Laurie Barclay, MD Medscape News
November 6, 2008 — Probiotics are microorganisms that may be helpful for conditions such as antibiotic-associated diarrhea, infectious diarrhea, irritable bowel syndrome, and atopic dermatitis in at-risk infants, according to a review published in the November 1 issue of American Family Physician.
"Probiotics are live microorganisms that benefit the health of the host when administered in adequate amounts," write Benjamin Kligler, MD, MPH, from Albert Einstein College of Medicine of Yeshiva University, and Andreas Cohrssen, MD, from the Beth Israel Residency Program in Urban Family Practice, both in New York, New York. "Several mechanisms have been proposed to explain the actions of probiotics. In most cases, it is likely that more than one mechanism is at work simultaneously."
Because of these multiple mechanisms of action, many different probiotics have potential applications to various diseases. Those in most widespread use, which have undergone the most clinical testing, include Lactobacillus species (such as L acidophilus, L rhamnosus, L bulgaricus, L reuteri, and L casei); Bifidobacterium species; and Saccharomyces boulardii, which is a nonpathogenic yeast.
Efficacy of a probiotic species taken orally requires that it be resistant to acid and bile so that it can pass through the upper gastrointestinal tract without loss of biological potency. However, even the hardiest microorganisms must be administered regularly to maintain colonization and typically can no longer be cultured from stool samples more than 1 to 2 weeks after ingestion of the probiotic.
Probiotics are considered to be both safe and effective for preventing and treating antibiotic-associated diarrhea and infectious diarrhea. The probable mechanism of action may be a combination of direct competition between pathogenic bacteria in the gut and immune modulation and enhancement.
Other specific applications supported to some degree by available studies include relief of gastrointestinal tract symptoms in irritable bowel syndrome and therapy for pediatric atopic dermatitis.
Although probiotics are sometimes used for other conditions, evidence is lacking to support these indications, and they were therefore not discussed in this review. These conditions include vaginal candidiasis, stomach infection with Helicobacter pylori, inflammatory bowel disease, and upper respiratory tract infections.
On the basis of dosages used in clinical studies documenting efficacy, frequently used dosages range from 5 to 10 billion colony-forming units per day for children and from 10 to 20 billion colony-forming units per day for adults, although these vary based on the specific microorganism or combination used. In most studies, the dosages of S boulardii range from 250 to 500 mg/day.
Probiotics have no reported drug interactions. Common adverse effects are mild and self-limited, including flatulence and mild abdominal discomfort. Septicemia and other severe adverse effects may rarely occur, and these have only been reported in severely ill or immunocompromised hosts or in children with short-gut syndrome. Therefore, probiotics should be used only with caution in patients with short-gut syndrome, and they are contraindicated in patients with conditions that severely compromise the immune system.
Available formulations of probiotics include capsules, powder, tablets, liquid, or incorporated into food.