Peripheral compartment options
Peripheral compartments can be connected to other PK compartments, including central and elimination compartments, by using a PK flow. If there is only one central compartment, the volumes of the peripheral compartments are determined by their surrounding constraints, or flow parameters.
Click 
in the Model toolbox.
Or
Select Insert > Compartment > Peripheral from the right-click menu.
Peripheral compartment options work the same as the central and absorption compartment options. Refer to the “Central compartment options” section for details on setting these parameters.
Elimination compartment options
The elimination compartment (which is shown as a urinecpt code statement) can be connected to any other PK compartment via a PK flow. The only difference between urinecpt and deriv is that urinecpt is ignored when determining a steady-state condition.
1. Click 
in the Model toolbox.
Or
Select Insert > Compartment > Elimination from the right-click menu.
2. Elimination compartment options work the same as the central compartment options, (except there is no Conc option to add volume and concentration parameters). Refer to the “Central compartment options” section for details on setting these parameters.
3. The fraction excreted (Fe) is an additional parameter that can be included in the code statement, as shown in the following example statement:
urinecpt(A0=(A1*Ke)
,fe=Fe
)
4. To indicate that the elimination compartment is set to zero right after being observed, edit the model as textual and change the PML code to:
observe(UrineObs=A0+eps, doafter={A0=0; })