Teratological evaluation of trimethyl phosphite in the rat

Trimethyl phosphite (TMP) is an organophosphorus alkylating agent used primarily in the synthesis of organophosphate compounds. To evaluate teratogenic potential, TMP was administered by gavage to pregnant rats at rates of 16, 49, or 164 mg/kg/day, on gestation Days 6 through 15. Acetyl salicylic acid (250 mg/kg/day) was also administered to a group of rats as a positive control. Teratologic evaluation revealed gross fetal abnormalities, skeletal defects, and soft tissue defects at a dose rate of 164 mg/kg/day of trimethyl phosphite, but not at the two lesser rates. An increased frequency of fetal resorption was also observed at 164 mg/kg/day.