtrex) is an antiviral medication used to treat conditions that the herpes simplex virus causes, such as cold sores, genital herpes, and shingles. Doctors may also use it to treat chickenpox, caused by the varicella-zoster virus.

Valacyclovir is a generic prescription drug that is also available under the brand name Valtrex.

Keep reading to learn about valacyclovir, how long it typically stays in your system, how long it takes to work, and how long you may still be contagious after taking it.

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How long does it take to get valacyclovir out of your system?

Valacyclovir typically stays in your system for over half a day. But this timeframe may vary based on your dose, individual health history, age, and kidney function.

When you take valacyclovir, your body converts it into acyclovir. Acyclovir has a half-life of 2 to 3 hours. A half-life is the time it takes for the amount of a drug’s active substance to reduce by half in your body. It usually takes 5 half-lives for a drug to leave your body completely.

So, if a person were to take a 1 gram (g) dose of valacyclovir, they would have 0.5 g remaining in their system after 2 to 3 hours. Even though a 1-g dose of valacyclovir would be out of your body 13 to 18 hours after taking it, there may be traces of acyclovir detectable in urine and feces for up to 4 days after your last dose.

How long do valacyclovir side effects last?

How long valacyclovir’s side effects last will vary. Typically, side effects of valacylovir are temporary and go away soon after you start or stop taking the drug.

But some side effects may last longer. These typically occur in people taking valacyclovir long term to suppress the herpes virus. Examples of long-term side effects reported with valacyclovir include sudden kidney failure and increased liver enzymes.

Talk with your doctor for more information about how long these side effects of valacyclovir may last.

How long does valacyclovir take to work?

How long valacyclovir takes to work depends on what condition you are taking it for.

• Oral and genital herpes: Most people notice herpes blisters or sores starting to heal within 2 to 3 days of taking valacyclovir. However, it can take 2 to 6 weeks for herpes blisters or sores to completely heal. Valacyclovir will work most effectively when you start treatment at the earliest symptom of a herpes outbreak. Early symptoms may include tingling, itching, or burning.
• Shingles: If you start taking valacyclovir within 3 days (72 hours) of developing a shingles rash, it will typically take about 2 to 3 days to start experiencing relief from shingles symptoms.
• Chickenpox: Valacyclovir will start to reduce symptoms of chickenpox within 2 to 3 days of starting it. When taking valacyclovir for chickenpox, it’s important to start treatment at the earliest signs of chickenpox. You may experience fever, headache, and loss of appetite for a day or two before developing the classic, itchy rash chickenpox is known for.

While valacyclovir does help speed up recovery, it does not completely remove the herpes virus from your body. So, future outbreaks are still possible.

How long after taking valacyclovir are cold sores still contagious?

After you take valacyclovir for a cold sore, genital herpes, or shingles, these conditions may still be contagious until the sores or blisters have completely healed and gone away. This typically takes about 2 weeks.

The herpes virus can spread even when you don’t have any symptoms of a cold sore. But you’re most likely to transmit the virus when you have cold sores. It’s important to know that cold sores can spread the virus until they go away completely. This means the common belief that cold sores do not transmit the virus once they’ve scabbed over isn’t true.

If you want to prevent the transmission of the herpes virus, you can take valacyclovir as a prevention, even when no symptoms are present. This reduces the risk of spreading the virus to a partner who doesn’t have the herpes infection.

Doctors often recommend that people with frequent herpes infection take valacyclovir regularly. This helps suppress the virus. They also recommend taking valacyclovir for couples where one partner is HSV positive, and the other is HSV negative to reduce the risk of transmission.

But valacyclovir does not completely rule out the possibility of transmission. Using barrier methods like condoms and avoiding sexual activity during outbreaks of cold sores or genital herpes will help prevent transmission.

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Summary

Valacyclovir typically stays in your system for about half a day or 12 to 18 hours. But this timeframe may vary based on your dose, individual health history, age, and kidney function. The drug starts to work as soon as you start taking it. Most people notice symptoms starting to reduce in 2 to 3 days. Although, it can take several weeks for herpes sores to heal and go away completely.

Although you will be less likely to transmit the virus after herpes sores or blisters heal and go away, taking valacyclovir does not completely rule out the possibility of transmission of the herpes virus.