[Effect of a new gestagen--dienogest--and its combination with ethinyl estradiol on the activity of biotransformation reactions].

Caffeine is mainly metabolized by 3-methyl-cholanthrene-inducible cytochrome P-450, whereas metamizol (Analgin) is probably mainly metabolized by phenobarbital inducible cytochromes P-450. Therefore the elimination of caffeine from serum and the amount of the main metabolites of metamizol excreted into urine reflect the activity of these two cytochrome P-450 families. Sex hormones can influence the activity of cytochrome P-450. Dienogest is a new gestagen, used for temporary contraception. We investigated the effect of this new sexual hormone alone and in combination with ethynylestradiol on the elimination of both testdrugs. In 10 healthy volunteers dienogest 2 mg daily for 14 days have no effect on the metabolism of model drugs whereas the combination with 0.05 mg ethynylestradiol has an influence on the elimination of caffeine and metamizol.