Giving probiotics to patients at risk of developing Clostridium difficile infection close to the time at which they received the first dose of their antibiotic reduces the risk of infection by more than 50% in hospital patients, according to a systematic review and meta-regression analysis. An analysis of 6,261 patients found:

• Pooled relative risk of Clostridium difficile infection in probiotic users was 1.6%, compared to 3.9% in controls, and meta-regression analysis concluded that starting the probiotics sooner rather than later was more effective.
• Every day that the supplements were delayed resulted in a decrease in efficacy. For example, giving the probiotics within 2 days of the initiation of antibiotic therapy produced a greater reduction in risk of an infection (RR, 0.32) while later administration was associated with relative risk of 0.70.