STUDIES ON THE PHARMACOKINETICS OF CONTRACEPTIVE STEROIDS UNDER STEADY-STATE CONDITIONS

Pharmacokinetic investigations (c0h. c2h, c6h, c24h, AUC24) were carried out both in the first and last four days of a treatment cycle in patients of different ages, who used oral contraceptives at least for 12 months. 57 women took the preparation Trisiston(R) (three-step-formulation with the components 0.03 mg ethinylestradiol (EE2) + 0.05 mg levonorgestrel (LNG), 0.04 mg EE2 + 0.075 mg LNG, 0.03 mg EE2 + 0.125 mg LNG), 23 subjects used Gravistat(R) (0.05 mg EE2 + 0. 125 mg LNG) and 17 patients were under Certostat(R), a preparation still in clinical evaluation (0,05 mg EE2 + 2.0 mg Dienogest (DNG)). The levels of EE2, LNG and DNG were measured by means of radioimmunoassays. Between the concentrations obtained after administration of a first and sin-le tablet (earlier investigations) and those determined in long-time users during the first 4 days following the tablet-free interval no qualitative and quantitative differences were observed. Between the levels of EE2 and LNG determined in the first and last days of the treatment cycle, marked differences were found in patients under the formulations Trisiston(R) and Gravistat(R) but not in those taking Certostat(R). It is concluded that a cyclical and reversible cumulating effect emerges under the influence of LNG-containing contraceptives, the mechanism of which cannot be explained solely by the increase of carrier protein capacity. It seems possibly due to an alteration of steroid metabolism resulting from the interaction between both components.