At any given time, more than 10 million women in the United States are pregnant or lactating, and exposing a fetus or newborn to antibiotics can pose a unique threat. Changes during pregnancy and lactation also can trigger pharmacokinetic and pharmacodynamic modifications that alter the effectiveness of antibiotics. Nahum and colleagues reviewed the literature on antibiotic use to provide updated, evidence-based information on antibiotic use in women who are pregnant or lactating.

The researchers examined published medical literature, sources on teratogenicity and prescribing for women who are lactating or pregnant, and they abstracted data from product labels for drugs approved by the U.S. Food and Drug Administration (FDA) for use during pregnancy. The authors identified 124 references that covered 11 commonly prescribed antibiotics, all of which cross the placenta and are excreted in human breast milk.

There was no teratogenic potential for penicillins G and V potassium (V-Cillink); unlikely potential for amoxicillin, chloramphenicol (Chloromycetin), ciprofloxacin (Cipro), doxycycline (Vibramycin), levofloxacin (Levaquin), and rifampin (Rifadin); and undetermined potential for clindamycin (Cleocin), vancomycin, and gentamicin (see accompanying table). All agents were FDA Pregnancy Category B (amoxicillin, clindamycin, penicillin G, penicillin V potassium, and vancomycin) or C (chloramphenicol, ciprofloxacin, gentamicin, levofloxacin, and rifampin), except for doxycycline, which was category D.

Evidence suggested that increased maternal dose or shorter dosing intervals should be considered for amoxicillin, gentamicin, and penicillins G and V potassium. However, information on pharmacokinetics during pregnancy was inadequate for the other antibiotics. There were limited data on several other aspects of antibiotic use during pregnancy, but the authors stress that conducting studies in this area would be challenging.

Despite the lack of scientific evidence, the authors conclude that physicians should make balanced judgments about the well-being of the mother and her child before making decisions about antibiotic use during pregnancy and lactation.

ANNE D. WALLING, M.D