ABSTRACT
The use of combinations of antimicrobial agents is a common practice during clinical therapy. There are several reasons why combination therapy is used or should be used, but all have the intention of increasing efficacy. Although one of the major reasons is the supposedly synergistic action between two antimicrobial agents, it is not always clear whether certain classes of antimicrobial agents can or do act synergistically in vivo. Indeed, in two recent meta-analyses, no significant difference in outcome was found between patients who received combination therapy and those who received monotherapy (1,2), except for perhaps infections caused by Pseudomonas aeruginosa. One of the reasons that no significant difference in outcome was found between the groups receiving monotherapy and combination therapy might have been diversity of patients and indications in the trials studied, and the finding that there is no difference between the groups a result of the relative low power of the analysis. If combination therapy is advantageous in certain settings and not in others, the ability to predict that synergistic effects exist would help to make a rational choice.
