The metabolism of drugs or drugs includes a set of chemical modifications that suffer the drugs in the body by the action of different enzymes, can be metabolized by reactions of oxidation, reduction, hydrolysis, hydration, verb conjugation, condensation or isomerization, with the objective of facilitating their excretion.
An inactive substance or weakly active which gives rise to an active metabolite is called a prodrug, especially when it has been designed to address more effectively the active form to your destination.
In many cases, the drug metabolism includes two phases. In the phase I reactions form, modify, or delete (oxidation, reduction or hydrolysis) a functional group; these reactions are not the synthetic character. Phase II reactions consist in the conjugation with endogenous substances (e.g., glucuronic acid, sulphate, glycine); these reactions are synthetic in nature. The metabolites that are formed in the synthetic reactions are more polar and therefore easier to excrete via the kidney (in the urine) or liver (in the bile) than they do in synthetic reactions. Some drugs only experience reactions of phase I or phase II; therefore, the numbering of the phases is a functional classification, not sequential.
Phase I reactions
tend to be oxidation, reduction or hydrolysis which introduce into the structure a group reactive it chemically more active, change of activity or inactivation.
Phase II reactions
tend to be conjugation reactions that inactivate the drug. Usually act on the body reagent introduced in Phase I.
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