Toxicity of the progestagen STS 557 compared to levonorgestrel in beagles after oral administration for 6 months.

Female and male beagle dogs were administered orally STS 557 (17 alpha-cyanomethyl-17 beta-hydroxy-13 beta-methyl-gon-4,9(10)-dien-3-one) for 6 months at dose levels of 0.01, 0.1, or 1.0 mg/kg/day, and levonorgestrel at a dose of 1.0 mg/kg/day, respectively. The results mainly confirmed the gestagenic efficacy on the reproductive organs of both compounds acting directly or via the anterior pituitary gland. In contrast to levonorgestrel, STS 557 did not show any androgenic activity, but had slightly estrogenic effects. Neither clinical, functional nor morphological investigations revealed toxic side effects of the drugs on the liver, the kidneys, the bone marrow, or on blood clotting function.