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2013-09-21 01:41:31

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    Absorption, distribution, metabolism, and excretion
    Absorption is defined as the movement of a drug from its site of administration into the blood.
    Distribution is defined as drug movement from the blood to the interstitial space of tissues and from there into cells.
    Metabolism (biotransformation) is defined as enzymatically mediated alteration of drug structure. Excretion is the movement of drugs and their metabolites out of the body.
    The four pharmacokinetic processes, acting in concert, determine the concentration of a drug at its sites of action.
    Excretion is the movement of drugs and their metabolites out of the body.
    The combination of metabolism plus excretioN
    • 1.channels or pores: very small few drugs can pass.
    • 2. transport systems:carriers that move drugs from one side of the cell membrane to the other. they are selective with the kind of drugs they carry.
    • 3. direct penetration: lipid soluble drugs only.
  9. one example of a protein transporter?
  10. 2 most commonly used med. administration, and explain?
    • enteral: via the GI tract PO
    • parenteral: outside the GI tract
  11. explain the barriers, advantages, disadvantages of drug absorption for intravenous med. route?
    • Intravenous (IV)
    • None (absorption is bypassed)
    • Instantaneous
    • Rapid onset, and hence ideal for emergencies
    • Precise control over drug levels
    • Permits use of large fluid volumes
    • Permits use of irritant drugs
    • Irreversible
    • Expensive
    • Inconvenient
    • Difficult to do, and hence poorly suited for self-administration
    • Risk of fluid overload, infection, and embolism
    • Drug must be water soluble
  12. describe barriers advantages and disadvantages of drug absorption for intramuscular med. route
    • ntramuscular (IM)
    • Capillary wall (easy to pass)
    • Rapid with water-soluble drugs
    • Slow with poorly soluble drugs
    • Permits use of poorly soluble drugs
    • Permits use of depot preparations
    • Possible discomfort
    • Inconvenient
    • Potential for injury
  13. describe barriers advantages and disadvantages of drug absorption for SubQ med. route?
    • Capillary wall (easy to pass)
    • Rapid with water-soluble drugs
    • Slow with poorly soluble drugs
    • Permits use of poorly soluble drugs
    • Permits use of depot preparations
    • Possible discomfort
    • Inconvenient
    • Potential for injury
  14. describe barriers advantages and disadvantages of drug absorption for PO med route?
    • Epithelial lining of GI tract; capillary wall
    • Slow and variable
    • Easy
    • Convenient
    • Inexpensive
    • Ideal for self-medication
    • Potentially reversible, and hence safer than parenteral routes
    • Variability
    • Inactivation of some drugs by gastric acid and digestive enzymes
    • Possible nausea and vomiting from local irritation
    • Patient must be conscious and cooperative
  15. what are enteric coated preparations?
    drugs that have been covered with a material designed to dissolve in the intestine but not the stomach.
  16. what are sustained release preparations?
    capsules filled with tiny spheres that contain the actual drug; the individual spheres have coatings that dissolve at variable rates. Because some spheres dissolve more slowly than others, drug is released steadily throughout the day
  17. explain drug distribution in the body by blood flow to tissues?
    rugs are carried by the blood to the tissues and organs of the body. The rate at which drugs are delivered to a particular tissue is determined by blood flow to that tissue. Since most tissues are well perfused, regional blood flow is rarely a limiting factor in drug distribution
  18. explain drug distribution in the body by the ability of a drug to exit the vascular system ?
    most drugs do not produce their effects within the blood, the ability to leave the vascular system is an important determinant of drug actions. Exiting the vascular system is also necessary for drugs to undergo metabolism and excretion. Drugs in the vascular system leave the blood at capillary beds.
  19. describe how drugs exit the vasculator through capillary bed transfer?
    • no resistance
    • pass between the pores in the capillary walls
  20. describe how drugs exit the vasculator through the blood brain barrier?
    junctions are so tight that they prevent drug passage. Consequently, in order to leave the blood and reach sites of action within the brain, a drug must be able to pass through cells of the capillary wall. Only drugs that are lipid soluble or have a transport system can cross the BBB to a significant degree.
  21. describe how drugs exit the vasculator through placental drug transfer?
    lipid-soluble, nonionized compounds readily pass from the maternal bloodstream into the blood of the fetus. In contrast, compounds that are ionized, highly polar, or protein bound (see below) are largely excluded—as are drugs that are substrates for P-glycoprotein, a transporter that can pump a variety of drugs out of placental cells into the maternal blood
  22. describe how drugs exit the vasculator through protein binding?
    Drugs can form reversible bonds with various proteins in the body. Of all the proteins with which drugs can bind, plasma albumin is the most important, being the most abundant protein in plasma. Like other proteins, albumin is a large molecule, having a molecular weight of 69,000. Because of its size, albumin always remains in the bloodstream: Albumin is too large to squeeze through pores in the capillary wall, and no transport system exists by which it might leave.
  23. define drug metabolism? and where doesmost of it take place.
    Drug metabolism, also known as biotransformation, is defined as the enzymatic alteration of drug structure. Most drug metabolism takes place in the liver.
  24. what is the pass effect of metabolism?
    refers to the rapid hepatic inactivation of certain oral drugs. As discussed earlier, when oral drugs are absorbed from the GI tract, they are carried directly to the liver via the hepatic portal vein. If the capacity of the liver to metabolize a drug is extremely high, that drug can be completely inactivated on its first pass through the liver. As a result, no therapeutic effects can occur
  25. discuss renal excretion through glomerular filitration?
    Renal excretion begins at the glomerulus of the kidney tubule. The glomerulus consists of a capillary network surrounded by Bowman's capsule; small pores perforate the capillary walls. As blood flows through the glomerular capillaries, fluids and small molecules—including drugs—are forced through the pores of the capillary wall. This process, called glomerular filtration, moves drugs from the blood into the tubular urine. Blood cells and large molecules (eg, proteins) are too big to pass through the capillary pores and therefore do not undergo filtration. Because large molecules are not filtered, drugs bound to albumin remain behind in the blood.
  26. discuss renal excretion through passive tubular re absorption?
    the vessels that deliver blood to the glomerulus return to proximity with the renal tubule at a point distal to the glomerulus. At this distal site, drug concentrations in the blood are lower than drug concentrations in the tubule. This concentration gradient acts as a driving force to move drugs from the lumen of the tubule back into the blood. Because lipid-soluble drugs can readily cross the membranes that compose the tubular and vascular walls, drugs that are lipid soluble undergo passive reabsorption from the tubule back into the blood. In contrast, drugs that are not lipid soluble (ions and polar compounds) remain in the urine to be excreted. By converting lipid-soluble drugs into more polar forms, drug metabolism reduces passive reabsorption of drugs and thereby accelerates their excretion.
  27. discuss renal excretion through active tubular re absorption?
    There are active transport systems in the kidney tubules that pump drugs from the blood to the tubular urine. The tubules have two primary classes of pumps, one for organic acids and one for organic bases. In addition, tubule cells contain P-glycoprotein, which can pump a variety of drugs into the urine. These pumps have a relatively high capacity and play a significant role in excreting certain compounds.
  28. how does pharmacokinetics relates to the pediatric population?
    they have underdeveloped liver, cant fully metabolize, kidneys cant excrete BBB underdeveloped, risk for CNS toxicity
  29. explain the plasma drug level MEC
    minimum effective concentration, means level below the therapeutic range.
  30. explain the plasma drug level, toxic concentration?
    drug levels way to high, toxic levels
  31. explain the therapeutic plasma drug level?
    plasma level that falls between MEC and Toxic
  32. explain drug half life?
    • the time required for the amount of drug in the body to decrease by 50%.
    • Drugs with short half-lives leave the body quickly. Drugs with long half-lives leave slowly.
  33. explain time to plateau?
    • When the amount of drug eliminated between doses equals the dose administered, average drug levels will remain constant and plateau will have been reached.
    • plateau will be reached in approximately four half-live
  34. explain decline from plateau?
    When drug administration is discontinued, most (94%) of the drug in the body will be eliminated over an interval equal to about four half-lives
  35. differentiate between a loading dose and a maintenance dose?
    When plateau must be achieved more quickly, a large initial dose can be administered. This large initial dose is called a loading dose. After high drug levels have been established with a loading dose, plateau can be maintained by giving smaller doses. These smaller doses are referred to as maintenance doses.