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Endometrial Effects Of Norethindrone Acetate/Ethinyl Estradiol

Norethindrone acetate protects the endometrium from oestrogen-induced hyperplasia, as well as changes in proliferative status, suggest investigators in the United States.

Women treated with norethindrone acetate/ethinyl estradiol in this study had significantly less endometrial proliferation than did a comparison group of women treated with 0.625 mg conjugated equine estrogens/2.5 mg medroxyprogesterone acetate.

This multi-centre double-blind, placebo controlled study was led by Dr D J Portman from the Columbus Center for Women's Health Research, Ohio.

Objective was to determine the incidence of endometrial hyperplasia in women on continuous combinations of norethindrone acetate and ethinyl estradiol versus unopposed ethinyl estradiol.

The 945 postmenopausal women participating were randomly selected for 12 months on any one of several different treatments: six blinded norethindrone acetate/ethinyl estradiol combinations (milligrams of norethindrone acetate/micrograms of ethinyl estradiol: 0/5, 0.25/5, 1/5, 0/10, 0.5/10, or 1/10) and open-label 0.625 mg conjugated equine estrogens/2.5 mg medroxyprogesterone acetate.

Investigators used biopsy to assess endometrial hyperplasia and endometrial proliferation at baseline and then again at 6 and 12 months.

Overall, endometrial hyperplasia developed in 26 subjects, one each in the placebo, 0/5 and 0.25/5 treatment groups and 23 in the 0/10 treatment group.

There was significantly less endometrial proliferation measured in the 1/5 norethindrone acetate/ethinyl estradiol and other norethindrone acetate/ethinyl estradiol combination groups, as well as in the 0.625 mg conjugated equine estrogens/2.5 mg medroxyprogesterone acetate group, than in the unopposed ethinyl estradiol groups. However, 1/5 norethindrone acetate/ethinyl estradiol and other dose groups of this combination significantly reduced endometrial proliferation as compared with 0.625 mg conjugated equine estrogens/2.5 mg medroxyprogesterone acetate.

Collaborators in this study were Pfizer Global Research and Development and the Structural Research Center.
Am J Obstet Gynecol 2003 Feb;188:2:334-42. "A randomized, double-blind, placebo-controlled, multicenter study that assessed the endometrial effects of norethindrone acetate plus ethinyl estradiol versus ethinyl estradiol alone."

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