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Evolving Issues in the Diagnosis, Evaluation, and Management of Irritable Bowel Syndrome
MedWatch forms showed that the rate of ischemic colitis was extremely high prevalence of SIBO in IBS patients.
19
As a natural consequence of
low (1.1 per 1,000 patient-years), and no patients with ischemic colitis this, antibiotics are now being evaluated as possible treatments for IBS.
had long-term sequelae.
16
Cilansetron is another 5HT-3 receptor Rifaximin has generated significant interest because it has low systemic
antagonist that has been shown to have similar efficacy in both men and absorption (<0.4%). A recent study evaluated the efficacy of rifaximin in
women with IBS-D. In April 2005 cilansetron was reviewed by the FDA men and women who met Rome I criteria for IBS.
20
Patients were
but was not approved, and further clinical trials were requested. randomized to either placebo or rifaximin 400mg orally three times daily
for 10 days and then followed for a total of 10 weeks. Patients
Probiotics randomized to rifaximin had an overall improvement in symptoms
Probiotics are defined as organisms that, when administered in adequate compared with placebo (p=0.020). Bloating was also better in the
amounts, exert a positive influence on the health of the host animal. While rifaximin group (p=0.01).
the precise therapeutic mechanism is unknown, it is theorized that
probiotics may ameliorate IBS symptoms by stimulating an immune Scores for abdominal pain, diarrhea, and constipation were no different
response, reducing inflammation, or altering the composition of gut flora. between the two treatment groups. This widely publicized study should
Although frequently used by IBS patients, objective data supporting their be interpreted with caution for a number of reasons, however. First, the
efficacy are limited. A preliminary report noted that Bifidobacterium rifaximin group had a higher level of pain at baseline. Second, subject
infantis improved some IBS symptoms, although the sample size was small recruitment may have been biased. Third, the end-point for analysis was
(n=75).
17
A recent study evaluated the efficacy of B. infantis in a large not typical for that used in IBS trials, and a treatment responder was not
group (n=362, all subtypes included) of IBS patients.
18
Women between the defined a priori. Finally, the authors did not report the results of the
ages of 18 and 65 years who met Rome II criteria were included. Subjects breath hydrogen tests that were performed in all of these patients.
were randomized in a blinded fashion to placebo or one of three daily
doses of B. infantis for the four-week trial period: 1x10
6
colony-forming Other research groups have not been able to replicate the high
units (CFUs), 1 x10
8
CFUs, or 1x10
10
CFUs. The primary efficacy end-point prevalence rates of SIBO in IBS patients reported by these authors. A
was daily abdominal pain and discomfort; secondary end-points included retrospective chart review was performed at the Mayo Clinic of all
individual symptoms of bloating, straining, bowel dysfunction, and patients who had a duodenal aspirate and culture over a one-year
incomplete evacuation. B. infantis, at a dose of 1x10
8
CFUs, improved period.
21
One hundred and fifty-one patients met the criteria for IBS after
abdominal pain and discomfort significantly more than placebo (p=0.023), a comprehensive chart review. Abnormal aspirate counts were present in
although the other two doses were not better than placebo. Analysis of 6% of those patients with IBS and in 11% of those with complaints of
secondary symptoms (bloating, passage of gas, straining, bowel bloating. The authors concluded that patients with IBS were not more
satisfaction, and feelings of incomplete evacuation) demonstrated that likely to suffer from SIBO. Using the lactulose breath test, the test most
B. infantis at 1x10
8
CFUs daily was significantly better than placebo commonly used by clinicians to evaluate a patient for SIBO, Bratten and
(p values all <0.05), although doses of 1x10
6
and 1x10
10
were not better colleagues also found that IBS patients were no more likely than healthy
than placebo. Of note, no dose was associated with a significant change volunteers to have SIBO.
22
Thus, the relationship between SIBO and IBS
in stool frequency. Adverse events were few in number and no different remains unclear and requires further study.
between B. infantis and placebo. Post hoc analysis found that the high-
dose capsules (1x10
10
) coagulated, thus preventing adequate release Conclusions
of the bacterium. In summary, this well-designed multicenter study IBS is a highly prevalent gastrointestinal motility disorder that is being
is the largest to date to evaluate the safety and efficacy of a probiotic for actively studied. In the last five years, new imaging techniques such as
the treatment of IBS. Further studies are needed to better define the PET scans have provided important information on the brain–gut axis.
mechanism of action of probiotics and to identify which IBS patients might Furthermore, several new therapies are now available to treat IBS and
respond with the greatest efficacy. many of them target the serotonin system, which plays a critical role in
normal gut pathophysiology. While novel research investigating the
Bacterial Overgrowth and Irritable Bowel Syndrome relationship between IBS and the gut flora is emerging, the role of
The role of small intestine bacterial overgrowth (SIBO) in the antibiotics and probiotics in the treatment of IBS remains controversial
pathogenesis of IBS remains controversial. Several studies have shown a and requires further investigation. ■
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US GASTROENTEROLOGY 71
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