The oral absorption<\/a>\n of drugs is often approximated assuming linear kinetics, typically when\n given in solution. The same is true for the absorption of drugs from \nmany other extravascular<\/a>\n sites, including subcutaneous tissue and muscle. Under these \ncircumstances, absorption is characterized by an absorption rate \nconstant and a corresponding absorption half-life. \n<\/p>\n\n\n\n However, the absorption of many drugs do not exactly\n follow linear kinetics. In some cases the drug may be absorbed at a \nconstant rate so that the same amount of drug is absorbed during each \ntime interval, mimicking constant rate intravenous infusion. Different \nfactors may be responsible for nonlinear absorption such as \ncontrolled-release formulations or saturable transport mechanisms of the\n drug from the intestinal lumen to the portal circulation. <\/p>\n\n\n\n Chart Pharmacokinetics<\/p>\n