Journal of Antimicrobial Chemotherapy, Vol 42, 61-65, Copyright © 1998 by The British Society for Antimicrobial Chemotherapy
ZY Zhu and RC Li
The postantibiotic effect (PAE) exhibited by Pseudomonas aeruginosa after
exposure to single doses of tobramycin was investigated under various
pharmacokinetic conditions using an established in-vitro kinetic model. At
equal doses of the antibiotic stimulating an intravenous bolus condition,
the effects of varying elimination half- life on PAE were assessed. The PAE
was longer when the rate of antibiotic elimination was lower. However,
after correcting for the different degrees of antibiotic exposure using the
area under the concentration-time curve above the MIC (AUC > MIC), a
coherent PAE versus antibiotic exposure profile was obtained. The effects
of increasing tobramycin dose and exposure time on PAE were investigated in
another series of experiments; PAE was assessed during antibiotic exposure
when the exponentially decreasing concentrations were above the MIC, at the
MIC and below the MIC. A longer PAE was achieved at higher doses and
changes were dependent on both the degree and time of exposure. For all the
doses tested, the PAE was longest when the decreasing antibiotic
concentrations were near or at the MIC. Shorter PAEs were detected at
sub-MIC concentrations and diminished rapidly as antibiotic concentrations
continued to decline. Such a decrease in PAE was counteracted by the longer
exposure time, so that the total time for which the organism was under the
influence of the antimicrobial effects, i.e. the sum of exposure time and
PAE, remained steady at sub- MIC concentrations. Under these simulated
pharmacokinetic conditions, present data support a substantial impact of
pharmacokinetics on PAE. Along with MIC, AUC > MIC can be a useful
pharmacokinetic parameter for PAE assessments. Should PAE be a relevant
factor in antibiotic chemotherapy, both time and degree of antibiotic
exposure would have to be considered.
ORIGINAL ARTICLES
Impact of pharmacokinetics on the postantibiotic effect exhibited by Pseudomonas aeruginosa following tobramycin exposure: application of an in-vitro model
Department of Pharmacy, Faculty of Medicine, Chinese University of Hong Kong, Shatin.
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