- Whether acyclovir is right for you in pregnancy is an individual decision to make with the OB, midwife, or maternal-fetal-medicine specialist who knows your history.
- MotherToBaby reports that studies of acyclovir and its relative valacyclovir have not found an increased chance of birth defects, including in large numbers of first-trimester exposures.
- Untreated herpes-type infections can themselves cause problems in pregnancy, so treatment is sometimes recommended precisely to protect parent and baby.
- Available research has not shown an increased chance of miscarriage with these medicines, though data are always weighed case by case.
- Only small amounts pass into breast milk, and acyclovir is commonly given directly to newborns, so problems are generally not expected.
- Never start or stop an antiviral on your own; the old FDA A/B/C/D/X letter categories are retired, so ask your clinician rather than relying on an old letter grade.
If you take acyclovir for cold sores, genital herpes, shingles, or chickenpox and you are pregnant or hoping to be, it is natural to wonder whether the medicine is still appropriate. The picture here is more reassuring than it is for many drugs, but the right answer still depends on your situation. This article gathers what a leading U.S. information service says so you can have a more informed conversation with the clinician who manages your pregnancy. It is general education only and is not a substitute for that conversation.
What acyclovir is and what it treats
Acyclovir is an antiviral medicine. It is used to treat and sometimes to prevent infections caused by herpes-type viruses, including the viruses behind cold sores and genital herpes, shingles (herpes zoster), and chickenpox (varicella). A closely related medicine, valacyclovir, is converted into acyclovir in the body and is often discussed alongside it. Acyclovir comes as tablets, a liquid, a cream or ointment, and, for serious infections, an intravenous form. It works by slowing the virus’s ability to copy itself, which helps the body bring an outbreak under control.
What the guidance says about pregnancy
MotherToBaby, a service of the non-profit Organization of Teratology Information Specialists, has reviewed the research on acyclovir and valacyclovir in pregnancy. Its overall message is generally reassuring.
Birth defects
According to MotherToBaby, taking acyclovir or valacyclovir during pregnancy is not expected to increase the chance of birth defects. It points to information gathered by the manufacturer and the U.S. Centers for Disease Control and Prevention covering more than 500 births, as well as a separate study that found no increased chance of birth defects in more than 1,500 infants exposed to acyclovir and more than 200 exposed to valacyclovir during the first trimester. Because the first trimester is when the baby’s organs are forming, that first-trimester data is particularly relevant, and it has been broadly reassuring.
Miscarriage and other outcomes
MotherToBaby reports that studies have not found an increased chance of miscarriage with these medicines. It does not describe a specific trimester in which the medicine becomes riskier, so the available findings are generally applied across pregnancy rather than being tied to a particular window.
The other side: untreated infection also matters
An important part of the picture is that leaving an infection untreated is not automatically the safer choice. MotherToBaby notes that these antivirals have been prescribed during pregnancy when a person has a first (primary) genital herpes infection, because a first infection can be serious and can lead to complications in pregnancy. It also notes that a rare but serious lung complication of chickenpox, called varicella pneumonia, may need treatment with these medicines. In other words, a clinician sometimes recommends acyclovir precisely to protect both parent and baby. That is exactly why the decision belongs in a conversation with your provider, who can weigh the benefit of treating your infection against any theoretical concern about the medicine.
Breastfeeding
On breastfeeding, MotherToBaby reports that acyclovir passes into breast milk only in small amounts, and that acyclovir is commonly given directly to newborns when needed, so problems are generally not expected. If you use a topical cream on or near the breast, MotherToBaby suggests cleaning the area before nursing so the baby does not ingest the cream. As always, confirm anything specific to your situation with your own clinician.
A note on the old FDA letter categories
You may run into older web pages or leaflets that assign medicines a pregnancy “letter category” such as B or C. The U.S. Food and Drug Administration retired that A/B/C/D/X letter system, replacing it with narrative labeling under the Pregnancy and Lactation Labeling Rule that describes what the data actually show. So a letter grade you find online is not current guidance, and it is not a substitute for a discussion with your clinician about your specific circumstances.
Do not start or stop on your own
Two principles are worth holding onto. First, do not start acyclovir in pregnancy on your own; check with your OB or midwife first, even for something that feels minor like a cold sore. Second, if acyclovir was prescribed to you, do not stop it abruptly without talking to the prescriber, because some infections need continued treatment and stopping can allow the infection to flare. The right answer is individualized and can depend on the type of infection, how far along you are, and your overall health.
When to call your OB or a specialist
Reach out to your obstetric provider before taking any antiviral in pregnancy, and promptly if you develop a first genital herpes outbreak, a widespread or painful rash, chickenpox exposure or symptoms, or any breathing difficulty. If you have a complex situation, your provider may involve a maternal-fetal-medicine specialist. For questions about a specific medication exposure, you can also call MotherToBaby at 1-866-626-6847, a free service that answers questions about medicines and other exposures in pregnancy and breastfeeding.
Frequently asked questions
Is acyclovir considered safe to use while pregnant? MotherToBaby reports that studies have not found an increased chance of birth defects with acyclovir or valacyclovir, including in large numbers of first-trimester exposures. Even so, whether to use it is a decision to make with your own clinician for your situation.
I used acyclovir before I knew I was pregnant. Should I worry? Try not to panic. The available first-trimester data reviewed by MotherToBaby has been reassuring. Let your OB know what you took and when, and ask any follow-up questions there or through MotherToBaby.
Why might a doctor prescribe acyclovir during pregnancy? To treat or prevent herpes-type infections that could themselves cause problems, such as a first genital herpes infection or a serious complication of chickenpox. The aim is to protect both parent and baby.
Is the cream safer than the tablets in pregnancy? Any use is worth clearing with your provider first. Less of a topical medicine is absorbed into the body than with tablets, but the safest approach still depends on your situation, so do not assume the form removes the need for that conversation.
Can I take acyclovir while breastfeeding? MotherToBaby reports that only small amounts reach breast milk and that acyclovir is commonly given to newborns, so problems are generally not expected. Confirm with your clinician, especially for a very young or unwell baby.
What about valacyclovir instead? Valacyclovir turns into acyclovir in the body, and MotherToBaby reviews the two together with similarly reassuring findings. Which one is right for you is a question for your prescriber.
This article is general education, not medical advice, and must not be used to start, stop, adjust, or taper any medication on your own. Suddenly stopping some medicines can be dangerous. Always work with the prescriber who manages your care. In an emergency call 911; for mental-health crisis call or text 988.
Sources
- MotherToBaby (Organization of Teratology Information Specialists) — Acyclovir (Zovirax) / Valacyclovir (Valtrex) fact sheet.