IBS is the most common functional bowel disease affecting up to 15% of the population, with women accounting for 70–75% of this group. The criteria used to diagnose IBS are the presence of symptoms that meet the Rome criteria [Longstreth et al. 2006
]. There is no biological marker or unifying framework available to explain the different symptoms of IBS [Talley, 2006
]. The majority of patients with IBS also have significant bloating and gas as part of their presentation, in addition to a degree of constipation, diarrhea and pain [Talley, 2006
]. Patients with IBS who present with bloating and gas usually have the perception of abdominal distention. Recent data suggest that abnormalities in gas production and its transit through the small intestine could explain these symptoms. Whether SIBO contributes to some of this gas and bloating in IBS remains an area of active investigation. A recent study was designed to test the effect of treatment with a nonabsorbable antibiotic for IBS in a double-blind design. Patients with IBS underwent a LBT with the results blinded. All patients were subsequently randomized into two treatment groups (neomycin or placebo). One week after completion of treatment, patients returned for repeat LBT. A symptom questionnaire was administered on both days. After exclusion criteria were met, 111 patients (55 on an antibiotic, 56 on placebo) entered the study, with 84% having an abnormal LBT compared with 20% of healthy controls [Pimentel et al. 2003
]. Antibiotic administration resulted in a 35% improvement in symptoms compared with 11.4% in those on placebo. In addition, bowel normalization was reported in 35.3% of patients after starting antibiotics compared with 13.9% for those on placebo. The study concluded that an abnormal LBT is common in patients with IBS. Normalization of LBT with an antibiotic leads to a significant reduction in IBS symptoms. This study provided more evidence to suggest the gut microbial origin of IBS [Pimentel et al. 2003
A more recent study that included patients who had IBS without constipation were assigned to either rifaximin at a dose of 550 mg or placebo, three times daily for 2 weeks. These patients were followed for an additional 10 weeks [Pimentel et al. 2011a
]. The primary endpoint was adequate relief of IBS symptoms. The proportion of patients who had adequate relief of IBS-related bloating and gas was assessed weekly. Adequate relief was defined as self-reported relief of symptoms for at least 2 of the first 4 weeks of treatment. The improvement was reported as 40.8% versus
31.2% for placebo (p
= 0.01). Secondary endpoints included the proportion of patients who had a response to treatment as assessed by daily self-ratings of global IBS symptoms and individual symptoms of bloating, abdominal pain and stool consistency during the 4 weeks after treatment. The outcome of treatment with rifaximin was that significant relief of IBS symptoms, including bloating, abdominal pain and loose or watery stools, was provided for 2 weeks after treatment among patients who had IBS without constipation. One limitation of this study was that no breath test was performed at baseline to define the percentage of patients who had SIBO, or after the course of rifaximin to assess symptom correlation. Hence the study did not specifically treat patients with SIBO but included all patients with IBS without constipation.
Another recent study comprised 106 of 150 patients with IBS (71%) who were LBT positive and treated with rifaximin. Assessment at week 4 following commencement of therapy showed that rifaximin provided significant improvement of the following IBS-associated symptoms: bloating, flatulence, diarrhea, pain. The authors concluded that rifaximin treatment alleviated symptoms in patients with IBS who were LBT positive and this improvement was observed for a period of 3 months after 2 weeks of treatment with rifaximin [Schoepfer, 2012
Therefore, if IBS symptoms are caused by an antibiotic-sensitive mechanism, would the improvement in symptoms persist even after rifaximin is withdrawn? A retrospective chart review examined the efficacy of rifaximin in both the treatment and retreatment of IBS compared with neomycin [Yang et al. 2008
]. Out of 98 patients, 84 received one course of rifaximin. Fifty (60%) had a follow-up breath test and, of these, 31 (62%) were clinical responders and 19 (38%) were nonresponders. Of the 31 responders, 25 (81%) had a normal follow-up breath test compared with only 3 of the 19 (16%) nonresponders. Of the patients given rifaximin, 69% (58 out of 84) had a clinical response compared with only 38% (9 out of 24) of those on neomycin and 44% (27 out of 61) of those on all nonrifaximin antibiotics, suggesting that rifaximin seems to be more effective than other antibiotics in the treatment and retreatment of IBS.