Effects of Subinhibitory Concentrations of Moxifloxacin in anIn-VitroDynamic Model

The postantibiotic effect (PAE), sub-MIC effect (SME) and postantibiotic sub-MIC effect (PASME) of moxifloxacin were investigated in an in-vitro dynamic model reproducing in-vivo elimination kinetics of the antibiotic. The PAE was induced by exposing strains of Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli and Klebsiella pneumoniae to 5 x MIC of the antibiotic for 1.5 hours. After induction, cultures were washed to eliminate the antibiotic and resuspended into the dynamic model either in the presence or absence of a subinhibitory concentration of the antibacterial agent of 0.5 x MIC. Unexposed controls were treated similarly. PASMEs were constantly longer than corresponding SMEs, but differences between them were not statistically significant. Both PASMEs (mean 11:17 hours, range from 8:17 to 14:57) and SMEs (mean 9:23 hours, range from 6:03 to 12:34) had an initial bactericidal effect and were significantly longer than PAEs (mean 1:31 hours, range from 0:21 to 2:14). The primary effect of moxifloxacin sub-MICs appears to be prevalent in PAE. The possibility of once-daily dosing of the drug is strengthened.