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54 Cards in this Set
- Front
- Back
Define First Order kinetics
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process by which a constant percentage of substrate is metabolized per unit time (i.e half life)
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Define zero order kinetics
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a constant amount of drug is metabolized per unit time
(i.e alcohol) |
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what is an agonist?
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a drug that binds to and activates a receptor
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what is a full agonist?
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a drug that binds to a recptor and has the ability to produce 100% of the maximal response
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what is a partial agonist?
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drugs that bind but produce less than 100% of the maximal possible biological response no matter how high their concentration
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what are antagonists?
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drugs that bind to receptors or other drugs and INHIBIT a biological response
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What does a competitive antagonist do?
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it binds reversibly to the same active site as the agonist, shifts the dose response curve to the right, increases the ED50
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How can a competitive antagonist be overcome?
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by increasing the concentration of the agonist; the maximal efficacy of the drug will not change
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what does a non competitive antagonist do?
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It binds irreversibly to a different site on the nzm than the agonist; it cannot be overcome by increasing the concentration of the drug; lowers Emax
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How does a non competitive antagonist effect the efficacy of a drug?
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it reduces the maximum efficacy will be reduced
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Define efficacy
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the ability to produce a biological effect
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Define potency
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a measure of the amount of drug needed to cause a biological effect; demonstrated by the ED50
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What is Kd?
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the conc. of drug yeilding 50% occupancy of the receptor; dissociation constant
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What is EC50?
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the drug concentration that produces 50% of the maximal possible response in a graded dose-response curve
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What is volume of distribution (Vd)?
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the apparent volume into which a drug is able to distribute
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Vd =
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= total drug in the body/ plasma concentration of drug
= x/Cp |
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What is the significance of a large Vd?
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a large Vd signifies that most of the drug is being sequestered in some organ or compartment
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What is maintenance dose?
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a dose of drug given to achieve a therapeutic plasma concentration over an extended period of time
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Maintenance Dose =
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= Clearance x desired steady state concentration
= CL x Css |
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What is loading dose?
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In some clinical situations the desired plasma concentration must be acheived quickly. In these cases a single loading dose is injected, followed by a routine maintenance dose
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Loading Dose =
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= Vd x desired Cp
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Define peak and trough concentrations
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maximum and minimum plasma concentrations, which are observed during dosing intervals
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What variables affect peak and trough concentrations?
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they will fluctuate around the steady state plasma concentration
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What is the steady state plasma concentraion (Css)?
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the point at which the rate of drug availability is equal to the rate of drug elimination
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How does frequency of dosing affect Css?
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it doesn't
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How many half lives are required to reach Css?
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approximately 4.3
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What is clearance (CL)?
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volume of plasma cleared of drug per unit time
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What is therapeutic index?
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the ratio of a drug's toxic dose to its therapeutic dose
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What do pharmacokinetics describe?
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Where the drug goes and how much needed for desired effect.
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What factors affect pharmacokinetics?
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Absorption, distribution, metabolism, and excretion.
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What affects absorption?
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Rate is affected by route of drug administration and extent is determined by metabolism and lipid solubility.
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What affects the distribution?
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Diffusion across gradient, lipid/water partitioning, charge and pH.
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Are drugs more likely to be trapped in ionized or neutral form?
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Ionized, since ions don't easily cross membranes.
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What is first pass metabolism?
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The reduction in bioavailability in orally administered drugs because of metabolism in the liver.
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What is the half-life of a drug?
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half-life = 0.693 * Vd/CL
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What are pharmacodynamics?
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This term describes how a drug works. This is determined by 1) drug-receptor interactions; 2) duration of drug action.
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What are the 2 phases in drug metabolism?
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Phase I = conversion of drug to more polar or reactive compound; Phase II = increase water solubility to increase water solubility.
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What are the cytochrome P-450 group of enzymes?
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Enzymes located in the smooth ER which help catabolize drugs.
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What is an alkanizing agent?
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bicarbonate
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What is and acidifying agent?
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ammonium chloride
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What are some factors that affect Vd?
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disease (obesity, renal disease), size (capillary permeability), lipid solubility, and charge
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What are the 3 basic reactions in Phase I of drug metabolism?
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oxidation, reduction, and hydrolysis
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P-450 is responsible for which Phase I reaction?
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oxidation
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What are 4 reactions in Phase II drug metabolism?
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glucoronidation, sulfation, acetylation and glutathione conjugation
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Which is the most important organ in drug metabolism?
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Liver is most important, followed by the kidney
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What are the 2 components of the cytochrome P-450 enzyme system?
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oxidase and reductase
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What are examples of P-450 inducers?
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barbiturates, ethanol, which enhance the metabolism of warfarin (anticoagulant) and tylenol (analgesic), respectively.
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What are examples of P-450 inhibitors?
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cimetidine and allopurinol, which decrease the metabolism of valium and tolbutamide, respectively
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What are 4 reactions in Phase II drug metabolism?
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glucoronidation, sulfation, acetylation and glutathione conjugation
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Which is the most important organ in drug metabolism?
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Liver is most important, followed by the kidney
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What are the 2 components of the cytochrome P-450 enzyme system?
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oxidase and reductase
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What are examples of P-450 inducers?
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barbiturates, ethanol, which enhance the metabolism of warfarin (anticoagulant) and tylenol (analgesic), respectively.
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What are examples of P-450 inhibitors?
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cimetidine and allopurinol, which decrease the metabolism of valium and tolbutamide, respectively
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what is an inverse agonist?
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inhibits receptor by locking it in an inactive conformation
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