Pharmacokinetics is that area of pharmacology concerned with the absorption, distribution, metabolism, and elimination of drugs. The processes by which absorption, distribution, and elimination take place are referred to as unit processes. These occur independently and concurrently, and involve such activities as absorption into the blood, elimination from the blood, distribution between the blood and tissue, inactivation in tissues, and finally, elimination from the blood. Drug handling by the body can be characterized by the rate for each step or, more often, the rate of all processes. Classification of observed kinetics for these rate processes includes first-order, zero-order, and capacity-limited kinetics. In the description of these processes, we will use total body elimination as the model, as this is the way most data are handled clinically
