Combination of mezlocillin and azlocillin with cephalosporin antibiotics: cefoxitin, cefoperazone, cefotaxime and moxalactam

Combination antibiotic therapy of two β -lactam agents has been used more frequently in view of the enlarged antibacterial spectrum of both penicillins and cephalosporins. The combination of these two classes could result in synergy, no effect or antagonism, depending upon the type of agents combined and their effect on binding proteins or β -lactamases. These studies were an attempt to evaluate the effect of combination of azlocillin or mezlocillin with cefoxitin, cefotaxime, cefoperazone, and moxalactam. The organisms studied were Escherichia coli, Klebsiella pnewnoniae, Enterobacter cloacae, Ent. aerogenes, Ent. agglomerans, Morganella, Proteus rettgeri, Pr. vulgaris, Citrobacter freundii, Pseudomonas aeruginosa . and Staphylococcus aureus for a total of 100 isolates. The combination of aziocillin and cefotaxime, cefoperazone and moxalactam rarely showed antagonism or complete synergy. However, combination of cefoxitin and azlocillin showed antagonism for some Citro. freundii, Ent. cloacae and Ps . aeruginosa strains with increase in the azlocillin MIC. For mezlocillin and cefotaxime, cefoperazone and moxalactam there was no antagonism. The mezlocillin MIC was increased for Citro. freundii and Enterobacter when cefoxitin was combined with mezlocillin. Significant antagonism was demonstrated in a few strains.