Probiotics as medical therapies

I am disappointed that the editors of CMAJ published a misleading and biased research letter on the “underuse of probiotics.”1 I believe that there is some biological plausibility to the potential effectiveness of probiotics as therapies for certain medical conditions.2 However, each of these agents must be tested and assessed in proper trials. In fact, I recently completed a study of the effectiveness of Lactobacillus rhamnosus GG in preventing Clostridium difficile-associated diarrhea (CDAD).

Lindsey Edmunds is incorrect in stating that antibiotic-related diarrhea can sometimes “cause pseudomembranous colitis.” Pseudomembranous colitis (or CDAD) is not caused by diarrhea. It is one type of antibiotic-associated diarrhea, accounting for approximately 40% of diarrhea in patients in hospital who are receiving antibiotics.

More importantly, her assertion that “probiotics … beneficially affect humans by altering their intestinal microbial balance” is unsubstantiated, yet she states it as fact. The mechanisms by which probiotics exert their effects are largely unknown.3 Describing the benefits of probiotics as if they were a single agent is similar to lumping all antihypertensive drugs together as a single drug type and saying that they are beneficial. In fact, even closely related probiotics, such as similar Lactobacillus species, have displayed varying effects when tested in humans.4 In addition, some “natural” probiotic products have been shown to contain only dead bacteria (owing to improper manufacturing or storage) or to have bacterial contents other than those stated on the label.2^,5 An authoritative review of probiotics recognized that the “definition of the pharmacodynamic profiles and viability of organisms in many commercially produced probiotic preparations are lacking.”2

I applaud Edmunds' use of a questionnaire to survey physicians' attitudes concerning probiotics. However, the author's assertion that all probiotics are beneficial but underutilized is a biased notion that is inappropriate as a starting point for a study of this type. The research letter should have been entitled “Attitudes of family physicians about probiotic use,” to avoid the assertion in the author's own title that underuse is bad. Such assertions only add to the myths surrounding such therapies, making it more difficult to test and develop the individual probiotics that would truly benefit humans.