Effect of prenatal administration of therapeutic doses of topiramate on ossification of ribs and vertebrae in rat fetuses.

There are few studies that have addressed the effects of prenatal exposure of topiramate on ossification of the bones derived from the paraxial mesoderm. This study aimed to evaluate skeletal ossification of ribs and vertebrae in 20-day-old rat fetuses after maternal exposure to two therapeutic doses of topiramate. Three groups of Sprague-Dawley pregnant rats were used: control, topiramate 50 mg/kg/day and topiramate 100 mg/kg/day treated groups. Topiramate was administered by gavage from day 6-19 of gestation. Fetuses were collected on day 20 by caesarean section. Fetal bones were stained with alizarin red and ossification was assessed. Results showed significant delayed ossification of ribs and vertebrae in topiramate-exposed fetuses at both doses and the effects were not dose dependent. In all examined groups, there was a direct correlation between the fetal weight and the number of complete ossified vertebral centers. Also, there were significant increases in skeletal abnormalities, particularly in ribs in both treated groups when compared to the control group. In conclusion, therapeutic doses of topiramate should be taken cautiously during pregnancy as they lead to fetal growth restriction and increases abnormalities of axial skeleton in rat fetuses.