Progestin-only contraceptive rings.

Area of Science:

• Reproductive Health
• Contraception
• Pharmacology

Background:

• Long-acting progestin-only contraceptives include implants and injectables.
• Vaginal rings represent a novel, user-controlled contraceptive delivery system in late-stage development.
• These devices offer constant drug release, enabling lower effective doses and non-coital, non-provider-dependent use.

Purpose of the Study:

• To review the development and clinical performance of progestin-only vaginal rings.
• To evaluate pregnancy rates, discontinuation reasons, and side effects associated with levonorgestrel and Nestorone vaginal rings.

Main Methods:

• Review of clinical trials, including a WHO-coordinated Phase III multicenter trial for a levonorgestrel ring (20 microg/day).
• Evaluation of a Nestorone vaginal ring study assessing ovulation inhibition and pregnancy rates at different release rates (50, 75, 100 microg/day) over six months.
• Analysis of reasons for discontinuation and reported adverse events.

Main Results:

• The levonorgestrel ring demonstrated a cumulative one-year pregnancy rate of 4.5%, with menstrual disturbances and ring expulsion as primary discontinuation reasons.
• Nestorone rings achieved over 97% ovulation inhibition.
• Six-month cumulative pregnancy rates for Nestorone rings were 0.0% (low-dose), 1.9% (intermediate-dose), and 2.1% (high-dose), with bleeding irregularities being common.

Conclusions:

• Vaginal rings are a promising long-acting contraceptive method with varying efficacy and side effect profiles.
• Further development, including more flexible devices and optimized release rates, is ongoing.
• Nestorone vaginal rings show potential, particularly for lactating women due to their oral inactivity.