Applied Evidence

What you must know before you recommend a probiotic

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Evidence for using probiotics for diarrhea and other GI ailments is mixed. This article—with an at-a-glance guide—summarizes when it's worth considering.


 

References

PRACTICE RECOMMENDATIONS

› Consider probiotics for patients with acute infectious diarrhea, antibiotic-associated diarrhea, or Clostridium difficile-associated diarrhea. A
› Do not recommend probiotics for preventing or treating Crohn’s disease or ulcerative colitis. B
› Consider the probiotic Bifidobacterium bifidum MIMBb75 for patients with irritable bowel syndrome. B

Strength of recommendation (SOR)

A Good-quality patient-oriented evidence
B Inconsistent or limited-quality patient-oriented evidence
C Consensus, usual practice, opinion, disease-oriented evidence, case series

Probiotics—live micoorganisms that are consumed as supplements or food for purported health benefits—are a popular over-the-counter remedy for various gastrointestinal (GI) ailments and other conditions, but the evidence supporting their use is mixed. Probiotics interact with the normal flora of the human body. They are believed to act by multiple mechanisms to deliver beneficial effects, including providing a protective barrier, altering intestinal pH to favor the growth of nonpathogenic bacteria, enhancing the host’s immunologic response, producing antimicrobial substances, and directly competing with pathogenic bacteria for receptors in the GI tract.1 (See “The normal human intestinal flora.”)

In the United States, Lactobacillus and Bifidobacterium are the probiotic genera that are most commonly used. (For a list of the specific probiotic species found in 5 popular products, see TABLE 1.2-6) The review that follows examines the evidence for using probiotics for select GI ailments, including several types of diarrheal illnesses, inflammatory bowel disease (Crohn’s disease and ulcerative colitis), and irritable bowel syndrome (IBS). These findings are summarized in TABLE 2.1,7-21

The normal human intestinal flora

The human body contains approximately 1014 prokaryotic organisms, with a biomass of >1 kg. Most of these organisms are indigenous and stable, although transient members such as enteric pathogens can be found.

The gastrointestinal tract is sterile at birth but is colonized immediately, and each individual has marked variations in microbial composition. The complex symbiotic relationship between the normal intestinal flora and the human host is beneficial to both. These microbes utilize complex carbohydrates undigested by the host as energy. Fermentation results in the formation of short-chain fatty acids, which can provide up to 15% of human energy requirements.

In addition to these metabolic benefits, microbial flora dampen the human inflammatory response, induce immunosuppressive T cells (Tregs), and competitively exclude pathogens.

Colonic epithelium is nourished and proliferates in the presence of normal intestinal flora. Disruption of the normal flora can cause disease.

SOURCE: Neish AS. Microbes in gastrointestinal health and disease. Gastroenterology. 2009;136:65-80.

Probiotics may help with some types of diarrhea

Acute infectious diarrhea. Viruses, bacteria, and parasites cause acute infectious diarrhea, and probiotics are thought to act against these pathogens by competing for available nutrients and pattern recognition receptors in the GI endothelium, acidifying the local environment, and increasing immune responses within the GI tract. In a meta-analysis of 63 studies (N=8014) that used multiple strains and dosages of probiotics, investigators found probiotics shortened the duration of acute infectious diarrhea by approximately 24 hours (95% confidence interval [CI], 15.9-33.6 hours).7 Probiotics also reduced both the risk of diarrhea lasting longer than 4 days (relative risk [RR]=0.41; 95% CI, 0.32-0.53) and stool frequency on Day 2 of illness (mean difference of 0.80 stools; 95% CI, 0.45-1.14).

Traveler’s diarrhea. The incidence of traveler’s diarrhea is >50% when traveling to high-risk areas such as the Middle East, North Africa, Latin America, and Southeast Asia, and 5% to 10% when traveling to areas such as North America, Northern Europe, the United Kingdom, Australia, and New Zealand.8 Traveler’s diarrhea may be caused by ingesting food and liquids contaminated with fecal material. Symptoms include diarrhea, cramps, and nausea that if untreated typically last from 2 to 6 days but can last for as long as a month.8

In a meta-analysis of 12 studies (N=5171) that evaluated various probiotic strains, researchers found probiotics effectively prevented traveler’s diarrhea in US and European travelers who visited a variety of vacation spots (pooled RR=0.85; 95% CI, 0.79-0.91).8 No serious adverse events were reported.

Radiation-induced diarrhea. Radiation treatments to the abdomen and pelvis can damage the lower GI tract and cause diarrhea. The pooled results from a meta-analysis that included 6 studies (N=1449) significantly favored the use of probiotics over placebo for decreasing the incidence of radiation-induced diarrhea (odds ratio [OR]=0.44; 95% CI, 0.21-0.92).9 Probiotics use also was associated with decreased loperamide use (OR=0.29; 95% CI, 0.01-6.80) and decreased incidence of watery stools (OR=0.36; 95% CI, 0.05-2.81), but these outcomes did not reach statistical significance.

Antibiotic-associated diarrhea. Antibiotic use has long been associated with the development of diarrheal illness, sometimes due to the acceleration of GI motility (eg, erythromycin) or by causing osmotic diarrhea by decreasing GI bacteria that assist in carbohydrate breakdown.11 A meta-analysis that evaluated 63 randomized controlled trials (RCTs) (N=11,811) showed that probiotics are effective for treating and preventing antibiotic-associated diarrhea (AAD).1 There was a statistically significant reduction in AAD among patients who received probiotics (RR=0.58; 95% CI, 0.50-0.68; number needed to treat [NNT]=13). Most of the studies in this meta-analysis used a Lactobacillus probiotic alone or in combination with another probiotic. Researchers did not analyze whether the efficacy varied by patient population, probiotic used, causative antibiotic, or duration of treatment.1

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