Pharmacokinetics of Etonogestrel and Ethinylestradiol Released from a Combined Contraceptive Vaginal Ring

To assess the pharmacokinetics of etonogestrel and ethinylestradiol released from a novel combined contraceptive vaginal ring (NuvaRing®) releasing etonogestrel 120µg and ethinylestradiol 15µg per day and compare them with those of a combined oral contraceptive containing desogestrel 150µg/ethinylestradiol 30µg (DSG/EE COC).

This was a nonblind, randomised, crossover study in 16 healthy women.

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 COC, a treatment period with NuvaRing® and an intravenous bolus injection of etonogestrel/ethinylestradiol (150µg/30µg). Those in group 2 received a NuvaRing® treatment period, 1 cycle of DSG/EE COC and the same intravenous bolus injection.

After the insertion of NuvaRing®, 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® 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® and the DSG/EE COC, whereas systemic exposure to ethinylestradiol with NuvaRing®was only approximately 50% of that for the DSG/EE COC.