Trimethoprim Pregnancy and Breastfeeding Warnings

Trimethoprim is also known as: Primsol, Proloprim, Trimpex

Trimethoprim Pregnancy Warnings

Trimethoprim has been assigned to pregnancy category C by the FDA. Animal studies have revealed evidence of teratogenicity. There are no controlled data in human pregnancy. Trimethoprim should only be given during pregnancy when benefit outweighs risk.

There are no reports of teratogenicity associated with trimethoprim as a single agent. However, the Michigan Medicaid surveillance study demonstrated possible teratogenic effects associated with the combination drug, trimethoprim-sulfamethoxazole (TMP-SMX). This report is a summary of information from two studies, one in which 1,116 of 104,000 pregnant women from 1980 to 1983, and one in which 2,296 of 229,000 pregnant women from 1985 to 1992 received TMP-SMX. In the first study, 83 total defects (13 cardiovascular defects) were observed (14 and 2 were expected, respectively). In the second study, 126 total defects (37 cardiovascular defects) were observed (98 and 27 were expected, respectively). Cleft palate was observed in three cases in the latter study. These data support an association between TMP-SMX and congenital defects, although other causes such as the underlying disease(s) of the mother and concomitant drug therapy are unaccounted for. Moreover, the individual contributions of TMP versus SMX are not known. There has also been a single report of Niikawa-Kuroki syndrome, characterized by mental and growth retardation and craniofacial abnormalities, associated with TMP-SMX.

Trimethoprim Breastfeeding Warnings

The average milk levels obtained after trimethoprim 160 mg twice a day range from 1.8 to 2.0 mcg/mL between two and three hours after dosing. No adverse effects of trimethoprim on nursing infants have been reported.

Trimethoprim is excreted into human milk in small amounts. The risk of interference with folic acid metabolism exists. The combination trimethoprim-sulfamethoxazole is considered compatible with breast-feeding by the American Academy of Pediatrics. The manufacturer recommends caution when trimethoprim is administered to nursing women.

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