A relatively new area of IBS research has been a focus on the use of antibiotics as a potential treatment. Not all antibiotics are thought to be helpful for IBS, just those that are not absorbed by the stomach and therefore can have an effect on bacteria within the small and large intestine. When prescribed as a treatment for IBS, antibiotics are only used on a short-term basis.

Why Use Antibiotics

The use of antibiotics for IBS came about when researchers looked at similarities between IBS and small intestinal bacteria overgrowth (SIBO). SIBO is a condition in which excess bacteria are found within the small intestine. Using hydrogen breath testing, researchers have found that a certain sub-set of IBS patients appeared to suffer from SIBO. Non-absorbable antibiotics were then tested for their effects on IBS symptoms.

The following antibiotics have been tested as to their effectiveness in treating IBS:

Rifaximin (Xifaxan)
Neomycin
Clarithromycin (Biaxin)
Metronidazole (Flagyl)

Effectiveness

Of the above antibiotics, Xifaxin is the only medication that has consistently been shown to be superior to placebo in easing symptoms in a subset of IBS patients. Xifaxan appears to be most effective at relieving symptoms of bloating and diarrhea. Xifaxan is generally well-tolerated and no serious side effects have been noted.

Bottom Line

As of now, only Xifaxan is approved by the FDA as a treatment for non-constipation IBS. It is important to know that most of the studies to date on the use of antibiotics for IBS have been of a short-term nature. Further research needs to be conducted to assess long-term safety and effectiveness of these medications, as well as to better identify those patients who will best benefit from this type of treatment.