An experimental Osteoporosis drug developed by Pfizer Inc. and Ligand Pharmaceuticals Inc. is an effective treatment for pain during intercourse in postmenopausal women, researchers said on Monday.

The drug, Oporia, is a selective estrogen receptor modulator designed to prevent and treat osteoporosis in postmenopausal women, a group at risk of losing bone as estrogen levels fall.

As many as 48 percent of these women experience pain during intercourse and less than half of them ever consult a doctor about the problem, said Dr. James Simon, clinical professor of obstetrics and gynecology at George Washington university in Washington, D.C., and lead author of a study comparing Oporia to placebo.

The 12-week study of 445 women with symptoms of vaginal atrophy compared two different doses of Oporia to placebo. The average age of women in the study was 59 years and 30 percent had had a hysterectomy.

Pain during intercourse was self-reported by 40 percent of the study participants as their most bothersome moderate-to-severe symptom at the start of the trial.

After 12 weeks, those patients reported a greater decrease in pain than patients receiving placebo. Vaginal bleeding during intercourse was rare and the incidence did not differ between the treatment groups, the study found.

The most common side effects of Oporia were hot flushes, cervical discharge and leg cramps, Simon said at a meeting here of the American College of Obstetricians and Gynecologists. Longer-term safety trials of the drug are ongoing.

Pfizer last August submitted an osteoporosis application for Oporia to the U.S. Food and Drug Administration and in December submitted an additional filing for use of the drug as a treatment for vaginal atrophy.