Data on acute toxicity of the progestin STS 557

In mice and rabbits of both sexes the acute toxicity of STS 557 (17 alpha-cyanomethyl-17 beta-hydroxy-estra-4, 9-dien-3-one) was determined after its oral or parenteral (i.p., s.c.) administration. In rabbits increasing lethality was observed following STS 557 suspended in tylose solution at the dose range of 1.0 to 3.0 g/kg p.o. or i.p. The approximate LD50-values were 1.0 to 1.5 g/kg for the i.p. route and 1.0 to 2.0 g/kg for the oral route. Levonorgestrel injected i.p. did not cause any lethality up to the dose of 3.0 g/kg. After oral or s.c. administration to mice, doses of 4.0 g/kg STS 557 were well tolerated. A dose-related toxicity occurred only after i.p. doses between 0.5 and 1.0 g/kg (STS 557), and between 2.0 and 4.0 g/kg (levonorgestrel), respectively. Using an oily vehicle for the oral route in mice, the lethal threshold dose for STS 557 was lowered to about 2.0 g/kg. In conclusion, a low oral acute toxicity was determined for STS 557 corresponding to that of other progestagens like levonorgestrel or norethisterone.