ABSTRACT
The processes of absorption and distribution determine not only how but also how quickly a drug will reach its site of action; they determine the speed of onset of drug effect. If nothing else happened to a drug after it entered the body, its action would continue indefinitely. Although this would be advantageous in chronic diseases such as epilepsy or diabetes, it would not be so in most other illnesses. But the interactions between a drug and the body are not confined to the changes that the drug brings about in the living organism; the body also acts on the drug. The same processes that the body normally utilizes to eliminate waste products associated with its growth and maintenance, or to stop the actions of chemicals that it has synthesized, e.g. hormones, also put an end to the actions of drugs introduced into the body. The processes of excretion and biotransformation and, to a lesser extent, redistribution terminate the actions of drugs by removing them from their sites of action.
