Metabolism of drugs is mostly done by which enzyme

Biotransformation reactions (metabolism) of drugs can be classified : A. Non-synthetic (phase I) reactions  Metabolism brings about a change in the drug molecule by: 1. Oxidation  2. Reduction 3. Hydrolysis 4. Cyclization 5. Decyclization  The new metabolite may retain biological activity or it may be an inactive metabolite.  Oxidation is the most important metabolizing reaction.  The most important enzyme for oxidation reaction is cytochrome P450 B. Synthetic (phase II or conjugation) reaction  Metabolism involves the union of the drug with one of several polar (water-soluble) endogenous molecules that are products of intermediary metabolism, to form a water-soluble conjugate which is readily eliminated by kidney or, if the molecular weight exceeds 300, in the bile.  Phase II metabolism almost invariably terminates biological activity, i.e. metabolites are usually inactive.  Reactions are:- 1. Acetylation 2. Glucuronide conjugation 3. Glycine conjugation 4. Glutathione conjugation 5. Sulfate conjugation 6. Methylation 7. Nucleotide synthesis