Chloroethynylnorgestrel
Chloroethynylnorgestrel is a steroidal progestin of the 19-nortestosterone group related to norgestrel that was investigated as an oral contraceptive in the 1970s but was never marketed.
In combination with mestranol, similarly to ethynerone and anagestone acetate, chloroethynylnorgestrel was found to produce striking mammary tumors in beagle dogs after administration at very high dosages for prolonged periods of time. This resulted in the discontinuation of its development, along with that of ethynerone and anagestone acetate, as well as the removal of several progestins, including chlormadinone acetate, medroxyprogesterone acetate, and megestrol acetate, from various markets as contraceptives. Subsequent research revealed that the risk is species-dependent and unique to canines and that there is no similar risk for humans.
s in beagle dogs treated by MK-665 and chloroethynylnorgestrel with mestranol for 4 years at a dosage of 1.05 mg/kg/day cyclically.
