[Reproduction study of 1,1,3-trimethyl-5-phenylbiuret (ST-281): teratological study in rabbits by oral...

Teratogenicity of 1,1,3-trimethyl-5-phenylbiuret (ST-281), a new anti-rheumatic agent, was evaluated in rabbits. ST-281 at doses of 0, 50, 100, 200 and 400 mg/kg/day were administered orally to pregnant NZW rabbits from day 6 to day 18 of pregnancy. Body weight and food consumption at the administration and the subsequent periods were significantly decreased in 400 mg/kg/day group, and 5 dams (41.7%) affected severely were dead. No remarkable changes were investigated in findings at near-term caesarean section in any dosed group including 400 mg/kg/day. In visceral and skeletal examinations, no significant increase in incidence of abnormal fetuses were observed. This report suggests that ST-281 has no embryotoxicity or teratogenicity in rabbits.