A randomized double-blind trial of two low dose combined oral contraceptives

Abstract

Fifty-five women using Loestrin-20 (20 microgram ethinyl oestradiol and 1 mg norethisterone acetate) as an oral contraceptive have been compared with a like number using Microgynon-30 (30 microgram ethinyl oestradiol and 150 microgram levonorgestrel) in a randomized, double-blind trial. Despite the small sample size, the main finding in the trial is clear-cut; Loestrin-20 provides poor cycle control and is thus less acceptable as an oral contraceptive than Microgynon-30. Although there is also a suggestion that Loestrin-20 may be less effective than Microgynon-30, the difference in the accidental pregnancy rates is not statistically significant.

PIP: A multicenter randomized double-blind trial was conducted to compare 55 women using Loestrin-20 (20 ug ethinyl estradiol and 1 mg norethisterone acetate) as an oral contraceptive with a like number of women using Microgynon-30 (30 ug ethinyl estradiol and 150 ug levonorgestrel). 7 family planning clinics agreed to collaborate in the trial and enrollment of patients which began in November 1974. The number of participating clinics was increased to 12 at a later date. 133 patients were recruited between November 1974 and September 1976. 23 were excluded from the analysis. 55 of the remaining 110 patients were admitted to each of the 2 treatment groups. It was found that women who used Loestrin-20 discontinued treatment because of abnormal bleeding more frequently that women using Microgynon-30, but that the discontinuation rates for other reasons were closely similar in the 2 treatment groups. Of the 13 women who stopped using Loestrin-20 because of abnormal bleeding, 6 complained of oligomenorrhea or amenorrhea while the other 7 complained of irregular bleeding. Of the 2 women who stopped using Microgynon-30 because of bleeding problems, 1 complained that the bleeding was irregular and the other that it was prolonged. Although the sample size is small, Loestrin-20 clearly provides poor cycle control and consequently is less acceptable than Microgynon-30. Loestrin-20 may be less effective than Microgynon-30, but the difference in the accidental pregnacy rates is not statistically significant.