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Antimicrobial Agents and Chemotherapy, July 1998, p. 1731-1737, Vol. 42, No. 7
ADCAPT,
Received 24 January 1997/Returned for modification 20 June
1997/Accepted 3 May 1998
Various suggestions have been made for empirical pharmacodynamic
indices of antibiotic effectiveness, such as areas under the drug
concentration-time curve in serum (AUC), AUC>MIC, AUC/MIC, area under
the inhibitory curve (AUIC), AUC above MIC, and time above MIC
(T>MIC). In addition, bacterial growth and killing models, such as the Zhi model, have been developed. The goal of the present study was to compare the empirical behavior of the Zhi model of bacterial growth and killing with the other empirical pharmacodynamic indices described above by using simulated clinical data analyzed with
the USC*PACK PC clinical programs for adaptive control of drug therapy,
with one model describing a concentration-dependent antibiotic
(tobramycin) and another describing a concentration-independent antibiotic (ticarcillin). The computed relative number of CFU was
plotted against each pharmacodynamic index, with each axis parameterized over time. We assumed that a good pharmacodynamic index
should present a clear and continuous relationship between the time
course of its values and the time course of the bacterial killing as
seen with the Zhi model. Preliminary work showed that some
pharmacodynamic indices were very similar. A good sensitivity to the
change in the values of the MIC was shown for AUC/MIC and also for
T>MIC. In addition, the time courses of some other
pharmacodynamic indices were very similar. Since AUC/MIC is easily
calculated and shows more sensitivity, it appeared to be the best of
the indices mentioned above for the concentration-dependent drug, because it incorporated and used the MIC the best. T>MIC
appeared to be the best index for a concentration-independent drug. We also propose a new composite index, weighted AUC (WAUC), which appears
to be useful for both concentration-dependent and
concentration-independent drugs.
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Comparisons between Antimicrobial Pharmacodynamic
Indices and Bacterial Killing as Described by Using the Zhi
Model
*
Corresponding author. Mailing address: ADCAPT, Service
Pharmaceutique, Hôpital Antoine Charial, 40 avenue de la Table de Pierre, 69340 Francheville, France. Phone: (33) 04-72-32-34-87. Fax:
(33) 04-72-32-39-08. E-mail:
adcapt{at}cismsum.univ-lyon1.fr.
Antimicrobial Agents and Chemotherapy, July 1998, p. 1731-1737, Vol. 42, No. 7
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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