Quantitative Pharmacokinetics Flashcards
What is drug synergy?
When you get a larger effect than you expected when you use two or more drugs together
What is drug antagonism?
when you get a smaller effect than you expected when you use two or more drugs together.
Equation for concentration?
Mass / Volume
Amount (moles) / volume
Dose / Vd
What is Volume of distribution (Vd)?
The volume of plasma that would be required to contain the drug dose at the concentration measured in plasma.
This can be greater than the total volume of a human due to tissue binding. This is because the drug accumulates and sticks to different tissues.
What is the unit for volume?
L
or
L/kg
What is the equation for dose?
Dose = C x Vd
or
Cl x AUCt
What is the equation for Ca?
Ca = Amount / Q
Q = the blood flow rate or volume
What is QCa and QCv?
QCa = The amount of drug entering per minute
QCv = The amount of drug leaving per minute
What is Q(Ca-Cv)?
The rate at which the drug is being eliminated by that particular tissue
What is E?
the fraction of drug removed
What is the equation for E?
the fraction of drug removed
Q (Ca-Cv)/QCa
= (Ca – Cv) / Ca -
What is extraction ratio?
The fraction of drug entering a tissue that is eliminated.
Explain values for E?
When E = 1, all is eliminated / metabolised
E = 0 when none is metabolised
What is the equation for rate of elimination?
the blood flow rate x Concentration of drug in the blood x fraction of blood cleared of drug
Q x C x E
or
Cl x C
What is Clearance, cl and what is the equation for it?
The volume of blood cleared of drug per minute
Cl = Q x E
Explain what Q and E are?
Q = how many ml of blood are entering the tissue, per minute
E = The fraction of drug that is getting cleared per minute
Why might Cl be less than Q?
Because sometimes the enzymes can’t metabolise the drug fast enough.
What is the equation for Amount of drug eliminated in time, t?
Volume cleared per unit time x [drug] x time = Cl x C x t
or
AUCt x Cl
Because AUC = C x t
AUCt = area under curve in time
What is the equation for area under the curve?
C x t = AUC
What is half-life?
The time required for elimination of half of the absorbed drug
Explain first order?
the rate is proportional to the concentration of the drug
so Rate = k[drug]
What is Zero rate?
The rate is constant
The rate depends on “zero variables”
What determines the rate?
The clearance and the concentration
