RESUMO
OBJECTIVE: Our purpose was to determine the relationship between bioavailability of contraceptive steroids and bleeding patterns. STUDY DESIGN: A randomized clinical trial evaluated 192 women on 50 micrograms of ethinyl estradiol and 1.0 mg of norethindrone (OC1), 35 micrograms ethinyl estradiol and 1.0 mg of norethindrone (OC2), and 35 micrograms ethinyl estradiol and 0.5 mg norethindrone (OC3) over nine cycles. RESULTS: Intermenstrual bleeding rates were higher for OC3 when compared with OC1 (p = 0.01). The number of intermenstrual bleeding days was highest for OC3 (p = 0.001) and higher for OC2 when compared with OC1 (p < 0.006). The onset of withdrawal bleeding occurred faster in OC3 patients (p < 0.02). Bioavailability of both contraceptive steroids as measured by baseline values and 1-hour slopes did not correlate with bleeding patterns at 3, 6, and 9 months of use. CONCLUSION: These data suggest that differences in biologic responses associated with pill use cannot be explained solely on the basis of these particular hormone measurements.
PIP: Breakthrough bleeding as a side effect of oral contraceptive (OC) use is considered one of the primary causes if discontinuation of oral contraceptives. In this study, the incidence and pattern of vaginal bleeding is examined and correlated with biologic responses and plasma steroid bioavailability. Between October 1, 1985 and October 15, 1987, subjects were randomly selected from eligible women beginning OC use as patients of the Department of Gynecology and Obstetrics at the Johns Hopkins Medical Institutions. Women were grouped by type of OC as follows: 1) 67 women taking 50 micrograms of ethinyl estradiol and 1.0 mg of norethindrone (OC1);l 2) 61 women taking 35 micrograms of ethinyl estradiol and 1.0 mg of norethindrone (OC2); and 3) 64 women taking 35 micrograms of ethinyl estradiol and .5 mg of norethindrone (OC3). Estrogen and progesterone concentrations in plasma were measured on the 21st day during the third, sixth, and ninth cycles. The samples was taken 24 hours after ingestion of the pill for day 20, and 1 hour after taking the pill on day 21. An extensive interview was also conducted for all study participants. Bleeding was recorded for any amount of bleeding occurring during days 2 through 21, and during days 21 through 28. Cycles were omitted where pills had been forgotten by the patient. An initial slope was calculated with the 1 hour value level and subtracting the 0 hour level over the actual time interval. Linear regression analysis was used to compare the slopes and bleeding days. Of the 316 women enrolled, 61% (192) completed the study. The findings were that the incidence of intermenstrual bleeding was not statistically different among the various preparations. For 59 patients eliminated from the study, 24% experienced intermenstrual bleeding. Those lose to follow-up were not among those unwilling to tolerate their bleeding pattern. There was similar incidence of other side effects among all three preparations: .5% amenorrhea of dysmenorrhea, 7% nausea, 16% headache, 26.5% depressed mood, 16.6% breast tenderness, and 44.3% acne. The low-dose OC3 had the statistically highest rates of intermenstrual bleeding. The bleeding patterns are described. Bleeding patterns were higher than those previously reported in the literature. Further research might focus on controlling for factors such as hormone-binding globulin capacity.
