People seeking treatment for irritable bowel syndrome (IBS) have had few options to ease the chronic or recurrent bouts of abdominal discomfort, constipation or diarrhea associated with the disorder. But in February, the U.S. Food and Drug Administration approved the prescription medication alosetron hydrochloride (Lotronex) for women with IBS who have diarrhea as the predominant symptom. The drug is still under investigation for men.
      IBS -- a puzzling condition that affects women at three times the rate of men -- may be caused by the overstimulation of intestinal nerves by the neurotransmitter serotonin, which makes the bowel abnormally sensitive. Alosetron appears to limit the activity of serotonin in the gut, thereby reducing symptoms. In clinical trials, alosetron was significantly more effective than a placebo in reducing IBS symptoms during 12 weeks of use, although symptoms returned within one week of stopping treatment. Constipation was the most common side effect, occurring in 28 percent of women who took the drug.
      Stephen J. Bickston, M.D., associate professor of medicine at the University of Virginia's Digestive Health Center, believes that alosetron is an important new drug for IBS. "However, since IBS is a lifelong condition, I generally recommend that my patients try dietary changes first and use mild over-the-counter agents to control specific symptoms," says Dr. Bickston. "If these options fail, alosetron may be a good next step for women with IBS."