Uses

What is valacyclovir used for?

Valacyclovir is an antiviral medicine commonly used for the following conditions caused by herpes viruses.

Valacyclovir may also be used for other conditions as determined by your healthcare provider.

How does valacyclovir work (mechanism of action)?

Valacyclovir is an antiviral medicine that stops the growth of herpes viruses and reduces the amount of outbreaks you have. Valacyclovir does not remove the viruses from your body. 

How is valacyclovir supplied (dosage forms)?

Valacyclovir is available as Valtrex and generic valacyclovir in the following dosage forms that are taken by mouth.

  • 500 mg oral tablets
  • 1 g oral tablets

How should I store valacyclovir?

Valacyclovir oral tablets should be stored at room temperature, between 59 F to 77 F (15 C to 25 C). Store in a cool, dry place, in a tightly closed container.

Side Effects

What are the most common side effects of valacyclovir?

The most common side effects of valacyclovir are listed below. Tell your healthcare provider if you have any of these side effects that bother you.

  • Headache
  • Nausea
  • Stomach pain

There may be other side effects of valacyclovir that are not listed here. Contact your healthcare provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

 

What are the serious side effects of valacyclovir?

While less common, the most serious side effects of valacyclovir are described below, along with what to do if they happen.

Kidney Damage. Kidney damage can happen when taking valacyclovir. Call your healthcare provider right away if you have any of the following symptoms of kidney damage.

  • Reduced need to pee
  • Swelling in your feet, ankles, or legs
  • Weakness or unusual tiredness
  • Difficulty catching your breath or chest pain/pressure
  • Confusion
  • Nausea
  • Seizures

Severe Allergic Reactions. Valacyclovir may cause allergic reactions, which can be serious. Stop taking valacyclovir and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Central Nervous System (CNS) Problems. Valacyclovir may affect your central nervous system (CNS). Call your healthcare provider right away if you have the following symptoms of CNS problems.

  • Feeling agitated or restless
  • Seeing or hearing things that others do not see or hear, also called hallucinations
  • Confusion
  • Trouble speaking
  • Feeling unsteady or shaky
  • Seizures
  • Sudden and severe mental or nervous system changes

Warnings & Precautions

Who should not use valacyclovir?

Allergies to Ingredients. People who are allergic to any of the following should not take valacyclovir.

  • Valtrex
  • Valacyclovir
  • Acyclovir
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific valacyclovir products they stock.

What should I know about valacyclovir before using it?

Do not take valacyclovir unless it has been prescribed to you by a healthcare provider. Take it as prescribed.

Do not share valacyclovir with other people, even if they have the same condition as you. It may harm them.

Valacyclovir is not a cure for cold sores, genital herpes, chickenpox, or shingles.

If you are prescribed valacyclovir to treat an outbreak of cold sores, genital herpes, shingles, or chickenpox, take it as soon as possible. You should take it when you first have symptoms, such as burning, itching, or tingling, or when the sore appears.

Genital herpes can be passed to others during sexual activity even if you have no signs or symptoms. Ask your healthcare provider about safe sex practices, such as condoms. If you have symptoms or open sores from genital herpes, do not have sexual contact to avoid spreading it to others.

Be sure to drink plenty of fluids while you are taking valacyclovir.

People who are 65 and older can be at greater risk for some side effects from valacyclovir. Talk to your healthcare provider about your risks if you are in this age group.

Your pharmacist can make a liquid form of this medicine. If you take this form, keep it refrigerated, between 36 F to 46 F (2 C to 8 C), for up to 4 weeks. Before each use, shake the liquid medicine. Use an accurate measuring device to measure your dose. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist to recommend an appropriate measuring device.

Keep valacyclovir out of the reach of children. If your pharmacist has made you a liquid form of this medicine that should be kept in a refrigerator, take special precautions to keep it away from children who also use the refrigerator.

What should I tell my healthcare provider before using valacyclovir?

Tell your healthcare provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if valacyclovir is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your healthcare provider if you have or have had any of the following.

Weak Immune System. Some people with a weak immune system who take valacyclovir may develop a condition called thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). These conditions can cause small blood clots throughout the body, reducing blood flow to organs like the brain, heart, and kidneys. TTP and HUS are serious and can lead to death. Tell your healthcare provider if you have a weak immune system before taking valacyclovir.

Vaccines. You may not be able to receive certain vaccines, such as the chickenpox (varicella) vaccine, right before or while taking valacyclovir. Tell your healthcare provider about any vaccines you have recently received or have scheduled.

Pregnancy. It is not known if or how valacyclovir could affect pregnancy or harm an unborn baby. Tell your healthcare provider if you are or plan to become pregnant. Your healthcare provider will advise you if you should take valacyclovir while you are pregnant or trying to get pregnant.      

Breastfeeding. Valacyclovir may pass into breast milk. Tell your healthcare provider if you are breastfeeding or plan to breastfeed. Your healthcare provider will advise you if you should take valacyclovir while breastfeeding. 

Interactions

Does valacyclovir interact with foods or drinks?

There are no known interactions between valacyclovir and foods or drinks.

It is unknown if drinking alcohol will affect valacyclovir.

Does valacyclovir interact with other medicines (drug interactions)?

There are no known interactions between valacyclovir and other medicines. However, taking medicines that can harm the kidneys may increase the risk of kidney damage with valacyclovir. Always tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much valacyclovir?

If you or someone else has used too much valacyclovir, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of valacyclovir?

If you miss a dose of valacyclovir, take it as soon as you remember.  If it is almost time for your next dose, do not take the missed dose and take the next dose at your regular time.  Do not take double or extra doses.