Medically reviewed by Sophia Entringer, PharmD. Last updated on Apr 1, 2021.
What is Valtrex?
Valtrex (valacyclovir) is an antiviral drug. It slows the growth and spread of the herpes virus to help the body fight the infection.
Valtrex is used to treat cold sores in children who are at least 12 years old, or chickenpox in children who are at least 2 years old.
Valtrex will not cure herpes and will not prevent you from spreading the virus to other people. However, this medicine can lessen the symptoms of an infection.
Valtrex may also be used for purposes not listed in this medication guide.
Before taking Valtrex, tell your doctor if you have HIV/AIDS, a weak immune system, kidney disease (or if you are on dialysis), or if you have had a kidney or bone marrow transplant.
Valtrex can be harmful to the kidneys, and these effects are increased when it is used together with other medicines that can harm the kidneys. Tell your doctor about all other medications you are using. You may need dose adjustments or special tests when taking certain medications together with Valtrex.
Treatment with Valtrex should be started as soon as possible after the first appearance of symptoms (such as tingling, burning, blisters).
Stop taking Valtrex and call your doctor right away if you have any signs of a serious side effect that can harm red blood cells, such as: fever, easy bruising or bleeding, red spots on the skin (not related to herpes or chickenpox), bloody diarrhea, vomiting, pale or yellowed skin, weakness, fainting, or urinating less than usual or not at all.
Before taking this medicine
You should not use Valtrex if you are allergic to valacyclovir or acyclovir (Zovirax).
To make sure Valtrex is safe for you, tell your doctor if you have:
kidney disease (or if you are on dialysis);
HIV/AIDS, or other conditions that can weaken the immune system; or
a history of kidney transplant or bone marrow transplant.
While Valtrex use in pregnant women is limited, there is no evidence of major risk to the human fetus from valacyclovir. However, herpes virus can be passed from an infected mother to her baby during childbirth. If you have genital herpes, it is very important to prevent herpes lesions during your pregnancy, so that you do not have a genital lesion when your baby is born.
Valacyclovir can pass into breast milk and may harm a nursing baby. Tell your doctor if you are breast-feeding a baby.
Do not give this Valtrex to a child without medical advice.
How should I take Valtrex?
Take Valtrex exactly as it was prescribed for you. Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.
Start taking Valtrex as soon as possible after the first appearance of symptoms (such as tingling, burning, blisters). This medicine might not be as effective if you first start taking it 1 or 2 days after the start of your symptoms.
Some herpes infections need to be treated for longer than others. Use this medicine for the full prescribed length of time. Your symptoms may improve before the infection is completely cleared. Skipping doses may increase the risk of your virus becoming resistant to antiviral medicine.
You may take Valtrex with or without food.
Tell your doctor if a child taking this medicine cannot swallow the tablet.
Drink plenty of water while you are taking Valtrex to keep your kidneys working properly.
Lesions caused by herpes viruses should be kept as clean and dry as possible. Wearing loose clothing may help to prevent irritation of the lesions.
Store Valtrex tablets at room temperature away from moisture and heat.
What happens if I miss a dose?
Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.
What to avoid
Taking this medicine will not prevent you from passing genital herpes to other people. Herpes infections are contagious and you can infect other people even while you are taking Valtrex.
Avoid sexual intercourse or use a latex condom to help keep you from spreading the virus to others. Avoid letting infected areas come into contact with other people. Avoid touching an infected area and then touching your eyes. Wash your hands frequently to prevent the spread of infection.
Do not share this medicine with another person, even if they have the same symptoms you have.
Valtrex side effects
Get emergency medical help if you have signs of an allergic reaction to Valtrex: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
confusion, aggression, or you feel shaky or unsteady;
hallucinations (seeing or hearing things that are not real);
problems with speech;
a seizure (convulsions); or
kidney problems--little or no urination, painful or difficult urination, swelling in your feet or ankles, feeling tired or short of breath.
Stop taking Valtrex and call your doctor right away if you have any of the following signs of a serious side effect that can harm red blood cells:
fever, pale skin;
unusual bleeding (nosebleeds, bleeding gums);
red or pink urine, little or no urination;
red spots on the skin (not related to herpes or chickenpox);
feeling weak or tired;
stomach pain, bloody diarrhea, vomiting; or
swelling in your face, hands, or feet.
Side effects may be more likely in adults who are 65 or older.
Common Valtrex side effects may include:
nausea, stomach pain; or
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
What other drugs will affect Valtrex?
Valtrex can harm your kidneys. This risk may increase when you also use certain other medicines, including: antivirals, chemotherapy, certain antibiotics, medicine for bowel disorders, medicine for high blood pressure, medicine to prevent organ transplant rejection, injectable osteoporosis medication, and some pain or arthritis medicines (including Advil, Motrin, and Aleve). Ask your pharmacist if you are concerned you are taking other medications that may harm your kidneys.
Other drugs may interact with valacyclovir, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.
Frequently asked questions
More about Valtrex (valacyclovir)
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- Drug class: purine nucleosides
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Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Valtrex only for the indication prescribed.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
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