The 4 Comp, Metabolites, Vs & Vnd model is a general compartment model for ligands which have recirculation metabolites entering tissue and contribution to the retained tissue activity. Two input curves are required: Cp(t) the authentic ligand in plasma, and Cm(t) the metabolites exchanging with tissue. Both the authentic ligand as well as the metabolites are described by a 2-tissue compartment model, and a transfer ktrans constant links the exchangeable compartments.
The Load input curve entry in the File menu has two sub-menus Plasma and Metabolites for loading the two input curves. The model has more parameters than can be fitted at once. Therefore it has been implemented with K1/k2 , K1m/k2m and Vs as fit parameters to allow fixing the distribution volume of the exchangeable compartment model, or to use them as common parameters in a coupled fit.