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21 Cards in this Set
- Front
- Back
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Name the four pharmacokinectic properties.
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Absorption
Distribution Metabolism/Biotransformation Elimination |
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Why is pharmacokinetics so critical for clinicians and pharmacists?
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Because pharmacokinetics is the basis of dosing. It helps them decide the
a) Route of administration b) The frequency and amount of dose (regime schedule) c) The duration of treatment |
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What is pharmacokinetics?
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It is the quantitative study of the rate of drug concentration in the plasma, and the 4 factors that affect it.
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A sequence of effects is produced when you take a dose. What does it look like?
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1. Administration (What the Dr gives you)
2. Drug concentration in blood (What is measured) 3. Drug at the site of action (Crucial) 4. Drugs that occupy receptors or intensity of effect (What is desired) |
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A) What does the duration of drug action refer to?
B) What does the intensity of drug action refer to? |
A) The number of drug molecules that remain at the site of action.
B) The number of drug molecules that occupy a receptor. |
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Clinical pharmacokinetics (or the application of pharmacokinetics by clinicians) is based on three principles. What are they?
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Clearance
The Plateau Principle Therapeutic window |
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When you calculate the half-life of a drug, you are looking at half of its initial ________, not the ________. Which means, that if you do want to find the _____, you have to divide the ____ by the _______.
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A) Dose (Do)
B) Concentration in blood (Co) C) Concentration in blood (Co) D) Dose (Do) E) Volume of Distribution (Vd) |
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What is the formula for:
a) Volume of distribution b) Clearance c) k d) Co (extrapolated from graph) e) Half-life |
a) Vd = Do / Co
b) Cl = kV c) slope = k / -2.303 k = -2.303 x slope d) Natural log of Co e) t 1/2 = 0.693 / k |
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Why is clearance so important for dosing?
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Because it helps determine the steady state concentration of a drug in the blood, and therefore, how frequently a dose should be given and its size.
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What is the Plateau Principle?
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It is a model that explains the time course of a drug action in the body. Anytime a drug is infused at a constant rate and is eliminated at a constant rate during a time interval.
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What is the time to reach a plateau for when a drug is entering AND/OR leaving the body?
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5 x half-life
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How long will it take to reach the steady state plasma concentration (or plateau) after starting infusion of a drug with a t 1/2 of 6 hours?
Clue: Steady state infusion depends on the half-life! |
5 x 6 = 30 hours
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Which of your drugs would take the longest time to reach a plateau or steady state if an infusion was started?
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Digoxin (Half-life of 50 hours)
Diazepam would be second highest (Half-life of 40 hours) |
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What is fractional attainment?
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It tells you the amount of time needed to reach a plateau when you do not start from 0.
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What is the formula for percent fluctuation?
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% Fluctuation = [(Cmax - Cmin) / Cmin] * 100
or % Fluctuation = f / 1 - f |
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What is the therapeutic window?
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It is the concentration of drug in blood where the first therapeutic effects are observed and where the first toxic effects are observed.
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Why is therapeutic window important for clinicians?
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They want to calculate the dosage at which drug concentration can stay within this level Ctox - Cther
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In the real world, Ctox is about ___ as much as Cther.
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Twice.
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What example drug has rapid absorption and slow elimination?
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Diazepam
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What happens when you double the dose of a drug?
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You increase its half-life by one half-life.
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What is the equation for bioavailability?
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Bioavailability = Area under the curve oral / Area under the curve intravenous
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