Suppression of ovarian activity with a drospirenone-containing oral contraceptive in a 24/4 regimen.

BACKGROUND: This study was conducted to compare ovarian activity of an oral contraceptive containing drospirenone (drsp) 3 mg plus ethinylestradiol (EE) 20 mcg administered in 24/4 regimen compared with the conventional 21/7 regimen, during intended use and following predefined dosing errors.

STUDY DESIGN: Women aged 18-35 years who ovulated or had a follicular diameter of >or=15 mm on or before Day 23 during a pretreatment cycle were admitted into this double-blind, randomized study. Participants underwent 3 treatment cycles with drsp 3 mg/EE 20 mcg in a 24/4 (n=52) or a 21/7 (n=52) regimen. In the third treatment cycle, the initial three pills in both groups were replaced with placebos. Ovarian activity was classified using the Hoogland scale during pretreatment and during Cycles 2 and 3.

RESULTS: Suppression of ovarian activity was more pronounced with the 24/4 regimen--the odds ratio for a lower Hoogland score (i.e., greater ovarian suppression) with the 24/4 regimen compared with the conventional 21/7 regimen were 6.01 (95% CI: 2.29-17.94) and 3.06 (95% CI: 1.44-6.65) for Cycles 2 and 3, respectively. More women in the 24/4 regimen group had no ovarian activity 87.8% vs. 56.0% during Cycle 2 and 55.1% vs. 30.0% during Cycle 3. The 24/4 regimen was associated with a more consistent suppression (less fluctuation) of endogenous estradiol.

CONCLUSION: The drsp 3 mg/EE 20 mcg oral contraceptive in a 24/4 regimen was associated with greater ovarian suppression (despite intentional dosing error), which results in decreased hormonal fluctuations, and may increase contraceptive efficacy with the low-dose formulation.