Today ' s Treatment Clinical pharmacology Elimination of drugs

This article outlines the principles ofdrug elimination, principally by the liver and kidneys. Most elimination processes of drugs follow first-order elimination kinetics. In such processes a defined and constant fraction of a drug-for example, half-is irreversibly eliminated in a constant time. The half-life time (t1) in such first-order processes is the time taken for the concentration of the drug to fall to half its previous value, regardless of the initial concentration of the drug. Some drugs-for example, ethyl alcohol-follow zero-order elimination kinetics. In these processes elimination of the drug occurs at a constant rate, because the enzymes responsible for metabolism of drugs, and the active excretion processes particularly in the kidney, become saturated.