Lippincott's Illustrated Reviews Pharmacology

Chapter 1 Pharmacokinetics

I. Overview

The goal of drug therapy is to prevent, cure, or control various disease states. To achieve this goal, adequate drug doses must be delivered to the target tissues so that therapeutic yet nontoxic levels are obtained. Pharmacokinetics examines the movement of a drug over time through the body. Pharmacological as well as toxicological actions of drugs are primarily related to the plasma concentrations of drugs. Thus, the clinician must recognize that the speed of onset of drug action, the intensity of the drug's effect, and the duration of drug action are controlled by four fundamental pathways of drug movement and modification in the body (Figure 1.1). First, drug absorption from the site of administration (Absorption) permits entry of the therapeutic agent (either directly or indirectly) into plasma. Second, the drug may then reversibly leave the bloodstream and distribute into the interstitial and intracellular fluids (Distribution). Third, the drug may be metabolized by the liver, kidney, or other tissues (Metabolism). Finally, the drug and its metabolites are removed from the body in urine, bile, or feces (Elimination). This chapter describes how knowledge of these four processes (Absorption, Distribution, Metabolism, and Elimination) influences the clinician's decision of the route of administration for a specific drug, the amount and frequency of each dose, and the dosing intervals.