Objectives: The primary objective was to determine the lowest trimegestone (TMG) dose, administered via a vaginal ring, that effectively inhibited ovulation.
Study design: Single-centre, open-label, single-dose, parallel-group clinical trial with adaptive design. Eighty healthy female volunteers with proven ovulatory cycles were allocated to treatment with a vaginal ring during 28 days, with an average daily release rate of either 46 µg, 94 µg, 147 µg, or 184 µg TMG (20 women/group). Ultrasound measurements of follicular growth and endometrial thickness, and blood sampling for follicle-stimulating hormone, luteinizing hormone, estradiol and progesterone determinations were performed every 3rd (±1) day from treatment day 4 (±1) until day 28 (±1), and in a follow-up phase after ring removal, until study day 39 (±1). Trimegestone concentrations were measured at each visit in the treatment phase.
Results: Mean age and body mass index were 28.8 years and 23.15 kg/m2. One subject in the lowest dose group (46 µg/day) ovulated, no ovulations were seen in the higher dose groups. The degree of ovarian suppression increased with the dose. Median estradiol levels were 119, 36.5, 33.2 and 27.2 pg/mL in the 46, 94, 147 and 184 µg/day groups, respectively. Ovarian activity was resumed in the follow-up phase. Plasma TMG levels gradually declined over the treatment period and showed dose proportionality. The study treatment was safe and well tolerated.
Conclusion: The release rate of 94 µg TMG per day was the lowest effective dose for ovulation inhibition. The study results justify further development of the TMG-ring as progestogen-only contraceptive.
Implications: The vaginal ring releasing TMG seems to be an effective new progestogen-only contraceptive preparation, having the advantage of once-a-month vaginal insertion.
Keywords: Contraception; Follicle; Hormone; Ovulation; Trimegestone; Vaginal ring.
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