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Km: Definition
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Km = Substrate at 0.5*Vmax
Km reflects the affinity of the enzyme for its substrate
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Vmax indicates what?
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Vmax is directly proportional to the enzyme concentration.
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Relationship between Km and affinity
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-The lower the Km, the higher the affinity
-Smaller Km means enzyme is saturated earlier, which means that small amounts of substrate are picked up by the enzyme.
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Reading an inverse curve: Y-intercept equals ?
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1/Vmax
The higher the Y-intercept the lower the Vmax
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Reading an inverse curve: X-intercept equals ?
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(1/-Km)
The further to the right the x-intercept, the greater the Km
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Reading an inverse curve: Slope equals ?
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Km/Vmax
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Reading an inverse curve: Effect of a competitive inhibitor
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X-intercept farther to the right, meaning Km is greater, because you need more substrate to get the same effect as the competitive inhibitor is hogging the enzyme.
The y-intercept is the same, meaning Vmax hasn't changed, because there isn't any more enzyme.
The slope is greater, because Km has increased while Vmax has stayed the same.
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Reading an inverse curve: Effect of a noncompetitive inhibitor
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The x-intercept is the same, meaning Km is the same, because the affinity for the enzyme hasn't changed, there's just less of it.
The y intercept has increased, meaning Vmax has decreased, because enzyme has been inactivated by the noncompetitive inhibitor
The slope is greater, because Vmax has decreased while Km has stayed the same.
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Competitive inhibitor: Resemble substrate
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Yes
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Competitive inhibitor: Overcome by increased substrate?
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Yes
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Competitive inhibitor: Binds active site?
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Yes
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Competitive inhibitor: Effect on Vmax
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Unchanged. The amount of enzyme has not changed.
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Competitive inhibitor: Effect on Km
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Increased. A lot more substrate needs to be available to seize the active sites.
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Noncompetitive inhibitor: Resemble substrate?
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No
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Noncompetitive inhibitor: Overcome by increased substrate?
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No
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Noncompetitive inhibitor: Binds active site?
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No
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Noncompetitive inhibitor: Effect on Vmax
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Decreased. Takes the enzyme out.
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Noncompetitive inhibitor: Effect on Km
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Unchanged. Does not change the affinity for the enzyme.
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Volume of distribution: Abbreviation
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Vd
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Vd: Stands for what?
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Volume of distribution
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Volume of distribution: definition
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Vd = (amount of drug in the body)/(plasma drug concentration)
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Volume of distribution: What alters it?
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Liver and kidney disease
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Where are drugs with a low Vd distributed?
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plasma
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Where are drugs with a medium Vd distributed?
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extracellular space
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Where are drugs with a high Vd distributed?
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tissues
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Clearance: definition
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=(rate of elimination of drug)/(plasma drug concentration)
=Vd x Ke where Ke=elimination constant
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Half life: definition
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The time required to change the amount of drug in the body by 1/2 during elimination (or during a constant infusion).
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What percentage of steady state is a drug at after: 1 half life
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50%
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What percentage of steady state is a drug at after: 2 half lives
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75%
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What percentage of steady state is a drug at after: 3 half lives
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87.5%
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What percentage of steady state is a drug at after: 3.3 half lives
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90%
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What percentage of steady state is a drug at after: 4 half lives
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94%
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How many half lives does it take for a drug to reach the following percentage of steady state: 50%
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1 half life
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How many half lives does it take for a drug to reach the following percentage of steady state: 75%
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2 half lives
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How many half lives does it take for a drug to reach the following percentage of steady state: 87.5%
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3 half lives
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How many half lives does it take for a drug to reach the following percentage of steady state: 90%
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3.3 half lives
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How many half lives does it take for a drug to reach the following percentage of steady state: 94%
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4 half lives
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Cp stands for what?
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target plasma concentration
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What is the abbreviation for target plasma concentration?
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Cp
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In pharmacology, what is F an abbreviation for?
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Bioavailability
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What is the abbreviation in pharmacology for bioavailability?
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F
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Loading dose: Definition
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Loading dose = (Cp * Vd)/F (where Cp equals the target plasma concentration, Vd equals volume of distribution, and F equals bioavailability)
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Maintenance dose: Definition
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Maintenance dose = (Cp * CL)/F (where Cp is the target plasma concentration and CL is clearance and F is bioavailability)
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Zero-order elimination: definition
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Constant elimination over time regardless of drug.
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How does Cp vary with time during zero-order elimination?
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Cp decreases linearly with time.
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Zero-order elimination: Drug examples
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-Ethanol
-Phenytoin
-Aspirin (at high concentrations)
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First-order elimination: definition
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Rate of elimination is proportional to drug concentration
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Zero-order elimination vs First-order elimination: Comparison
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Zero-order: Constant amount of drug eliminated per unit time
1st-order: Constant fraction of drug eliminated per unit time
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How does Cp vary with time during first-order elimination?
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Cp decreases exponentially with time.
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Urine: Which species get trapped in urine?
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Ionized species
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