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Excretion of drugs

Excretion of drugs. Prepared of Prof. Abdulkader El Daibani. Excretion of drugs. Excretion of drugs Drugs are excreted from the body either unchanged or as metabolites – excretory organs with the exception of lungs excrete polar drugs more readily than non-polar drugs .

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Excretion of drugs

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  1. Excretion of drugs Prepared of Prof. Abdulkader El Daibani

  2. Excretion of drugs Excretion of drugs • Drugs are excreted from the body either unchanged or as metabolites –excretory organs with the exception of lungs excrete polar drugs more readily than non-polar drugs . • The kidney in the major organ for elimination of drugs and their metabolites. • Drug excreted in feces are polar drugs or metabolites excreted in bile and not reabsorbed by G.I.T. • Pulmonary excretion is imp. in excretion of gases and vapors.

  3. Excretion of drugs The major mechanisms of drug excretion are: A) Renal excretion-3 mechanisms : • Glomerular filtration (G.F): Only free drugs can be excreted in plasma, Therefore plasma bound are not excreted by G.F. It depends on G.F rate and size of drugs.

  4. 2) Active tubular secretion In proximal renal tubule. some organic acid can be secreted and compete for the same mechanism which secrete uric acid.e.g. penicillin and probenecid-the carrier mechanism is not selective ,so probenecid is secreted on the expense of penicillin and thus ↑ plasma conc. of penicillin.

  5. Excretion of drugs 3) passive tubular reabsorption • in the proximal and distal tubules the non-ionized forms of weak acid s and bases are reabsorbed. This mechanism is pH dependent therefore alkalization of urine increase the excretion of weak acid e.g. aspirin, phenobarbitone, while acidatification of urine increase excretion of basic drugs.e.g.amphetamine, lidocaine

  6. Excretion of drugs B) Biliary excretion • Many metabolites are excreted in bile to G.I.I. the metabolite is excreted in feces if not are metabolized by glucuronidases in G.I.T. But if metabolized drugs are released and reabsorbed from G.I.T.(E.H.C) into blood and excreted by the renal system. C) Excretion in other organs Lipid solubility is the limiting factor. 1) Saliva : for some drugs the conc. of dug saliva is parallel to that in plasma e.g. Rifampin. 2) Hair, nails, skin : used for detection of toxic metals in forensic medicine( e.g. arsenic , mercury).

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