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  • Title: Bioavailability and pharmacokinetics of norethisterone in women after oral doses of ethynodiol diacetate.
    Author: Vose CW, Butler JK, Williams BM, Stafford JE, Shelton JR, Rose DA, Palmer RF, Breckenridge AM, Orme ML, Serlin MJ.
    Journal: Contraception; 1979 Feb; 19(2):119-27. PubMed ID: 428229.
    Abstract:
    Measurement by radioimmunoassay of plasma norethisterone (NE) has been used to compare the bioavailability of tablets containing ethynodiol diacetate (EDA) with that of a standard oral solution of this progestogen in 12 normal women. The tablets investigated were from three batches which showed different in vitro dissolution rates. There were no significant differences in the bioavailability of the tablet formulations, which were essentially bioequivalent to the solution. Peak blood levels of NE were reached within 4h of EDA administration in solution or tablets. After the peak, NE plasma levels declined in two phases, with a mean terminal elimination half lives of 4 to 6.9h. The pharmacokinetics of NE after EDA administration showed some similarity to those observed by other workers after oral doses of NE itself. Bioavailability and pharmacokinetics of norethisterone (NE) were studied in 12 women, aged 21-37 years, after oral doses of ethynodiol diacetate (EDA). Plasma NE levels, measured by radioimmunoassay, were used to compare the bioavailability of EDA tablets (Ovulen 50; 1 mg EDA plus .05 mg ethinyl estradiol) with that of a standard oral solution of EDA. The 3 different batches of tablets studied showed different in vitro dissolution rates, 82.6%, 94.6%, and 99% at 3 hours. No marked differences were seen in the bioavailability of the tablet formulations, which were essentially bioequivalent to the solution. Peak plasma NE levels were reached within 4 hours of EDA administration in solution or tablets. Following the peak, NE plasma levels declined in 2 phases, with mean terminal elimination 1/2-lives of 4-6.9 hours. These results have shown that small variations in in vitro dissolution rates do not affect the bioavailability of NE from tablets containing EDA.
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