title: Pharmacokinetic studies with a vaginal delivery system releasing levonorgestrel at a near zero order rate for one year.
abstract: Vaginal rings releasing approximately 20 micrograms levonorgestrel per 24 hours were used continuously by ten women for a period of one year. Circulating plasma levels of levonorgestrel (L-NOG) were measured every second week. Steroid hormone binding globulin (SHBG) levels were measured in the first and last four blood samples drawn. A linear relationship between the logarithms of L-NOG concentrations and duration of use was found, indicating an exponential character of decrease in L-NOG levels during the study year. An average of 72% of the mean initial levels of L-NOG was found in the circulation after 6 months' and 52% after one year's use. The L-NOG levels decreased daily by 1.1 pmol/l (0.13%) on the average. The SHBG levels were not influenced by the long-term exposure to L-NOG. The initial SHBG levels were significantly correlated (r = 0.88; P less than 0.001) to the initial L-NOG levels. The rings were well tolerated. Only in two of the ten subjects did the average number of bleeding days per month increase from a pretreatment value of 4.5 days per month to 8.3 and 9.5 days per month, respectively.
mesh_terms: D000282:Administration, Intravaginal; D003274:Contraceptive Devices, Female / Q000009:adverse effects; D005260:Female; D006801:Humans; D007700:Kinetics; D016912:Levonorgestrel; D009644:Norgestrel / Q000008:administration & dosage / Q000009:adverse effects / Q000378:metabolism*; D012738:Sex Hormone-Binding Globulin / Q000032:analysis; D014592:Uterine Hemorrhage / Q000209:etiology
chemical_list: D012738:Sex Hormone-Binding Globulin; D009644:Norgestrel; D016912:Levonorgestrel