ABSTRACT
The study of drug metabolism or biotransformation is particularly important to our understanding of the time course of drugs in the body, the structuring of dosage regimens, the pharmacology and toxicology of drug metabolites, and the interactions of multivalent drug combinations. Although several enzyme systems participate in oxidation of xenobiotics, the most important enzymes that catalyze by far the greatest number of drugs metabolic pathways are cytochrome P450s. FMOs oxygenate a number of drugs and xenobiotics, which contain heteroatoms such as nitrogen, sulfur and phosphorus. An important role in reduction of xenobiotics belongs to intestinal bacteria that will be discussed in further text. Metabolism of drugs and other orally ingested xenobiotics at intestinal level may largely affect bioavailability of certain drugs. Synergistic action of P-glycoprotein and CYP3A4 may significantly limit the absorption, thus affecting the bioavailability of various drugs and other xenobiotics.
