Drugs Metabolism - Overview - DRUGMETABOLISM OVERVIEW...

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    1 DRUG  METABOLISM -  OVERVIEW Dr.V.Jagadeesan Former Deputy Director (Sr. Grade) National Institute of Nutrition
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    2 Drugs Compounds designed to have biological activity. So likely to elicit toxic  reactions. Several factors influence the reactions Dose Toxicity threshold Genetic variation  Age Gender  Diet  Co-exposure to other chemicals  Nature of toxic response  Adverse or side effects are due to  Overdose  Interaction with other drugs  Habitual use 
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    3 First Pass Effect After a chemical has entered the blood stream, it is  potentially available to all tissues in the body. However the biologic activity at or near the site of absorption  may greatly reduce the availability of the chemical to distant  sites. THIS PHENOMENON IS TERMED “ THE FIRST PASS  EFFECT This comes into effect  following absorption after the  ingestion of the chemical. In general, the first pass effect after oral absorption is the  result of efficient uptake and metabolism of compounds  by  the liver.
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    4 First Pass Effect Since blood filtering through the GI tract collected in the portal vein, all  subst. absorbed with blood, must first enter the liver prior to distribution  to other organs The liver has a high capacity for extraction and biotransformation of  compounds and thus may efficiently limit  the availability of chemicals  from reaching other sites in the body. Although hepatc extrn. is generally considered the most important site of  chemicals, demonstrating a first pass effect following oral administration,  extraction and biotransformation by epithelial cells of the GI tract may  also occur.
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    5 Binding and Storage Many chemicals bind to plasma proteins  Acidic drugs - albumin  Basic drugs - alpha1 acid glycoprotein  Free drug concentration determines drug activity  A small shift between 98% binding to 96% binding means  double  the  free drug conc. And so the possibility of drug toxicity. This might happen during Drug - Drug Interactions. Ex ;  Many anti diabetic  drugs (A.D.) are bound to proteins. Sulphonamide drugs have greater affinity for the same proteins . So A.D. drugs are released. RESULT : HYPOGLYCEMIC COMA 
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    6 Barriers to Distribution Blood Brain Barrier  Effective anatomical barrier to the penetration of water soluble   chemicals into brain  It consists of: A system of tightly joined capillary endothelial cells A number of glial foot processes that surround the capillary endothelium A contiguous basement membrane Relatively low protein conc of the interstitial fluid of the brain decreases 
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Drugs Metabolism - Overview - DRUGMETABOLISM OVERVIEW...

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