Comparative study of the teratogenic effects of chlordiazepoxide and diazepam in the fetal hamster

A single, intraperitoneal injection of either chlordiazepoxide (280–3100 mg/kg) or diazepam (120–980 mg/kg) was administered to pregnant hamsters on day 8 of gestation. These dosages produced a dose-dependent sedation of pregnant animals lasting up to 36 hours, and a combined maternal mortality rate of 21% (chlordiazepoxide) and 5% (diazepam). Animals were sacrificed on gestation day 12 and the fetuses were examined for gross malformations. Although there was a dose-related increase in the frequency of malformed fetuses (3.4%–54.7% for chlordiazepoxide, and 0–58.7% for diazepam), the lowest teratogenic dose was noted to be 280 mg/kg, i.e., almost 500 times and 1000 times the average daily recommended therapeutic doses for chlordiazepoxide and diazepam, respectively. The majority of fetal malformations observed with both compounds were either exencephaly or cranioschisis. The results of this study should be interpreted with caution in so far as their relevance to humans is concerned. The terata were observed at exceedingly high doses (700–7000 times the average human use dose), and the malformations noted by us have not been associated with the use of minor tranquilizers in human pregnancy. Also, although we found no gross anomalies in the litters of dams deprived of food and water for up to 72 hours, the confounding role of prolonged periods of sedation and resulting inactivity, and possible hypoxia and hypothermia needs to be explored further.