THE INTRODUCTION of a number of clinically effective antibiotics within the past few years has inevitably led to their use in combination, in the hope either of obtaining a higher percentage of favorable responses or of shortening the time necessary to eradicate the infection. Laboratory experiments have shown that combinations of antibiotics in vitro may give four types of results, namely, synergistic, additive, antagonistic, or indifferent.
The evidence for the synergistic action of certain antibiotics both in vitro and in vivo is well established. Combinations of the so-called bactericidal antibiotics, i. e., penicillin, bacitracin, and streptomycin, in doses individually far from adequate may produce an antibacterial effect greatly in excess of what could be expected on a purely additive basis. Eagle and co-workers1 have shown that penicillin and bacitracin in vivo as well as in vitro have a remarkable synergistic action on the spirochete of rabbit syphilis. It