Functional Disease, Dysbiosis, and Dyspepsia: How Helpful Is Rifaximin?

Excerpt

Functional dyspepsia (FD) and irritable bowel syndrome (IBS) are functional gastrointestinal disorders abnormal gut-brain interactions. FD is defined as foregut symptoms such as heartburn, dyspepsia, and nausea whereas IBS is defined as altered bowel habits related to abdominal pain, with both conditions diagnosed in the absence of demonstratable pathology. These disorders may occur either in isolation or may overlap with other functional gastrointestinal disorders (FGID), usually on a background of anxiety and depression. When FD and IBS overlap, the severity of symptoms of both disorders increases [1]. Interestingly, both share similar pathophysiological mechanisms including altered gastrointestinal motility and sensory function, increased intestinal paracellular permeability, low-grade mucosal inflammation, microbial dysbiosis, and dysfunction of the brain‐gut axis with psychiatric comorbidities [2]. Microbial dysbiosis and small intestinal bacterial overgrowth (SIBO) are associated with both FD and IBS. Wide variations in prevalence rates of SIBO have been reported in patients with FGID. In IBS, over 20 studies have reported the frequency of SIBO in affected patients of 2%—84% [3]. A recent meta-analysis showed the prevalence of SIBO in FD was 2.8 times higher than in controls [4]. The prevalence of SIBO is higher in patients with overlap compared to isolated FD and IBS. The conventional diagnosis of SIBO is based on jejunal aspirate culture, with colony count ≥ 10⁵ CFU/ml diagnostic of SIBO. Non-invasive tests for diagnosis of SIBO used primarily in clinical practice are the glucose hydrogen breath test (GHBT) and lactulose hydrogen breath test (LHBT) [5]. Though popular, their accuracy is doubtful, with a recent meta-analysis showing both tests to have low sensitivity with high specificity. Rifaximin is the one of first-choice therapies in SIBO, where it acts as a poorly absorbed oral antibiotic that alters the composition of the gut microbiota. This effect is also useful in patients with IBS and FD where disturbances in gut microbial composition are common. A recent network meta-analysis showed significant benefit of rifaximin over placebo in patients with IBS. Rifaximin was also the safest drug in patients with IBS [6]. On the other hand, data on the efficacy of rifaximin in FD remains sparse. The benefits of rifaximin in the patients with overlap of FD and IBS remain elusive. …