- Whether cephalexin is appropriate in pregnancy is an individual decision made with the OB or midwife who knows your history.
- Cephalexin is a cephalosporin antibiotic, a class often considered among the more acceptable antibiotic options in pregnancy, though data specific to cephalexin are limited.
- In one study of 262 women, MotherToBaby reports no increased chance of birth defects; findings on miscarriage were mixed across studies.
- Untreated infections in pregnancy can carry their own risks to parent and baby, so the goal is safe, appropriate treatment rather than avoiding antibiotics.
- Antibiotics should be taken exactly as prescribed and the full course finished unless your clinician tells you otherwise.
- Cephalexin passes into breast milk in small amounts and is generally not expected to cause problems, per MotherToBaby.
If you have been prescribed cephalexin, often known by the brand name Keflex, and you are pregnant or trying to conceive, it is natural to want to know whether it is safe. Antibiotics can feel especially worrying during pregnancy. This article gathers what an authoritative source says about cephalexin so you can have a more informed conversation with the clinician managing your pregnancy. It is general education only and is not a substitute for that conversation.
What cephalexin is and what it treats
Cephalexin is an antibiotic in a family called cephalosporins. It is used to treat a range of bacterial infections, including those caused by common organisms such as Staphylococcus aureus (staph) and Escherichia coli (E. coli). In everyday practice it is prescribed for infections such as certain skin, respiratory, and urinary tract infections. Antibiotics like cephalexin work only against bacteria; they do not treat viral illnesses such as colds or the flu.
What the guidance says about cephalexin in pregnancy
MotherToBaby, a service of the non-profit Organization of Teratology Information Specialists, provides one of the clearest plain-language summaries of what is known. It is honest about the limits of the evidence, noting that information on the use of cephalexin specifically in pregnancy is limited.
Birth defects
MotherToBaby reports that in a study of 262 women who took cephalexin during pregnancy, there was no increased chance for birth defects. It adds that another study, which grouped cephalexin together with similar medications, also did not report an increased chance of birth defects. As background, MotherToBaby notes that every pregnancy starts with a baseline chance of a birth defect, generally described as around 3 to 5 in 100, regardless of any exposure.
Miscarriage
The picture on miscarriage is less uniform. MotherToBaby reports that in the same study of 262 women, there was no increase in miscarriage compared with a similar group of women who did not take cephalexin. However, it notes that another study did report an increased chance of miscarriage with cephalexin exposure. When studies do not fully agree, that is a reason to discuss your specific situation with your clinician rather than to draw a firm conclusion on your own.
Other pregnancy outcomes
MotherToBaby is candid that some questions have not been well studied. It states that studies have not been done to see whether cephalexin increases the chance of pregnancy-related problems such as preterm delivery (birth before 37 weeks) or low birth weight. A lack of studies is not the same as evidence of harm, but it does mean the honest answer to some questions is that the data are limited.
The other side: untreated infections also matter
It is important not to read caution as a reason to leave an infection untreated. MotherToBaby points out that having certain infections during pregnancy, such as a staph or E. coli infection, can itself increase the chance of pregnancy-related problems or of infections in a newborn. Urinary infections in particular are often treated in pregnancy precisely because leaving them untreated can lead to more serious problems. The aim of care is safe, appropriate treatment of the infection, not avoidance of all medicine. This is exactly why the decision belongs in a conversation with your provider, who can weigh the specific infection against the options.
Take it as prescribed
If your clinician prescribes cephalexin, an important principle is to take it exactly as directed and to finish the full course unless your provider tells you to stop. Stopping an antibiotic early because you feel better can allow an infection to return and can contribute to antibiotic resistance. If you develop side effects or have concerns, contact the prescriber rather than simply stopping on your own. And never take leftover antibiotics, or someone else’s prescription, to self-treat a suspected infection in pregnancy.
A note on drug “categories”
You may see older references sorting pregnancy medicines into letter categories such as A, B, C, D, and X. Those FDA letter categories have been retired. They were replaced with a narrative labeling system (the Pregnancy and Lactation Labeling Rule) that describes what is actually known from studies rather than assigning a single letter. If you find an old “category” for cephalexin, treat it as outdated and rely on current guidance and your care team.
Breastfeeding
MotherToBaby reports that cephalexin passes into breast milk in small amounts and is generally not expected to cause side effects in a breastfed child. It notes that among reports of 20 babies exposed through breast milk, a few had loose stools, and there is a single report of a rash attributed to a sensitivity. As always, mention any medication to your clinician, especially if your baby is a newborn or has health concerns, and report anything unusual.
When to call your OB or clinician
Contact your provider if your infection symptoms are not improving or are getting worse, if you develop a fever, if you have signs of an allergic reaction such as rash, swelling, or trouble breathing (seek emergency care for serious reactions), or if you have questions about whether to continue the medicine. For questions about a specific medication exposure in pregnancy or breastfeeding, you can also call MotherToBaby at 1-866-626-6847, a free service that answers questions about medicines and other exposures.
Frequently asked questions
Is cephalexin safe to take while pregnant? Cephalexin is often considered among the more acceptable antibiotic options in pregnancy, and MotherToBaby reports no increased chance of birth defects in one study, though it notes the overall data are limited. Whether it is right for you is a decision for your clinician based on your infection.
I took cephalexin before I knew I was pregnant. Should I worry? Try not to panic. MotherToBaby’s summary does not point to a clear increase in birth defects. Let your OB know what you took and when, and ask any follow-up questions there or through MotherToBaby.
Can an untreated infection hurt my pregnancy? It can. MotherToBaby notes that some infections in pregnancy can raise the chance of pregnancy-related problems or newborn infections, which is why appropriate treatment is emphasized rather than avoidance.
Should I finish the whole course? Unless your provider tells you otherwise, yes. Stopping early can let an infection return and can contribute to resistance. Contact the prescriber before stopping.
Can I breastfeed while taking cephalexin? MotherToBaby reports that only small amounts pass into breast milk and problems are generally not expected. Confirm with your clinician, especially for a newborn.
Is a different antibiotic safer in pregnancy? Some antibiotics are used more cautiously in pregnancy than others, and the best choice depends on the infection. This is a decision for your clinician, who can match the antibiotic to your situation.
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) — Cephalexin (Keflex, Keftab) fact sheet.