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For the radioimmunological determination (RIA) of the progestagen dienogest (1, 17 alpha-Cyanomethyl-17 beta-hydroxy-estra-4,9-dien-3-one) in plasma three methods of sample preparation were tested and compared: Extraction of plasma samples with dichlormethane (I), binding of plasma dienogest to an antiserum added; removal of non-bound steroids by means of activated charcoal, extraction of dienogest using dichlormethane (II), using the RIA without extraction of plasma samples after partial precipitation of proteins by means of ammonium sulphate (III). The reliability of the dienogest-RIA is, characterized by a limit of detection of 3.2 pg (I, III) and 5 pg (II) per tube, respectively, by "within-assay"- and "between-assay" variation coefficients of 3 to 5% and 3 to 9%, respectively, in parallel determinations and by a high rate of recovery of dienogest (greater than 90%) added to plasma. The application of the parallelism test method to different plasma volumes confirms the accuracy of method I and II. When method III was applied to plasma samples with low concentrations of dienogest parallelism wasn't found in all cases.

Disposition and excretion of the progestin Dienogest (17 alpha-cyanomethyl-17 beta-hydroxy-estra-4,9-dien-3-one, STS 557) were investigated in female rabbits. Following single and repeated administration of the tritium-labelled compound the plasma concentration courses of total radioactivity (Dienogest + metabolites) and of the parent drug alone were estimated and also the urinary and fecal excretion of total radioactivity. From these data basic pharmacokinetic parameters were calculated. Additionally, the enterohepatic recirculation of biliary excreted metabolites was studied using bile of donors for oral administration to recipients. Following oral administration the high bioavailability of Dienogest which was already found in other animal species and in man could also be confirmed with rabbits. The parameters of Dienogest disposition do not differ significantly from those of the progestin levonorgestrel. Thus, the different effects of the both progestins in the McPhail-Clauberg assay in the rabbit cannot be attributed to differences in pharmacokinetics.

Following administration of 14 alpha, 15 alpha-3H-Dienogest (STS 557, 17 alpha-cyanomethyl-17 beta-hydroxy-4, 9-estradien-3-one) to female rabbits, extracts from urine, bile and plasma were separated by means of HPLC. Urinary and biliary metabolites are characterized by patterns of high complexity. From the mass spectra and UV absorption data of the urinary Dienogest metabolites a variety of biotransformation reactions has been derived like: hydroxylation in different positions of the Dienogest molecule, among these the 11-position; reduction of the 3-oxo group to 3-hydroxy; introduction of 2 and 4 hydrogen atoms; aromatization of ring A; transformation of 17 alpha-CH2CN to CH2OH, and formation of compounds with a 5(10), 9(11)-diene structure. Some of these reactions occur simultaneously resulting in a very complicated metabolite spectrum. Possibly the multiple effects of Dienogest established in animals are partially caused by metabolites.

Following oral administration of 2 mg of dienogest (17 alpha-cyanomethyl-17 beta-hydroxy-4,9-estradien-3-one) to female volunteers, the dienogest concentration courses in plasma and saliva were determined by means of a specific radioimmunoassay (RIA). Three different procedures of the plasma sample preparation prior to the RIA were compared. The dienogest RIA was directly applied to saliva. There is a high correlation between the dienogest concentrations in plasma and saliva. The dienogest plasma elimination half life of about 9 hrs is not significantly different from that derived from saliva. The salivary dienogest concentrations indicate a relatively high non-protein bound portion of this steroid drug in plasma. Following repeated oral administration of dienogest (tau = 24 hrs), there is no significant cumulation of plasma dienogest.