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28 Cards in this Set

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How is the difference between a one vs a two compartment model determined?
It is delineated only by the rapidity of tissue dissemination (ie by the rate of equilibration across all tissues)
what is the equation for rate of elimination?
Vel = kel*[A]
kel = elimination rate constant
[A] = concnetration of drug at site
In a first order process what would happen to elimination rate if you double the concentration of drug?
Elimination rate would also double by the equation Vel=kel*[A]
How is the rate of elimination determined in a first order process?
As concentration decreases the rate of elimination also decreases
In zero order kinetics what type of drug absorption is occuring and what are some parameters associated with it?
It is a transport typically active which utilizes carriers, energy, and can become saturated. Saturation is key to zero order kinetics because then its elimination or absorption rate is constant
What is t1/2 and what does it mean?
T1/2 is the half life of the drug and indicates the rate at which half of the drug will have been absorbed or eliminated.
How can you calculate for T1/2 given the kel?
T1/2 = 0.693/kel or
T1/2 = ln0.5 Vd/Clt
If on an a plot you see a break in an elimination curve that should be linear what does this imply?
It indicates that there is a two compartment system at work.
What would occur to the half life of a drug if the volume of distribution increases?
The half life also increases! Remember equation
T1/2 = 0.5ln Vd/Clt
What does a lower kel indicate vs a higher kel? And how is that displayed on a log plot of elimination?
lower kel is indicative of a longer half life while a shorter kel is indicative of a shorter half life. On a log plot you would see a line that slopes further than the other to indicate a lower kel.
How do you calculate for volume of distribution of a drug?
Concentration = grams of drug/volume --> C = X/V
How is total body clearance calculated?
ClT = Kel * Vd
How is area under the curve calculated?
ClT = Xo/AUC
How is clearance combined from all the different compartments?
Additive ie ClT = Clliver + Cl kidney + Cl other
How is rate of entry of a drug calculated?
Vin = Qblood * Cdrug in or
Vout = Qblood *C drug out
How would one calculate Velim?
Velimination = Vin - Vout
How is the extraction ratio calculated?
(QCin - QCout) / QCin = E
How do you calculate for clearance of the liver?
Clliver = E*Qblood
What is meant by intrinsic clearance?
Maximum ability of drug to be eliminated by a specific organ
What are the components of renal clearance?
Glomerular filtration
Renal secretion
tubular reabsorption
Clr = Clgfr+CLs - Cltr
Because some compounds are bound to plasma proteins and not filtered how is renal clearance calculated for?
Clr = Fu*GFR + Cls - Cltr
What does a Clrenal > than GFR imply and what does a Clrenal < GFR imply?
Clr < GFR Compound is being reabsorbed
Clr > GFR Compound is being excreted
What does bioavailability tell us?
Fraction of the drug that reaches the systemic circulation
How do you calculate the bioavailability ratio?
AUC extra/ AUCiv = bioavailability
How many half lives does it take to reach a steady state and about what percentage is this steady state?
It takes about 4-5 half lives to reach steady state with about a 95-97% steady state concentration level.
How do you calculate for steady state concentration?
Css = Dose rate/ClT
Steady state conc = dose rate divided by total body clearance
ClT = Kel * Vd can be substituted in for ClT
How much should the loading dose be?
about 2x that of the maintenance dose
X* = Css * Vd
In drugs that undergo a first order process Css related to dose rate in what way?
Css is directly proportional to the dose rate up to a point in which the enzymes are completely saturated.