Drug metabolism is that the term wont to describe the biotransformation of pharmaceutical substances within the body in order that they will be eliminated more easily. the bulk of metabolic processes that involve drugs occur within the liver, because the enzymes that facilitate the reactions are concentrated there. Drug metabolism is that the metabolic breakdown of medicine by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is that the set of metabolic pathways that modify the chemical structure of xenobiotics, which are compounds foreign to an organism's normal biochemistry, like any drug or poison. These pathways are a sort of biotransformation present altogether major groups of organisms and are considered to be of ancient origin. These reactions often act to detoxify poisonous compounds (although in some cases the intermediates in xenobiotic metabolism can themselves cause toxic effects). The study of drug metabolism is named pharmacokinetics. The metabolism of pharmaceutical drugs is a crucial aspect of pharmacology and medicine. for instance , the speed of metabolism determines the duration and intensity of a drug's pharmacologic action. Drug metabolism also affects multidrug resistance in infectious diseases and in chemotherapy for cancer, and therefore the actions of some drugs as substrates or inhibitors of enzymes involved in xenobiotic metabolism are a standard reason for hazardous drug interactions. These pathways also are important in ecology , with the xenobiotic metabolism of microorganisms determining whether a pollutant are going to be weakened during bioremediation, or continue the environment. The enzymes of xenobiotic metabolism, particularly the glutathione S-transferases also are important in agriculture, since they'll produce resistance to pesticides and herbicides. Drug metabolism is split into three phases. In phase, I, enzymes like cytochrome P450 oxidases introduce reactive or polar groups into xenobiotics. These modified compounds are then conjugated to polar compounds in phase II clinical trial reactions. These reactions are catalysed by transferase enzymes like glutathione S-transferases. Finally, in phase III clinical trial , the conjugated xenobiotics could also be further processed, before being recognised by efflux transporters and pumped out of cells. Drug metabolism often converts lipophilic compounds into hydrophilic products that are more readily excreted.