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Distribution & Fate

This lesson explores the distribution and fate of drugs in the body, including how drugs disperse throughout the system, their redistribution and depot binding, and the role of protein binding. It also covers drug metabolism and excretion through various routes.

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Distribution & Fate

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  1. Distribution & Fate Lesson 5

  2. Distribution • Drug disperses throughout system • does not reach target • silent receptors • Distributes in • Blood & extracellular fluid • organs & tissues ~

  3. Redistribution • Drug releases re-enters circulatory system from • Depot binding • Protein binding • Ion trapping • Bound / unbound drug • Ratio maintained • Prolongs drug effects ~

  4. Depot Binding • Unable to cross membranes • Slow drug effects • or prevent • Prolong drug effects • not metabolized • Termination of drug effects • Redistribution ~

  5. ProteinBinding T A DepotBinding Organs & Tissues Blood Brain CTZ

  6. Protein Binding • Large blood proteins • albumin most abundant • Nonselective binding • Prevents drug from reaching target • multiple drugs  compete • higher effective dose for 1 • Seldom clinical implications • Valium 99% bound, 1% free • Redistribution ~

  7. Drug Fate • Immediate & long-term drug disposal • Determines duration of drug effects • drug in system  drug effects • Terminates drug effects ~

  8. Half-life - t½ • After complete absorption • Plasma half-life • time blood levels drop by half • distribution half-life • elimination half-life • metabolism & excretion ~

  9. Biotransformation • Metabolism • structure altered  metabolite • By enzymes • site of action • blood plasma • liver • Inactivation • Some metabolites active • e.g., valium, codeine ~

  10. Liver • Main site of metabolism • nutrients • detoxification • 1st pass metabolism • GI tract  liver ~

  11. Cytochrome P-450 • Main detoxification enzyme • liver and intestine • enzyme induction • contributes to tolerance • Inhibited by… • grapefruit juice • 6',7'-dihydroxybergamottin? • red wine to lesser extent ~

  12. Excretion: Kidneys • Filtration of blood • Excretion in urine • Ionization required • ion-trapping • Active & inactive form • Koryak tribesmen (Siberia) • Amanita muscaria ~

  13. Excretion: Kidneys • Smoking cessation • diet ­ alkalinity of urine • stress ­ excretion • Antidiuretic Hormone (ADH) • regulation of water • alcohol, caffeine inhibit • dehydration ~

  14. Excretion: Other routes • Lungs • alcohol breath • Breast milk • acidic  ion traps alkaloids • alcohol: same concentration as blood • antibiotics • Also bile, skin, saliva ~~

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