Concentration of ethinyl estradiol in the serum of 31 young women following a treatment period of 3 months with two low-dose oral contraceptives in an intraindividual cross-over design.

Two low-dose oral contraceptives, both containing the same dose of ethinyl estradiol (EE2) but different progestins (gestodene and desogestrel, respectively), were compared with respect to the relative bioavailability of EE2. The study was conducted with 31 women as an open intraindividual comparison with the ingestion of both preparations for 3 months, respectively. On days 1, 10 and 21 of the 1st, 3rd and 6th cycle, blood was sampled at 0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10 and 24 h following administration. The concentrations of EE2 were determined in the serum samples of each individual and the area under the serum concentration versus time curves, AUC (0-4 h) and AUC (0-24 h), were calculated. Corresponding parameters obtained on days 1, 10 and 21 of the 3rd and 6th month of treatment were compared on a statistical basis, and no differences were found. This result was in concordance with a previously performed study, where both formulations were administered to 18 women in a single-dose cross-over design. However, the results of the previous and the present study are at variance with the result of one other study, reporting higher EE2 levels in the serum of women taking the gestodene-containing formulation as compared to those taking the desogestrel-containing formulation.