Metabolism is the major elimination pathway of a drug from the body. Drug metabolizing enzymes (DMEs) are mainly present in the liver, intestine, and blood and are responsible for converting lipophilic drugs to more hydrophilic compounds to facilitate their excretion from the body. DMEs are classified as either Phase I or Phase II enzymes. Phase I DMEs are responsible for oxidation, reduction, and hydrolysis, and Phase II DME are responsible for conjugation (not necessarily sequential). Here we discuss the DMEs involved in Phase I and Phase II reactions, their subcellular locations, cofactors, organ distributions, mechanisms of reactions, and typical substrates and inhibitors.
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