title: An investigation of the pharmacokinetics of ethynylestradiol in women using radioimmunoassay.
abstract: A radioimmunoassay for ethynylestradiol (EE) which is applicable to plasma samples obtained from women, who have taken a combination type oral contraceptive, has been developed and fully validated. Plasma concentration of EE rise to a peak of 128 pg/ml following the oral administration of 50 microgram EE. Following the intravenous administration of the same dose of EE, plasma concentrations of the steroid declined biexponentially, the two half-lives being 0.83 and 6.75 hours. Comparison of the results of the intravenous and oral administration of the steroid suggested that its oral bioavailability is 42%. Although EE thus has a lower bioavailability than norethindrone, the pharmacokinetics of the two steroids, as reflected by half-lives, plasma clearance and volume of distribution, are very similar. The occurrence of a secondary peak in plasma at around 12 hours after dosing gave strong evidence that EE undergoes enterohepatic circulation in women; an event that may have considerable clinical significance.
mesh_terms: D000284:Administration, Oral; D000328:Adult; D000818:Animals; D002855:Chromatography, Thin Layer; D004997:Ethinyl Estradiol / Q000097:blood / Q000378:metabolism*; D005260:Female; D006801:Humans; D007275:Injections, Intravenous; D007700:Kinetics; D009640:Norethindrone / Q000097:blood; D009644:Norgestrel / Q000097:blood; D011817:Rabbits; D011863:Radioimmunoassay; D013997:Time Factors
chemical_list: D009644:Norgestrel; D004997:Ethinyl Estradiol; D009640:Norethindrone