Cranial neural tube defect after trimethoprim exposure.

Liquid Chromatography Tandem Mass spectrophotometry analysis of the TELSE tablet confirmed the presence of trimethoprim as the active compound. The TELSE tablet-treated females produced significant numbers of embryos with exencephaly (n = 8, 36.4%, *P < 0.0001), in all litters. The TELSE tablet-treated females subsequently given folic acid did not result in pregnancies despite there being evidence of possible resorption. Furthermore, after multiple rounds of mating which did not yield viable pregnancies, eventually, 2 embryos with exencephaly were harvested in a litter of 6 at 0.05% w/v pure trimethoprim once. The use of trimethoprim, a folic acid antagonist, peri-conceptionally increased the risk of exencephaly in the mouse.