Clinical Applications of Pharmacokinetics Flashcards
Clearance
Cl= rate of elimination/C
Slope of the Log C vs T relationship is…
Inverse of Half-life! Steeper slope, shorter half life
Vd equation
Vd=A/C
T1/2 Equation
T1/2 = (.7xVd)/Cl
Vd after distribution is complete
Vd extrap = A / C0extrap
Does a higher concentration of free drug increase or decrease Vd?
Increases Vd! More available to move into tissues. This also increases the half life.
Css
Steady state concentration that occurs when a drug is infused. This is assuming that nothing happens to change the clearance of the drug.
At Css, rate of infusion = _________ .
Rate of elimination.
Equation for Css
Css=IR/Cl
Does Vd affect css?
No, but a drug with a higher Vd will take longer to reach Css.
How long does it take to reach Css?
Generally about 4-5 half lives.
How long does it take to get from one Css to a new one?
4-5 more half lives. New Css is reached when infusion rate is increased.
How to reach Css without waiting 4-5 half lives?
Loading dose!
Correct loading dose equation
Dl = Css * Vd
What else do we need to consider for oral administration of a drug?
Bioavailability and rate of absorption
How to determine bioavailability (F)?
Compare AUC oral vs AUC IV.
Amount of drug entering body after oral administration?
A=Dose * F
Clearance equation w/bioavailability
Cl = (D*F)/ AUCoral
Slow absorption effect on Cmax and T max
Decreases Cmax, increases Tmax
What happens to rate of elimination of average concentration rises?
Rate of elimination increases
Does it take more time to remove all of a drug from a previous dose during repeated administration or a single dose?
Single dose
Cssav equation
DF/TCl
Where T is the interval between doses.
Does slower oral absorption result in larger or smaller peaks and troughs?
Smaller - more even activation.
