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27 Cards in this Set
- Front
- Back
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First-Order Processes
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Non-saturating
Glomerular filtration, diffusion and ion trapping, active renal secretion, metabolic processes at small substrate concentrations [drug] << Km hyperbolic curve of elimination first-order region of metabolism occurs very much to left of plot, where drug conc. is low |
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First-order Rate
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-Kel [drug]
the higher the drug conc, the higher the rate of elimination exponential decay plot log of drug conc. vs time for a straight line analysis |
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First order half-life
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the fraction of the dose eliminated ina given time is independent of the dose
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Rate constant of decay, 1st order
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= .693 / t1/2
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Apparent volume of distribution
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Vd = dose / plasma conc.
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Zero-order elimination
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saturating
metabolic processes at large substrate conc. Rate of metabolism does NOT depend on amount of drug present Rate = -Kel drug conc. is decreasing As the drug conc. continues to get smaller, eventually the elimination will pass into first-order region |
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Zero-order Graph
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plot of drug conc. vs time is linear
No logarithms involved |
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Generally no half-time for zero order...
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constant amount of drug is eliminated per hour, no a constant fraction
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First-order examples
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Metoclopramide, Vancomycin
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Zero-order example
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Ethanol, Phenytoin, Salicylate
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Zero-order elimination
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the time it takes for blood level of drug to drop below an arbitrary level is directly proportional to amount ingested
processes show a conc. increase that is steep and unpredictable, does not reach a plateau |
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Plateau Principle
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for 1st order, the time to reach the plateau level (steady state) is determined solely by Kel
Time to reach 50% of plateau = t1/2 75% = 2t1/2 87.5% = 3t1/2 96.9% = 5t1/2 |
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Maintenance Dose
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dose needed to maintain steady state
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Repeated Dosage
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plateau principle holds roughly, absorption is rapid relative to elimination
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Clearance
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Cl = Kel x Vd
Inulin: Cl = 130 ml/min, measures glomerular filtration rate p-aminohippurate and penicillin: Cl = 650 ml/min, measure maximal active renal secretion |
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Rate of Infusion
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= Kel x Vd x [drug]ss
= Cl x [drug]ss |
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Loading Dose
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Vd x [drug]ss
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Rate of drug eliminated
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= Cl x [drug]ss
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Maintenance Dose
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= Cl x [drug]ss x Tm
(Tm = dose interval) |
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Multi-compartment System
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Thiopental
used to induce anesthesia given by IV anesthetic action of thiopental is terminated by redistribution to other tissues such as muscle, skin, fat |
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Elimination Rate Constant
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Kel = .693 / t1/2
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[drug]ss
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therapeutic concentration desired at steady state
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Loading Dose
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= Vd x [drug]ss
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Clearance
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Cl = Kel x Vd
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Rate of Infusion = Rate of Elimination
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= Cl x [drug]ss
= Kel x Vd x [drug]ss |
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Dose Interval
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= Tm
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Maintenance Dose
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= Cl x [drug]ss x Tm
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