Pharmacokinetics 1

Question 0

Bioavailability

Answer 0

Fraction of drug that gets in to the body

Dose=amount needed/bioavailability

Question 1

First pass metabolism

Answer 1

Metabolised first time in the liver-> immediately metabolised
Fraction metabolised indicates clearance
Less reaches systemic circulation-> reduced bioavailability

Question 2

Volume of distribution

Answer 2

How much drub must be accumulated in the body to reach and sustain the desired concentration
=dose/concentration

Question 3

Half life

Answer 3

Time it takes for plasma conc to halve

=0.69/Cl

Question 4

Kinetics

Answer 4

Zero order-> rate independent of conc
First order-> rate dependent on conc-> rate of removal matches/ directly proportional to conc-> most drugs
If removal is saturated becomes zero order-> alcohol
Elimination is not usually saturated so rate of elimination is proportional to plasma conc

Question 5

Exponential elimination equation

Answer 5

Ct= Co e to the power of -kt

Ct-> drug conc at time t
Co-> drug conc at time 0
K-> elimination rate constant
Use to predict plasma concs

Question 6

Exponential decay and area under curve

Answer 6

Exponential decay-> take log of equation-> produces straight line-> first order
Area under curve of exponential decay-> effect of the magnitude of that plasma conc over time

LnCt=lnCo -ke to the power of Ct -> log graph
Use to work out rate constant

Question 7

Clearance

Answer 7

Volume of plasma from which all the drug molecules would need to be removed per unit time to achieve the overall rate of elimination of the drug from the body

Cl=VdxK
Cl=dose/AUC

Proportional to the rate of administration

Question 8

Calculating the rate constant using the log graph

Answer 8

Take log to isolate kel
Plotting Ct on a log scale against t
-> straight line-> -kel take inverse
= total clearance/volume distribution
If k=1/10-> 1/10/h of the drug remaining in the body is removed or hour.
kel-> fraction of drug in the body eliminated per unit time
Extrapolate log graph back to t 0 to get conc at t 0 -> use to find Vd

Question 9

Volume of distribution

Answer 9

Fluid volume that would have to contain all the drug in the body at the same time
Determines plasma conc
Conc=dose/Vd
Expressed in l/kg
Helps work out loading does and where the drug has gone
High Vd-> drug must of stayed in blood! not distributed
If Vd calculation produces a large number of l-> dose must be widely distributed to produce a low plasma con eg bound to tissues

Question 10

Rate constant equation

Answer 10

Fraction of drug eliminated per unit time

K=clearance/ Vd

Question 11

Elimination

Answer 11

Elimination rate constant, half life and clearance
T1/2= 0.69V/Cl

K=Cl/Vd Cl=kxVd