Nancy Toedter Williams


Am J Health Syst Pharm. 2010;67(6):449-458. 

In This Article

Abstract and Introduction


Purpose. The pharmacology, uses, dosages, safety, drug interactions, and contraindications of probiotics are reviewed.
Summary. Probiotics are live nonpathogenic microorganisms administered to improve microbial balance, particularly in the gastrointestinal tract. They consist of Saccharomyces boulardii yeast or lactic acid bacteria, such as Lactobacillus and Bifidobacterium species, and are regulated as dietary supplements and foods. Probiotics exert their beneficial effects through various mechanisms, including lowering intestinal pH, decreasing colonization and invasion by pathogenic organisms, and modifying the host immune response. Probiotic benefits associated with one species or strain do not necessarily hold true for others. The strongest evidence for the clinical effectiveness of probiotics has been in the treatment of acute diarrhea, most commonly due to rotavirus, and pouchitis. More research is needed to clarify the role of probiotics for preventing antibiotic-associated diarrhea, Clostridium difficile infection, travelers' diarrhea, irritable bowel syndrome, ulcerative colitis, Crohn's disease, and vulvovaginal candidiasis. There is no consensus about the minimum number of microorganisms that must be ingested to obtain a beneficial effect; however, a probiotic should typically contain several billion microorganisms to increase the chance that adequate gut colonization will occur. Probiotics are generally considered safe and well tolerated, with bloating and flatulence occurring most frequently. They should be used cautiously in patients who are critically ill or severely immunocompromised or those with central venous catheters since systemic infections may rarely occur. Bacteria-derived probiotics should be separated from antibiotics by at least two hours.
Conclusion. Probiotics have demonstrated efficacy in preventing and treating various medical conditions, particularly those involving the gastrointestinal tract. Data supporting their role in other conditions are often conflicting.


In recent years, both research and consumer interest in probiotics have grown. Increasing clinical evidence supports some of the proposed health benefits related to the use of probiotics, particularly in managing certain diarrheal diseases. Probiotics are defined as "live microorganisms which when administered in adequate amounts confer a health benefit on the host."[1] The term probiotic was initially used in the 1960s and comes from a Greek word meaning "for life." Although a relatively new word, the beneficial effects of certain foods containing live bacteria have been recognized for centuries. However, it was not until the early 20th century that investigators suggested gut flora could be altered with beneficial bacteria replacing harmful microbes, leading to the concept of probiotics.[2–4]

Probiotics, which are regulated as dietary supplements and foods, consist of yeast or bacteria. They are available as capsules, tablets, packets, or powders and are contained in various fermented foods, most commonly yogurt or dairy drinks. Probiotic products may contain a single microorganism or a mixture of several species. Table 1 lists common microorganisms used as probiotics. The most widely used probiotics include lactic acid bacteria, specifically Lactobacillus and Bifidobacterium species. The yeast Saccharomyces boulardii also appears to have health benefits. It is noteworthy that probiotic effects tend to be specific to a particular strain, so a health benefit attributed to one strain is not necessarily applicable to another strain, even within one species. Therefore, generalizations about potential health benefits should not be made.[2,5,6,8,9]

The rationale for using probiotics involves restoring microbial balance. More than 500 different bacterial species reside in the adult gastrointestinal tract.[6,8] Some microbes are considered beneficial to the human host, while others are pathogenic. An appropriate balance of gut flora is generally maintained; however, antibiotics, immunosuppressive medications, surgery, and irradiation can cause an increase in the pathogenic bacteria and disrupt this homeostasis. Probiotics, which contain beneficial bacteria and yeast, may restore the microbial balance in the gastrointestinal tract.[5–7]

In order for probiotics to be successful, they must possess certain characteristics. Probiotic organisms must be able to withstand passage through the gastrointestinal tract (i.e., survive acid and bile degradation), colonize and reproduce in the gut, attach and adhere to the intestinal epithelium, and stabilize the balance of the gut flora. Furthermore, probiotic strains must be safe and effective in humans, remain viable for the shelf life of the product, and not have pathogenic properties.[2,9–11] Products containing more than one organism are particularly appealing for two reasons: colonization in some patients may occur with one strain and not another, and probiotic mixtures may be synergistic in suppressing pathogens.


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