This sheet is about exposure to acyclovir or valacyclovir in a pregnancy or while breastfeeding. This information should not take the place of medical care and advice from your healthcare provider.
What is acyclovir?
Acyclovir (Zovirax®) is an antiviral medication. Acyclovir has been used to treat symptoms from cold sores and genital herpes caused by the herpes virus. It is also prescribed to treat chickenpox and shingles. Acyclovir can help relieve the pain and help the healing of sores or blisters. It is not a cure for herpes and infections can return at a later time.
Is valacyclovir the same as acyclovir?
Valacyclovir (Valtrex®) is like acyclovir and used to treat the same types of infections. Valacyclovir changes to acyclovir once in a person’s body.
I take acyclovir or valacyclovir. Can it make it harder for me to get pregnant?
It is not known if acyclovir/valacyclovir can make it harder to become pregnant.
I just found out I am pregnant. Should I stop taking acyclovir/valacyclovir?
Talk with your healthcare providers before making any changes to how you take your medication. The benefit of treatment should be weighed against the risks of untreated illness. Acyclovir/valacyclovir have been prescribed during pregnancy when the person has a primary genital herpes infection. A “primary” infection means it is the first time for the infection. Primary infection can be life threatening or lead to complications in a pregnancy. A rare but serious infection called varicella pneumonia might also require treatment with these medications. Your healthcare providers can talk with you about the benefits of treating your condition and the risks of untreated illness during pregnancy.
Does taking acyclovir/valacyclovir increase the chance for miscarriage?
Miscarriage is common and can occur in any pregnancy for many different reasons. Studies have not found an increased chance for miscarriage following acyclovir use.
Does taking acyclovir/valacyclovir increase the chance of birth defects?
Every pregnancy starts out with a 3-5% chance of having a birth defect. This is called the background risk. Based on the information available, acyclovir/valacyclovir is not expected to increase the chance for birth defects.
The manufacturer, along with the Centers for Disease Control and Prevention (CDC), looked at the effects of acyclovir on the developing baby. No increase in birth defects was seen in over 500 births. Also, a separate study found no increase in birth defects in over 1,500 infants exposed to acyclovir and over 200 infants exposed to valacyclovir during the first trimester of pregnancy.
Does taking acyclovir/valacyclovir in pregnancy increase the chance of other pregnancy related problems?
The use of acyclovir/valacyclovir later in pregnancy has not been well studied to see how its use might affect pregnancy replated problems, such as preterm delivery (birth before week 37) or low birth weight (weighing less than 5 pounds, 8 ounces [2500 grams] at birth). However, clinical experience has been reassuring. Untreated infections could cause problems for the newborn.
Does taking acyclovir/valacyclovir in pregnancy cause long-term problems in behavior or learning for the baby?
Studies have not been done to see if acyclovir/valacyclovir can cause behavior or learning issues for the child.
Breastfeeding while taking acyclovir/valacyclovir:
Acyclovir enters breast milk in small amounts. Acyclovir is commonly given to newborns and does not typically cause problems for babies. If you are applying acyclovir cream or ointment directly on your breast, clean the area before nursing. Be sure to talk to your healthcare provider about all of your breastfeeding questions.
If a male takes acyclovir/valacyclovir, could it affect fertility (ability to get partner pregnant) or increase the chance of birth defects?
Effects on sperm have not been studied in fathers or sperm donors. One study in 20 males did not find lower sperm production when given high doses of acyclovir for six months. In general, exposures that fathers or sperm donors have are unlikely to increase risks to a pregnancy. For more information, please see the MotherToBaby fact sheet Paternal Exposures at https://mothertobaby.org/fact-sheets/paternal-exposures-pregnancy/.
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OTIS/MotherToBaby encourages inclusive and person-centered language. While our name still contains a reference to mothers, we are updating our resources with more inclusive terms. Use of the term mother or maternal refers to a person who is pregnant. Use of the term father or paternal refers to a person who contributes sperm.