The Teratogenicity of Halothane in the Rat

Rats were exposed to 0.8 per cent halothane for 12-hour periods at different stages of pregnancy. Fetuses near term were suitably prepared and the skeletons examined. Lumbar ribs and separation of normally single ossification centers into paired lateral centers in the lower thoracic vertebral bodies were common. Incidences of these anomalies were compared with those of a control series and found significantly higher following exposure to halothane on day 8 or day 91/2 (or day 10 for ribs only). Diurnal variation in the incidence of resorptions following halothane was noted, more fetal deaths occurring after exposure during the day than during the night. The anomalies found are similar to those seen following exposure to nitrous oxide.