Postantibiotic effect of aminoglycosides on gram-negative bacteria evaluated by a new method.

The in-vitro postantibiotic effect (PAE) of amikacin, gentamicin, netilmicin and tobramycin was investigated by a bioluminescent assay of bacterial ATP. Two strains each of Escherichia coli and Pseudomonas aeruginosa were exposed for 1 h to different concentrations of the aminoglycosides. The aminoglycoside was removed by a 10(-3) dilution, and regrowth of bacteria was followed at hourly intervals by monitoring bacterial ATP. This method simplified the PAE studies and made such studies possible at high aminoglycoside concentrations. The length of the PAE was dose-dependent for all the aminoglycosides studied. The PAEs ranged between three and seven hours for all four strains at the aminoglycoside concentrations normally reached in serum during standard dosing. The long PAE of aminoglycosides, especially after exposure to high drug concentrations, constitutes an argument in favour of administering aminoglycosides in higher-than-usual doses with longer intervals between doses. This proposal is also supported by recent pharmacokinetic, bacteriological and toxicity data.