Review article: potential mechanisms of action of rifaximin in the management of irritable bowel syndrome with diarrhoea

The gut microbiome in disorders of gut-brain interaction

Functional gastrointestinal disorders (FGIDs), chronic disorders characterized by either abdominal pain, altered intestinal motility, or their combination, have a worldwide prevalence of more than 40% and impose a high socioeconomic burden with a significant decline in quality of life. Recently, FGIDs have been reclassified as disorders of gut-brain interaction (DGBI), reflecting the key role of the gut-brain bidirectional communication in these disorders and their impact on psychological comorbidities. Although, during the past decades, the field of DGBIs has advanced significantly, the molecular mechanisms underlying DGBIs pathogenesis and pathophysiology, and the role of the gut microbiome in these processes are not fully understood. This review aims to discuss the latest body of literature on the complex microbiota-gut-brain interactions and their implications in the pathogenesis of DGBIs. A better understanding of the existing communication pathways between the gut microbiome and the brain holds promise in developing effective therapeutic interventions for DGBIs.

Distinct Effects of Non-absorbed Agents Rifaximin and Berberine on the Microbiota-Gut-Brain Axis in Dysbiosis-induced Visceral Hypersensitivity in Rats

Background/Aims

Irritable bowel syndrome (IBS) is accepted as a disorder of gut-brain interactions. Berberine and rifaximin are non-absorbed antibiotics and have been confirmed effective for IBS treatment, but there is still lack of direct comparison of their effects. This study aims to compare the effect of the 2 drugs on the alteration of gut-brain axis caused by gut microbiota from IBS patients.

Methods

Germ-free rats received fecal microbiota transplantation from screened IBS patients and healthy controls. After 14 days' colonization, rats were administrated orally with berberine, rifaximin or vehicle respectively for the next 14 days. The visceral sensitivity was evaluated, fecal microbiota profiled and microbial short chain fatty acids were determined. Immunofluorescence staining and morphological analysis were performed to evaluate microglial activation.

Results

Visceral hypersensitivity induced by IBS-fecal microbiota transplantation was relieved by berberine and rifaximin, and berberine increased sucrose preference rate. Microbial α-diversity were reduced by both drugs. Compared with rifaximin, berberine significantly changed microbial structure and enriched Lachnoclostridium. Furthermore, berberine but not rifaximin significantly increased fecal concentrations of acetate and propionate acids. Berberine restored the morphological alterations of microglia induced by dysbiosis, which may be associated with its effect on the expression of microbial gene pathways involved in peptidoglycan biosynthesis. Rifaximin affected neither the numbers of activated microglial cells nor the microglial morphological alterations.

Conclusions

Berberine enriched Lachnoclostridium, reduced the expression of peptidoglycan biosynthesis genes and increased acetate and propionate. The absence of these actions of rifaximin may explain the different effects of the drugs on microbiota-gut-brain axis.

Antibiotics and Probiotics for Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a disorder of a gut-brain interaction characterised by abdominal pain and a change in stool form or frequency. Current symptom-based definitions and the classification of IBS promote heterogeneity amongst patients, meaning that there may be several different pathophysiological abnormalities leading to similar symptoms. Although our understanding of IBS is incomplete, there are several indicators that the microbiome may be involved in a subset of patients. Techniques including a faecal sample analysis, colonic biopsies, duodenal aspirates or surrogate markers, such as breath testing, have been used to examine the gut microbiota in individuals with IBS. Because of a lack of a clear definition of what constitutes a healthy gut microbiota, and the fact that alterations in gut microbiota have only been shown to be associated with IBS, a causal relationship is yet to be established. We discuss several hypotheses as to how dysbiosis may be responsible for IBS symptoms, as well as potential treatment strategies. We review the current evidence for the use of antibiotics and probiotics to alter the microbiome in an attempt to improve IBS symptoms. Rifaximin, a non-absorbable antibiotic, is the most studied antibiotic and has now been licensed for use in IBS with diarrhoea in the USA, but the drug remains unavailable in many countries for this indication. Current evidence also suggests that certain probiotics, including Lactobacillus plantarum DSM 9843 and Bifidobacterium bifidum MIMBb75, may be efficacious in some patients with IBS. Finally, we describe the future challenges facing us in our attempt to modulate the microbiome to treat IBS.

Modulation of the microbiota across different intestinal segments by Rifaximin in PI-IBS mice

BACKGROUND

Rifaximin has been increasingly applied in irritable bowel syndrome (IBS) treatment. Whether there were differences in the effects of rifaximin on microbiota from different intestinal segments, especially the small intestine where rifaximin predominantly acted, has not been confirmed.

METHODS

In this study, we used Trichinella spiralis infection to induce post infectious irritable bowel syndrome (PI-IBS) and measured visceral sensitivity of mice by means of abdominal withdrawal reflex (AWR) tests to colorectal distention (CRD). We compared the effects of rifaximin on the composition of ileal, colonic mucosal and fecal microbiota in PI-IBS mice.

RESULTS

Rifaximin significantly reduced AWR scores and increased pain threshold in PI-IBS mice, and this effect was associated with the change in the relative abundance of ileal mucosal microbiota. Rifaximin could obviously decrease ileum mucosal microbiota alpha diversity assessed by Shannon microbial diversity index. Meanwhile, the analysis of beta diversity and relative abundance of microbiota at phylum, family and genus levels showed that rifaximin could improve the microbiota structure of ileal mucosa. However, for colonic mucosal and fecal microbiota, this effect of rifaximin was not obvious. Rifaximin could reshape the correlation of genera between different intestinal segments.

CONCLUSION

Rifaximin improved visceral hypersensitivity in PI-IBS mice. Rifaximin mainly affected ileal mucosal microbiota, and its improvement effect on IBS might be closely related to the improvement of ileal microbiota structure.

Bile acid-gut microbiota crosstalk in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common disorder of gut-brain interaction with an increasing prevalence, and its precise aetiology remains unclear. Gut microbiota dysbiosis has been found to be associated with IBS pathogenesis. In addition, a high incidence of bile acid diarrhoea and disturbed bile acid metabolism has been observed in IBS patients. The abundant microorganisms inhabited in human gut have essential functions in bile acid biotransformation, and can immensely affect the size and constitution of bile acid pool. Meanwhile, the alterations of bile acid profile can inversely interfere with the gut microbiota. This review discussed the role of intricate correlations between bile acids and gut microbiota in IBS pathogenesis and delineated the possible molecular mechanisms, mainly the signalling induced by farnesoid X receptor and transmembrane G protein-coupled receptor 5. Besides, some biomarkers for identifying bile acid diarrhoea in IBS population were listed, assisting the diagnosis and classification of IBS. Moreover, it also assessed some therapeutic strategies for IBS that regulate the bile acid-gut microbiota axis, such as dietary modulation, probiotics/prebiotics, faecal microbiota transplantation, and antibiotics. Collectively, this article illustrated the relationship between bile acids and gut microbiota in IBS pathophysiology and might offer some novel therapeutic options for IBS.

Targeting the Gut Microbiota to Relieve the Symptoms of Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a common, chronic, functional disorder with a large impact on world population. Its pathophysiology is not completely revealed; however, it is certain that dysregulation of the bidirectional communications between the central nervous system (CNS) and the gut leads to motility disturbances, visceral hypersensitivity, and altered CNS processing characterized by differences in brain structure, connectivity and functional responsiveness. Emerging evidence suggests that gut microbiota exerts a marked influence on the host during health and disease. Gut microbiome disturbances can be also important for development of IBS symptoms and its modulation efficiently contributes to the therapy. In this work, we review the current knowledge about the IBS therapy, the role of gut microbiota in pathogenesis of IBS, and we discuss that its targeting may have significant impact on the effectiveness of IBS therapy.

Non-Celiac Gluten Sensitivity in the Context of Functional Gastrointestinal Disorders

Gluten-free diets are increasingly chosen in the Western world, even in the absence of a diagnosis of celiac disease. Around 10% of people worldwide self-report gluten-related complaints, including intestinal and extra-intestinal symptoms. In most cases, these subjects would be labeled as patients suffering from irritable bowel syndrome (IBS) who place themselves on a gluten-free diet even in the absence of celiac disease. In some instances, patients report a clear benefit by avoiding gluten from their diet and/or symptom worsening upon gluten reintroduction. This clinical entity has been termed non-celiac gluten sensitivity (NCGS). The symptoms referred by these patients are both intestinal and extra-intestinal, suggesting that similarly to functional gastrointestinal disorders, NCGS is a disorder of gut-brain interaction. It remains unclear if gluten is the only wheat component involved in NCGS. The mechanisms underlying symptom generation in NCGS remain to be fully clarified, although in the past few years, the research has significantly moved forward with new data linking NCGS to changes in gut motility, permeability and innate immunity. The diagnosis is largely based on the self-reported reaction to gluten by the patient, as there are no available biomarkers, and confirmatory double-blind challenge protocols are unfeasible in daily clinical practice. Some studies suggest that a small proportion of patients with IBS have an intolerance to gluten. However, the benefits of gluten-free or low-gluten diets in non-celiac disease-related conditions are limited, and the long-term consequences of this practice may include nutritional and gut microbiota unbalance. Here, we summarize the role of gluten in the clinical features, pathophysiology, and management of NCGS and disorders of gut-brain interaction.

Functional Bowel Disease

Functional bowel disorders refer to disorders of gut-brain interaction that affect the intestinal tract. Irritable bowel syndrome (IBS) is the most common functional bowel disorder and affects individuals regardless of age and gender. It can result in impaired quality of life and significant health care utilization and is therefore important to recognize and manage. The diagnosis of IBS is based on clinical symptoms. IBS is categorized based on predominant bowel habit (constipation, diarrhea, mixed, or unclassified), and the treatment of IBS is individually tailored based on subtype and symptom severity.

Faecal calprotectin levels after rifaximin treatment in patients with irritable bowel syndrome with diarrhoea: A single-center prospective study

BACKGROUND AND STUDY AIMS

Although unclear, the pathophysiology of irritable bowel syndrome (IBS) is considered to be multifactorial. Recent studies have suggested that IBS is a low-grade inflammatory bowel disease (IBD) with high faecal calprotectin (FC) levels. Rifaximin is a potential therapeutic agent for IBS with diarrhoea (IBS-D) due to its ability to decrease FC levels. This study evaluated the role of FC as a follow-up marker of IBS-D after short-course rifaximin treatment.

PATIENTS AND METHODS

Ninety-six patients with chronic diarrhoea who fulfilled the Rome IV criteria for IBS-D were enrolled in this study from outpatient clinics. After excluding 18 patients who did not complete the study due to treatment noncompliance or missing follow-up visits, 78 patients (mean age, 39.2 ± 6.9 years) with IBS-D and elevated baseline FC levels were included. An FC level of <50 μg/g was considered normal. Abdominal symptoms were assessed using a Likert scale. All patients received oral rifaximin (550 mg three times daily) for 2 weeks, followed by assessment for abdominal symptoms and FC levels; the treatment was extended to 4 weeks if FC levels remained elevated after 2 weeks of treatment.

RESULTS

FC levels normalised in 66 (84.6%) patients, including 60 and 6 patients treated for 2 and 4 weeks, respectively. The remaining 12 (15.4%) patients with persistently elevated FC levels despite 4 weeks of treatment also showed a significant decline in their final FC levels compared with the baseline, accompanied with a significant improvement in abdominal symptoms (p = 0.001). A cutoff baseline FC value of 148.5 μg/g could predict non-responders with 100% sensitivity and 50% specificity.

CONCLUSION

Short-course oral rifaximin treatment results in FC normalisation in IBS-D patients with high baseline FC values. Therefore, FC should be considered as a biomarker of follow-up after rifaximin treatment for IBS-D.

Short-course Rifaximin therapy efficacy and lactulose hydrogen breath test in Chinese patients with diarrhea-predominant irritable bowel syndrome

Background

Gut microbiota alterations including small intestinal bacterial overgrowth (SIBO) might play a role in pathogenesis of irritable bowel syndrome (IBS). Rifaximin could effectively and safely improve IBS symptoms. The aim of this study was to investigate the effect of rifaximin on Gastrointestinal (GI) symptoms, quality of life (QOL) and SIBO eradication in Chinese IBS-D patients.

Methods

This study included 78 IBS-D patients defined by the Rome IV criteria. Patients received 400 mg rifaximin twice daily for 2 weeks and 10-week follow-up. GI symptoms were assessed at week 0, 2, 4, 8 and 12. QOL and lactulose hydrogen breath test (LHBT) results were estimated at week 0 and 4.

Results

All participants showed significant improvements in GI symptom subdomains after rifaximin treatment (all P < 0.05), which could maintain at least 10 weeks of follow-up. Additionally, QOL scores were increased with concomitant improvement of clinical symptoms (all P < 0.05). The 45 rifaximin-responsive patients (57.7%) achieved significantly greater GI-symptom improvement than non-responders (all P < 0.05). No GI symptoms were associated with SIBO (all P > 0.05). SIBO normalization after rifaximin treatment measured by LHBT was found in 44.4% (20/45) of patients with SIBO before treatment.

Conclusion

A short course (2 weeks) of rifaximin improved GI symptoms and QOL in Chinese IBS-D patients whether they had SIBO or not. However, the efficacy of rifaximin could not be explained by the successful eradication of SIBO. Further studies on the therapeutic mechanisms of rifaximin in IBS are urgently needed.

Systemic review and network meta-analysis: Prophylactic antibiotic therapy for spontaneous bacterial peritonitis

BACKGROUND

Spontaneous bacterial peritonitis (SBP) is an important prognostic factor for outcomes in patients with cirrhosis. Antibiotic prophylaxis is recommended in patients at high risk for developing SBP, but the choice of antibiotics remains unclear.

AIM

To evaluate the efficacy of various antibiotics for prophylaxis of SBP based on randomized control trials (RCTs).

METHODS

Electronic databases were searched through November 2018 for RCTs evaluating the efficacy of therapies for primary or secondary prophylaxis of SBP. The primary outcome was the development of SBP. Sensitivity analyses limited to studies of primary or secondary prophylaxis and studies reported after 2010 were performed. The secondary outcome was the risk of all-cause mortality or transplant. The outcomes were assessed by rank of therapies based on network meta-analyses. Individual meta-analyses were also performed.

RESULTS

Thirteen RCTs (1742 patients) including norfloxacin, ciprofloxacin, rifaximin, trimethoprim-sulfamethoxazole (TMP-SMX), or placebo/no comparator were identified. Individual meta-analyses showed superiority of rifaximin over norfloxacin as well as norfloxacin and TMP-SMX over placebo. Network meta-analysis demonstrated the rank of efficacy in reducing the risk of SBP as: Rifaximin, ciprofloxacin, TMP-SMX, norfloxacin, and placebo/no comparator. Rifaximin ranked highest in sensitivity analyses limited to studies of primary or secondary prophylaxis and studies reported after 2010. Similarly, rifaximin ranked highest in reducing the risk of death/transplant.

CONCLUSION

The present comprehensive network meta-analysis provides RCT based evidence for superior efficacy of rifaximin compared to other antibiotics for the prophylaxis of SBP and reducing risk of death/transplant. Further RCTs are warranted to confirm our findings.

Duodenal and rectal mucosal microbiota related to small intestinal bacterial overgrowth in diarrhea-predominant irritable bowel syndrome

BACKGROUND AND AIM

Small intestinal bacterial overgrowth (SIBO) has been proposed as an etiologic factor in irritable bowel syndrome, particularly the diarrhea-predominant subtype (IBS-D). We aimed to identify potential intestinal microbial pattern in IBS-D patients with SIBO.

METHODS

Diarrhea-predominant irritable bowel syndrome patients fulfilling Rome III criteria were recruited and randomly divided into an exploratory cohort (57 cases) and a validation cohort (20 cases). SIBO was identified according to standard glucose hydrogen breath test. For 16S rRNA gene sequencing, samples of duodenal mucosa, duodenal fluid, rectal mucosa, and fresh feces were collected and performed. The α and β diversity, as well as differences in microbial composition and function, in SIBO⁺ and SIBO^- IBS-D subjects were evaluated.

RESULTS

The microbial diversity and composition obviously differed between SIBO⁺ and SIBO^- IBS-D in duodenal and rectal mucosa but not in duodenal fluid and fresh feces. For rectal mucosal microbiota, it displayed markedly reduced aerobe and Gram-negative bacteria and increased facultative anaerobe and Gram-positive bacteria, moreover, altered functions of microbial metabolism in SIBO⁺ IBS-D. Significantly higher rectal mucosa-related microbial dysbiosis index was observed in SIBO⁺ IBS-D, and a cut-off value at -0.37 had a sensitivity of 56.55% and specificity of 90.91% to identify the SIBO in IBS-D subjects.

CONCLUSIONS

Mucosal microbiota, rather than luminal bacteria, has a more apparent dysbiosis in SIBO⁺ IBS-D patients relative to those without SIBO. Rectal mucosa-associated microbiota may act as a potential predictor of SIBO in IBS-D patients.

Presentation and Characteristics of Abdominal Pain Vary by Irritable Bowel Syndrome Subtype: Results of a Nationwide Population-Based Study

INTRODUCTION

Abdominal pain is a cardinal feature of irritable bowel syndrome (IBS); however, differences in abdominal pain among IBS subtypes remain unknown. We aimed to characterize abdominal pain symptoms among established IBS subtypes using data from the National Gastrointestinal (GI) Survey.

METHODS

Individuals participating in the National GI Survey completed National Institutes of Health GI Patient-Reported Outcomes Measurement Information System (GI-PROMIS) questionnaires. Adults meeting modified Rome III IBS criteria and reporting abdominal pain in the previous 7 days were eligible. Outcomes included abdominal pain severity, bothersomeness, interference with daily activities, frequency, and location. Results were stratified by subtype (diarrhea [IBS-D], constipation [IBS-C], and mixed [IBS-M]). Regression models adjusted for demographics and comorbidities.

RESULTS

One thousand one hundred fifty-eight individuals (245 IBS-D, 232 IBS-C, and 681 IBS-M) with active IBS symptoms (defined as abdominal pain in the past 7 days) were included. Demographics were similar among the subtypes except for age, race/ethnicity, education, and marital status. The GI-PROMIS score was lower for IBS-D (percentile score of 68.6, SD = 25.1; P = 0.001) and IBS-M (69.1, SD = 25.1; P < 0.001) compared with IBS-C (75.5, SD = 20.7). Abdominal pain was more bothersome (P = 0.001), caused more interference with daily activities (P = 0.03), and was more frequent (P = 0.047) for individuals with IBS-C compared with individuals with IBS-D. No differences in these domains were seen between individuals with IBS-D and IBS-M. Individuals with IBS-C and IBS-M had more widespread pain compared with those with IBS-D.

DISCUSSION

In this population-based study, we found that abdominal pain characteristics differ between the IBS subtypes. Namely, individuals with IBS-C experience more bothersome, frequent, and diffuse abdominal pain compared with those with IBS-D.

Effect of cognitive behavior therapy combined with exercise intervention on the cognitive bias and coping styles of diarrhea-predominant irritable bowel syndrome patients

BACKGROUND

Irritable bowel syndrome (IBS) is a common digestive system disease with a high incidence rate and is common in women. The cause of IBS remains unclear. Some studies have shown that mental and psychological diseases are independent risk factors for IBS. At present, the treatment of IBS is mainly symptomatic treatment. Clinically, doctors also use cognitive behavioral therapy to improve patients' cognitive ability to diseases and clinical symptoms. In recent years, exercise therapy has attracted more and more attention from scholars. Improving the symptoms of IBS patients through psychosomatic treatment strategy may be a good treatment method.

AIM

To explore the effects of an intervention of cognitive behavioral therapy combined with exercise (CBT+E) on the cognitive bias and coping styles of patients with diarrhea-predominant irritable bowel syndrome (IBS-D); and to provide a theoretical reference for the management of IBS.

METHODS

Sixty IBS-D patients and thirty healthy subjects were selected. The 60 IBS-D patients were randomly divided into experimental and control groups. The experimental group was treated with the CBT+E intervention, while the control group was treated with conventional drugs without any additional intervention. The cognitive bias and coping styles of the participants were evaluated at baseline and after 6 wk, 12 wk and 24 wk using the Automatic Thoughts Questionnaire (ATQ), Dysfunctional Attitudes Scale (DAS) and Pain Coping Style Questionnaire (CSQ) instruments, and the intervention effect was analyzed using SPSS 17.0 statistical software.

RESULTS

At baseline, the scores on the various scales showed that all subjects had cognitive bias and adverse coping styles. The IBS Symptom Severity Scale (IBS-SSS) scores, ATQ total scores, DAS scores and CSQ scores of the two groups were not significantly different (P > 0.05). Compared with baseline, after 6 wk of the CBT+E intervention, there were significant differences in the ATQ scores, the dependence and total scores on the DAS, and the catastrophization, distraction and prayer scores on the CSQ (P < 0.05). After 12 wk, there were significant differences in the scores for perfectionism on the DAS and in the scores for reinterpretation, neglect and pain behavior on the CSQ in the experimental group (P < 0.05). After 24 wk, there were significant differences in the vulnerability, dependence, perfectionism, and total scores on the DAS and in the catastrophization, distraction and prayer scores on the CSQ in the experimental group (P < 0.01). The IBS-SSS scores were negatively correlated with the ATQ and DAS total scores (P < 0.05) but were positively correlated with the CSQ total score (P < 0.05).

CONCLUSION

Intervention consisting of CBT+E can correct the cognitive bias of IBS-D patients and eliminate their adverse coping conditions. CBT+E should be promoted for IBS and psychosomatic diseases.

Norfloxacin, ciprofloxacin, trimethoprim-sulfamethoxazole, and rifaximin for the prevention of spontaneous bacterial peritonitis: a network meta-analysis

For the prevention of spontaneous bacterial peritonitis (SBP) in cirrhotic patients with ascites, prophylactic antibiotics are recommended as a standard regimen. This study aimed to assess the efficacy of norfloxacin (N), ciprofloxacin (C), trimethoprim-sulfamethoxazole (T-S), and rifaximin (R) in the prevention of SBP. We searched the electronic databases including PubMed, Cochrane Library, Embase, and Web of Science from inception till 1 August 2018. The randomized-controlled trials that compared N, C, T-S, R, and placebo (P) were identified. A network meta-analysis (NMA) was carried out using the software STATA 14.0 and Revman 5.3. We included 16 studies involving 1984 participants in the NMA for SBP prevention. The NMA results showed that, compared with those treated with P (reference), patients treated with C, N, or R had a lower incidence of SBP and mortality. Similarly, the incidences of SBP and mortality for R were lower than those for N. The probabilities of ranking results showed that R ranked first with respect to the outcomes of the incidence of SBP and mortality. According to our results, R seemed to be the optimal regimen for protecting against SBP in patients with cirrhosis and ascites. However, considering the limitations of our study, additional high-quality studies are required in this respect.

Does Irritable Bowel Syndrome Exist? Identifiable and Treatable Causes of Associated Symptoms Suggest It May Not

Significant shortcomings in irritable bowel syndrome (IBS) diagnosis and treatment may arise from IBS being an “umbrella” diagnosis that clusters several underlying identifiable and treatable causes for the same symptom presentation into one classification. This view is compatible with the emerging understanding that the pathophysiology of IBS is heterogeneous with varied disease mechanisms responsible for the central pathological features. Collectively, these converging views of the pathophysiology, assessment and management of IBS render the traditional diagnosis and treatment of IBS less relevant; in fact, they suggest that IBS is not a disease entity per se and posit the question “does IBS exist?” The aim of this narrative review is to explore identifiable and treatable causes of digestive symptoms, including lifestyle, environmental and nutritional factors, as well as underlying functional imbalances, that may be misinterpreted as being IBS.

Antibiotics and the nervous system: More than just the microbes?

The use of antibiotics has recently risen to prominence in neuroscience due to their potential value in studying the microbiota-gut-brain axis. In this context they have been largely employed to illustrate the many influences of the gut microbiota on brain function and behaviour. Much of this research is bolstered by the abnormal behaviour seen in germ-free animals and other well-controlled experiments. However, this literature has largely failed to consider the neuroactive potential of antibiotics themselves, independent from, or in addition to, their microbicidal effects. This is problematic, as clinical as well as experimental literature, largely neglected through the past decade, has clearly demonstrated that broad classes of antibiotics are neuroactive or neurotoxic. This is true even for some antibiotics that are widely regarded as not absorbed in the intestinal tract, and is especially concerning when considering the highly-concentrated and widely-ranging doses that have been used. In this review we will critically survey the clinical and experimental evidence that antibiotics may influence a variety of nervous system functions, from the enteric nervous system through to the brain and resultant behaviour. We will discuss substantial evidence which clearly suggests neuro-activity or -toxicity by most classes of antibiotics. We will conclude that, while evidence for the microbiota-gut-brain axis remains strong, clinical and experimental studies which employ antibiotics to probe it must consider this potential confound.

Randomised clinical trial: pregabalin vs placebo for irritable bowel syndrome

BACKGROUND

Pregabalin is a calcium channel α2δ ligand that modifies visceral hypersensitivity in IBS patients. Clinical data for pregabalin in IBS are lacking.

AIM

To test the efficacy of pregabalin on gastrointestinal symptoms in IBS patients.

METHODS

A double-blind, placebo-controlled trial was performed. Adults meeting IBS Rome III criteria with ≥3 pain attacks per month were randomised to pregabalin 225 mg vs placebo twice daily for 12 weeks. Questionnaires were completed weekly. The primary endpoint was average pain Bowel Symptom Scale (BSS) scores weeks 9-12. An intention-to-treat analysis of covariance evaluated treatment effects on quantitative endpoints, adjusting for age and gender. Adequate relief and change in pain score were assessed using a chi-squared test.

RESULTS

Eighty-five patients were recruited and randomised. Sample characteristics include: mean age 39.4 (SD = 14.6); 73 (86%) female; 37 (44%) IBS-D, 29 (35%) IBS-M, 18 (21%) IBS-C. The pregabalin arm had lower average pain-BSS scores weeks 9-12 (25 vs 42, P = 0.008). Compared with placebo, the overall IBS BSS severity score was lower in the pregabalin arm (26 vs 42, P = 0.009). Differences were observed for the diarrhoea-BSS and bloating-BSS scores (P = 0.049 and 0.016, respectively). No differences between groups were seen for constipation-BSS scores. Adequate relief was not different between the two arms (46% vs 36%, P = 0.35). 63% pregabalin vs 45% placebo had a change in pain score ≥30 at week 12 from baseline (P = 0.10). Post-treatment IBS-QoL scores did not differ between groups.

CONCLUSION

This trial suggests that pregabalin may be beneficial for IBS abdominal pain, bloating and diarrhoea.

New concepts on intestinal microbiota and the role of the non-absorbable antibiotics with special reference to rifaximin in digestive diseases

Digestive diseases are a broad range of chronic disorders that substantially and negatively impact the patients' quality of life. Here, we review our current understanding on the pathophysiology of hepatic encephalopathy, irritable bowel syndrome, and diverticular disease, with a special focus on the gut microbiota composition associated with these disorders. Furthermore, we review the current clinical practice for their therapeutic treatments, including probiotics, diet change, non-adsorbable disaccharides, and antibiotics. We highlight that broad-spectrum non-adsorbable antibiotics, such as rifaximin, are quite effective and safe for the treatment of all essayed digestive diseases.

Fecal Microbiota Alterations Associated With Diarrhea-Predominant Irritable Bowel Syndrome

Altered gut microbiota are assumed to be involved in the pathogenesis of irritable bowel syndrome (IBS). However, gut microbiota alterations reported in different studies are divergent and sometimes even contradictory. To better elucidate the relationship between altered gut microbiota and IBS, we characterized fecal microbiota of diarrhea-predominant IBS (IBS-D) patients and further explored the effect of rifaximin on gut microbiota using bacterial 16S rRNA gene-targeted pyrosequencing. In our study, IBS-D patients defined by Rome III criteria and age-and-gender matched healthy controls (HC) were enrolled to investigate the fecal microbiota alterations. These IBS-D patients were then treated with rifaximin for 2 weeks and followed up for 10 weeks. Fecal microbiota alterations, small intestine bacterial overgrowth (SIBO) and gastrointestinal (GI) symptoms of IBS-D patients were analyzed before and after treatment. Our results showed fecal microbiota richness but not diversity was decreased in IBS-D patients as compared to HC and there were alterations of fecal microbiota at different taxonomy levels. The abundant phyla Firmicutes was significantly decreased and Bacteroidetes was increased in IBS-D patients. Moreover, the alterations of predominant fermenting bacteria such as Bacteroidales and Clostridiales might be involved in the pathophysiology of IBS-D. In addition, rifaximin was effective in terms of SIBO eradication and even GI symptoms of IBS-D patients achieved at least 10-week improvement after treatment. Furthermore, rifaximin induced alterations of some special bacteria rather than affected the overall composition of microbiota in IBS-D patients. Meanwhile, a potential decrease in propanoate and butanoate metabolism was found in these IBS-D patients after rifaximin treatment. Taken together, there were alterations of gut microbiota in IBS-D patients as compared to HC. Rifaximin could relieve GI symptoms, modify gut microbiota in IBS-D patients and eradicate SIBO in those patients with SIBO, suggesting an additional therapeutic mechanism of rifaximin in the treatment of IBS-D. Our findings of compositional gut microbiota alterations in IBS-D and the effect of rifaximin on the gut microbiota implied that altered gut microbiota were associated with the pathogenesis of IBS.

Advancements in drug development for diarrhea-predominant irritable bowel syndrome

INTRODUCTION

Diarrhea-predominant irritable bowel syndrome (IBS-D) is a common disorder characterized by a complex pathophysiology hampering optimal targeted drug development. Recent advances in our understanding of key underlying mechanisms prompted novel therapeutics including novel pharmacological approaches.

AREAS COVERED

This review summarizes the latest advancements in the pipeline of IBS-D drugs focusing on new pharmacological targets, efficacy and safety of medicinal products considering the recent harmonization of regulatory requirements by the FDA and the EMA.

EXPERT OPINION

The new 5-HT₃ receptor antagonist ramosetron appears a promising therapeutic approach devoid of significant adverse events, although it is presently unavailable in Western countries, most likely because of the precautionary approach taken by regulatory agencies with this drug class. New pharmacological concepts on full agonists/antagonists, mixed-receptor activity and novel drug targets may streamline the present drug pipeline along with the adherence on new regulatory guidelines on outcome measures. Eluxadoline can be taken as an example of this paradigm shift. It has now been granted marketing authorization for IBS-D on both sides of the Atlantic, but it is still considered as a second-line agent by the NICE. There is still much work to be done to fully cover clinical needs of patients with IBS-D.

A Review of Microbiota and Irritable Bowel Syndrome: Future in Therapies

Irritable bowel syndrome (IBS), one of the most frequent digestive disorders, is characterized by chronic and recurrent abdominal pain and altered bowel habit. The origin seems to be multifactorial and is still not well defined for the different subtypes. Genetic, epigenetic and sex-related modifications of the functioning of the nervous and immune-endocrine supersystems and regulation of brain-gut physiology and bile acid production and absorption are certainly involved. Acquired predisposition may act in conjunction with infectious, toxic, dietary and life event-related factors to enhance epithelial permeability and elicit mucosal microinflammation, immune activation and dysbiosis. Notably, strong evidence supports the role of bacterial, viral and parasitic infections in triggering IBS, and targeting microbiota seems promising in view of the positive response to microbiota-related therapies in some patients. However, the lack of highly predictive diagnostic biomarkers and the complexity and heterogeneity of IBS patients make management difficult and unsatisfactory in many cases, reducing patient health-related quality of life and increasing the sanitary burden. This article reviews specific alterations and interventions targeting the gut microbiota in IBS, including prebiotics, probiotics, synbiotics, non-absorbable antibiotics, diets, fecal transplantation and other potential future approaches useful for the diagnosis, prevention and treatment of IBS.

Beneficial effects of Rifaximin in post-infectious irritable bowel syndrome mouse model beyond gut microbiota

BACKGROUND AND AIMS

Rifaximin is a minimally absorbed antibiotic, which has shown efficacy in irritable bowel syndrome (IBS) patients. However, the mechanism on how it effects in IBS is still incompletely defined. In this study, Trichinella spiralis-infected post-infectious (PI) IBS mouse model was used, to assess the action of rifaximin on visceral hypersensitivity, barrier function, gut inflammation, and microbiota.

METHODS

Post-infectious IBS model was established by T. spiralis infection in mice. Rifaximin were administered to PI-IBS mice for seven consecutive days. The abdominal withdrawal reflex and threshold of colorectal distention were employed to evaluate visceral sensitivity. Smooth muscle contractile response was recorded in the organ bath. Intestinal permeability was measured by Ussing chamber. Expression of tight junction protein and cytokines were measured by Western blotting. Ilumina miseq platform was used to analyze bacterial 16S ribosomal RNA.

RESULTS

Post-infectious IBS mice treated with rifaximin exhibited decreased abdominal withdrawal reflex score, increased threshold, reduced contractile response, and intestinal permeability. Rifaximin also suppressed the expression of interleukin-12 and interleukin-17 and promoted the expression of the major tight junction protein occludin. Furthermore, rifaximin did not change the composition and diversity, and the study reavealed that rifaximin had a tiny effect on the relative abundance of Lactobacillus and Bifidobacterium in this PI-IBS model.

CONCLUSIONS

Rifaximin alleviated visceral hypersensitivity, recovered intestinal barrier function, and inhibited low-grade inflammation in colon and ileum of PI-IBS mouse model. Moreover, rifaximin exerts anti-inflammatory effects with only a minimal effect on the overall composition and diversity of the gut microbiota in this model.

Gut dysbiosis and irritable bowel syndrome: The potential role of probiotics

OBJECTIVE

To discuss the role of gut dysbiosis in the development of irritable bowel syndrome (IBS) and the impact of probiotics as a potential therapeutic measure.

METHODS

PubMed was used to search for all of the studies published over the last 15 years using the key words: "irritable bowel syndrome" and "gut dysbiosis" or "probiotic". More than 800 articles were found, but only those published in English or providing evidence-based data were included in the evaluation.

RESULTS

IBS is a common disease for which no resolutive therapy is presently available. In recent years, strong evidence of a possible relationship between modifications of the gut microbiota composition and development of IBS has been collected. Moreover, the evidence showed that attempts to treat acute infectious and post-antibiotic gastroenteritis with some probiotics were significantly effective in a great number of patients, leading many experts to suggest the use of probiotics to address all of the clinical problems associated with IBS.

CONCLUSION

The available data are promising, but presently, a precise definition of which probiotic or which mixture of probiotics is effective cannot be made. Moreover, the dose and duration of treatment has not been established. Finally, we do not know whether probiotic treatment should be different according to the type of IBS. Further studies are needed before probiotics can be considered a reliable treatment for IBS.

Systematic review with meta-analysis: rifaximin for the prophylaxis of spontaneous bacterial peritonitis

BACKGROUND

The primary and secondary prevention of spontaneous bacterial peritonitis (SBP) is recommended in high-risk patients with cirrhosis. Several studies evaluating the efficacy of rifaximin for SBP prophylaxis have yielded conflicting results. Rifaximin has the potential advantage of preventing bacterial overgrowth and translocation without the systemic side effects of broad-spectrum antibiotics.

AIM

To evaluate the efficacy of rifaximin in the primary and secondary prevention of SBP.

METHODS

A literature search using five databases was performed to identify studies on the association between rifaximin and SBP. We performed two meta-analyses: (1) rifaximin compared to systemic antibiotics and (2) rifaximin compared to no antibiotics. Random-effect modelling was conducted to determine overall pooled estimates and 95% confidence intervals (CIs).

RESULTS

Five studies with 555 patients (295 rifaximin, 260 systemic antibiotics) compared rifaximin with systemic antibiotics. The pooled odds ratio (OR) for SBP was 0.45 (95% CI 0.16-1.27; P = .13) in patients receiving rifaximin and strengthened on sensitivity analysis (OR 0.38, 95% CI 0.19-0.76, P = .01). In the analysis comparing rifaximin with no antibiotics, there were five studies with 784 patients (186 rifaximin, 598 no antibiotics). The OR for SBP was 0.34 (95% CI 0.11-0.99; P < .05) in patients receiving rifaximin. In subgroup analysis, rifaximin reduced the risk of SBP by 47% compared to no antibiotics for primary prophylaxis and by 74% compared to systemic antibiotics for secondary prophylaxis.

CONCLUSION

Rifaximin may be effective in preventing SBP in patients with cirrhosis and ascites compared to systemically absorbed antibiotics and compared to placebo.

Symptom Severity Following Rifaximin and the Probiotic VSL#3 in Patients with Chronic Pelvic Pain Syndrome (Due to Inflammatory Prostatitis) Plus Irritable Bowel Syndrome

This study investigated the effects of long-term treatment with rifaximin and the probiotic VSL#3 on uro-genital and gastrointestinal symptoms in patients with chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) plus diarrhoea-predominant irritable bowel syndrome (D-IBS) compared with patients with D-IBS alone. Eighty-five patients with CP/CPPS (45 with subtype IIIa and 40 with IIIb) plus D-IBS according to the Rome III criteria and an aged-matched control-group of patients with D-IBS alone (n = 75) received rifaximin and VSL#3. The primary endpoints were the response rates of IBS and CP/CPPS symptoms, assessed respectively through Irritable Bowel Syndrome Severity Scoring System (IBS-SSS) and The National Institute of Health Chronic Prostatitis Symptom Index (NIH-CPSI), and performed at the start of therapy (V0) and three months after (V3). In IIIa prostatitis patients, the total NIH-CPSI scores significantly (p < 0.05) decreased from a baseline mean value of 21.2 to 14.5 at V3 , as did all subscales, and in the IIIb the total NIH-CPSI score also significantly decreased (from 17.4 to 15.1). Patients with IBS alone showed no significant differences in NIH-CPSI score. At V3, significantly greater improvement in the IBS-SSS and responder rate were found in IIIa patients. Our results were explained through a better individual response at V3 in IIIa prostatitis of urinary and gastrointestinal symptoms, while mean leukocyte counts on expressed prostate secretion (EPS) after prostate massage significantly lowered only in IIIa cases.

The influence of rifaximin on diverticulitis rate and quality of life in patients with diverticulosis

Diverticulosis, its associated symptoms and complications are one of the most common pathologies of the gastrointestinal tract in more economically developed countries. Presence of diverticuli and their clinical consequences can be divided into four categories: 1) diverticulosis, i.e. an asymptomatic presence of diverticuli that are usually found by accident 2) symptomatic uncomplicated diverticulosis 3) diverticulitis (acute uncomplicated diverticulitis) 4) complications of diverticulitis (conditions requiring hospital stay). The aim of this study was to retrospectively analyze the efficacy of rifaximin in preventing diverticulitis in patients visiting proctology clinics. The diagnostic criterium for diverticulosis was confirmation by colonoscopy, barium enema or CT colography (virtual colonoscopy) as well as history of at least one documented episode of diverticulosis. History of diverticulosis was evaluated based on medical records, clinical symptoms, elevated level of CRP (&gt;5.0) and/or diagnostic imaging (ultrasound, CT). After setting strict exclusion criteria, 248 patients were qualified for the study out of 686, and they were later divided into two groups: control group (group I - 145 patients) and studied group (group II - 103 patients receiving rifaximin prophylaxis). Diverticulitis rate was comparable in both groups over a period of 6 months before study (p = 0.1306) and 6 months of treatment (p=0.3044). Between the 6th and 12th month of treatment, a significantly lower rate of diverticulitis was noted in the group receiving rifaximin compared to control group (p&lt;0.0001). Patients receiving rifaximin reported higher quality of life (which was assessed using the VAS scale) compared to control group after 12 months. The results confirmed the efficacy of riaximin in prevention of diverticulitis, even in the scheme of repeated courses every 3 months. Not only did application of rifaximin lower the rate of diverticulitis and its complications in patients after an episode of diverticulitis, but also it improved the patients' quality of life. It seems that diverticulitis prophylaxis based on rifaximin can be economically efficient, however, it requires further research.

Review of Rifaximin: Latest Treatment Frontier for Irritable Bowel Syndrome Mechanism of Action and Clinical Profile

Background:

Irritable bowel syndrome is classified as a functional gastrointestinal disorder with the primary symptom of abdominal pain in conjunction with bloating and bowel movement disorder. It affects up to 15% of the world’s population. Among its subtypes, the most common is diarrhoea predominant. However, the current treatment options for diarrhoea-predominant irritable bowel syndrome have had not very promising results; most, such as antispasmodics, only provide partial symptomatic relief. Treatment with antidepressants and alosetron (a 5HT3 antagonist) has shown the most promise to date. The latest drug to be approved for the treatment of irritable bowel syndrome-diarrhoea is rifaximin, which was approved in May 2015. It is a minimally absorbed antibiotic that is used to change the gut microbiota. Small intestinal bacterial overgrowth is one of the causes suggested for irritable bowel syndrome, particularly for the diarrhoea-predominant type. There are various methods for detecting bacterial overgrowth, the simplest of which is breath tests. Rifaximin has been shown to be of benefit to these patients.

Purpose:

The purpose of the study is to discuss the potential mechanism of action of rifaximin, a minimally absorbed antibiotic. In addition, we evaluate the various clinical trials undertaken to study the efficacy and safety profile of rifaximin.

INTESTINAL MICROBIOTA IN DIGESTIVE DISEASES

BACKGROUND

In recent years, especially after the development of sophisticated metagenomic studies, research on the intestinal microbiota has increased, radically transforming our knowledge about the microbiome and its association with health maintenance and disease development in humans. Increasing evidence has shown that a permanent alteration in microbiota composition or function (dysbiosis) can alter immune responses, metabolism, intestinal permeability, and digestive motility, thereby promoting a proinflammatory state. Such alterations can mainly impair the host's immune and metabolic functions, thus favoring the onset of diseases such as diabetes, obesity, digestive, neurological, autoimmune, and neoplastic diseases. This comprehensive review is a compilation of the available literature on the formation of the complex intestinal ecosystem and its impact on the incidence of diseases such as obesity, non-alcoholic steatohepatitis, irritable bowel syndrome, inflammatory bowel disease, celiac disease, and digestive neoplasms.

CONCLUSION:

Alterations in the composition and function of the gastrointestinal microbiota (dysbiosis) have a direct impact on human health and seem to have an important role in the pathogenesis of several gastrointestinal diseases, whether inflammatory, metabolic, or neoplastic ones.

Dietary and pharmacological treatment of abdominal pain in IBS

This review introduces the principles of visceral sensation and appraises the current approaches to management of visceral pain in functional GI diseases, principally IBS. These approaches include dietary measures including fibre supplementation, low fermentable oligosaccharides, disaccharides, monosaccharides and polyols diet, and pharmacological approaches such as antispasmodics, peppermint oil, antidepressants (tricyclic agents, selective serotonin reuptake inhibitors), 5-HT₃ receptor antagonists (alosetron, ondansetron, ramosetron), non-absorbed antibiotic (rifaximin), secretagogues (lubiprostone, linaclotide), μ-opioid receptor (OR) and κ-OR agonist, δ-OR antagonist (eluxadoline), histamine H1 receptor antagonist (ebastine), neurokinin-2 receptor antagonist (ibodutant) and GABAergic agents (gabapentin and pregabalin). Efficacy and safety are discussed based on pivotal trials or published systematic reviews and meta-analysis, expressing ORs or relative risks and their 95% CIs. Potential new approaches may be based on recent insights on mucosal expression of genes, and microRNA and epigenetic markers in human biopsies and in animal models of visceral hypersensitivity.The objectives of this review are to appraise the physiology and anatomy of gut sensation and the efficacy in the relief of visceral pain (typically in IBS) of several classes of therapies. These include fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs) and different classes of medications (box 1). Box 1Classes of pharmacological agents for visceral painAntidepressants (tricyclic agents, selective serotonin reuptake inhibitors)Peppermint oil5-HT₃ receptor antagonists (alosetron, ondansetron, ramosetron)Non-absorbed antibiotic (rifaximin)Secretagogues (lubiprostone, linaclotide)μ-Opioid receptor (OR) and κ-OR agonist and δ-OR antagonist (eluxadoline)Histamine H1 receptor antagonist (ebastine)Neurokinin-2 receptor antagonist (ibodutant)GABAergic agents (gabapentin and pregabalin).

Small Intestinal Bacterial Overgrowth and Other Intestinal Disorders

Gut microbiota is the largest organ of the human body. Although growth of bacteria more than 10⁵ colony forming unit (CFU) per milliliter in culture of upper gut aspirate is used to diagnosis small intestinal bacterial overgrowth (SIBO), 10³ CFU or more is being considered to suggest the diagnosis, particularly if colonic type bacteria are present in the upper gut. Although neither very sensitive nor specific, hydrogen breath tests are widely used to diagnose SIBO. Rifaximin is the best treatment for SIBO due to its broad spectrum, lack of systemic absorption, and safety profile.

PREVALENCE OF SMALL INTESTINE BACTERIAL OVERGROWTH IN PATIENTS WITH GASTROINTESTINAL SYMPTOMS

BACKGROUND

Small intestine bacterial overgrowth is a heterogeneous syndrome characterized by an increase in the number and/or the presence of atypical microbiota in the small intestine. The symptoms of small intestine bacterial overgrowth are unspecific, encompassing abdominal pain/distension, diarrhea and flatulence. Due to the increased cost and complexity for carrying out the jejunal aspirate, the gold standard for diagnosis of the syndrome, routinely the hydrogen (H 2 ) breath test has been used, utilizing glucose or lactulose as substrate, which is able to determine, in the exhaled air, the H 2 concentration produced from the intestinal bacterial metabolism. However, due to a number of individuals presenting a methanogenic microbiota, which does not produce H 2 , the testing on devices capable of detecting, concurrently, the concentration of exhaled H 2 and methane (CH 4 ) is justified.

OBJECTIVE

This study aimed to determine the prevalence of small intestine bacterial overgrowth in patients with digestive symptoms, through a comparative analysis of breath tests of H 2 or H 2 and CH 4 associated, using glucose as substrate .

METHODS

A total of 200 patients of both sexes without age limitation were evaluated, being directed to a Breath Test Laboratory for performing the H 2 test (100 patients) and of exhaled H 2 and CH 4 (100 patients) due to gastrointestinal complaints, most of them patients with gastrointestinal functional disorders.

RESULTS

The results indicated a significant prevalence of small intestine bacterial overgrowth in the H 2 test and in the test of exhaled H 2 and CH 4 (56% and 64% respectively) in patients with gastrointestinal symptoms, and higher prevalence in females. It found further that methane gas was alone responsible for positivity in 18% of patients.

CONCLUSION

The data found in this study is consistent with the findings of the current literature and underscores the need for using devices capable of capturing the two gases (exhaled H 2 and CH 4 ) to improve the sensitivity and hence the accuracy of small intestine bacterial overgrowth diagnosis in daily medical practice.

Therapeutic Modulation of Gut Microbiota in Functional Bowel Disorders

Functional bowel disorders (FBDs) are functional gastrointestinal disorders with symptoms attributable to the middle or lower gastrointestinal tract. These include irritable bowel syndrome, functional bloating, functional constipation, functional diarrhea, and unspecified FBD. Increasing evidence has emerged of late that intestinal microbiota is involved in the pathogenesis of FBDs. In this review, the therapeutic benefits and future perspectives of the currently available strategies for modifying the gut microbiota in FBDs are described, focusing primarily on irritable bowel syndrome and functional constipation.

The Role of the Gastrointestinal Microbiota in Visceral Pain

A growing body of preclinical and clinical evidence supports a relationship between the complexity and diversity of the microorganisms that inhabit our gut (human gastrointestinal microbiota) and health status. Under normal homeostatic conditions this microbial population helps maintain intestinal peristalsis, mucosal integrity, pH balance, immune priming and protection against invading pathogens. Furthermore, these microbes can influence centrally regulated emotional behaviour through mechanisms including microbially derived bioactive molecules (amino acid metabolites, short-chain fatty acids, neuropeptides and neurotransmitters), mucosal immune and enteroendocrine cell activation, as well as vagal nerve stimulation.The microbiota-gut-brain axis comprises a dynamic matrix of tissues and organs including the brain, autonomic nervous system, glands, gut, immune cells and gastrointestinal microbiota that communicate in a complex multidirectional manner to maintain homeostasis and resist perturbation to the system. Changes to the microbial environment, as a consequence of illness, stress or injury, can lead to a broad spectrum of physiological and behavioural effects locally including a decrease in gut barrier integrity, altered gut motility, inflammatory mediator release as well as nociceptive and distension receptor sensitisation. Centrally mediated events including hypothalamic-pituitary-adrenal (HPA) axis, neuroinflammatory events and neurotransmitter systems are concomitantly altered. Thus, both central and peripheral pathways associated with pain manifestation and perception are altered as a consequence of the microbiota-gut-brain axis imbalance.In this chapter the involvement of the gastrointestinal microbiota in visceral pain is reviewed. We focus on the anatomical and physiological nodes whereby microbiota may be mediating pain response, and address the potential for manipulating gastrointestinal microbiota as a therapeutic target for visceral pain.

Gastrointestinal Pharmacology

There is little evidence for most of the medications currently used to treat functional abdominal pain disorders (FAPDs) in children. Not only are there very few clinical trials, but also most have significant variability in the methods used and outcomes measured. Thus, the decision on the most appropriate pharmacological treatment is frequently based on adult studies or empirical data. In children, peppermint oil, trimebutine, and drotaverine have shown significant benefit compared with placebo, each of them in a single randomized clinical trial. A small study found that cyproheptadine was beneficial in the treatment of FAPDs in children. There are conflicting data regarding amitriptyline. While one small study found a significant benefit in quality of life compared with placebo, a large multicenter study found no benefit compared with placebo. The antidepressant, citalopram, failed to meet the primary outcomes in intention-to-treat and per-protocol analysis. Rifaximin has been shown to be efficacious in the treatment of adults with IBS. Those findings differ from studies in children where no benefit was found compared to placebo. To date, there are no placebo-controlled trials published on the use of linaclotide or lubiprostone in children. Alpha 2 delta ligands such as gabapentin and pregabalin are sometimes used in the care of this group of children, but no clinical trials are available in children with FAPDs. Similarly, novel drugs that have been approved for the care of irritable bowel with diarrhea in adults such as eluxadoline have yet to be studied in children.

CONCLUSIONS

Little data support the use of most medications commonly used to treat FAPDs in children. More randomized, placebo-controlled studies are needed to assess the efficacy of pharmacological interventions in the treatment of FAPDs in children.

Microbiome, antibiotics and irritable bowel syndrome

INTRODUCTION

Irritable bowel syndrome (IBS) is the most prevalent functional gastrointestinal (GI) disorder. Increasing evidence implicates the GI microbiota in IBS pathogenesis and its modulation represents an emerging therapeutic strategy.

SOURCES OF DATA

Original and review articles were identified through selective searches performed on PubMed and Google Scholar.

AREAS OF AGREEMENT

The role of gut microbiota in IBS is supported by evidence from animal and human studies. Randomized controlled trials demonstrate efficacy of the non-systemic antibiotic rifaximin in reducing IBS symptoms.

AREAS OF CONTROVERSY

Existing studies on microbiota alterations are often inconsistent and limited by the heterogeneity of IBS. The exact mechanism of rifaximin remains to be elucidated. Identifying predictors of response to rifaximin and treatment strategies for symptom recurrence are important clinical questions.

GROWING POINTS

High-throughput molecular methods are leading to rapid advances in our understanding of GI microbiota in IBS AREAS TIMELY FOR DEVELOPING RESEARCH: Future well designed longitudinal studies are required to identify characteristic microbial signatures and potential biomarkers to identify therapeutic targets and predict clinical response.

The Intestinal Microbiota in the Irritable Bowel Syndrome

The irritable bowel syndrome (IBS) is a chronic abdominal symptom complex occurring in a bowel devoid of discernible relevant pathology. There is growing interest in the role of the intestinal microbiota as a basis for the intestinal and possibly behavioral manifestations of this condition. Molecular-based microbial profiling has revealed compositional changes in the microbiota of at least a subset of IBS patients but the data are often conflicting and no microbial signature for this condition has yet been defined. Animal studies in which a previously stable intestinal microbiota is perturbed, by antibiotics or dietary change, results in alterations in intestinal function reminiscent of that seen in IBS patients. These include visceral sensitivity to painful stimuli, altered motility and intestinal barrier function as well as immune activation, and low-grade inflammation. More recent studies have shown that perturbation of the microbial composition of the gut alters brain chemistry and behavior. In a step toward establishing a causal link between an altar microbiota and gut-brain manifestations of IBS, colonization of germ-free mice with microbiota from IBS patients results in an IBS-like phenotype, including alterations and behavior if the donor exhibited psychiatric comorbidity, such as high levels of anxiety. This model provides an opportunity for exploring the mechanisms underlying host-microbe interactions relevant to the pathogenesis of IBS and for developing novel therapeutic targets.

Limited prolonged effects of rifaximin treatment on irritable bowel syndrome-related differences in the fecal microbiome and metabolome

Irritable bowel syndrome (IBS) is a chronic functional disorder and its development may be linked, directly and indirectly, to intestinal dysbiosis. Here we investigated the interactions between IBS symptoms and the gut microbiome, including the relation to rifaximin (1200 mg daily; 11.2 g per a treatment). We recruited 72 patients, including 31 with IBS-D (diarrhea), 11 with IBS-C (constipation), and 30 with IBS-M (mixed constipation and diarrhea) and 30 healthy controls (HCs). Of them, 68%, 64%, and 53% patients with IBS-D, IBS-C, and IBS-M, respectively, achieved 10-12 week-term improvement after the rifaximin treatment. Stool samples were collected before and after the treatment, and fecal microbiotic profiles were analyzed by deep sequencing of 16S rRNA, while stool metabolic profiles were studied by hydrogen 1-nuclear magnetic resonance ((1)H-NMR) and gas chromatography-mass spectrometry (GC-MS). Of 26 identified phyla, only Bacteroidetes, Firmicutes, Proteobacteria, and Actinobacteria were consistently found in all samples. Bacteroidetes was predominant in fecal samples from HCs and IBS-D and IBS-M subjects, whereas Firmicutes was predominant in samples from IBS-C subjects. Species richness, but not community diversity, differentiated all IBS patients from HCs. Metabolic fingerprinting, using NMR spectra, distinguished HCs from all IBS patients. Thirteen metabolites identified by GC-MS differed HCs and IBS patients. However, neither metagenomics nor metabolomics analyses identified significant differences between patients with and without improvement after treatment.

Mechanism-Oriented Therapy of Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a common and well-accepted diagnosis but often imprecisely applied to patients in usual clinical practice. Diagnosis is entirely based on symptom criteria that tend to include broad strata of abdominal complainers. Established criteria for diagnosis are strictly followed in controlled clinical trials for new therapeutic agents, but physicians are more lax in the clinic. Predictably, in light of the above ambiguities, many pathogenetic mechanisms and pathophysiological disturbances appear to be involved in IBS, but so far no mechanism-based subgroupings to guide specific therapy have been soundly established. Thus, diverse therapeutic approaches coexist and are discretionally prescribed by attending clinicians on the basis of major manifestations (i.e., diarrhea-predominance or constipation-predominance), more or less apparent psychological disturbances, and patient preferences (pharmacological versus dietary or microbiological approaches). In this review, we have attempted to update scientific knowledge about the more relevant disease mechanisms involved and relate this more fundamental basis to the various treatment options available today.

Effects of Rifaximin on Transit, Permeability, Fecal Microbiome, and Organic Acid Excretion in Irritable Bowel Syndrome

Objectives:

Rifaximin relieves irritable bowel syndrome (IBS) symptoms, bloating, abdominal pain, and loose or watery stools. Our objective was to investigate digestive functions in rifaximin-treated IBS patients.

Methods:

In a randomized, double-blind, placebo-controlled, parallel-group study, we compared the effects of rifaximin, 550 mg t.i.d., and placebo for 14 days in nonconstipated IBS and no evidence of small intestinal bacterial overgrowth (SIBO). All subjects completed baseline and on-treatment evaluation of colonic transit by scintigraphy, mucosal permeability by lactulose–mannitol excretion, and fecal microbiome, bile acids, and short chain fatty acids measured on random stool sample. Overall comparison of primary response measures between treatment groups was assessed using intention-to-treat analysis of covariance (ANCOVA, with baseline value as covariate).

Results:

There were no significant effects of treatment on bowel symptoms, small bowel or colonic permeability, or colonic transit at 24 h. Rifaximin was associated with acceleration of ascending colon emptying (14.9±2.6 h placebo; 6.9±0.9 h rifaximin; P=0.033) and overall colonic transit at 48 h (geometric center 4.0±0.3 h placebo; 4.7±0.2 h rifaximin; P=0.046); however, rifaximin did not significantly alter total fecal bile acids per g of stool or proportion of individual bile acids or acetate, propionate, or butyrate in stool. Microbiome studies showed strong associations within subjects, modest associations with time across subjects, and a small but significant association of microbial richness with treatment arm (rifaximin vs. treatment).

Conclusions:

In nonconstipated IBS without documented SIBO, rifaximin treatment is associated with acceleration of colonic transit and changes in microbial richness; the mechanism for reported symptomatic benefit requires further investigation.

Rifaximin for the treatment of irritable bowel syndrome - a drug safety evaluation

INTRODUCTION

Irritable bowel syndrome is a functional gastrointestinal disorder with a multifactorial etiology. Alterations of intestinal motility and immunity, gut-brain interactions, as well as gut microbiota dysbiosis contribute to the development of irritable bowel syndrome. Therefore, gut microbiota modulation by non-absorbable antibiotics is a therapeutic option in patients with IBS.

AREAS COVERED

Published articles including patients with irritable bowel syndrome reporting data about rifaximin activity and safety have been searched throughout the literature and selected.

EXPERT OPINION

The optimal antibiotic molecule should be local-acting, long-acting and safe-acting. Rifaximin is a non-absorbable antibiotic with additional anti-inflammatory and gut microbiota-modulating activity. It is effective in inducing symptoms relief in patients with IBS, even after repeated treatment courses. Rifaximin-related side effects in patients with IBS are reported to be mild and infrequent; microbial resistance is rare and transient, due to the high local concentration of the drug and to the absence of horizontal transmission. Clostridium difficile infection is not usual in patients receiving rifaximin in absence of predisposing conditions such as hospitalization and immunosuppression, which are uncommon in patients affected by irritable bowel syndrome. Nevertheless rifaximin is an antibiotic active against Clostridium difficile infection. Rifaximin has limited metabolic interactions and is not expected to interfere with drug metabolism in patients with normal hepatic function. These properties make rifaximin a safe antibiotic for gut microbiota modulation in patients with IBS.