Reduced vaginal bleeding in postmenopausal women who receive combined norethindrone acetate and low-dose ethinyl estradiol therapy versus combined conjugated equine estrogens and medroxyprogesterone acetate therapy

Objective: The purpose of this study was to compare the effects on vaginal bleeding patterns of continuous combined hormone replacement therapy with norethindrone acetate and ethinyl estradiol versus conjugated equine estrogens and medroxyprogesterone acetate. Study Design: Three hundred fifty-seven postmenopausal women were selected randomly (in a blinded manner) to 12 months of treatment with 1 mg norethindrone acetate/5 μg ethinyl estradiol, placebo, or open-label 0.625 mg conjugated equine estrogens/2.5 mg medroxyprogesterone acetate (conjugated equine estrogens/medroxyprogesterone acetate [CEE/MPA]; Prempro). The incidence and duration of vaginal bleeding were assessed throughout the study. Statistical analyses used Cochran-Mantel-Haenszel methodology and analysis of variance. Results: At 3 months, 1 mg norethindrone acetate/5 μg ethinyl estradiol therapy reduced the incidence of bleeding (12% vs 23%; P< .029) and bleeding and/or spotting (22% vs 44%; P< .001), compared with conjugated equine estrogens/medroxyprogesterone acetate therapy. The mean duration of bleeding and bleeding and/or spotting were also reduced with 1 mg norethindrone acetate/5 μg ethinyl estradiol therapy versus conjugated equine estrogens/medroxyprogesterone acetate (P = .004 and P< .001, respectively). The incidence of cumulative amenorrhea at every monthly interval was significantly better with 1 mg norethindrone acetate/5 μg ethinyl estradiol therapy versus conjugated equine estrogens/medroxyprogesterone acetate therapy (P< .05). Associated adverse event (ie, headache, breast pain) incidence rates were similar in the 2 active treatment groups. Conclusion: The 1 mg norethindrone acetate/5 μg ethinyl estradiol therapy provides significantly better control of vaginal bleeding than conjugated equine estrogens/medroxyprogesterone acetate therapy at all time points investigated in this 12-month study. (Am J Obstet Gynecol 2003;188:92-9.)