Contraceptive Effect of Varying Dosages of Progestogen in Silastic Vaginal Rings

Abstract

The contraceptive effect of 50, 100, 200 and 400 mg doses of medroxyprogesterone acetate (MPA) in silastic cylindrical vaginal rings (75 mm outside diameter, 7 mm thick) molded around metal springs and placed in diaphragm position was investigated in 19 noncontracepting, regularly-cycling women (7 of whom were placebo controls) over 2 pretreatment control cycles, 1 treatment cycle (rings inserted for 3 weeks) and 1 post-treatment recovery cycle. Basal body temperature (BBT) was recorded daily, and 24-hour urine collected on the eighth and twenty-second day of each cycle. Erosion and ulceration of vaginal mucosa was observed in 13 women with medicated and nonmedicated rings. Rings were removed in 4 out of 10 nulliparas due to discomfort. Of 8 women with treated rings in place for 3 weeks who had presumptive evidence of ovulation in control cycles (biphasic BBT curve, significant elevation in excreted pregnanediol level in luteal phase compared to follicular phase), none had llteal phase elevation of pregnanediol excretion; a sustained rise in BBT to luteal phase levels within 1-3 days of insertion was observed in all and a fall in BBT in 6 of 8 after removal; 2 showed breakthrough bleeding during treatment, and 7 showed withdrawal bleeding, which was no greater in amount or duration than previous menses, after removal. In the recovery cycle, 5 of 8 showed a biphasic BBT curve. 7 subjects with nonmedicated rings showed no early sustained rise in BBT after insertion, nor any breakthrough bleeding; 5 had presumptive evidence of ovulation. After removal it was determined that 11-27 mg of MPA was lost from each ring during the 3 weeks. Future studies are needed (1) with smaller rings without psrings to determine if rings stay in place and if vaginal erosion is decreased; (2) to determine the incidence and duration of delay of ovulation following removal; and (3) to determine if use of progestogen impregnated silastic rings is practical for prolonged contraception.