Drug administration is the giving of a drug by one of several means (routes). Drug kinetics (pharmacokinetics) describes how the body handles a drug and accounts for the processes of absorption, distribution, metabolism, and elimination.

Drug treatment requires getting a drug to its specific target site or sites in tissues where the drug performs its action. Typically, the drug is introduced (the process of administration) into the body far from this site. The drug must move into the bloodstream (the process of absorption) and be transported to the target sites where the drug is needed (the process of distribution). Some drugs are chemically altered (the process of metabolism) by the body before they perform their action; others are metabolized afterward; and still others are not metabolized at all. The final step is the removal of the drug and its metabolites from the body (the process of elimination).

Many factors, including a person's weight, genetic makeup, and kidney or liver function, can influence these kinetic processes (see Factors Affecting Response to Drugs: Overview of Response to Drugs). Changes due to aging also affect how the body processes drugs (see Aging and Drugs).

Last full review/revision July 2012 by Jennifer Le, PharmD, BCPS-ID