AUC(0-t)/MIC is a continuous index of fluoroquinolone exposure and predictive of antibacterial response for Streptococcus pneumoniae in an in vitro infection model.
OBJECTIVE
To conduct a comprehensive pharmacodynamic analysis of moxifloxacin and levofloxacin against Streptococcus pneumoniae in an in vitro infection model.


METHODS
In dose escalation studies, single doses with peak concentrations equivalent to 1 x, 2 x, 4 x, 8 x, 16 x and 32 x MIC against two isolates of S. pneumoniae were studied over 24 h. Traditional pharmacodynamic indices, including peak concentration divided by MIC (peak/MIC), time of concentration above MIC (T > MIC) and AUC24/MIC, were estimated for all regimens. As a continuous index of fluoroquinolone exposure, AUC0-t/MIC was also calculated, as AUC from time 0 to 1, 2 and 6 h divided by MIC. Correlations between pharmacodynamic indices and antibacterial effects were examined using linear and non-linear methods. In validation experiments, the pharmacodynamic model was used to predict bacterial kill curves, produced by simulated clinical doses of moxifloxacin and levofloxacin against two other S. pneumoniae isolates.


RESULTS
Peak/MIC was most predictive of early bacterial kill, whereas T > MIC was significantly associated with final bacterial counts at 24 h. Antibacterial effects were bacteriostatic when T > MIC was 48% and bactericidal when values exceeded 55%. AUC0-t/MIC was strongly associated with bacterial kill throughout the dosing interval. Bactericidal activity and bacterial eradication were associated with AUC0-t/MICs of 28 and 135, respectively. AUC0-t/MIC was also highly predictive of bacterial kill curves produced by simulated clinical doses of moxifloxacin and levofloxacin (precision 0.36 log10 cfu/mL, bias 0.02 log10 cfu/mL).


CONCLUSIONS
This study demonstrated the novel application of AUC0-t/MIC as a continuous index of antibiotic activity, and provided extensive characterization of fluoroquinolone pharmacodynamics against S. pneumoniae.
Zelenitsky
Sheryl A
SA
Faculty of Pharmacy, University of Manitoba, Winnipeg, Canada. zelenits@ms.umanitoba.ca
Ariano
Robert E
RE
Iacovides
Harris
H
Sun
Siyao
S
Harding
Godfrey K M
GK
D000890:Anti-Infective Agents / Q000493:pharmacokinetics* / Q000494:pharmacology* / Q000627:therapeutic use; D019540:Area Under Curve; D001372:Aza Compounds / Q000493:pharmacokinetics / Q000494:pharmacology; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial; D024841:Fluoroquinolones; D064704:Levofloxacin; D008826:Microbial Sensitivity Tests; D008954:Models, Biological; D000077266:Moxifloxacin; D015242:Ofloxacin / Q000493:pharmacokinetics / Q000494:pharmacology; D011008:Pneumococcal Infections / Q000188:drug therapy / Q000382:microbiology*; D011237:Predictive Value of Tests; D011804:Quinolines / Q000493:pharmacokinetics / Q000494:pharmacology; D013296:Streptococcus pneumoniae / Q000187:drug effects*
D000890:Anti-Infective Agents; D001372:Aza Compounds; D003470:Culture Media; D024841:Fluoroquinolones; D011804:Quinolines; D064704:Levofloxacin; D015242:Ofloxacin; D000077266:Moxifloxacin