ABSTRACT
Disposition from plasma is generally the p) (i.e., the volume of plasma irreversibly removed of a given substance (e.g., hormone) per unit time). More specifically, this is equivalent to the mass removed/unit time divided by the circulating mass/unit volume (Part A), and it carries the units ml/min (not mg/min). Plasma clearance is a useful pharmacokinetic concept because it is reasonably constant over the range of concentrations clinically encountered in healthy animals, and it can be normalized between animals of varying size by dividing through by the body weight (kg). Systems for hormone or drug elimination are not usually saturated and, thus, the absolute rate of elimination is a linear function of its plasma concentration. Elimination of hormones and drugs from the body usually conforms to first-order kinetic principles. Clearance by means of multiple organs of elimination is additive, and these separate clearances will equal total systemic clearance (CLsystemic; Part A).
