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Guide Attribution

This guide is a derivative of the Introduction to Evidence-Based Practice tutorial by Duke University Medical Center Library and the Health Sciences Library at the University of North Carolina at Chapel Hill. It is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International LicenseCC BY-NC-SA

Practice Case 1: The case for probiotics

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ASSESS the patient

Start with the patient -- a clinical problem or question arises from the care of the patient


Ms. MP is an 86 year old highly-functional resident of Croasdaile who presents to the emergency room after a fall in her home.  Workup identifies a right femur fracture.  The orthopaedic surgeon recommends urgent repair and perioperative antibiotics.  Ms. MP, who with her husband operated a health food store for 40 years, has spent her life avoiding medications and using natural remedies.  Her husband mentions concern over the possibility of diarrhea as a side effect of the antibiotics and asks if using fermented milk with lactobacillus or some other probiotic product would prevent this side effect. Should she start taking a form of probiotic to prevent this problem?

ASK the question

Choose the BEST clinical question:

What is the best treatment for diarrhea?

In patients taking antibiotics, are probiotics helpful in preventing diarrhea?

Do probiotics prevent diarrhea in the elderly hospitalized patient?


ACQUIRE the evidence

Choose the best PubMed search strategy to address the clinical question.

Search: diarrhea AND best treatment Limited to Free Full Text

Search: diarrhea AND probiotics AND elderly AND female AND adult  Limited to English 

Search: antibiotics AND diarrhea AND probiotics   Limited to randomized controlled trial


APPRAISE the evidence

Read the following article and determine if it meets the validity criteria.  (Click on title to access free full text)

Beausoleil M. Effect of a fermented milk combining Lactobacillus acidophilus Cl1285 and Lactobacillus casei in the prevention of antibiotic-associated diarrhea: a randomized, double-blind, placebo-controlled trial. Can J Gastroenterol. 2007 Nov;21(11):732-6. PMCID: PMC2658588 PMID: 18026577


BACKGROUND: Antibiotic-associated diarrhea is an important problem in hospitalized patients. The use of probiotics is gaining interest in the scientific community as a potential measure to prevent this complication. The main objective of the present study was to assess the efficacy and safety of a fermented milk combining Lactobacillus acidophilus and Lactobacillus casei that is widely available in Canada, in the prevention of antibiotic-associated diarrhea. METHODS: In this double-blind, randomized study, hospitalized patients were randomly assigned to receive either a lactobacilli-fermented milk or a placebo on a daily basis.
RESULTS: Among 89 randomized patients, antibiotic-associated diarrhea occurred in seven of 44 patients (15.9%) in the lactobacilli group and in 16 of 45 patients (35.6%) in the placebo group (OR 0.34, 95% CI 0.125 to 0.944; P=0.05). The median hospitalization duration was eight days in the lactobacilli group, compared with 10 days in the placebo group (P=0.09). Overall, the lactobacilli-fermented milk was well tolerated. CONCLUSION: The daily administration of a lactobacilli-fermented milk was safe and effective in the prevention of antibiotic-associated diarrhea in hospitalized patients.

Are the results valid?

You will need to read the methodology section of the article to address the validity questions. Evaluating the medical literature is a complex undertaking. You will find that the answers to the questions of validity may not always be clearly stated in the article and that you may have to use your own judgment about the importance and significance of each question.

Randomization: Were patients randomized?

Concealed allocation: Was group allocation concealed?

Baseline characteristics: Were patients in the study groups similar with respect to known prognostic variables?

Blinding: To what extent was the study blinded?

Follow-up: Was follow-up complete?

Intention to Treat: Were patients analyzed in the groups to which they were first allocated?

Equal treatment: Aside from the experimental intervention, were the groups treated equally?

What are the results & how can I apply them to patient care?

Results:  Among 89 randomized patients, antibiotic-associated diarrhea occurred in seven of 44 patients (15.9%) in the lactobacilli group and in 16 of 45 patients (35.6%) in the placebo group (OR 0.34, 95% CI 0.125 to 0.944; P=0.05). The median hospitalization duration was eight days in the lactobacilli group, compared with 10 days in the placebo group (P=0.09). Overall, the lactobacilli-fermented milk was well tolerated.


Outcome Present

ADD occurrence

Outcome NOT present

ADD no occurrence

lactobacilli group 7 37
placebo group 16 29

Experimental (lactobacilli)  Event Rate = 7 / 44 = 15.9%

Control (placebo) Event Rate = 16 / 45 =  35.5%

Absolute Risk Reduction = 35.5% - 15.9% = 19.6%

Relative Risk reduction = 19.6% / 35.5% = 53.5%

Number Needed-to-Treat = 1/ 19.6% = 5

The results of Beausoleil and colleagues are consistent with those of a recent systematic review showing that probiotics reduce the frequency of antibiotic-associated diarrhea and accelerate resolution of C. difficile–associated colitis. The study was underpowered to demonstrate an effect on more clinically important outcomes. The intervention is simple, rational, and presumably relatively inexpensive. Thus, it could be reasoned that it should be implemented more widely without further study. On the other hand, there have been isolated reports of systemic infection with organisms used as probiotics. Moreover, in light of the potential importance of minimizing the adverse effects of systemic antibiotics in hospitalized patients, further studies should be powered to probe the effects of probiotics on rates of acquisition of nosocomial infections (with both typical nosocomial pathogens and the probiotic itself) and on clinically important outcomes, such as length of stay and nutritional status. In addition, further work to determine which microbial species exert optimal probiotic effects will aid in defining a role for probiotics in routine clinical practice.  [ACP Journal Club 15 July 2008 - Volume 149, Number 1)


Questions to consider before applying the results of a study to your patient:

  • Were the study patients similar to my population of interest?
  • Does your patient match the study inclusion criteria? If not, are there compelling reasons why the results should not apply to your patient?
  • Were all clinically important outcomes considered?
  • Are the likely treatment benefits worth the potential harm and costs?

APPLY: talk with the patient

Return to the patient -- integrate that evidence with clinical expertise, patient preferences and apply it to practice


Think about your patient, her goals, your treatment recommendation for her, the cost and adverse effects of probiotics, and help her decide whether to start taking the probiotics.



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