Valtrex

Medically Reviewed by Dr. Harshi Dhingra, M.D.

Last Reviewed: Jul 05, 2022

Warnings

What are the risks of taking Valtrex (valacyclovir)?

Valtrex can cause serious health problems, especially in certain high-risk groups. Some of the potential risks of Valtrex treatment include:

BLOOD DISORDER: Very rarely, Valtrex can harm red blood cells and cause a blood disorder. The risk is higher in people on high doses of Valtrex, those living with HIV disease, and those who have received a bone marrow transplant or kidney transplant. Call your doctor immediately if you experience fever, confusion, weakness, extreme tiredness, bleeding, bruising, shortness of breath, or blood in the urine.
CNS PROBLEMS: Some people can develop central nervous system (CNS) problems while on Valtrex. Symptoms can include confusion, hallucinations, and seizures. The risk is greater for people on high doses of Valtrex, older individuals, and people with kidney problems. Call your doctor without delay if you notice any such symptoms during Valtrex treatment.
ACUTE RENAL FAILURE: Valtrex can cause severe harm to the kidneys. The risk is higher with high doses of Valtrex, in older individuals, in people with pre-existing kidney problems, in people with dehydration, and in people taking other drugs that can also harm the kidneys. Stay well hydrated while you are taking Valtrex. Give your doctor a complete list of medications. Keep all your healthcare appointments because your doctor may want to order some lab tests to keep an eye on your kidney function.

Talk to your doctor or pharmacist about the risks of taking Valtrex. Call your doctor immediately if you experience any unusual symptoms while on this medication.

What should I tell my doctor before starting Valtrex (valacyclovir)?

Tell your doctor if you have previously had allergic reactions to valacyclovir (Valtrex), acyclovir (Zovirax), or other medications.

Give your doctor a complete medical history. Valtrex may not be suitable for people with certain medical conditions such as kidney disease, liver disease, or HIV.

Tell your doctor about all your prescription drugs, nonprescription drugs (over-the-counter medicines), nutritional supplements, vitamins, and herbal products—this can help avoid serious drug interactions.

Tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding.

What precautions should I take while on Valtrex (valacyclovir)?

Keep all your healthcare appointments. Your doctor may want to order lab tests to check your response to Valtrex.

You should know that Valtrex will treat your symptoms but will not cure your viral infection. Refrain from sexual intercourse if you can see genital herpes lesions. However, you should know that you can spread genital herpes even if you do not have visible lesions.

Call your doctor if you become pregnant while taking Valtrex.

Call your doctor immediately or go to the emergency room if you experience signs and symptoms of a serious allergic reaction such as rash or itching or if you develop fever, confusion, yellowing of the skin or eyes, or blood in the urine.

What are Valtrex (valacyclovir) interactions?

Taking Valtrex with some other medications can affect how it works. Drug interactions can also increase the risk of serious adverse effects. Your physician may choose a different medication to treat your viral infection, change the dose or frequency of one or both medicines, and/or monitor you carefully for side effects if there are known interactions between Valtrex and your other medications.

Taking Valtrex with the following medications is not recommended:

Dichlorphenamide
Teriflunomide
Leflunomide
Nitisinone
Foscarnet

There can also be interactions between Valium and medicines, such as:

Cimetidine (Tagamet)
Probenecid (Benemid)
Valproic acid
Phenytoin
Fosphenytoin

This list does not describe all possible Valtrex interactions. Give your healthcare providers a complete list of your medications, including prescription drugs, over-the-counter medicines, dietary supplements, and herbal products. Also, tell your healthcare providers if you smoke, drink alcohol, or use illegal drugs because some of these substances can cause serious health complications or increase the risk of side effects when used with prescription drugs.

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