Drugs counteract irritable bowel syndrome

The holidays bring family and friends together for sumptuous feasts that make stomachs groan. For people suffering from irritable bowel syndrome (IBS), however, even small meals can have extremely distressing consequences. The condition causes abdominal pain, cramps, diarrhea, constipation, and bloating.

Of unknown cause, IBS is the most frequently diagnosed gastrointestinal ailment in the United States. It affects up to 35 million people here. Physicians often arrive at a diagnosis by ruling out other ailments, such as intestinal blockage, colon cancer, and thyroid problems.

Treatments, ranging from Chinese herbs to antidepressants, have been largely limited to symptomatic relief. Now, researchers report that antibiotics knock out—at least temporarily—many of the bacteria that seem to be responsible for this condition.

The finding builds on earlier research suggesting a role in IBS for bacteria. In 1997, for instance, scientists in Bombay found that people with the condition improved markedly when given the antibiotic metronidazole. Other recent work, by British scientists, suggests that an overabundance of bacteria in the large intestine leads to excess fermentation, gas production, and an irritated bowel.

Gastroenterologist Mark Pimentel and his colleagues at Cedars-Sinai Medical Center and the University of California, Los Angeles suggest a slightly different scenario. They suspect that bacterial culprits spread backwards from the large intestine into the small intestine—which normally hosts relatively few bacteria—to cause the troublesome fermentation.

To diagnose whether people with irritable bowel syndrome have this bacterial overload, the researchers gave patients a special sugar syrup. People can’t digest the syrup, but bacteria in the intestines break it down. Hydrogen produced by this bacterial reaction in the small intestine readily enters the blood stream and can be detected by a breathalyzer test.

Of 202 people examined, the breath test revealed that 157 had an overload of bacteria in the small intestine.

The researchers then treated these patients with a 10-day course of antibiotics. The drugs had apparently eradicated the bacteria in the small intestines of 25 of the 47 people who came back for a second breath test. Among these 25 patients, irritable bowel symptoms had either disappeared or were greatly reduced, says Pimentel.

In the remaining 22 patients, the breath tests indicated the antibiotics killed only a portion of the bacteria. Even so, these patients improved significantly, Pimentel and his colleagues report in the December American Journal of Gastroenterology.

The status of many of the original pool of patients remains unknown because they didn’t return for follow-up. Pimentel’s research team is now conducting a larger study with breath tests on hundreds of patients before and after they receive either antibiotics or a placebo.

Gastroenterologist John O. Hunter of Addenbrooke’s Hospital in Cambridge, England, rates the study as “interesting.” However, he says that the work doesn’t firmly establish that the hydrogen detected is being produced by bacteria in the small intestine rather than the large intestine.

He also notes that the lower gut harbors “a complex little ecosystem.” Antibiotics can destroy valuable bacteria in the large intestine and throw the system off balance, Hunter cautions.

“We don’t want people just to give antibiotics to everybody,” Pimentel says. He acknowledges that wholesale killing of bacteria in the small intestine also zaps microbes in the large intestine. But these grow back within about 5 days, Pimentel says.

Some of the people who improved dramatically from the antibiotics, suffered relapses within a few months, he notes. For that reason, he and his colleagues don’t yet consider antibiotics a cure for IBS.

Nevertheless, the findings could guide future research. Says Pimentel: “We think we’ve found a target.”

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