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Pharmacokinetics

Pharmacokinetics. Elimination. Pharmacokinetics (PK). The study of the disposition of a drug The disposition of a drug includes the processes of ADME - A bsorption D istribution M etabolism E xcretion. ADME. Importance.

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Pharmacokinetics

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  1. Pharmacokinetics

  2. Elimination Pharmacokinetics (PK) • The study of the disposition of a drug • The disposition of a drug includes the processes of ADME - • Absorption • Distribution • Metabolism • Excretion

  3. ADME

  4. Importance • Without the knowledge gained from PK studies, patients may suffer: • Toxic drugs may accumulate • Useful drugs may have no benefit because doses are too small to establish therapy • A drug can be rapidly metabolized.

  5. Routes Of Administration Routes Of Drug Administration Parenteral Enteral Injection Topical Respiratory Rectal Oral

  6. Absorption • The passage of drug from the site of administration into the general circulation. • Exception: Intravenous injections

  7. The Process • Absorption relies on • Passage through membranes to reach the blood • passive diffusion of lipid soluble species.

  8. Absorption & Ionization Non-ionised drug More lipid solubledrug Diffuse across cell membranes more easily

  9. Site Of Absorption • Most drugs are absorbed in the small intestine, because • It is the portal for absorption of nutrients into blood • Itis surrounded by a very thin membrane with a large surface • area

  10. Rate & Extent • Rate - How rapidly does the drug get from its site of administration, to the general circulation? • Extent - How much of the administered dose enters the general circulation

  11. Distribution • The movement of drug from the blood to and from the tissues

  12. Plasma Protein Binding • Many drugs bind to plasma proteins in the blood steam • Plasma protein binding limits distribution. • A drug that binds plasma protein diffuses less efficiently, than a drug that doesn’t.

  13. Elimination • The irreversible removal of the parent drugs from the body Elimination Excretion Drug Metabolism (Biotransformation)

  14. Drug Metabolism • The chemical modification of drugs with the overall goal of getting rid of the drug • Enzymes are typically involved in metabolism Metabolism More polar (water soluble) Drug Excretion Drug

  15. Sites of Drug Metabolism • Metabolism occurs in many tissues • E.g. brain, kidney, lung • But mostly in the liver because … all of the blood in the body passes through the liver.

  16. Intravenous Administration Oral Administration Liver Metabolism Intestines

  17. Consequences Of Metabolism • Drug metabolism != Drug inactivation • The metabolite may have • Equalactivity to the drug • Noor reducedactivity • Increasedactivity (Prodrugs) • Toxicproperties, not seen with the parent drug

  18. The Most Important Enzymes • Microsomal cytochrome P450 monooxygenase family of enzymes, which oxidize drugs • Act on structurally unrelated drugs • Metabolize the widest range of drugs.

  19. Excretion • The main process that body eliminates "unwanted" substances. • Most common route - biliary or renal • Other routes - lung (through exhalation), skin (through perspiration) etc. • Lipophylic drugs may require several metabolism steps before they are excreted

  20. ADME - Summary

  21. Pharmacodynamics (PD) • The study of the biochemical and physiological effects of drugs.

  22. Drug Interaction • When a drug alters the effects of another drug • Drug A may alter these factors of drug B: • Efficiency • Rate of effect • Side effects.

  23. Drug Interaction Pharmacodynamic: The drug effect is altered Pharmacokinetic: Amount of drug in blood is altered

  24. References • A First Course in Pharmacokinetics and Biopharmaceutics - available at http://www.boomer.org/c/p1/ • http://www.le.ac.uk/pa/msc/pklecture.pdf • http://web.vet.cornell.edu/public/pharmacokinetics/pharmacokinetics.html • The Liver and Drug Metabolism - available at http://adultpain.nursing.uiowa.edu/MedGen/Liver.htm • http://www.ttuhsc.edu/pharm/Freeman/med/DrugElim1.ppt • http://www.bps.ac.uk/epharnet/adme.ppt • http://www.usask.ca/medicine/pharmacology/Mon11SEP.pdf • http://www.usask.ca/medicine/pharmacology/Fri08SEP.pdf

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