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A drug administered orally undergoes three phases of its metabolism. The liver is the main organ for drug metabolism. The gastrointestinal tract (GIT) is also involved in the first two phases of drug metabolism. In Phase I, oxidation reactions mainly occur through cytochrome P450 (CYP450) enzymes. Lipophilic drugs are converted into soluble metabolites. This can lead to activation, inactivation of the drug, or toxic metabolites. In Phase II, detoxification occurs. Here, metabolites from Phase I are conjugated via UDP-glucuronosyltransferase (UGT) / Glucuronosyltransferase, leading to the formation of highly hydrophilic metabolites. In Phase III, these are eliminated from the body.
see also:
Drugs / Medications & Gut microbiota
Microbiota-Gut-Liver-Axis (GLA)