Interactions of antimicrobial agents and antineoplastic agents.

The in-vitro interactions of four antimicrobial agents (piperacillin, dibekacin, minocycline, norfloxacin) and four antineoplastic agents (mitomycin C, bleomycin, doxorubicin, 5-fluorouracil) were examined by the chequerboard dilution method using 108 clinical isolates of four species of Gram-negative bacilli. Among the antimicrobial agents, piperacillin showed the greatest degree of synergism and norfloxacin the least. The frequency of synergism was essentially similar among the antineoplastic agents, although 5-fluorouracil was more frequently synergistic than other antineoplastic agents against Pseudomonas aeruginosa. Among the four species, synergism was most frequently shown against Proteus vulgaris and least against Escherichia coli. Antagonism was rarely seen.