Drug Metabolism

Drug metabolism is the metabolic cessation of drugs by living organisms, usually through specialized enzymatic systems. More usually, xenobiotic metabolism (from the Greek xenon "stranger" and biotic "related to living beings") is that the set of metabolic pathways that alter the chemical structure of xenobiotics, which are compounds external to an organism's standard biochemistry, like any drug or poison. These pathways are a kind  biotransformation existing together with the major groups of organisms and are measured to be an ancient origin. These reactions often act to detoxify poisonous compounds (although in some cases the intercedes in xenobiotic metabolism can themselves  toxic effects). The study of drug metabolism is known as pharmacokinetics. it's divided into three phases. In phase 1, enzymes like cytochrome P450 oxidases introduce reactive or polar group into xenobiotics. These compounds then conjugated to polar compounds in clinical test phase II. These reactions are catalysed by transferase enzymes like glutathione S-transferases. And in last phase these conjugated xenobiotics could even be further processed, before being recognized by efflux transporters and pumped out of cells.