Combination antimicrobial therapy for bacterial infections. Guidelines for the clinician.

Therapy with antimicrobial combinations has been used as long as antimicrobials have been available. Combinations of antibiotics are often used to take advantage of different mechanisms of action and/or toxicity profiles. Well established indications for combination antimicrobial therapy include: (a) empirical treatment of life-threatening infections; (b) treatment of polymicrobial infections; (c) prevention of the emergence of bacterial resistance; and (d) for synergism. Disadvantages of combination therapy include: (a) increased expense; (b) increased risk of adverse effects; (c) antagonism; and (d) superinfection. Combination antimicrobial therapy should be considered for the treatment of serious Gram-negative infections caused by Enterobacter cloacae, Pseudomonas aeruginosa and Serratia marcescens, and certain Gram-positive infections caused by Enterococcus spp. and Staphylococcus spp. Selection of agents should be dependent upon local susceptibility patterns, clinical experience, site of infection, potential toxicities and cost.