[The pharmacokinetics of Oral-Turinabol in humans]

Disposition and excretion of the anabolic steroid Oral-Turinabol (1;4-chloro-17 alpha-methyl-androsta-1,4-diene-17 beta-hydroxy-3-one) were investigated in male volunteers. Following single p.o. and i.v. administration of the tritium-labelled compound the plasma concentration courses of total radioactivity (1 and 1-metabolites) and of the unchanged parent drug as well as the urinary excretion were estimated. From these data model independent pharmacokinetic parameters based on statistical moments were calculated. 1 is almost completely absorbed after p.o. administration of 10 mg per volunteer. Peak concentrations of total radioactivity and of 1 in plasma were reached about 3 h p.a. Irregularities observed in the plasma level profile following both p.o. and i.v. administration of 1 are due to a marked enterohepatic circulation. Orally given 1 is subject to a first-pass effect, resulting in a diminished systematic availability. The AUC-ratio of the unchanged drug and the total radioactivity of 1 : 13 shows the predominance of metabolites in plasma. After i.v. administration the disposition of unchanged 1 was found biphasically with a terminal half-life of 16 h. 1 and its metabolites are preferentially excreted via the kidneys. The urinary total radioactivity represented about 60% of the dose following both administrations. Due to its affinity to SHBG 1 is able to compete for the protein binding of testosterone, resulting in an increased plasma level of non protein-bound testosterone.