<P> The metabolism of a drug or toxin in a body is an example of a biotransformation . The body typically deals with a foreign compound by making it more water - soluble, to increase the rate of its excretion through the urine . There are many different processes that can occur; the pathways of drug metabolism can be divided into: </P> <Ul> <Li> phase І </Li> <Li> phase II </Li> </Ul> <P> Drugs can undergo one of four potential biotransformations: Active Drug to Inactive Metabolite, Active Drug to Active Metabolite, Inactive Drug to Active Metabolite, Active Drug to Toxic Metabolite (biotoxification). </P> <Ul> <Li> Includes oxidative, reductive, and hydrolytic reactions . </Li> <Li> In these types of reactions, a polar group is either introduced or unmasked, so the drug molecule becomes more water - soluble and can be excreted . </Li> <Li> Reactions are non-synthetic in nature and in general produce a more water - soluble and less active metabolites . </Li> <Li> The majority of metabolites are generated by a common hydroxylating enzyme system known as Cytochrome P450 . </Li> </Ul>

Which of the following is not a stage of biotransformation