Drugs, pregnancy, and lactation: anti-infectives. (Obstetrics).

This is the third installment in a series of columns on anti-infective drugs. * Sulfonamides. This class is rated C during most of pregnancy and D near term. Sulfonamides readily cross the placenta throughout pregnancy, and significant drug levels may persist in newborns for several days after birth. Even though they aren't teratogenic, they can cause toxic effects in the newborn, including jaundice, hemolytic anemia, and----theoretically----kernicterus. These risks are greatest for premature infants, so a sulfonamide should not be used in premature labor. Sulfonamides can be taken during breast-feeding, but should be avoided in women whose babies are jaundiced or have glucose-6-phosphate dehydrogenase (G6PD) deficiency, or are ill, stressed, or premature.

* Aztreonam (Azactam). There is no evidence that this [beta]-lactam, rated B, is teratogenic or embryo-fetotoxic in animals. But there are no reports in human pregnancy, so I recommend avoiding it in the first trimester until such data are available. Because of low concentrations in breast milk, exposure is probably not a risk to the nursing infant.

* Carbapenems. The combination agent imipenem-cilastatin (Primaxin), rated C, is not teratogenic in animals but was embryocidal and lethal in pregnant monkeys at about three times the recommended human dose. Human reports indicate that it is safe during the second half of gestation; these data are limited, and there are no first-trimester reports. I'd be cautious about using it early in gestation until we know more. There are no reports of use during lactation; only small amounts are found in breast milk so it is probably safe.

Meropenem (Merrem), rated B, is considered safe during the second half of gestation, because there's no. evidence of fetal harm in rats and monkeys. Still, there are no reports of meropenem use in humans during pregnancy or lactation. If a pregnant or nursing woman really needs this agent, and there is no alternative, the benefit probably outweighs the risk.

* Metronidazole (Flagyl). This agent is rated B because studies in mice and rats have found no evidence of fetal harm. But it is mutagenic in bacteria and carcinogenic in rodents, which has raised concern about use during pregnancy. To date, however, these effects have not been demonstrated in human studies.

The many studies of this drug during human pregnancy include two metaanalyses and two population-based studies. These four studies found no association with birth ...