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How Long is Valacyclovir (Valtrex) in Your System?

Kristin Hall, FNP

Medically reviewed by Kristin Hall, FNP

Written by Our Editorial Team

Last updated 10/06/2020

Valacyclovir (commonly sold as Valtrex®) is one of the most widely used herpes medications on the market. Highly effective at controlling herpes outbreaks, it’s used for everything from HSV-1 and HSV-2, to shingles and chickenpox.

In this guide, we’ll look at how long valacyclovir stays in your system after you take each tablet, as well as the process the drug undergoes inside your body as it converts into acyclovir, its key active ingredient.

Understanding Valacyclovir’s Conversion Process

Valacyclovir is a prodrug, meaning it converts into a different substance once it’s absorbed and metabolized in the body. In the case of valacyclovir, your body will convert it into the active drug acyclovir (or ACV) after it’s absorbed and metabolized.

Acyclovir is itself a powerful antiviral drug that’s highly effective in treating herpes. However, it’s less bioavailable than valacyclovir, meaning that a larger percentage of valacyclovir is absorbed per dose compared to a direct dose of acyclovir.

Because valacyclovir is a prodrug, it’s only active in your body for a short period of time after it’s taken. On its own, its half-life is approximately 30 minutes.

However, once valacyclovir has converted into acyclovir, it has a half-life of 2.5 to 3.3 hours in people with normal renal function.

This means that a single dose of valacyclovir, after conversion into acyclovir by your body, will reduce in concentration every 2.5 hours to 3.3 hours. 

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Valacyclovir Dosage Guidelines and Usage Periods

Like most antiviral medication, valacyclovir generally isn’t designed to be used as a “one off” treatment for HSV-1 or HSV-2. Instead, most dosage protocols recommend using valacyclovir over the course of several days (often as long as one week) to control a herpes outbreak.

Dosage guidelines for valacyclovir can vary based on the symptoms you’re treating. Generally, valacyclovir usage periods and dosages are more conservative for cold sores and chickenpox than for an initial herpes simplex virus infection.

Our valacyclovir dosages guide includes sample therapeutic protocols for cold sores, genital herpes, shingles, chickenpox and other common conditions that are treated using valacyclovir. And if you want to learn more about valacyclovir in general, check out our Valacyclovir 101 guide, which goes over all the nitty gritty—potential valacyclovir interactions, valacyclovir dosage, how it's used, what it's used to treat, where you can buy it, etc.

As always, the best approach to treating any viral infection, including HSV-1 and HSV-2, is to discuss your situation with your doctor and follow the advice they provide.

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.