Clinical significance of
pharmacokinetic/pharmacodynamic modeling (Cont’d)

The pharmacodynamic models can be very useful in predicting the change in drug effect relative to the change in drug conc.

When the drug conc is much higher than the EC50, the drug effect will be near the maximum effect. The drug conc may change several folds with little change in drug effect.

Emax

1

2E max
EC50
Assume that the drug conc-effect
relationship is described by the
Emax pharmacodynarnic model.
Emax

1

2E max
EC50
Assume that the drug conc-effect
relationship is described by the
Emax pharmacodynarnic model.

When the drug conc is in the range of EC50, small change in drug conc will result in a significant change in drug effect.

Also, the dosing regimens that achieve average drug conc in the range of EC50 will produce significant changes in the drug effec during the dosing interval. However, when the average conc is much higher than the EC50, minor changes in the effect will be observed during the dosing interval.

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