WASHINGTON (AP) - The government should not approve an experimental drug for irritable bowel syndrome because it may pose a serious risk to some women and may not be effective, a consumer advocacy group said Thursday.

Public Citizen petitioned the Food and Drug Administration to stop the expected approval of Zelmac. It cited FDA documents suggesting Zelmac could increase the risk of ovarian cysts threefold, and pointed to five women who needed surgery after taking the experimental pills.

The manufacturer, Novartis Pharmaceuticals, insists Zelmac did not cause the cysts, saying surgery showed some women's pain was not caused by cysts and that others had cysts before taking the pills.

Public Citizen acknowledged that FDA records show one surgery did not find the expected cyst, but says animal testing has linked Zelmac to cysts and questions if the drug might worsen existing minor cysts.

Also, three studies did not find Zelmac worked until the company altered the studies' original goals, something controversial in science but that Novartis says the FDA approved of doing. Even then, the research found just a modest effect, Public Citizen said.

The consumer group said FDA risks another scandal if it does not more fully investigate Zelmac before approving it, referring to another bowel-disease treatment pulled from the market last year after causing deadly intestinal side effects. The FDA had approved the modestly effective Lotronex despite some early signs of that risk.

Novartis submitted another study of 1,500 people to FDA in December, saying it proves Zelmac works and is safe for the serious, painful bowel disorder.

Related MEDLINEplus Pages:

• Irritable Bowel Syndrome