Pharmacokinetics of etonogestrel and ethinylestradiol released from a combined contraceptive vaginal ring

Objective: To assess the pharmacokinetics of etonogestrel and ethinylestradiol released from a novel combined contraceptive vaginal ring (NuvaRing(R)) releasing etonogestrel 120 mu g and ethinylestradiol 15 mu g per day and compare them with those of a combined oral contraceptive containing desogestrel 150 mu g/ethinyl-estradiol 30 mu g (DSG/EE COG). Design and setting: This was a nonblind, randomised, crossover study in 16 healthy women. Methods: All volunteers received one cycle of DSG/EE COC before being randomised to 1 of 2 treatment groups. The participants in group 1 received 1 cycle of DSG/EE COG, a treatment period with NuvaRing(R) and an intravenous bolus injection of etonogestrel/ethinylestradiol (150 mu g/30 mu g). Those in group 2 received a NuvaRing(R) treatment period, 1 cycle of DSG/EE COC and the same intravenous bolus injection. Results and conclusions: After the insertion of NuvaRing(R), maximum serum concentrations of etonogestrel and ethinylestradiol were achieved in approximately 1 week. The concentrations subsequently showed a gradual linear decrease in time. The maximum serum concentrations of etonogestrel and ethinylestradiol were approximately 40 and 30%, respectively, of those for the DSG/EE COC. In comparison with the DSG/EE COC, the absolute bioavailability for NuvaRing(R) was higher for etonogestrel (102.9 vs 79.2%) and similar for ethinylestradiol (55.6 vs 53.8%). Taking the difference in daily doses into account, systemic exposure to etonogestrel was similar for NuvaRing(R) and the DSG/EE COC, whereas systemic exposure to ethinylestradiol with NuvaRing(R) was only approximately 50% of that for the DSG/EE COC.