- Sexually Transmitted Diseases (STDs) Slideshow Pictures
- Take the Quiz on STDs
- Impotence Slideshow Pictures
- Valtrex (valacyclovir) vs. Zovirax (acyclovir): What's the difference?
- What is Valtrex? What is Zovirax?
- What are the side effects of Valtrex and Zovirax?
- What is the dosage for Valtrex vs. Zovirax?
- What supplements interact with Valtrex and Zovirax?
- Are Valtrex and Zovirax safe to use while pregnant or breastfeeding?
Valtrex (valacyclovir) vs. Zovirax (acyclovir): What's the difference?
- Valtrex (valacyclovir) and Zovirax (acyclovir) are antiviral drugs used to treat infections with shingles (herpes zoster), genital herpes (herpes simplex genitalis), and cold sores (herpes labialis).
- Zovirax is also used to treat Epstein-Barr virus (mononucleosis).
- Side effects of Valtrex and Zovirax that are similar include headache, nausea, vomiting, diarrhea, and rash.
- Side effects of Valtrex that are different from Zovirax include abdominal pain, cold symptoms, increased liver enzymes, reduced white blood cells, joint pain, and dizziness.
- Side effects of Zovirax that are different from Valtrex include agitation, confusion, anemia, muscle pain, hypersensitivity reactions, seizures, agitation, confusion, anemia, hepatitis, and muscle pain.
What is Valtrex? What is Zovirax?
Valtrex (valacyclovir) is a type of antiviral drug called a nucleoside analog used to treat infections with shingles (herpes zoster), genital herpes (herpes simplex genitalis), and cold sores (herpes labialis). Nucleoside analogs mimic one of the building blocks of DNA and they stop the spread of the herpes virus by preventing the viral DNA replication that is necessary for viruses to multiply. Acyclovir (Zovirax) and famciclovir (Famvir) are also nucleoside analogs. Valacyclovir is called a "prodrug," in that it is not active itself but rather, it is converted to acyclovir in the body, and it is the acyclovir that is active against the viruses. (Acyclovir itself is available as a topical, oral, and intravenous medication.) Valtrex thus is active against the same viruses as acyclovir, but Valtrex has a longer duration of action than acyclovir and can be taken fewer times each day.
Zovirax (acyclovir) is an antiviral drug, a synthetic nucleoside analogue, that has inhibitory activity (interferes with viral replication) against the herpes viruses, including herpes simplex 1 and 2 (cold sores and genital herpes), varicella-zoster (shingles and chickenpox), and Epstein-Barr virus (mononucleosis). Viruses take over living cells and reproduce themselves, often at the expense of the host cell. Zovirax is converted to an active form by the virus itself, and the virus then uses the active form of acyclovir rather than the nucleoside it normally uses to manufacture DNA, a critical component of viral replication. Incorporation of active acyclovir into new viral DNA stops the production of the DNA. Virally infected cells absorb more Zovirax than normal cells and convert more of it to the active form, which prolongs its antiviral activity.
What are the side effects of Valtrex and Zovirax?
The side effect profile of Valtrex is similar to that of acyclovir (Zovirax).
Common side effects are:
- Abdominal pain
- Cold symptoms
- Increased liver enzymes
- Reduction of white blood cells
Other important side effects are:
More serious side effects include central nervous system side effects which are more likely to happen in the elderly, for example:
- Increased heart rate (tachycardia)
- Encephalopathy (a disorder of the brain)
- Decreased number of blood platelets
- Increased heart rate
- High blood pressure (hypertension)
The most common side effects are
Other reported side effects include:
- anemia, and
- muscle pain,
- hypersensitivity reactions,
- hepatitis, and
- muscle pain.
Latest Sexual Health News
What is the dosage for Valtrex vs. Zovirax?
- 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.
Acyclovir may be taken with or without food.
- Adult oral doses for treating genital herpes are 200 mg every 4 hours (5 times daily) for 7-10 days or 400 mg three times daily for 5-10 days.
- Herpes Zoster (shingles) is treated with 800 mg every 4 hours (5 times daily) for 7 to 10 days.
- The dose for treating chicken pox is 800 mg 4 times daily. The usual adult intravenous dose is 5-10 mg/kg every 8 hours for 7-10 days.
What supplements interact with Valtrex and Zovirax?
Acyclovir may decrease levels of phenytoin (Dilantin) or valproic acid (Depakote, Depakote ER). Probenecid (Benemid) may increase acyclovir serum levels by decreasing renal excretion of acyclovir. Acyclovir may increase serum levels of theophylline (Theo-Dur, Respbid, Slo-Bid, Theo-24, Theolair, Uniphyl, Slo-Phyllin).
Subscribe to MedicineNet's General Health Newsletter
Are Valtrex and Zovirax safe to use while pregnant or 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.
There are no adequate studies of acyclovir in pregnant women. In a patient registry of women who used acyclovir during the first trimester, the rate of birth defects was similar to the rate of birth defects in the general population.
Acyclovir is excreted in breast milk, and a significant amount may be transferred to the infant.
Valtrex (valacyclovir) and Zovirax (acyclovir) are antiviral drugs used to treat infections with shingles (herpes zoster), genital herpes (herpes simplex genitalis), and cold sores (herpes labialis). Zovirax is also used to treat Epstein-Barr virus (mononucleosis). Side effects of Valtrex and Zovirax that are similar include headache, nausea, vomiting, diarrhea, and rash.
Multimedia: Slideshows, Images & Quizzes
Genital Herpes: Causes, Treatment, and Prevention
What's going on down there? WebMD shows you pictures of genital herpes symptoms and treatments -- and how to avoid getting the...
Shingles Quiz: Symptoms, Vaccine & Pictures
Shingles falls within a well-known family of viruses that cause itching, burning, blisters, and pain. Take the Shingles Quiz to...
Genital Herpes Quiz: What is Genital Herpes?
What is genital herpes? Learn the causes, symptoms in men and women, and treatments for this common sexually transmitted skin...
Picture of Herpes Zoster
Also called shingles, zona, and zoster. The culprit is the varicella-zoster virus. Primary infection with this virus causes...
Picture of Herpes Blister (Cold Sore)
Cold sores (fever blisters) are caused by the herpes simplex virus (HSV), passed on through contact with infected skin or body...
Picture of Herpes Simplex Virus Type 1
A herpes virus that causes cold sores and fever blisters in and around the mouth. See a picture of Herpes Simplex Virus Type 1...
Picture of Herpes Simplex Virus Type 2
A herpes virus that causes genital herpes, which is characterized by sores in the genital area. See a picture of Herpes Simplex...
Related Disease Conditions
Cold Sores (Nongenital Herpes Simplex Infections)
Herpes simplex infections are common and when they appear around the mouth and lips, people often refer to them as "cold sores" and "fever blisters." Canker sores are different than cold sores. Air droplets can spread the virus, as can direct contact with the fluid from the blisters. Cold sore treatment include over-the-counter medication, as well as prescription medications.
Shingles, or herpes zoster, is a painful rash caused by the varicella zoster virus. Other shingles symptoms include headache, fever, nausea, and body aches. Treatment focuses on pain management and shortening the duration of the illness with antiviral medications.
Genital Herpes in Women (Symptoms, Signs, Treatment)
Genital herpes is a sexually transmitted disease (STD) caused by the herpes simplex virus (HSV). Symptoms of genital herpes include painful blisters and often fever, body aches, and swollen lymph nodes for first time infection. Genital herpes is diagnosed with lab tests to test for the presence of the virus. Treatment for genital herpes includes antiviral medications to shorten the duration of the outbreak or reduce the risk of future outbreaks. There is no cure for genital herpes. Condoms may help prevent the spread of genital herpes.
Herpes Viral Infections of the Eye
Herpes of the eye occurs due to herpes simplex virus-1 (HSV-1). Symptoms of herpes of the eye include pain in and around the eye, rash or sores on the eyelids, redness, swelling, and cloudiness of the cornea.
Treatment & Diagnosis
Medications & Supplements
- acyclovir ointment - topical, Zovirax
- acyclovir cream - topical, Zovirax
- valacyclovir - oral, Valtrex
- acyclovir - injection, Zovirax
- acyclovir - oral, Zovirax
- Valtrex (valacyclovir)
- acyclovir, Zovirax
- Valtrex (valacyclovir) vs. Famvir (famciclovir)
- Valtrex (valacyclovir) vs. Abreva (docosanol)
- Valtrex (valacyclovir) vs. Valcyte (valganciclovir)
Prevention & Wellness
Health Solutions From Our Sponsors
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.