The assessment of antimicrobial combinations.

The traditional approach to the study of the interaction between antimicrobial agents relies on the assumption that inhibition of growth by antimicrobial agents follows a linear dose-response curve. Because this assumption is invalid, we propose that antimicrobial combinations should be assessed by empiric dose-response curves that would distinguish synergistic, additive, and antagonistic effects on the rate of cell growth. This approach predicts synergy for the model combination of trimethoprim and sulfamethoxazole and should also be applicable to other combinations of antimicrobial agents nd to combinations of antitumor agents.