[Combination antibacterial effects between aztreonam and eight other antibiotics]

In vitro interactions between aztreonam (AZT) and 8 other antibiotics were studied using the agar dilution checkerboard technique against 88 clinical isolates of Escherichia coli, Proteus vulgaris, Serratia marcescens and Pseudomonas aeruginosa. Combinations of AZT with 8 other antibiotics were generally additive or indifferent. Synergism was occasionally seen against S. marcescens or P. aeruginosa with AZT plus isepamicin (ISP). Antagonism was observed only between AZT and latamoxef against P. vulgaris. In a phase-contrast microscopic study, synergistic effects between AZT and aspoxicillin or ISP were confirmed against E. coli 177 and P. aeruginosa 15846. AZT in combination with ISP demonstrated a synergy against experimental urinary tract infection in mice caused by P. aeruginosa 15846. We believe that combinations of several antibiotics with AZT should be considered for initial therapy of infections because synergism and additive action were observed and antagonism was rarely found in our study.