Dimethadione-induced fetotoxicity in rats.

The fetotoxic potential of dimethadione was studied in rats given single daily oral dosages of 0, 54, 433 or 541 mg/kg on days 1--21 or 6--15 of gestation. No maternal toxicity was observed following treatment on days 6--15. When administered from days 1 to 21 only the highest dose (541 mg/kg) produced a significant reduction in maternal body weight gain. Dimethadione caused a dose-related decrease in fetal weight and an increased incidence of umbilical hernia, ecchymoses and subcutaneous edema. There were also increased incidences of non-specific skeleton defects which consisted of unilateral or bilateral wavy ribs, additional ribs (14th rib, uni- and bilateral), retarded ossification of calvaria and a wide variety of sternal defects. Specific defects were bent radius and ulna, and bent tibia and fibula which increased with increasing dosages of dimethadione. Fetal mortality and incidence of skeletal anomalies were higher when the treatment was given on days 1--21 of gestation than on days 6--15 of pregnancy.