Pharmacokinetics II Flashcards
What is the equation for the volume of distribution of a drug?
Amt of drug in body / C : C=concentration
How can you tell how much of the drug is within the vasculature?
compare the volume of the drug, with the volume of blood.
What is the formula for clearance?
rate of elimination / C
What is zero-order elimination?
Rate of elimination is independent of drug concentration
What is first-order elimination?
Elimination of a constant fraction of a drug
What is capacity-limited elimination?
Body has a saturable rate of elimination.
What is flow dependent elimination?
The capacity of the body to eliminate is dependent on the flow of blood to the liver/kidneys
What is a half-life?
The time it takes for the concentration of a drug in the plasma to decrease by 50%, expressed in units of time
What is the equation for half life?
= 0.693*V / CL
How many half-lives are needed to eliminate a drug?
4-5
Why can you not extrapolate the rate of drug [c] in a two compartment model?
You’d ignore the distribution that takes place
Accumulation of a drug will begin to occur, if you dose shorter than how many half-lives?
4
What is the accumulation factor?
1/ fraction lost in one dosing interval
What is bioavailability?
The amount of drug that reaches the systemic circulation.
How do you calculate the bioavailability of a drug, given some f(x)?
Integrate
Bioavailability is influenced by what two factors?
Rate and extent of absorption
What is the extraction ratio?
The effect of first pass metabolism which will impact the extent to which a drug will reach the circulation
What is the equation for the extraction ratio?
ER = Cl(liver) / Q : Q= hepatic blood flow
What is the equation for the bioavailability of a drug, F?
F = f*(1-ER) : f = extent of gut absorption
What is the equation for the steady state concentration?
Dosing rate / CL
What is the steady state concentration?
The point during a dosing regimen, when elimination of a drug, is equal to the bioavailability of the drug
How many half lives does it take to reach a steady state concentration?
4-5
What is a maintenance dose?
Dose needed to maintain a steady state concentration, and enough drug is administered to replace the amount of drug lost in the proceeding dose
What is the equation for the dosing rate via IV?
CL * TC
What is the equation for the dosing rate (oral)?
Dosing rate / Foral
What is the equation for the maintenance dose?
Dosing rate * dosing interval
Why is a smaller dosing interval important?
Will lead to a narrower range of [drug]
What is the equation for the loading dose?
V*TC / F
Do the problem at the end of the slideset
