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36 Cards in this Set
- Front
- Back
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What is the goal of drug therapy?
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To maintain a concentration of a drug in the body that is high enough to produce the desired effect, for an appropriate length of time.
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What do we want to avoid in drug therapy?
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Toxicity
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What is the Therapeutic Window?
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The difference between minimum drug toxicity and minimum drug effect
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What do we know about the amount of drug at its site of action over time?
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That it is variable
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What 2 factors do we need to calculate the amount of drug in the body?
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-Volume of distribution of drug
-Blood concentration of drug (or serum, or plasma) |
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How is the volume of distribution of a certain drug defined?
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Based on the concentration of the drug used.
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What is Drug distribution?
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The movement of a drug from the intravascular space to the extravascular space.
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What is the Central volume?
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The hypothetical volume into which a drug is immediately distributed upon administration
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How can the central volume be calculated?
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Dose/Peak serum level
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What does knowing the Central volume value allow for future drug administrations?
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Estimating the peak serum level of the drug.
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What is the Peripheral volume?
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The sum of all tissue spaces outside the central compartment
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What is the Apparent Volume of Distribution?
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The apparent space in the body that contains all of the drug.
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On what assumption is the Volume of Distribution based?
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Based on the assumption that the concentration of the drug throughout the body is the same as in the central volume.
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What is the nature of the Vd for a drug that does not leave the central volume at all?
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Small
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What is the Vd of a drug that does move from the central volume to peripheral volume and achieves an equal distribution?
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Vd will be equal to the volume of the body (70 L)
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What will be the Vd of a drug that leaves the central volume and actually is sequestered in the peripheral space?
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Vd will be larger than the body
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What is Chloroquine's Vd?
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13000 L!!!
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Where is chloroquine sequestered?
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In RBCs
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How does Vd compare between individuals?
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It is variable
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What can alter Vd within a single individual?
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Disease states
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What does knowing the Vd for a given drug allow us to calculate?
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The dose of a drug that would need to be given to achieve a desired effective concentration in the blood.
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What is the dose of drug that would need to be given for an IV?
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Dose = Vd x Conc desired
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What is the dose of drug that would need to be given for an oral drug?
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Dose = (Vd x Conc desired)/F
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What is Clearance?
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A term that describes the efficiency of drug removal from the body
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What is Clearance NOT?
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Not the amount of drug removed
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What is Clearance mathematically?
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Rate of Elimination by kidney
--------------------------- Concentration |
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What are the units for Cl?
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Mg/time
------ = Vol/time Mg/vol |
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What are the 3 main processes by which drugs are eliminated?
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-Renal
-Liver -Pulmonary |
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How do the different elimination processes combine?
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Additively
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How does Renal clearance occur?
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By removal of UNCHANGED drug from the blood into urine.
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How does Hepatic clearance occur?
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By removal into bile of either:
-Biotransformed drug metabolites and/or -Unchanged drug |
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Are the elimination processes for most drugs saturable?
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No, not in the range of drug concentrations normally used.
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What is the effect of most drug elimination processes being nonsaturable?
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Clearance is a CONSTANT
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What is a helpful way to think of Clearance?
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As a proportionality constant used to describe the relationship between Rate in = Rate out at steady states in drug therapy
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What is the RATE of elimination directly proportional to, and why?
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Rate is proportional to the drug concentration in blood, serum, or plasma; because most drugs follow 1st order kinetics.
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How do we know that rate of elimination is proportional to the drug C?
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Because if we plot in on a graph we see a linear relationship.
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