Figure 1. Model for predicting Vss.
A model with two compartments is used, with plasma and tissue represented by the two compartments. Plasma proteins exist in both the vascular (plasma; Pp) and extravascular (tissue; Pt) space. Unbound drug (D) in the plasma is at equilibrium with drug bound to plasma protein (PpD) and with free drug (D) in the tissue. The free drug in tissue can bind to extravascular plasma proteins (PtD) and to lipids (LD). Additionally, binding to neutral lipids (NLD) and lysosomes (LysD) are represented by the dashed arrows.