The frequency of excessive bacterial growth and the effectiveness of its treatment in patients with irritable bowel syndrome

Objective — to study the frequency of the syndrome of intestinal bacterial overgrowth (SIBO) and to establish the effects of its eradication on the clinical course of various subtypes of the irritable bowel syndrome (IBS). Materials and methods. The examinations in an open comparative randomized study involved 88 patients with IBS (35 men, 53 women) aged 26 to 56 years (mean age — 40 ± 14 years). The IBS diagnosis in all patients was established on the basis of Roma criteria IV. The IBS with diarrhea (IBS‑D) was established in the majority of patients (47 subjects, 53.4 %), a mixed subtype of IBS (IBS‑M) was revealed in 30 (34.1 %) patients, and IBS with constipation (IBS‑C) in 11 (12.5 %). The following IBS duration was defined: less than 5 years in 37 (42 %) of patients, 5 ‑ 10 years in 35 (39.8 %) subjects, more than 10 years in 16 (18.2 %) patients. The IBS course was mild in 30 (34.1 %) patients, mild to moderate in 45 (51.1 %) and severe disease was in 13 (14.8 %). The control group consisted of 30 clinically healthy people (18 women, 12 men, the mean age (33 ± 12) years).  Diagnosis of SIBO was performed using the H2‑breath test with lactulose (H2‑LDT). Results. The overall frequency of SIBO detection (positive H2‑LDT) in patients with IBS (73.9 %) significantly exceeded its frequency in the controls (6.6 %, p < 0.005). The frequency of SIBO was significantly higher in IBS‑D and IBS‑M (78.7 % and 73.3 %, respectively) compared to IBS‑C (54.3 %, p < 0.005). Also, SIBO frequency was significantly higher in women with a history of the disease up to 5 years, in most patients a moderate course of IBS‑D was observed. The SIBO eradication after treatment with rifaximin was achieved in 73.8 % of cases, and eradication frequency in IBS‑D patients (78.4 %) significantly exceeded this parameter in patients with IBS‑C (66.6 %). Moreover, it was established that rifaximin at a dose of 1600 mg/day for 14 days was slightly more effective (eradication in 76.6 % of cases) than rifaximin at a dose of 1200 mg/day (eradication in 71.4 % of cases, p = 0.63). Conclusions. The results of the study indicate that SIBO is very often present in patients with IBS, and its elimination is accompanied by an increase in both clinical and anti‑relapse effects. Rifaximin is an effective agent for the eradication of SIBO, and increase of its dosage (from 1200 mg/day to 1600 mg/day) correlates with some increase in clinical and antibacterial efficacy. Clinical improvement and reduction of recurrence rates after eradication of SIBO suggests that the latter may play a pathogenetic role in IBS.