Bazedoxifene, a novel selective estrogen-receptor modulator, is as safe as placebo in terms effects on the endometrium and will be a new therapy for preventing and treating postmenopausal osteoporosis, according to data presented at the annual meeting of the North American Menopause Society.
Dr. David F. Archer, professor of obstetrics and gynecology at Eastern Virginia Medical School, Norfolk, and a consultant for Wyeth Pharmaceuticals (the study's sponsor), presented data on endometrial safety in a subset of women in a large phase III trial comparing the efficacy of bazedoxifene, raloxifene, and placebo in reducing the relative risk of new vertebral fractures.
The results of that trial found bazedoxifene at 20 mg or 40 mg per day significantly reduced new vertebral fractures, versus placebo. Similar results were obtained with raloxifene 60 mg per day.
However, in the subanalysis raloxifene was linked to more endometrial hyperplasia, Dr. Archer said.
“Importantly, bazedoxifene exerted its beneficial effect on bone without increasing endometrial thickness or causing endometrial bleeding,” Dr. Archer added in an interview.
The endometrial safety substudy focused on 643 women who had transvaginal ultrasonography at baseline and at month 24. Endometrial biopsies also were performed at these two time points.
Endometrial thickness between baseline and 24 months increased by 0.1 mm with both doses of bazedoxifene and placebo, compared with an increase of 0.3 mm with raloxifene, Dr. Archer said.
About five women in each of the four treatment arms had 4 mm or more growth in endometrial thickness, but when they were biopsied, no evidence of hyperplasia was detected.
“We are not sure what the exact cause of this increase in endometrial thickness is, but it does not appear to be mycotic,” he commented.
Food and Drug Administration approval of bazedoxifene is pending, and Wyeth, the drug's developer, expects the FDA to approve it for the treatment of postmenopausal osteoporosis by the end of 2007, Dr. Archer said.