antibioticsbooks

chapter 4 Pharmacodynamics 39
with the time above the MIC but with the ratio
of the peak concentration of the drug to the MIC
(concentration-dependent or time- independent
activity). For some antibiotics, the best predictor
of activity is the ratio of the area under
the concentration–time curve to the MIC.
Figure 4–2 illustrates these pharmacokinetic/
pharmacodynamic (PK/PD) parameters schematically,
and Table 4–2 shows which parameter is
most predictive of efficacy for antibiotic classes.
The practical implications of these findings are
in the design of antibiotic dosing schedules: aminoglycosides
are now frequently given as a single
large dose daily to leverage the concentrationdependent
activity, while some clinicians are
administering beta-lactam drugs such as ceftazidime
as continuous or prolonged infusions because
of their time- dependent activity. As target values
for these parameters that predict efficacy are
found, there may be an increase in the individualization
of dosing of antibiotics to achieve these
target values.
Concentration
Peak: MIC
AUC
MIC
Time > MIC
Time
Figure 4–2
Pharmacokinetic/Pharmacodynamic Relationships