A randomized open label pilot study evaluating the efficacy of two dosing regimens of rifamycin SV MMX in the treatment of small intestinal bacterial overgrowth

Abstract

Antibiotics have demonstrated efficacy in the eradication of the underlying overgrowth bacteria and improvement of symptoms of small intestinal bacterial overgrowth (SIBO). The use of standard antibiotics may cause intolerable side effects such as development of multidrug-resistant enteric bacteria, Clostridioides difficile infections and dysbiosis. Nonabsorbable antibiotics have the advantage of minimized side effects. Rifaximin, an antibiotic of the ansamycin class has been shown to be effective in the treatment of SIBO. We evaluated the use of another ansamycin antibiotic, rifamycin SV MMX (AEMCOLO) in the treatment of SIBO. One difference from rifaximin is the site of delivery of AEMCOLO which appears to be the distal small intestine and colon. Hence by maintaining the microbial milieu of the proximal small intestine, the clearance of the overgrowth bacteria might be enhanced. The side effect profile of Rifamycin SV MMX has been described elsewhere in the pivotal trials; there were no safety signals noted in this study. This randomized open label pilot study evaluated the efficacy of two dosing regimens of AEMCOLO in treating SIBO. We used a simple randomization method to assign participants into study groups. The participants included 31 patients, split between two treatment arms: one receiving the medication twice daily and the other - three times daily. The outcomes were assessed based on symptom improvement and breath test normalization. The results indicated a beneficial response with both dosing regimens leading to symptom improvement and breath test normalization. Further evaluation revealed that in the three-time daily regimen, greater symptomatic improvement was observed. For clinicians treating SIBO, this study suggests that AEMCOLO is a viable treatment option. A double-blind, placebo-controlled design will probably be necessary to ascertain the true efficacy of different dosing regimens of AEMCOLO in treating SIBO.

Trial registration

This study was registered on ClinicialTrials.gov; clinical trial registration number: NCT04501380. Date of registration: July 28, 2020.

Background

SIBO is defined as the presence of excessive bacteria in the small intestine [1]. SIBO is frequently implicated as a cause of otherwise unexplained chronic gastrointestinal symptoms. The small intestine aims to prevent overgrowth and maintain stable levels of intestinal bacteria via homeostatic processes including mechanisms of gastrointestinal motility including the migrating motor complex and the phase III interdigestive waves. When this is interrupted, SIBO can develop [2]. The four main mechanisms that can lead to SIBO include: gut dysmotility (possibly related to post-infectious irritable bowel syndrome [PI_IBS] [3]), anatomical changes (small intestine with stagnation) altered gastrointestinal secretions (gastrocolic or colo-enteric fistulas), and impaired gut immunity (IgA deficiency, combined variable immunodeficiency, fibromyalgia, and celiac disease) [3]. Once SIBO is present, bacterial overgrowth may induce an inflammatory response in the intestinal mucosa or permanent changes in small bowel motility further exacerbating symptoms [4]. Typical symptoms of SIBO include flatulence, abdominal distention, abdominal pain/cramping, diarrhea, and/or constipation [1].

The prevalence of SIBO may be underrecognized because of the need for diagnostic testing. Noninvasive breath tests are now more accessible to the public and can be collected in the comfort of the patient’s home versus aspiration collection by upper endoscopy. The use of breath tests has improved our ability to diagnose SIBO and underscore our recognition that SIBO may be associated with irritable bowel syndrome or PI-IBS. Breath tests determine whether bacterial overgrowth is hydrogen or methane predominant, a factor that often correlates with the type of symptoms present [4]. Hydrogen predominant SIBO typically presents with diarrhea, whereas methane predominant SIBO is usually associated with constipation and abdominal bloating and distention [5].

The treatment options for SIBO include the treatment of any underlying associated illness as well as the use of certain antibiotics [6]. Unfortunately, treatment of SIBO by modifying risk factors or underlying disease states is usually not effective once SIBO has developed. Previous studies have shown that antibiotics have been found to be helpful in eradicating excess bacteria and ameliorating symptoms. However, the use of systemic antibiotics may be associated with unacceptable side effects such as tendinopathies, development of Clostridium difficile infections, acquisition of multidrug-resistant enteric bacteria and disruption of the gut microbiome.

Rifamycin SV MMX is a member of the ansamycin class of broad-spectrum antibiotics, is nonabsorbable, and has activity in the distal small bowel and colon [7]. Rifamycin SV MMX mechanism of action inhibits the beta subunit of the bacterial DNA dependent RNA polymerase blocking one of the steps to DNA transcription. The formulation of rifamycin SV MMX features a multimatrix (MMX) delivery system designed facilitate the release of high concentrations of the active drug homogenously distributed throughout the distal small intestine and entire colonic segments, including the distal colonic tract, which previously was the most difficult to facilitate absorption when given orally [8]. This ensures that the active drug plays a therapeutic role where targeted, minimizing both systemic absorption of the drug, and decreasing exposure to the proximal upper GI tract. Another member of the ansamycin class of antibiotics, rifaximin, a drug with a similar chemical structure and spectrum of activity, has been shown to be effective in the treatment of SIBO [9]. Although the site of delivery of AEMCOLO is different (distal small intestine and colon), there might be reason to believe that by maintaining the saprophytic bacteria in the small intestine the microbial milieu might favor clearance of the overgrowth bacteria [6]. It is important to acknowledge the minimum inhibitory concentration (MIC) of the antimicrobial agents active in the GI tract and their ability to achieve high concentrations against pathogens while also treating a wide range of microorganisms responsible for gastrointestinal disease is important.

Our goal was to evaluate the effectiveness of a novel antibiotic, rifamycin SV MMX, in the treatment of SIBO. The primary objective of this randomized open-label pilot study was to evaluate the clinical efficacy of two dosing regimens for the treatment of SIBO comparing twice daily versus three times daily. The primary outcome was to assess this objective via normalization of an abnormal breath test (hydrogen and/or methane) and improvement in gastrointestinal symptoms.

Methods

The trial design for this study was a parallel group trial design and a 1:1 allocation ratio. Participants were selected through a screening interview process. All participants were recruited and enrolled at the New York Center for Travel and Tropical Medicine, and outpatient facility, where all data was collected and analyzed. All participants were provided with a screening questionnaire to determine their eligibility for the study. The inclusion criteria for the selection of participants were as follows: ages 18–70 years, symptoms compatible with SIBO, and one positive breath test (either hydrogen predominant, methane predominant, or both mixed gases). The exclusion criteria comprised: ages < 18 years old or > 70 years old, history of diabetes mellitus, diarrhea predominant irritable bowel syndrome (IBS-D), symptomatic bowel obstruction, diverticulitis and/or adhesions, an autoimmune disorder, immunosuppression by medication or disease, pregnant or breastfeeding, or the use of antibiotics, probiotics, or prebiotics in the last 30 days, known hypersensitivity to rifamycin or any other rifamycin class antimicrobial agents (e.g. rifaximin), or any of the components of AEMCOLO. We focused on patients with symptoms of abdominal pain/bloating, gas, and constipation and excluded those with diarrhea as the differential diagnosis of chronic diarrhea (enteric infections, inflammatory bowel disease, disaccharidase deficiency, pancreatic insufficiency, etc.) was felt to be beyond the scope of the study inclusion criteria testing. Participant recruitment and data collection occurred in the Principal Investigator’s medical office, The New York Center for Travel and Tropical Medicine as well as via telemedicine visits.

After an eligibility screening questionnaire and visual analog scale for visit 1 (VAS1) symptom questionnaire (Table 1) were completed, patients were instructed on the method for completing the breath test with lactulose substrate [10]. All patients followed a specific diet and fasted for 12 h before the test, avoiding complex carbohydrates, fermentable foods, and other substances that could interfere with the results. The measurements used to measure the presence or absence of hydrogen and methane to detect SIBO were as follows: a rise of ≥ 20 p.p.m. from baseline in hydrogen by 90 min or a level of ≥ 10 p.p.m. for methane was considered a positive test for SIBO by breath test. When both hydrogen and methane were combined in the breath test, a rise of ≥ 15 p.p.m. from baseline at 90 min was considered a positive test for SIBO. These parameters were measured at study entry and after taking the study medication. If the breath test was positive for SIBO either by a rise in hydrogen of greater than or equal to 20 ppm from baseline at 90 min, or if methane was present at greater than 10 ppm at 90 min, patients were then randomized to one of two treatment arms: arm A (rifamycin 194 mg two tablets 2 times/day) or arm B (194 mg two tablets 3 times/day). At the second visit, patients were provided instructions for a second breath test to be completed one month following completion of the study medication. On visit three, one month after the second breath test and completion of the medication and another VAS symptom questionnaire (VAS3) was completed.

Table 1 Symptom questionnaire

The primary outcome measure was to assess the change in an abnormal breath test following the AEMCOLO regimen. A hydrogen and methane breath test were used to measure the presence or absence of SIBO.

The secondary outcome measure was to evaluate the change in clinical symptoms followed by a regimen of AEMCOLO. The symptoms were assessed by a validated visual analog scale (VAS) questionnaire and the responses were assessed using a Likert scale from 0 to 5: 0-not bothered, 1 - rarely bothered, 2 - occasionally bothered, 3 - frequently bothered, 4 - very frequently bothered. A symptom questionnaire was also distributed as a daily diary to participants during their treatment and posttreatment for a period of two months solely to minimize recall bias but was not part of the evaluation. The results of the survey were evaluated at the third visit (posttreatment).

Fifty potential participants were withdrawn and did not complete the study. The causes for withdrawal included: loss to follow-up, initial breath test results were negative, failure to complete study procedures and ineligibility. Thirty-one eligible patients were randomized to one of two dosing regimens: 16 patients received rifamycin SV MMX 194 mg two tablets to take twice daily for 14 days (56 tablets), and 15 patients received rifamycin SV MMX 194 mg two tablets three times daily for 14 days (84 tablets). This pilot open label randomized control trial was nonblinded. No placebo agents were used for this study.

In the 31 study participants, we assessed the following variables: symptomatic improvement, breath test normalization, and the distribution of these outcomes across the two treatment arms (A and B). For randomized sequence generation, participants were distributed using a randomizer software, and a simple randomization technique was utilized by simulating flipping a coin.

All participants were issued a breath test in the beginning of the study before initiation of treatment, and after they completed a randomly assigned AEMCOLO treatment regimen. Symptomatic Improvement (Sx) was recorded as Y = Yes, > 50% Symptomatic Improvement, N = No, < 50% Improvement. Breath Test (BT) Improvement was recorded as N for No (< 50%) or Y for Yes (> 50%) with the corresponding gas (hydrogen = H, methane = M) (Table 2).

Table 2 Baseline data and participant flow

The qualitative data related to patient symptoms was assessed on a 0–4 scale to generate a maximum score of 20 and a minimum score of 0. A composite score (CS) calculated from the main SIBO symptoms including abdominal pain/discomfort, bloating/distention, flatulence, belching/burping, and constipation was assessed on a 0–4 scale to generate a score of 0–20. The percentage improvement in the CS was compared between the two treatment arms of AEMCOLO. A positive clinical response defined as a 50% reduction in CS was assessed between the two treatment arms. This method of analysis closely followed the multinational consensus recommended guidelines for data analysis in IBS clinical studies.

The research team provided support to the study as collaborators, generated the random allocation sequence, assisted in the enrollment of the participants, and assigned the participants to the interventions. The period of recruitment began on June 30, 2020, and the study ended on January 12, 2023.

Results

Symptom improvement comparison between arm A and arm B

A comparative analysis was conducted to compare the individual symptom improvement reported between the pre and postintervention data available from the VAS symptom questionnaire between the two treatment arms (A and B) which was recorded prior to the initiation of rifamycin via VAS 1 and one month later via VAS 3. Those who received rifamycin three times a day in Arm B had an approximate 66.7% improvement in overall symptoms versus an approximate 25% improvement in Arm A receiving rifamycin twice daily (Fig. 1). This showed that there was a 41.7% difference in improvement between Arm B versus Arm A.

Fig. 1

Pre-Post Treatment Comparison of Symptoms. Visual Analog Scale (VAS) score for Arm A vs. Arm B. VAS 1 (Pre) and VAS 3 (Post 1 month treatment). Scores were added for an overall score out of a possible 60 points. Based on those in Arm B there was a 66.7% improvement in overall symptoms vs. a 25% improvement in Arm A showing a 41.7% difference of improvement between Arm B vs. Arm A

Statistical significance

To determine the statistical significance of the differences observed between the two treatment arms, we conducted a hypothesis test given the proportions calculated for symptomatic improvement [11]. A paired sample t-test and power calculation were conducted to determine if there was statistical significance between the two arms and the symptoms reported by patients via the VAS symptom questionnaire administered prior to the initiation of rifamycin and repeated one month afterwards. The t-test resulted in a degree of freedom (df) of 30 and p-value of < 0.01 (Table 3). This p-value indicated that there is statistical significance between the two treatment arms (A and B) on either side of the t-test distribution. The power calculation analysis equaled 0.807, meaning there is an ≥ 80% chance of finding a statistically significant difference when one exists (Table 4). Therefore, based on this analysis, we can reject the null hypothesis.

Table 3 Paired sample T-Test results

Table 4 Power calculation analysis

Clinical improvement

The proportion of outcomes related to the participants experiencing symptomatic improvement across both treatment arms was approximately 45.2% (Fig. 2). The proportion of participants with normalized breath test results was approximately 58.1%. In treatment arm A (twice daily dosing), approximately 25% of the participants experienced both symptomatic improvement and normalization of the breath test. In treatment arm B (three times daily dosing), approximately 53.3% of the participants experienced both symptomatic improvement and normalization of the breath test. These results suggest that the three times daily dosing regimen (Arm B) was associated with a greater proportion of participants experiencing both symptomatic improvement and normalization of the breath test compared to the twice daily dosing regimen (Arm A). This per-protocol analysis provides an overview of the efficacy of the two dosing regimens of rifamycin SV MMX in the treatment of SIBO, indicating a potential preference for the more frequent dosing schedule in terms of clinical outcomes.

Fig. 2

Proportions of Outcomes in SIBO Treatment Study. Both treatment arms (Arms A &B) experienced symptomatic improvement of 45.2%. Both arms also experienced breath test normalizations (Greater than 50% improvement in Hydrogen, Methane, or both) of 58.1%. Arm A (twice daily dosing), 25% of participants experienced both symptomatic improvement and normalization of the breath test. In treatment arm B (three times daily dosing), 53.3% of participants experienced both symptomatic improvement and normalization of the breath test. These results suggest three times daily dosing regimen (Arm B) was associated with a 28% increase in participants experiencing both symptomatic improvement and breath test normalization compared to the twice daily dosing regimen

Discussion

This pilot study evaluated the efficacy of two dosing regimens of rifamycin SV MMX in treating small intestinal bacterial overgrowth (SIBO). All the participants included 31 patients, split between two treatment arms: one receiving the medication twice daily and the other three times daily. The outcomes were assessed based on symptom improvement and breath test normalization. The results indicated an overall beneficial response, with both dosing regimens leading to symptom improvement and breath test normalization. Further evaluation revealed that a three-time daily regimen showed a greater improvement in breath test normalization (Arm B = 53.3%) over those that received rifamycin SV MMX twice daily (Arm A = 25%) and a reported symptomatic improvement between pre-treatment (VAS 1) and one-month post treatment (VAS 3) of 66.7% in Arm B versus a 25% improvement in Arm A.

The internal validity of the study was challenged due to sample attrition, with 50 potential participants who did not complete the study. The causes for withdrawal included ineligibility, loss to follow-up, initial negative breath test results, and failure to complete study procedures. Given the pilot nature of the study and the relatively small sample size, further research with larger sample sizes and possibly a double-blind, placebo-controlled design is needed to ascertain the efficacy of different dosing regimens of rifamycin SV MMX in treating SIBO. Additionally, exploring the long-term outcomes of treatment, including the recurrence rates of SIBO and the impact on quality of life, would be valuable.

A limitation of this study is the small number of patients enrolled, and the exclusion of patients with diarrhea. Our rationale was that by focusing on patients with symptoms of abdominal pain/bloating, gas, or constipation and excluding those with diarrhea we eliminated the lengthy differential diagnosis of chronic diarrhea which may include enteric infections, inflammatory bowel disease, disaccharidase deficiency, pancreatic insufficiency, etc., which we felt was beyond the scope of the study inclusion criteria testing. This might have eliminated some patients who might have been positive for SIBO on breath testing but did not affect the results of this study.

In addition, our understanding of SIBO and its treatment has become much more nuanced since the beginning of the study. For example, we now know that rather than testing for hydrogen and methane alone, testing for hydrogen sulfide by hydrogen lactulose breath testing increases the ability to diagnose SIBO when it results in the production of this gas. In addition to nonabsorbable antibiotics, the use of adjunctive pharmacotherapies such as neomycin and metronidazole and/or bismuth compounds may be necessary to eradicate overgrowth bacteria, especially in cases of methane-predominant SIBO.

Conclusion

For clinicians treating SIBO, this study suggests that rifamycin SV MMX may be a viable treatment option. This study demonstrated that rifamycin SV MMX, administered in either of the two dosing regimens, can lead to symptomatic improvement and normalization of breath test results in some patients with small intestinal bacterial overgrowth (SIBO). These findings suggest the potential efficacy of this medication in treating this condition. Compared with the two-day dosing regimen (Arm A), the three-day dosing regimen (Arm B) resulted in a greater proportion of participants experiencing both symptomatic improvement and normalization of the breath test results, suggesting that more frequent dosing may suggest better outcomes. Overall, this study contributes to the growing body of evidence on the treatment of SIBO and highlights the need for continued research to optimize treatment strategies for this condition.