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Chapter 4

Chapter 4. What Happens After A Drug Has Been Administered. Pharmocokinetics. Describes how the body handles drugs Drug movement Absorption Distribution Metabolism Excretion. Drug Movement.

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Chapter 4

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  1. Chapter 4 What Happens After A Drug Has Been Administered

  2. Pharmocokinetics • Describes how the body handles drugs • Drug movement • Absorption • Distribution • Metabolism • Excretion

  3. Drug Movement • Absorption – process of involving the movement of a substance from the site of administration across one or more body membranes • Occurs across the skin, associated mucous membranes or across membranes that line blood vessels

  4. Drug Movement • Distribution – process by which drugs are transported after they have been absorbed or administered directly into the bloodstream • Factors that affect movement: binding of drugs and substances present in the bloodstream (plasma proteins) such as albumin • Barriers brain, placenta, and testes (require lipid soluble substances)

  5. Drug Movement • Blood brain- barrier - some medications do cross, like antianxiety, sedatives, and psychoactive drugs • Blood –placental barrier –regulates substances from the mother to the fetus, there are certain drugs that do cross and cause harm • Blood-testicular barrier – between the blood supply and the male reproductive tissue

  6. Drug Movement • Metabolism – process occurs at almost every cell with the liver (the primary site), kidneys, and the intestinal tract • First-pass effect – intestinal wall, enter the blood vessels (hepatic portal circulation- carries blood to the liver)

  7. Drug Movement • Oral drugs go to the liver via veins in the upper digestive tract, this causes as much as 90% to be deactivated • Other factors that affect metabolism: Age, kidney and liver disease, genetics • Enzyme activity is decreased in children and the elderly making them more sensitive to medications

  8. Drug Movement • Excretion –process of removing drugs from the body, via urination, exhalation, defecation, and/or sweating • Via kidneys, respiratory tract, or glandular activity • Main organ – kidney • Drugs that become gaseous are excreted via the respiratory tract

  9. Drug Movement • Affected by gas exchange (diffusion, gas solubility, blood flow)

  10. Drug Movement • Enterohepatic recirculation- bile is recirculated back to the liver which are metabolized in the liver and excreted by the kidneys, what is not recirculated is excreted in the feces • Glands – saliva, sweat – eliminate substances naturally as urea or other waste products, substances that cross membranes in the breast may affect the infant if breast feeding

  11. Rate of Elimination • Amount of drug removed per unit of time from the body by normal physiological processes • Determines amount of time it stays in the bloodstream and its effect

  12. Rate of Elimination • Half life – length of time required for a drug to decrease concentration in the plasma by one-half • The larger the half-life value the longer it takes to be eliminated • Plasma half-life will increase with renal and hepatic disease

  13. Pharmacodynamics • Mechanism of action or how the drug exerts its effects • Things that influence therapy are the rate of administration, frequency of dosing, and a change in medical condition

  14. Receptors • Structural component of a cell to which a drug binds in a dose related manner in order to produce a response • To treat disease drug must interact with specific receptors

  15. Receptors • Agonists – are capable of binding with receptors and inducing a cellular response, they are facilitators of cellular action • Antagonists – inhibit or block the responses of agonists, called blockers

  16. Potency • Potency – drug’s strength at a certain concentration or dose • The higher the potency will produce a more intense effect • A smaller dose may be needed to produce the same effect as another drug

  17. Efficacy • Efficacy – ability of a drug to produce a more intense response as the concentration is increased • if the doses of two similar acting drugs are increased, they produce the same intense effect, but one will have a maximum intensity that is lower than the other drug

  18. Efficacy • Lower efficacy - The one with the lower maximum intensity • It is better to have a drug with a higher efficacy than one with a higher potency

  19. End

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