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20 Cards in this Set
- Front
- Back
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half-life
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- time it takes for plasma concentration of a drug to decrease by 50% after absorption & distribution are complete
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In a first order elimination behavior, the rate is proportional to ___. The clearance is ______ of Cp. A constant _____ is eliminated per unit time.
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- Cp
- independent - fraction |
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In a zero order elimination behavior, the rate is _____ & ____ of Cp. Clearance is _____ on Cp. A constant _____ is eliminated per unit time.
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- constant & independent
- dependent - amount |
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If the system is saturable it usually obeys ____ order kinetics
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- zero
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Therapeutic levels for drugs usually lie above or below Km?
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- below
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What are two good examples of drugs that behavior in a zero order reaction fashion?
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- phenytoin & alcohol
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How do phenytoin & alcohol behavior like zero order reactions? Where is Km?
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- at low doses there is a proportional increase in Cp when drug is administered
- get to a point where a low increase in a dose gives us a bigger increase in the blood stream than we thought = zero order - Km is below the therapeutic range |
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What is the formula for t 1/2?
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- t1/2 = ln 2 / k
- t1/2 = (0.693 x Vd) / Cl |
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What are two formulas for k?
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- k = Cl/Vd
- k = ln (C1/C2) / t |
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if you have the half-life how would you solve for k? how could you then calculate clearance?
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- T1/2 = ln2/k
- Cl = Vd x k |
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when you're given Vd & Cl even without half life how can you predict who has the longest half-life?
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- the one with the biggest ration of Vd/Cl
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how many half-lives does it take for over 90% of the substance to be removed?
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- 4
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half-life is independent of ____ & ____
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- route
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how long does it require to get to steady state?
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- 3-5 hrs (use 4)
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why can failure to recognize that you are not at steady state be dangerous?
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- because you might end up at a higher steady state if you keep increasing the dose
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if you're infusing at Q and your plasma [ ] is 3, what will it be when you're infusing at 2Q? 1/2Q?
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- 2Q = 6
- 1/2Q = 1.5 |
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what is the formula for giving a new dose?
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- dose new = dose old x (Css desired/ Css observed)
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if they don't tell us the elimination process what do we assume it is?
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- zero order
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for a two compartment model the plot on a semi-log scale appears _____
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- bi-phasic
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what are the alpha & beta phases in a two compartment model?
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- alpha: distribution phase
- beta: elimination phase |
