Results of small intestinal bacterial overgrowth testing in irritable bowel syndrome patients: clinical profiles and effects of antibiotic trial.

PURPOSE: Small intestinal bacterial overgrowth (SIBO) may coexist with irritable bowel syndrome (IBS) and eradication therapy has been reported as effective in reducing IBS symptoms. Aims of this study were to: (1) Assess the clinical profiles of IBS patients, who underwent breath testing with a glucose substrate--glucose breath test (GBT); (2) Evaluate hydrogen and methane parameters in various IBS groups; (3) Assess the role of inhibition of gastric acid in contributing to SIBO; (4) Investigate efficacy and safety of non-absorbable antibiotic rifamixin for eradication and symptom relief. METHODS: 204 IBS patients met the ROME II criteria for IBS (170F & 34M; mean age 46.4; range 18-88) and underwent GBT. 8 of these patients with positive GBT were treated with rifaximin 200 mg, 4 times a day for 1 month and symptom assessments and GBT were repeated. RESULTS: 93 (46%) had a positive GBT. 68 (73%) of these 93 IBS-diarrhea dominant (IBS-D), 12 (13%) were constipation dominant (IBS-C) and 13 (14%) IBS with alternating bowel pattern. 48% of SIBO positive patients were receiving PPI therapy compared to 40% of IBS patients with negative GBT. 61 (66%) produced only hydrogen, 27 (29%) methane only, and 5 (5%) both-hydrogen and methane. There were more methane producers in IBS-C then IBS-D group (58% vs 28%) while IBS-D had more hydrogen formers (71% vs 42%). 8 patients with SIBO (7F & IM; mean age 55, range 31-85) received rifamixin 800 mg/day. Repeat GBT was normal in 6 (75%), 1 patient (12.5%) normalized according to hydrogen criteria but methane remained positive. Symptoms score improved in 7 (87.5%) patients and no adverse events were noted. CONCLUSIONS: (1) SIBO was present in nearly half of this large cohort of IBS patients based on the results of GBT; (2) Chronic PPI use was not associated with SIBO; (3) Methane formers on the GBT are more likely to be constipated; (4) Rifaximin is effective in treatment of SIBO in IBS and controlled trials are warranted.