Anti-infectives. (Drugs, Pregnancy, and Lactation).

This is my fourth and final installment on anti-infectives

* Anthelmintics. All three agents in the benzimidazole class of the anthelmintics are rated pregnancy category C. In humans, their bioavailability is extremely low, but increases substantially when taken with fatty foods.

There are few data concerning use of these three drugs during lactation, although it is likely that they are safe because of their low bioavailability.

Albendazole (Albenza) is embryotoxic, fetotoxic, and teratogenic in rabbits and rats at doses less than the recommended human dose. There are only about 60 reports of human pregnancy exposures, including 10 in the first trimester; all had normal outcomes. But because of limb reduction effects observed with all doses in one animal study and the potential for greater bioavailability if taken with a fatty meal, this drug should be avoided during pregnancy especially in the first trimester.

Mebendazole (Vermox) is also teratogenic in rats at doses about equal to the dose in humans, but not in other animal species. Because the more than 5,000 reports of human pregnancy exposures to this drug have found no association with abortions or birth defects, mebendazole is preferred over albendazole during pregnancy.

The third benzimidazole, thiabendazole (Mintezol), was not teratogenic in mice, rats, or rabbits at doses equal to the human dose, but birth defects were seen when it was suspended in olive oil, indicating that it may pose a danger when the patient has a fatty diet. There are no reported human exposures to thiabendazole in the first trimester.

Another anthelmintic, pyrantel, rated C, is not teratogenic in rats or rabbits, but there are no human reports of its use in pregnancy or lactation.