Synergy between aminoglycosides and semi-synthetic penicillins against gentamicin-resistant Gram-negative rods

Abstract

Synergy was measured between three aminoglycosides, gentamicin, tobramycin and amikacin, and three semi-synthetic penicillins, carbenicillin, azlocillin and mezlocillin, against strains of 138 gentamicin resistant Gram-negative rods. A distinction was made between in vitro synergy and what is possibly ‘useful synergy’ as judged by attainable serum levels. Potentially useful synergy was found between gentamicin and carbenicillin for Pseudomonas aeruginosa (71% of strains), Proteus spp. (63%), Providencia spp. (39%), Acinetobacter spp. (38%) and Alcaligenes spp. (25%). Aziodillin and gentamicin showed marked synergistic action against P. aeruginosa. No relationship was observed between the degree of hydrolysis of the three penicillins by beta-lactamases in P. aeruginosa and Klebsiella aerogenes and the antibacterial effect on them by the penicillin/aminoglycoside combinations.