The Emax block represents an Emax or a sigmoidal Emax model, where the output is the effect level as a function of drug concentration. The baseline effect level (E0) is always zero.
The Emax block contains five input nodes and one output node.
The input nodes are made available depending on the options that are selected in the Structure tab. If an input node cannot be used, it is marked with an X.
The input nodes on the Emax block can be connected to output nodes on PK compartments, observation blocks, PD blocks, and parameter blocks.
Once an output node is connected its name cannot be changed.
Insert an Emax block by selecting Insert > PD > Emax from the right-click menu.
With the Emax block. selected, enter a name for the Emax block in the Emax field, or use the default.
Check the Baseline box if the model has a baseline response.
Selecting Baseline adds a new parameter, “first”, which has the default value E0 and is the baseline response. The Fractional checkbox is also made available.
Check the Fractional box if the Emax model is fractional.
Selecting Fractional modifies the E0 equation statement.
Check the Inhibitory checkbox if the Emax model is inhibitory.
The structural parameters EC50 and Emax change to IC50 (concentration producing 50% of maximal inhibition) and E0 (baseline effect).
Check the Sigmoid checkbox if the Emax model is sigmoidal.
A new parameter, Gam, which is a shape parameter, is added.
In each parameter field, accept the default names or type new names for each parameter.
Each parameter corresponds to an input node on the Emax block. Possible Emax parameters include:
C: Drug concentration in plasma, or another input variable.
EC50: Input level that achieves 50% of predicted maximum effect in an Emax model.
IC50: Input level required to produce 50% of the maximal inhibition.
first (E0): Baseline effect.
EMax: Maximum drug effect.
IMax: Maximum drug inhibition (requires that both Baseline and Inhibitory checkboxes be checked).
Gam: Shape parameter.