In metabolism of xenobiotics all of the following reactions occur in phase one except?
Ans. is 'c' i.e., ConjugationDrugs are not intrinsic cellular constituents. They are xenobiotics.They are eliminated from the body mainly through kidney.Drug metabolism means necessary changes in the drug molecule which are essential for easy excretion from the body.Drug metabolism usually converts lipophilic chemical compounds into more readily excreted polar / water soluble / ionizable compounds.When the drug turns polar it becomes more soluble in the extracellular fluid and thus more filterable in the renal tubules. The drug also becomes highly ionizable so it is less reabsorbale and hence readily excretable from the kidney.The metabolism occcurs more or less in every tissue but mainly in the liver.Usually the drug metabolism occurs in two phases -Phase I andPhase IIPhase I and phase II reactions are biotransformations of chemicals that occur during drug metabolism.Phase I reactionsPhase I reactions usually precede phase II reactions though not necessarily. During these reactions, polar molecules are either added or unmasked, which results in more polar metabolites of the original chemicals. These metabolites are more water soluble than the original compound.Phase I reactions can lead to either activation or inactivation of the drug.Phase I reactions are usually of the following types:OxidationReductionHydrolysisCyclizationDecyclizationIf the metabolites of phase I reactions are sufficiently polar they may be readily excreted at this point.However many phase I products are not eliminated rapidly and undergo a subsequent reaction in which an endogenous substrate combines with the newly incorporated functional group to form a highly polar conjugate (Phase II reaction).Phase II reactionsPhase II reactions are usually known as "conjugation reactions".This involves conjugation with glucuronic acid, sulfonates and glutathione.The phase II reactions are -MethylationSulfationAcetylationGlucuronidationThe products of conjugation have increased molecular weight and are usually inactive unlike phase I reactions which often produce active metabolites.
Oxidation
Reduction
Conjugation
Hydrolysis
Pharmacokinetics