The drug conc-time profile at the site of action determines the drug effect-time profile. It is usually not possible to measure the drug conc at the site of action.
When the drug at the site of action is in rapid equilibrium with the drug in plasma, the drug plasma conc can be used instead of the drug conc at the site of action.
In this case, the drug plasma conc and the observed effect can be used to choose the appropriate pharmacodynamic model that describes the drug conc-effect relationship.
The pharmacodynamic model parameters can be estimated by fitting the plasma conc and the observed effect to the mathematical equation for the model. These parameters can be used to predict the expected drug effect at a given drug plasma conc.
