Antibiotics Home > Flagyl and Pregnancy

There is some concern that exposure to Flagyl during pregnancy might increase the risk of childhood (or even adult) cancers. However, animal studies on Flagyl generally show that the medication does not cause birth defects or other problems during pregnancy. If you are taking Flagyl and pregnancy occurs, notify your healthcare provider.

An Overview of Flagyl During Pregnancy

Flagyl® (metronidazole) is a prescription antibiotic. At this time, it is not clear if Flagyl is safe for use during pregnancy. There is some concern about the carcinogenic (cancer-causing) potential of Flagyl when used during pregnancy.

Flagyl and Pregnancy Category B

The U.S. Food and Drug Administration (FDA) uses a pregnancy category system to classify the possible risks to a fetus when a specific medicine is taken during pregnancy. Pregnancy Category B is given to medicines that have not been adequately studied in pregnant humans but do not appear to cause harm to the fetus in animal studies.
Flagyl crosses the placenta. In general, animal studies have failed to show that the drug causes problems during pregnancy (although one study suggested that Flagyl injected into the abdominal cavity might cause miscarriages). Surveys and other similar types of studies in humans seem to suggest that Flagyl probably does not cause birth defects.
There is some concern that exposure to Flagyl during pregnancy might increase the risk of childhood (or even adult) cancers. Flagyl increases the risk of certain cancers in mice and rats; it is unknown if the same is true for humans. Studies have failed to consistently show that Flagyl exposure does (or does not) increase the risk of childhood cancers.
However, it is important to note that animals do not always respond to medicines the same way that humans do. Therefore, a pregnancy Category B medicine should be given to a pregnant woman only if a healthcare provider believes that the benefits to the pregnant woman outweigh any possible risks to the unborn child. Because of the possible risks, Flagyl is not recommended for treating trichomoniasis or bacterial vaginosis during the first trimester of pregnancy. If no other alternatives are available, Flagyl may be used to treat other types of infections if necessary (if the infection is very serious).
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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