Small intestine bacterial overgrowth in irritable bowel syndrome: a retrospective study with rifaximin

Irritable bowel syndrome (IBS) is a frequent diagnosis in gastroenterology, but it is now clear that an altered dynamic equilibrium and bacterial overgrowth in the small intestine may mimic an IBS-like syndrome.

We have, therefore, evaluated the real prevalence of small intestinal bacterial overgrowth (SIBO) by retrospectively examining the glucose hydrogen (H(2)) breath test in 96 patients with a previous symptoms-based IBS diagnosis. Moreover, we wished to evaluate the efficacy of the locally acting antibiotic rifaximin in eradicating a SIBO syndrome.

The breath test showed a SIBO syndrome in 44 out 96 IBS patients (45.8%), who had H(2) peaks in the expired air higher than 10 ppm over the baseline value (mean: 36.2+/-18.7 ppm). All these patients were treated with rifaximin (1 200 mg/day for 14 days) followed by a twenty-day cycle of probiotics. Twenty-three of them returned to a control visit within 4-5 months: the glucose breath test became negative in 19 cases (82.6%; P<0.01) and mean peak value of H(2) significantly decreased from 40.9+/-20.4 to 4.78+/-8.42 ppm (P<0.001). Patients reported also a substantial improvement of the IBS symptoms. No adverse effect was observed.

These data indicate a SIBO syndrome is present in about half of patients with an IBS diagnosis and, therefore, it should always be suspected in these patients. Moreover, the use of broad-spectrum non absorbable antibiotics, such as rifaximin, represents a safe and effective approach to SIBO with a low risk of causing microbial resistance.