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Drug Actions and Handling by the Body - Pharmacokinetics

Drug Actions and Handling by the Body - Pharmacokinetics. David Henry. Discipline of Clinical Pharmacology. Introduction: What we will cover. How do drugs act and how are they handled by the body? Drug Action, Drug Absorption, Drug Distribution and Drug Elimination

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Drug Actions and Handling by the Body - Pharmacokinetics

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  1. Drug Actions and Handling by the Body - Pharmacokinetics David Henry Discipline of Clinical Pharmacology

  2. Introduction: What we will cover • How do drugs act and how are they handled by the body? • Drug Action, Drug Absorption, Drug Distribution and Drug Elimination • The application of these principles to the ways in which drugs are used in treating patients

  3. Drug Action • Drugs tend to be small lipid-soluble molecules • Drugs must get access to sites of action • Drugs tend to bind to tissues, usually protein molecules • Drugs alter the actions of enzymes, ion channels and receptors

  4. Overview of Drug Action • ENZYME: example Angiotensin Converting enzyme inhibitors ACE I ----X---------->ACE II lowered ACE II -----> Reduced BP • ION CHANNELS: example Local Anesthetics Block Na channels--->Anesthesia

  5. Receptor Binding • Receptors are specialised binding sites - often on cell surface- which have specificity for certain substances (incl drugs). Drugs may activate or block the receptor • Activation of the receptor changes the activity of the cell: eg adrenaline activates the beta 1 receptors in the heart and speeds up the heart • Drugs have selectivity for receptors: eg Histamine2 antagonists- reduce histamine-induced acid secretion and heal peptic ulcers

  6. Pharmacokinetics • The action of the body on the drugs • The way the body handles drugs determines the dose, route and frequency of administration • The handling of drugs by the body can be split into absorption, distribution and elimination

  7. Pharmacokinetics • Rate of absorption determines the time to the peak concentration • The extent of absorption determines the height of the peak concentration

  8. Pharmacokinetics • The fraction absorbed after oral dosing can only be obtained from a comparison of oral and IV dosing • F = AUCo AUCiv

  9. High First Pass Clearance • Reduces the height of the peak • Propranolol a beta- blocking drug has a high first pass clearance

  10. Pharmacokinetics • The pattern of concentrations after IV dosing often follows a series of exponential functions reflecting distribution and ultimately elimination of the drug T1/2

  11. Multiple Dosing Approx 5 half-lives to reach steady state

  12. Summary • State what has been learned • Define ways to apply training • Request feedback of training session

  13. Where to get more information • Other training sessions • List books, articles, electronic sources • Consulting services, other sources

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