Clindamycin is an antibiotic that is generally considered safe during pregnancy, especially considering that some untreated infections can lead to preterm labor. Doctors most often prescribe clindamycin in pregnancy to eliminate the threat of bacterial vaginosis and infections inside the uterus or fetal tissue. The U.S. Food and Drug Administration (FDA) placed this medication in Pregnancy Category B, because studies show no harmful effects on animal fetuses. On the other hand, it is known that this drug crosses the placenta and, with studies performed on humans insufficient to confirm its safety, it should only be used when the doctor believes its benefits outweigh any risks to the woman and fetus.
Bacterial vaginosis is a common infection that should typically be treated during pregnancy, because it can harm the fetus. The main risks include the increased likelihood of premature delivery and low birth weight. While taking clindamycin can treat the infection, this condition is often asymptomatic, so women who are prone to preterm delivery may be tested for this despite a lack of symptoms. This shows how dangerous it can be when left untreated, and why clindamycin in pregnancy is often necessary when bacterial vaginosis is diagnosed.
This drug also is sometimes used to treat infections in the fetal tissue or uterus, because it can cross the placenta. On the other hand, doctors may wait until the baby is born to treat certain infections in the mother, as long as they are minor and do not present a danger to the mother or baby. For example, doctors are unlikely to use clindamycin in pregnancy for treatment of acne, because the risks of this condition do not typically outweigh the risks of most drugs during pregnancy. Instead, they may wait until the baby is born or choose an antibiotic that has been properly studied in humans.
Though studies in animals show no increased risk of birth defects with the use of clindamycin in pregnancy, which is why it is in Pregnancy Category B, it should still be used with caution. This is because the studies performed on humans were not sufficiently controlled to determine the exact effect on human fetuses. To be on the safe side, many doctors only prescribe this medication during the second trimester, which may reduce risks of miscarriage or birth defects. In addition, it should be noted that this medication does show up in small amounts in breast milk, so breastfeeding mothers are advised to wait several hours before nursing if they have to take this drug.