Elimination

Elimination refers to the irreversible removal of drug from the body so that it is no longer able to exert a pharmacological effect. This may result from excretion, which refers to the direct removal of drug from the body, usually in the urine or in the bile, or it may result from the metabolism of the drug to a different species, even though the metabolite is still present in the body. It is not even necessary for the metabolite to be pharmacologically inactive in order for elimination to have occurred; for example, codeine is converted by CYP enzymes to morphine. When codeine is oxidised by CYP, the codeine has been eliminated. The therapeutic effect persists (in fact, it may have been enhanced) and the morphine metabolite now will also be eliminated in due course.