An herbal extract that is sold in health food stores and promoted as an allergy and fat loss aid may improve treatment of bladder infections when it is taken with antibiotics, research suggests.

Some 90 percent of bladder infections are caused by E. coli bacteria. They affect women four times more often than men, sometimes recurring over and over.

The bladder is lined with small pouches that allow it to stretch as it fills. Researchers at Duke University reported in Sunday's online edition of Nature Medicine that some bacteria were able to hide in those pouches, escaping the antibiotics used to treat the infection.

In tests in mice, the extract forskolin can cause the pouches to kick out the bacteria, allowing antibiotics to kill them, said the lead researcher, microbiologist Soman N. Abraham. Forskolin is derived from the Indian coleus plant.

"If we combine this with antibiotics we would be in a very good position to eradicate urinary tract infection," he said in a telephone interview.

In the experiments, forskolin was injected into some mice and placed directly into the bladders in others, Abraham said.

The extract is available in health food stores and some people take it by mouth as a supplement, he said. It is promoted as a treatment for allergies, breathing problems and even fat loss.

That availability does "absolutely not" mean people should attempt to treat themselves for bladder infections, Abraham said.

Urinary tract infections must be treated with antibiotics because they can quickly spread to the kidneys, so infected people needed to see their doctor, he said. But the fact that forskolin is being used by some people does help indicate it is safe, he said.

Abraham said the next step for the researchers is to experiment in larger animals to see if they can completely eliminate a bladder infection.

"If we can show an impact in combination with antibiotics it should not be too long before we can go to clinical trials" in people, he said.

Extracts from the Indian coleus were used in ancient Asia to treat a variety of diseases including urinary tract infections, Abraham said. "So, we have come full circle," he said.

Walter Hopkins, a scientist in the Division of Urology at the University of Wisconsin School of Medicine and Public Health, said the research shows "forskolin may provide a means to interrupt the infection-reinfection cycle" and lead to a quicker resolution of the illness.

"If these results could be duplicated in human studies, forskolin could offer a new treatment option for recurrent" urinary tract infection said Hopkins, who was not part of the research team.

Dr. Gregor Reid of the Lawson Health Research Institute in London, Ontario, said the research was interesting.

"In some patients, such augmentation may be beneficial. Once human studies are done, we'll have a better idea," he said. "For now, this concept is a long way from being used in patients," said Reid, who was not part of the research team.

The research was funded by the National Institutes of Health.