Pharmacokinetics of cyproterone acetate and ethinylestradiol in 15 women who received a combination oral contraceptive during three treatment cycles

Abstract

The pharmacokinetics of cyproterone acetate (CPA) and ethinylestradiol (EE 2) were determined in 15 healthy women (age 19 to 34 years), following single dose administration of a combination oral contraceptive, containing 2.0 mg CPA together with 0.035 mg EE 2 (Dia-ne-35 R). After a wash-out period of one week, the same preparation was administered during a treatment period of three months. After single dose administration, maximum concentrations of CPA in the serum were 15.2 ± 6.6 ng/ml. Post maximum drug levels declined biphasically with half-lives of 0.8 ± 0.4 h and 54.0 ± 26.0 h, respectively. The apparent clearance was calculated to be 3.6 ± 0.9 ml × min −1 × kg −1 and the volume of distribution (V z) was 986 ± 437 1. The free fraction of CPA was 3.5 ± 1.9% and the fractions bound to heat labile proteins and albumin were 4.6 ± 2.2 % and 92.0 ± 3.5%, respectively. Trough levels of CPA in the serum increased during a treatment cycle, reaching a steady-state around day 16. An about two-fold accumulation of CPA was observed, which was less than expected theoretically. SHBG concentrations in the serum increased by a factor of three during a cycle, without having any effect on the protein binding of CPA. At the end of treatment cycle three, the terminal half-life of CPA had increased to a mean value of 78.6 ± 16.0 h and the volume of distribution to a value of 1304 ± 427 1. The apparent clearance showed a small, although significant decrease to a value of 3.0 ± 0.4 ml × min −1 × kg −1. The observed changes V z and t 1/2 during the treatment period were attributed to the distribution of CPA into a deep compartment and the slow release of the drug from this compartment. The AUC(0–4h) values of EE 2 following single dose administration of the combination oral contraceptive were found to be 187.5 ± 79.7 pg × ml −1 × h. On the last day of cycles one and three, the AUC(0–4h) values were 311.2 ± 109.3 and 304.8 ± 121.5 pg × ml −1 × h, respectively, which corresponds to an about 60% increase as compared to single dose administration. Total and free testosterone concentrations decreased during treatment cycles one and three by about 39 % and 62%, respectively, compared with the corresponding values measured prior to treatment.