Plasma levels of norethindrone after single oral dose administration of norethindrone and lynestrenol
Odlind, V.; Weiner, E.; Victor, A.; Johansson, E.D.
Clinical Endocrinology 10(1): 29-38
1979
ISSN/ISBN: 0300-0664 PMID: 436304 DOI: 10.1111/j.1365-2265.1979.tb03030.xDocument Number: 450048
Single oral doses of 0.3 mg, 0.5 mg and 15 mg Norethindrone (NET) and 0.5 mg and 5 mg Lynestrenol (lyn) were given to 5 women. Lyn is probably metabolized through NET and exerts its main biological activity as NET. Plasma concentrations of NET were determined by a radioimmunoassay at different intervals after administration of the tablets. Peak concentrations of NET were found within 2 h after intake of each tablet. The plasma half life of NET after NET and lyn administration for the period 8-24 h was 8-11 h. No significant difference was found between the half life of NET after the NET tablets and after the lyn tablets. When 5 mg NET was given the plasma half life of NET for the period 24-72 h was around 10 h and this was significantly shorter than the half-life of NET after 5 mg lyn, which was 16 1/2 h. The systematic availability of the drugs was estimated by calculating and comparing the areas under the plasma concentration versus time curve (AUC) 0-24 h. The AUC 0-24 after 0.3 mg NET was almost identical to the AUC 0-24 after 0.5 mg lyn. The AUC 0-24 after 0.5 mg NET was significantly larger than after 0.5 mg lyn. No difference was found between the AUC 0-24 after 5 mg lyn and 5 mg NET. A conversion from lyn to NET probably occurs. There were only minor pharmacokinetic differences between the drugs when all samples were measured as NET.