Mestranol.

This monograph on mestranol includes chemical and physical data (synonyms and trade names), structural and molecular formulae and molecular weight of the substance, chemical and physical properties of mestranol, and the production, use, occurrence, and analysis of mestranol. Production of mestranol, which is not known to occur naturally, is synthesis via the reaction of 3-methoxy-1,3,5-oestratrien-17-one with potassium acetylide. All known methods for analyzing mestranol for purity and chemical clarity are summarized tabularly. Biological data relevant to the evaluation of carcinogenic risk to humans of mestranol, which is used mainly in contraceptive preparations, are also presented in brief. Studies of various experimental species and routes of administration led to the conclusion that there is sufficient for the carcinogenicity of mestranol in experimental animals. Data on humans are not available, but it is reasonable to assume mestranol holds potential risk for humans. When mestranol was tested in mice and rats (studies on dogs and monkeys are still in progress) orally in combination with a progestin, it produced pituitary tumors and vaginal and cervical squamous cell carcinomas. Increased incidence of mammary tumors was also noted in both males and females of different species. When used alone, mestranol, by the oral route, increased incidences of pituitary tumors in both sexes, mammary tumors in castrated males, and mammary tumors in females of another mouse species. Mestranol is embryolethal for pre- and postimplantation embryos in some species.