Objective: To explore the optimal dose of the progestogen, nomegestrol acetate (NOMAC), required in a monophasic oral contraceptive, in combination with 1.5 mg 17β-oestradiol (E(2)), to inhibit ovulation.
Methods: A double-blind, randomised study assessing 41 normally cycling women (aged 18-35 years) over two screening cycles, one control cycle and one consecutive treatment cycle; 38 women completed the treatment period. Subjects received 0.625 mg NOMAC/1.5 mg E(2) (n = 9), 1.25 mg NOMAC/1.5 mg E(2) (n = 10), 2.5 mg NOMAC/1.5 mg E(2) (n = 10) or 2.5 mg NOMAC alone (n = 9) for 21 days.
Results: During the treatment cycle, ovulation was suppressed in all treatment groups. The lowest plasma E(2) levels were observed with 2.5 mg NOMAC given alone. Addition of 1.5 mg E(2) to 2.5 mg NOMAC resulted in statistically significant increases in E(2) levels and decreases in mean follicle-stimulating hormone and luteinising hormone levels. In the three NOMAC/E(2) combination groups, a statistically significant inverse correlation was found between E(2) plasma levels and NOMAC dose.
Conclusion: The dose of 2.5 mg NOMAC was confirmed to be optimal to inhibit both ovulation and follicular maturation. The antigonadotropic effect of 2.5 mg NOMAC was reinforced when combined with 1.5 mg E(2).