Rifaximin is associated with modest, transient decreases in multiple taxa in the gut microbiota of patients with diarrhoea-predominant irritable bowel syndrome

Mechanism of action and therapeutic benefit of rifaximin in patients with irritable bowel syndrome: a narrative review

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder with a multifactorial pathophysiology. The gut microbiota differs between patients with IBS and healthy individuals. After a bout of acute gastroenteritis, postinfection IBS may result in up to approximately 10% of those affected. Small intestinal bacterial overgrowth (SIBO) is more common in patients with IBS than in healthy individuals, and eradication of SIBO with systemic antibiotics has decreased symptoms of IBS in some patients with IBS and SIBO. The nonsystemic (i.e. low oral bioavailability) antibiotic rifaximin is indicated in the United States and Canada for the treatment of adults with IBS with diarrhea (IBS-D). The efficacy and safety of 2-week single and repeat courses of rifaximin have been demonstrated in randomized, placebo-controlled studies of adults with IBS. Rifaximin is widely thought to exert its beneficial clinical effects in IBS-D through manipulation of the gut microbiota. However, current studies indicate that rifaximin induces only modest effects on the gut microbiota of patients with IBS-D, suggesting that the efficacy of rifaximin may involve other mechanisms. Indeed, preclinical data reveal a potential role for rifaximin in the modulation of inflammatory cytokines and intestinal permeability, but these two findings have not yet been examined in the context of clinical studies. The mechanism of action of rifaximin in IBS is likely multifactorial, and further study is needed.

Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome - An Update

Small intestinal bacterial overgrowth (SIBO) is one manifestation of gut microbiome dysbiosis and is highly prevalent in IBS (Irritable Bowel Syndrome). SIBO can be diagnosed either by a small bowel aspirate culture showing ≥10³ colony-forming units (CFU) per mL of aspirate, or a positive hydrogen lactulose or glucose breath test. Numerous pathogenic organisms have been shown to be increased in subjects with SIBO and IBS, including but not limited to Enterococcus, Escherichia coli, and Klebsiella. In addition, Methanobrevibacter smithii, the causal organism in a positive methane breath test, has been linked to constipation predominant irritable bowel syndrome (IBS-C). As M. smithii is an archaeon and can overgrow in areas outside of the small intestine, it was recently proposed that the term intestinal methanogen overgrowth (IMO) is more appropriate for the overgrowth of these organisms. Due to gut microbiome dysbiosis, patients with IBS may have increased intestinal permeability, dysmotility, chronic inflammation, autoimmunity, decreased absorption of bile salts, and even altered enteral and central neuronal activity. As a consequence, SIBO and IBS share a myriad of symptoms including abdominal pain, distention, diarrhea, and bloating. Furthermore, gut microbiome dysbiosis may be associated with select neuropsychological symptoms, although more research is needed to confirm this connection. This review will focus on the role of the gut microbiome and SIBO in IBS, as well as novel innovations that may help better characterize intestinal overgrowth and microbial dysbiosis.

Current US Food and Drug Administration-Approved Pharmacologic Therapies for the Treatment of Irritable Bowel Syndrome with Diarrhea

Irritable bowel syndrome (IBS) is a functional bowel disorder characterized by abdominal pain and alterations in stool form and/or frequency, leading to reduced quality of life. Pharmacologic agents currently approved by the US Food and Drug Administration for treatment of IBS with diarrhea (IBS-D) in adults are the nonsystemic antibiotic rifaximin, the mixed µ- and κ-opioid receptor agonist/δ-opioid antagonist eluxadoline, and the selective serotonin 5-HT₃ antagonist alosetron (the last of which is indicated only in women with severe IBS-D refractory to conventional therapy). Both eluxadoline and alosetron are administered as chronic daily therapies; rifaximin is given as a 2-week course of treatment with repeat courses administered as needed for symptom recurrence. Presumed mechanisms of action of rifaximin include modulation of the gut microbiota, anti-inflammatory activity, normalization of visceral hypersensitivity, and reduction in intestinal permeability. Eluxadoline targets opioid receptors in the gastrointestinal (GI) tract, resulting in decreased GI motility, fluid secretion, and visceral pain perception. Alosetron antagonizes serotonergic afferent neural signals and also slows GI motility. The efficacy and safety of these agents have been investigated in several rigorous clinical trials, and it has been demonstrated that they improve global and individual IBS symptoms. This review highlights the pivotal efficacy and safety data of the three pharmacologic agents currently indicated in the USA for the management of IBS-D in adults.Funding: Salix Pharmaceuticals.

Lactulose Breath Testing as a Predictor of Response to Rifaximin in Patients With Irritable Bowel Syndrome With Diarrhea

OBJECTIVES

The nonsystemic antibiotic rifaximin is indicated for irritable bowel syndrome with diarrhea (IBS-D) in adults; however, determinants of response remain unclear. The utility of lactulose breath testing (LBT) in predicting response to rifaximin was examined.

METHODS

Adults with IBS-D received open-label rifaximin 550 mg 3 times daily for 2 weeks, followed by a 4-week posttreatment assessment period. Thirteen centers prospectively participated in this substudy. LBT was conducted before (day 1) and after (day 14) therapy (breath samples obtained every 15 minutes; up to 240 minutes). Patient response (decrease from baseline of ≥30% in abdominal pain and ≥50% decrease in frequency of mushy/watery stool), symptom improvement, and the relationship of clinical outcomes to LBT results were assessed.

RESULTS

A total of 93 patients were included; 62 (66.7%) had positive baseline LBT results. Overall, 48.4% (45/93) of patients responded to rifaximin; of these, 59.7% (37/62) had a positive baseline LBT vs 25.8% (8/31) with a negative LBT (P = 0.002; odds ratio 4.3, 95% confidence interval, 1.5-12.7). Patients with a positive baseline LBT result experienced significantly greater improvement from baseline in 6 of 7 individual IBS symptoms. LBT results after rifaximin therapy did not correlate with clinical response in the 86 patients with evaluable breath tests (P = 0.21); however, patients whose LBT results normalized after rifaximin had the highest response rate of 76.5% (13/17).

DISCUSSION

A positive baseline LBT result predicted a higher likelihood of response to rifaximin in IBS-D, suggesting a gut microbiome modulatory mechanism of action for rifaximin.

Management of irritable bowel syndrome with diarrhea: a review of nonpharmacological and pharmacological interventions

Irritable bowel syndrome (IBS) is a common gastrointestinal (GI) condition involving numerous potential causative factors (e.g. alterations in gut microbiota, motility, brain-gut axis). Several interventions are available for the management of patients with IBS, but no universal management algorithm currently exists. The aim of this article is to review interventions that may be considered in the management of patients with IBS with diarrhea (IBS-D). Nonpharmacological interventions include dietary and lifestyle modification, which are generally used as first-line therapy. Probiotics have demonstrated efficacy and safety in patients with IBS, but studies are inconsistent in strains examined, dosing, and treatment duration. Psychological therapies (e.g. cognitive behavioral therapy, hypnotherapy) also may improve IBS symptoms. Pharmacological interventions for the management of IBS-D include the US Food and Drug Administration-approved agents eluxadoline, rifaximin, and alosetron, as well as loperamide, smooth muscle antispasmodics, bile acid sequestrants, and antidepressants (i.e. tricyclic antidepressants, selective serotonin reuptake inhibitors). Eluxadoline and rifaximin have been shown to improve abdominal pain and stool consistency in patients with IBS-D. In addition, data indicate that alosetron improves IBS symptoms; however, it is approved only for women with severe IBS-D. Of the three approved agents, rifaximin has the most favorable safety profile. The risk-benefit ratio is an important consideration with every medication, but is especially important in the treatment of functional GI disorders such as IBS-D. Thus, the most troublesome symptoms, quality of life, symptom intensity, and individual patient preferences should be considered when formulating a management plan for patients with IBS-D.

Actinomycete-Derived Polyketides as a Source of Antibiotics and Lead Structures for the Development of New Antimicrobial Drugs

Actinomycetes are remarkable producers of compounds essential for human and veterinary medicine as well as for agriculture. The genomes of those microorganisms possess several sets of genes (biosynthetic gene cluster (BGC)) encoding pathways for the production of the valuable secondary metabolites. A significant proportion of the identified BGCs in actinomycetes encode pathways for the biosynthesis of polyketide compounds, nonribosomal peptides, or hybrid products resulting from the combination of both polyketide synthases (PKSs) and nonribosomal peptide synthetases (NRPSs). The potency of these molecules, in terms of bioactivity, was recognized in the 1940s, and started the "Golden Age" of antimicrobial drug discovery. Since then, several valuable polyketide drugs, such as erythromycin A, tylosin, monensin A, rifamycin, tetracyclines, amphotericin B, and many others were isolated from actinomycetes. This review covers the most relevant actinomycetes-derived polyketide drugs with antimicrobial activity, including anti-fungal agents. We provide an overview of the source of the compounds, structure of the molecules, the biosynthetic principle, bioactivity and mechanisms of action, and the current stage of development. This review emphasizes the importance of actinomycetes-derived antimicrobial polyketides and should serve as a "lexicon", not only to scientists from the Natural Products field, but also to clinicians and others interested in this topic.

Obesity, Motility, Diet, and Intestinal Microbiota-Connecting the Dots

PURPOSE OF REVIEW

The goal of the present review is to explore the relationship between dietary changes and alterations in gut microbiota that contribute to disorders of gut motility and obesity.

RECENT FINDINGS

We review the microbiota changes that are seen in obesity, diarrhea, and constipation and look at potential mechanisms of how dysbiosis can predispose to these. We find that microbial metabolites, particularly short chain fatty acids, can lead to signaling changes in the host enterocytes. Microbial alteration leading to both motility disorders and obesity may be mediated by the release of hormones including glucagon-like peptides 1 and 2 (GLP-1, GLP-2) and polypeptide YY (PYY). These pathways provide avenues for microbiota-targeted interventions that can treat both disorders of motility and obesity. In summary, multiple mechanisms contribute to the interplay between the microbial dysbiosis, obesity, and dysmotility.

The diagnosis of small intestinal bacterial overgrowth: Two steps forward, one step backwards?

Small intestinal bacterial overgrowth (SIBO) was originally described decades ago as a cause of malabsorption among individuals with abnormal intestinal anatomy and/or impaired gastric acid secretion and intestinal motor functions. More recently, the concept of SIBO has been expanded to explain symptoms among a much broader patient population-a move that brings the definition of SIBO into much sharper focus. For largely logistical reasons, breath tests and, especially, those based on the excretion of hydrogen consequent on the fermentation of unabsorbed carbohydrate substrates, have almost entirely replaced jejunal aspirates in the diagnosis of SIBO. Ever bedeviled by concerns regarding their reliability, hydrogen breath tests have now come under even more critical scrutiny with the study from Sundin and colleagues in this issue suggesting that their sole function is to detect carbohydrate malabsorption and that they are incapable of defining SIBO.

Review article: an analysis of safety profiles of treatments for diarrhoea-predominant irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is multifactorial in nature, and a wide range of therapies is available to manage symptoms of this common disorder.

AIM

To provide an overview of the safety of interventions that may be used to manage patients with diarrhoea-predominant IBS (IBS-D).

METHODS

Medline and Embase database searches (through 02 May 2018) to identify clinical studies that evaluated treatment safety and/or efficacy in adults with IBS-D.

RESULTS

IBS-D treatments include dietary modification, probiotics, serotonin receptor antagonists, opioid receptor agonists and antagonists, nonsystemic antibiotics, bile acid sequestrants, antidepressants, and complementary and alternative therapies. These treatments vary in administration frequency (eg, daily; short-course therapy) and target various pathophysiologic factors. Safety profiles vary considerably by treatment among IBS-D therapies. The number needed to harm (defined as the number of patients treated to encounter an adverse event) was lowest (worse) for antidepressants (8.5) and highest (best) for probiotics (35), and the number needed to harm (defined as the number of patients who discontinued due to an adverse event) was lowest for tricyclic antidepressants (9) and highest for rifaximin (8971). Notable safety concerns with IBS-D treatments include pancreatitis with eluxadoline, ischaemic colitis and serious complications of constipation with alosetron, and cardiac adverse events with loperamide and tricyclic antidepressants. Treatment decisions need to account for medication risks and adverse events for each patient.

CONCLUSIONS

Multiple treatment options are now available for patients with IBS-D. However, the safety profiles of these agents vary widely by number needed to harm value. Providers should consider both safety and efficacy of a specific intervention when determining how best to manage patients' IBS-D symptoms.

Short-course therapy for diarrhea-predominant irritable bowel syndrome: understanding the mechanism, impact on gut microbiota, and safety and tolerability of rifaximin

Irritable bowel syndrome (IBS) is a common gastrointestinal (GI) disorder characterized by abdominal pain that occurs with defecation or alterations in bowel habits. Further classification is based on the predominant bowel habit: constipation-predominant IBS, diarrhea-predominant IBS (IBS-D), or mixed IBS. The pathogenesis of IBS is unclear and is considered multifactorial in nature. GI dysbiosis, thought to play a role in IBS pathophysiology, has been observed in patients with IBS. Alterations in the gut microbiota are observed in patients with small intestinal bacterial overgrowth, and overgrowth may occur in a subset of patients with IBS. The management of IBS includes therapies targeting the putative factors involved in the pathogenesis of the condition. However, many of these interventions (eg, eluxadoline and alosetron) require long-term, daily administration and have important safety considerations. Agents thought to modulate the gut microbiota (eg, antibiotics and probiotics) have shown potential benefits in clinical studies. However, conventional antibiotics (eg, neomycin) are associated with several adverse events and/or the risk of bacterial antibiotic resistance, and probiotics lack uniformity in composition and consistency of response in patients. Rifaximin, a nonsystemic antibiotic administered as a 2-week course of therapy, has been shown to be safe and efficacious for the treatment of IBS-D. Rifaximin exhibits a favorable benefit-to-harm ratio when compared with daily therapies for IBS-D (eg, alosetron and tricyclic antidepressants), and rifaximin was not associated with the emergence of bacterial antibiotic resistance. Thus, short-course therapy with rifaximin is an appropriate treatment option for IBS-D.

Fecal microbiota transfer for bowel disorders: efficacy or hype?

PURPOSE OF REVIEW

Dysbiosis has been related to the pathophysiology of disorders of - gut-brain interaction (DGBI) including irritable bowel syndrome (IBS) and functional constipation (FC). Accordingly, modulation of gut microbiota has been proposed as a potential treatment for these disorders. Gut microbiota modulation can be effected by probiotics, prebiotics, symbiotics, postbiotics, antibiotics and fecal transplantation (FMT) or bacteriotherapy. The latter is currently used for recurrent or severe Clostridium difficile colitis and has been the focus of recent research in IBS and FC.

RECENT FINDINGS

Several case series reported promising results for FMT in patients with IBS and FC, which prompted the conduction of randomized controlled trials (RCT) in these DGBI.

SUMMARY

Both case series and RCTs are herein discussed. To the best of our knowledge, as of yet, 5 RCTs have been published on IBS and one in FC with slow colonic transit. In IBS, the majority of studies have used the IBS severity scoring system (IBS-SSS) as an outcome measure; however, the selection criteria were different among the trials as well as the route and form of administration of the FMT. Therefore, the results are inconsistent and no conclusion can be drawn. Some studies suggest that the presence of post-infection (PI)-IBS and the baseline microbiota status in the donors could be predictor factors of successful FMT in IBS. In constipation with slow colonic transit, the FMT seems to be more effective, although the data is based on only one RCT. We believe that larger RCTs, controlled with true placebos and considering baseline intestinal microbiota of the study subjects as well as donors' microbiota are still needed before recommending FMT in IBS and/or FC. History of previous GI infection (e.g. PI-IBS) and IBS subtypes should also be taken into account.

The gut microbiome and irritable bowel syndrome

Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders encountered in clinical practice. It is a heterogeneous disorder with a multifactorial pathogenesis. Recent studies have demonstrated that an imbalance in gut bacterial communities, or "dysbiosis", may be a contributor to the pathophysiology of IBS. There is evidence to suggest that gut dysbiosis may lead to activation of the gut immune system with downstream effects on a variety of other factors of potential relevance to the pathophysiology of IBS. This review will highlight the data addressing the emerging role of the gut microbiome in the pathogenesis of IBS and review the evidence for current and future microbiome based treatments.