The pharmacokinetics of 12-week continuous contraceptive patch use

We sought to assess the change in serum ethinyl estradiol (EE2) and norelgestromin (NGMN) levels over 12 weeks of continuous contraceptive patch use.

We asked participants (n=30) to apply consecutive patches to be worn continuously (without a patch-free interval) for 12 weeks. We collected blood samples at the end of each patch week and two times during weeks 4, 8, and 12 (with the additional blood draw occurring mid-week). Liquid chromatography-tandem triple quadrupole mass spectrometry (LC-MS/MS) was utilized to assess EE2 and NGMN levels.

Twenty-seven women completed the study; 26 were compliant with patch use. Ethinyl estradiol levels ranged from 0 to 193 pg/mL over the period. We observed an accumulation over the 12-week time at an estimated rate of 2.15 pg/mL per week (95% confidence interval 0.95-3.35, p<.001). The change in NGMN levels ranged from 0 to 2.52 ng/mL over the 12 weeks (95% confidence interval 0.021-0.019, p=.915). The most common side effects reported were vaginal spotting, breast tenderness and abdominal pain/cramping. There were no serious adverse events reported.

While the range of weekly EE2 values was quite wide, the absolute values remain low and generally within the expected range described in product labeling. Providers may consider prescribing continuous use of the patch, but given the slow accumulation of EE2 over time, 12 weeks should not be exceeded in the absence of safety data.