Valtrex (valacyclovir) for Cold Sores: Side Effects & Dosage

What is Valtrex (valacyclovir)? What are its uses?

Valtrex (valacyclovir) is an oral antiviral drug which is active against the herpes viruses. It is used to treat infections with:

• Shingles (herpes zoster)
• Genital herpes (herpes simplex genitalis)
• Cold sores (herpes labialis)

What are the side effects of Valtrex (valacyclovir)?

The side effect profile of Valtrex is similar to that of acyclovir (Zovirax).

Common side effects are:

• Headache
• Nausea
• Vomiting
• Abdominal pain
• Cold symptoms
• Increased liver enzymes
• Reduction of white blood cells

Other important side effects are:

• Diarrhea
• Rash
• Joint pain
• Dizziness

More serious side effects include central nervous system side effects which are more likely to happen in the elderly, for example:

• Agitation
• Hallucinations
• Confusion
• Delirium
• Depression
• Increased heart rate (tachycardia)
• Seizures
• Encephalopathy (a disorder of the brain)
• Decreased number of blood platelets
• Increased heart rate
• High blood pressure (hypertension)

Acanthosis Nigricans
Browse through our medical image collection to see and discover unique diseases and conditions
See Images

What is the dosage for Valtrex (valacyclovir)?

• Valtrex may be taken with or without food.
• In people with kidney disease, doses need to be reduced.
• For the treatment of herpes zoster (shingles), the usual dose is 1 gm. three times a day for 7 days. Treatment should begin at the first symptom and is most effective if started within 48 hours of the onset of rash.
• The dose for chickenpox is 20 mg/kg 3 times daily for 5 days (maximum dose is 1000 mg 3 times daily) and treatment should start at the earliest sign or symptom.
• For the treatment of an initial episode of genital herpes, the usual dose is 1 gram (1000 mg) twice daily for 10 days. For the treatment of recurrent genital herpes, the usual dose is 500 mg twice daily for 3 days. For best results, treatment should be initiated within 12 hours of the start of symptoms.
• The dose for cold sores is 2000 mg (2 grams) every 12 hours for 1 day.

Which drugs or supplements interact with Valtrex (valacyclovir)?

Probenecid (Benemid) and cimetidine (Tagamet) may reduce the kidney's clearance of Valtrex, leading to higher concentrations in the blood. This may lead to side effects of Valtrex.

Latest Skin News

• Five Sunscreens Recalled Due to Benzene
• Shining a Light on Sunscreens
• Dyeing Your Hair? Beware Chemical Burns
• Are You Absorbing Toxins From Your Makeup?
• Medieval Shoe Trend Brought Bunions
• Want More News? Sign Up for MedicineNet Newsletters!

Daily Health News

• H5N6 Bird Flu Infection in China
• COVID Vaccine Misinformation
• Antibiotic-Resistant Pneumonia
• Mask Mandate Returns to L.A.
• Fermented Foods Help Microbiome
• More Health News »

Trending on MedicineNet

• Guillain-Barre Syndrome
• What Triggers Shingles?
• Normal Blood Sugar Levels
• Identify Tick Bites
• Why Is Autism Increasing?

Is Valtrex (valacyclovir) safe to use during pregnancy or while breastfeeding?

• Valtrex showed no effects on the fetus in animal studies; however, there has been no adequate evaluation of valacyclovir or (acyclovir) in pregnant women. The incidence of birth defects in women taking acyclovir is about the same as in the general population. Valtrex should only be used during pregnancy when the benefits to the mother outweigh risks to the fetus.
• It is not known whether Valtrex is excreted into breast milk. It is known, however, that among women taking acyclovir, concentrations of acyclovir in breast milk are about four times higher than in the mother's blood. The safety of valacyclovir in breastfeeding infants has not been established. Methods other than breastfeeding should be considered if valacyclovir must be taken while nursing.

Shingles is a painful rash caused by the same virus that causes chickenpox.
See Answer

How does Valtrex (valacyclovir) work (mechanism of action)?

Valtrex belongs to a class of drugs called nucleoside analogs that mimic one of the building blocks of DNA. It stops the spread of herpes virus in the body by preventing the replication of viral DNA that is necessary for viruses to multiply. Other drugs in the same class include acyclovir (Zovirax) and famciclovir (Famvir). Valacyclovir is actually a "prodrug," in that it is not active itself. Rather, it is converted to acyclovirin the body, and it is the acyclovir that is active against the viruses. (Acyclovir itself is available as a topical, oral and intravenous medication.) Valacyclovir, therefore, is active against the same viruses as acyclovir, but valacyclovir has a longer duration of action than acyclovir, and, therefore, can be taken fewer times each day.

The FDA approved valacyclovir in 1995.

What else should I know about Valtrex (valacyclovir)?

• Valacyclovir) is available as tablets of 500 and 1000 mg
• Valtrex should be kept stored between 2 C and 30 C (36 F and 86 F).
• Valacyclovir is available in generic form. You need a prescription from your doctor for it.