1. Irritable Bowel Syndrome (IBS) Slideshow Pictures
2. Digestive Disease Myths Slideshow Pictures
3. Diverticulitis (Diverticulosis) Slideshow Pictures

Medical Author:

Jay W. Marks, MD

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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Medical Editor:

Bhupinder Anand, MD

In this Article

• What is small intestinal bacterial overgrowth (SIBO)?
• What causes small intestinal bacterial overgrowth?
• What are the small intestinal bacterial overgrowth symptoms?
• What is the normal relationship between bacteria and the small intestine?
• What conditions cause increased production of gas?
• How does small intestinal bacterial overgrowth cause symptoms?
• How is small intestinal bacterial overgrowth diagnosed?
• Is there a relationship between small intestinal bacterial overgrowth and irritable bowel syndrome?
• How is small intestinal bacterial overgrowth treated?
• What's new in small intestinal bacterial overgrowth?
• Small Intestinal Bacterial Overgrowth (SIBO) At A Glance
• Patient Comments: Small Intestinal Bacterial Overgrowth - Symptoms
• Patient Comments: Small Intestinal Bacterial Overgrowth - Causes
• Find a local Gastroenterologist in your town
• Small Intestinal Bacterial Overgrowth Index

"Classic" SIBO

SIBO has been recognized for many years as a problem with severe disorders of intestinal muscles and intestinal obstruction. The treatment has been antibiotics, and they are very effective. The difficulty is that the disease causing the SIBO often cannot be corrected. As a result, symptoms frequently return when the antibiotics are stopped, and it may be necessary to treat the patient with antibiotics repeatedly or even continuously.

SIBO associated with IBS

There are very few rigorous, scientific studies on the treatment of irritable bowel syndrome with therapies that are directed specifically to the possibility of underlying SIBO. That has not stopped physicians from trying unproven treatments. The discussion of treatment that follows is based on the minimal scientific evidence that is available (two trials) as well as the anecdotal (observed but not scientifically demonstrated) experience of physicians who see patients with irritable bowel syndrome.

The two most common treatments for SIBO in patients with IBS are oral antibiotics and probiotics. Probiotics are live bacteria that, when ingested by an individual, result in a health benefit. The most common probiotic bacteria are lactobacilli (also used in the production of yogurt) and bifidobacteria. Both of these bacteria are found in the intestine of normal individuals. There are numerous explanations for how probiotic bacteria might benefit individuals. However, the beneficial action has not been identified clearly. It may be that the probiotic bacteria inhibit other bacteria in the intestine that may be causing symptoms, or it may be that the probiotic bacteria act on the host's intestinal immune system to suppress inflammation.

Several antibiotics either alone or in combination have been reported in scientific studies to be successful in treating IBS. Treatment success, when measured by either symptom improvement or by the normalization of the hydrogen breath test, ranges from 40%-70%. When one antibiotic fails, the doctor may add another antibiotic or change to a different antibiotic. However, the doses of antibiotics, the duration of treatment, and the need for maintenance therapy to prevent recurrence of SIBO have not been adequately studied. Most physicians use standard doses of antibiotics for one to two weeks. Probiotics may be used alone, in combination with antibiotics, or for prolonged maintenance. When probiotics are used, it probably is best to use one of the several probiotics that have been studied in medical trials and shown to have an effect on the small intestine, though not necessarily in SIBO. The commonly sold probiotics in health-food stores may not be effective. Moreover, they often do not contain the bacteria stated on the label or the bacteria are dead. The following are some treatment options:

• Neomycin orally for 10 days. Neomycin is not absorbed from the intestine and acts only within the intestines.
• Levofloxacin (Levaquin) or ciprofloxacin (Cipro) for 7 days.
• Metronidazole (Flagyl) for 7 days.
• Levofloxacin (Levaquin) combined with metronidazole (Flagyl) for 7 days.
• Rifaximin (Xifaxan) for 7 days. Rifaximin like neomycin is not absorbed from the intestine, and, therefore, acts only within the intestine. Because very little rifaximin is absorbed into the body, it has few important side effects. Higher than normal doses of rifaximin (1200 mg/day for 7 days) were superior to the standard lower doses (800 or 400 mg/day) in normalizing the hydrogen breath test in patients with SIBO and IBS. However, it is not yet known whether the larger dose is any better at suppressing symptoms.
• Commercially available probiotics such as VSL#3 or Flora-Q, which are mixtures of several different bacterial species, have been used for treating SIBO and IBS, but their effectiveness is not known. Bifidobacterium infantis 35624 is the only probiotic that has been demonstrated to be effective in treating patients with IBS.

Treatment with antibiotics versus probiotics

It is the author's personal belief that for short-term (1-2 weeks) treatment, antibiotics are more effective than probiotics. However, antibiotics do have certain disadvantages. Specifically, symptoms tend to recur after treatment is discontinued, and prolonged or repeated courses of treatment may be necessary in some patients. Physicians are reluctant to prescribe prolonged or repeated courses of antibiotics because of concern over long-term side effects of the antibiotics and the emergence of bacteria that are resistant to the antibiotics. Physicians have less concern over long-term side effects or the emergence of resistant bacteria with probiotics and, therefore, are more willing to prescribe probiotics repeatedly and for prolonged periods. One option is to initially treat the patient with a short course of antibiotics and then long-term with probiotics. Long-term studies comparing antibiotics, probiotics, and combinations of antibiotics and probiotics are badly needed.