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12 Cards in this Set
- Front
- Back
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First Order Kinetics
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-when a constant fraction of drug is absorbed, distributed, or eliminated per unit time
-decrease of drug conc at a time is directly proportional to the drug conc at said time -the elim rate is constant -curve of drug disappearance from admin site v. time is exponential |
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Zero Order Kinetics
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-when a constant AMOUNT of the drug is absorbed, distributed, or eliminated per unit time
-rate-limiting or saturable process -clearance and half-life are dose dependent -etoh, salicyclic acid, and phenytoin are zero order at high therapeutic doses -most first order drugs follow zero order when at toxic doses -graph of time course of drug disappearance from admin site is linear with neg slope |
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One Compartment Model
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-body is single compartment in which drug is uniformly distributed
-since elim is from same compartment = open model |
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Two Compartment Model
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-Central compartment where drug admin and elim occur (open model)
-drug can distribute back and forth to peripheral compartment -graph of conc v time, see 2 phases of decrease: dist and elim |
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Plasma conc v time curve
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-conc increases first because of absorption, then maxes out (Cmax at Tmax), then decreases due to elim
-Area under the curve (AUC) is related to the total amount of the drug that reaches systemic circulation |
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Bioavailability (F)
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-fraction of unchanged drug that reaches the systemic circulation
- F = AUCother route/AUCiv |
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Volume of Distribution (Vd)
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-the apparent vol of fluid that would be required to contain the total amount of drug in the body at the same conc as in the plasma
-Vd=(DosexF)/C0 -lipid solubility increases Vd |
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Clearance (CL)
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-vol of bio fluid from which drug is cleared per unit time
-CLt=Clrenal+CLhepatic+CLother |
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Half-Life of Elim (t1/2)
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-time required for conc of drug in circulation to decrease by one-half
-constant for first order -t1/2 = t@2C-t@C -or t1/2=0.693/Ke -or t1/2 = .693Vd/CL -drug is generally considered elim by 4 half lives |
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Continuous Infusion
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-in first order kinetic drug given by IV, rate of infusion will eventually =rate of elim >STEADY STATE conc (Css)
-Infusion rate =CssxCL |
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Maintenance dosing
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-if dosing interval is shorter that 4 half-lives, accumulation occurs.
-conc increases until rate of admin is equal to rate of elim - time to reach steady state is determined only by elim half-life of drug -dosing rate (DR) = (Dose x F)/T -Css=DR/CL -4 half lifes to get to steady state |
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Loading dose
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-large dose given initially to get the drug levels up to target conc rapidly
-once target achieved, take maintenance dose -loading dose = (CssxVd)/F -loading dose not needed if toxicity of OD is low |
