Vaginal rings releasing progesterone with 3 different initial release rates (5, 8 and 20 mg/day) were used by 11, 10 and 10 women, respectively. The period of insertion was 90 days. The 5 and 8 mg/day rings consisted of a core loaded with progesterone, the 20 mg/day ring contained progesterone homogeneously distributed throughout the mass of the ring. Notwithstanding these differences, the total progesterone levels (areas under curve) were directly related to the release rates. So were the rates of decrease of progesterone levels during the 90 days of insertion of the ring. They were 25, 31 and 47% for the rings releasing 5, 8 and 20 mg/day, respectively.
PIP: Physicians from Karolinska Hospital in Stockholm, Sweden and a scientist form WHO in Geneva, Switzerland examined the pharmacokinetic behavior of progesterone released from vaginal rings over 90 days in 31 women who took a combined oral contraceptive (OC) each day. The OC suppressed ovarian function. The physicians inserted a vaginal ring with a core which released 5 mg progesterone/day in 11 women and a 8 mg/day ring in 10 women. The inserted a 20 mg/day vaginal ring with progesterone homogeneously distributed throughout the mass of the ring in 10 women. Total circulating progesterone levels were significantly correlated with initial release rates of the 3 vaginal rings (p.001). Further, at the end of 90 days, progesterone levels decreased significant from initial levels in all women (25% for the 5 mg/day vaginal ring, 31% for the 8 mg/day ring, and 47% for the 20 mg/day ring). These results matched those of earlier in vitro studies with the same vaginal rings. Researchers next need to determine which type of vaginal ring and release rate optimally protects against pregnancy and induces an acceptable bleeding pattern. WHO promotes research in vaginal rings saturated with progesterone as a possible contraception for postpartum mother since progesterone does not adversely affect breast fed infants. Furthermore progesterone suppresses ovulation.