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May 13, 2024

Everyday Health

Valacyclovir: A Medication to Treat Cold Sores and Shingles

Valacyclovir, commonly known by its brand name Valtrex, is an antiviral medication that helps manage infections caused by specific types of viruses. It is used to treat several viral infections, with treatment guidelines varying between adults and children:

For Adults
  • Cold sores (oral herpes): Helps reduce the number and severity of outbreaks.
  • Genital herpes: Used for treatment of outbreaks and as a daily preventive therapy.
  • Shingles (herpes zoster): Aids in reducing pain and the duration of the infection.
For Children
  • Cold sores (oral herpes): Approved for use in children aged 12 years and older.
  • Chickenpox (varicella zoster): Can be prescribed for children between 2 to 17 years of age to help decrease the severity and duration of chickenpox.

How Does Valacyclovir Work?

Valacyclovir works by interfering with the virus's ability to replicate DNA, which is crucial for the virus to multiply and spread. By blocking this replication process, valacyclovir helps to:

  • Reduce the severity and length of the infection: It shortens the duration of acute symptoms and accelerates healing time.
  • Prevent outbreaks (in chronic viral infections): When taken regularly as preventive therapy, it can decrease the frequency and severity of outbreaks.
  • Limit the spread of the infection to others: Especially important in contagious stages of diseases like herpes and chickenpox.

Although effective in managing symptoms, valacyclovir does not cure these viral infections. The viruses that cause these diseases can remain dormant in the body and may reactivate. Therefore, valacyclovir is often part of a long-term management strategy, particularly in cases of chronic infections such as genital herpes.


Administering Valacyclovir effectively depends on the specific viral infection it's being used to treat. It's crucial to begin valacyclovir treatment at the earliest signs of an infection. For example, if you’re treating a cold sore, start the medication as soon as you feel the initial tingling sensation. Early intervention can enhance the medication’s effectiveness in managing the infection.

  • Acute Treatment: For immediate outbreaks such as shingles, genital herpes, or cold sores, valacyclovir is typically prescribed 2-3 times daily. The length of the treatment can vary from 1 to 10 days, depending on the severity and specifics of the infection.
  • Suppressive Treatment: To prevent recurrent outbreaks, especially in conditions like genital herpes, valacyclovir may be prescribed for long-term use, taken once daily. This ongoing regimen helps keep the virus in a dormant state and reduces the frequency of flare-ups.

For individuals who have difficulty swallowing pills, valacyclovir can be compounded into a liquid suspension. This form makes it easier to administer, especially for children or adults who find tablets challenging.

Side Effects

Like most medications, there are a number of different side effects that can occur while taking valacyclovir. This may include:

  • Headache: This was the only side effect noted significantly in children
  • Nausea
  • Stomach pain

If you notice that any side effects are causing significant discomfort, speak with your healthcare provider about your continued use of the medication.

The Difference Between Acyclovir and Valacyclovir

Acyclovir and valacyclovir are both antiviral medications widely used to treat infections caused by herpes viruses. While they are similar in their effectiveness and safety, there are some differences in their usage and formulations that might influence a person's choice between the two.

  • Effectiveness: Are effective in treating herpes simplex virus types 1 and 2, which cause oral and genital herpes, as well as varicella-zoster virus, which causes chickenpox and shingles.
  • Safety: Have a well-established safety profile when used as directed.
  • Bioavailability and Dosage Frequency: Valacyclovir has higher bioavailability, which means a greater portion of the drug is absorbed into the bloodstream compared to acyclovir. This allows for less frequent dosing. For example, during the initial outbreak of genital herpes, valacyclovir may be taken just twice per day, whereas acyclovir requires five doses per day.
  • Formulations: Acyclovir offers more versatility in how it can be administered. It is available in oral tablets, capsules, and suspensions; as a cream for topical application; and as an eye ointment. Valacyclovir, on the other hand, is only available in oral form.
Usage Scenarios
  • Convenience: Many people prefer valacyclovir for its convenience, as it requires fewer doses throughout the day, making it easier to adhere to treatment schedules.
  • Specific Needs: Acyclovir might be chosen for specific types of infections. For example, acyclovir cream is used for treating herpes simplex virus infections that affect the skin, and the eye ointment is used for treating herpes simplex infections of the eye.


  1. Herpes Simplex Virus (HSV) Mouth Infection. Cedars Sinai. (n.d.). Retrieved December 23, 2023, from
  2. VALTREX® (valacyclovir hydrochloride) Caplets. Food and Drug Administration. (1995, Revised 12/2019). Retrieved Dec 23, 2023, from
  3. FIFE, K. H., BARBARASH, R. A., RUDOLPH, T., DEGREGORIO, B., & ROTH, R. (1997). Valaciclovir versus acyclovir in the treatment of first-episode genital herpes infection. Journal of the American Sexually Transmitted Diseases Association, 24(8), 481–486.

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