The effect of a drug on the body depends on a number of processes that the drug undergoes as it moves through the body. All these processes together are known as pharmacokinetics (literally, “motion of the drug”). First in these processes is the administration of the drug after which it must be absorbed into the bloodstream. From the bloodstream, the drug is distributed throughout the body to various tissues and organs. As the drug is metabolized, or broken down and used by the body, it goes through chemical changes that produce metabolites, or altered forms of the drug, most of which have no effect on the body. Finally, the drug and its metabolites are eliminated from the body.

 Drug Mode of Action

 Certain drugs work by interacting with receptors, special sites on the surface of body cells. Drugs may bind to a specific receptor, possibly preventing naturally occurring chemicals from binding to the receptor. In so doing, if a drug enhances cell activity, it is called an agonist; if it blocks cell activity, it is called an antagonist.