title: Postantibiotic effect in Pseudomonas aeruginosa following single and multiple aminoglycoside exposures in vitro.
abstract: The effect of single and multiple 2-h aminoglycoside exposures on the duration of the postantibiotic effect (PAE) and bacterial killing were investigated using a reference strain (ATCC 27853) and four clinical isolates of Pseudomonas aeruginosa. Concentration-dependent PAE and bacterial killing were demonstrated following single exposures to amikacin, gentamicin or tobramycin. Cultures were also repeatedly exposed to peak aminoglycoside concentration simulating traditional (three times a day) and once daily dosing regimens. Aminoglycoside re-exposures every 8 h at the original culture MIC produced significant, successive reductions in PAE (P < 0.05) and bacterial killing (P < 0.01) coincident with increases in culture MICs. Identical experiments re-exposing cultures to their predetermined, induced MICs demonstrated similar to significantly longer PAEs (P < 0.05) than those observed following first exposure. Multiple gentamicin or tobramycin exposures at 8 mg/L (traditional peak) every 8 h or 24 mg/L (once daily peak) once every 24 h both showed significant reductions in PAE (P < 0.05) and bacterial killing (P < 0.05) on repeated dosing. However, the once-daily high peak concentration exposure demonstrated significantly longer PAEs and greater bacterial killing both initially and upon re-exposure compared with the 8-hourly exposure. In addition, the once daily dosing regimen maintained substantially larger aminoglycoside concentration/MIC ratios. We conclude that multiple exposure of P. aeruginosa in-vitro, to aminoglycosides at the intervals tested, reduces the PAE and bacterial killing and increases the MICs.
authors.affiliation: Department of Medical Microbiology, University of Manitoba, Winnipeg, Canada.
authors.forename: J A
authors.initials: JA
authors.lastname: Karlowsky
authors.forename: G G
authors.initials: GG
authors.lastname: Zhanel
authors.forename: R J
authors.initials: RJ
authors.lastname: Davidson
authors.forename: D J
authors.initials: DJ
authors.lastname: Hoban
mesh_terms: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003470:Culture Media; D008826:Microbial Sensitivity Tests; D011550:Pseudomonas aeruginosa / Q000187:drug effects*
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D003470:Culture Media