Clinical Pharmacokinetics 1

Question 1

Pharmacokinetics parameters

Answer 1

Volume of distribution
Clearance
Bioavailability

Question 2

Volume of distribution Vd =

Answer 2

Amount of drug in the body/plasma drug concentration

Unit: volume

Question 3

Vd is the volume required to

Answer 3

Contain all of the drug in the body at the same concentration as it is in the blood

Question 4

Vd =

With respect to C0

Answer 4

Dose/C0

Question 5

Plot of plasma drug concentration vs. time of IV bolus

Answer 5

Rapid fall: distribution phase
Slower phase: elimination phase
C0 is the intercept of y-axis and linearized elimination phase

Question 6

To achieve quickly a target plasma drug concentration

Dose =

Answer 6

Vd * TC

Question 7

Clearance (CL) is defined as

Answer 7

The volume of blood cleared of drug per unit time

Question 8

CL =

Answer 8

Rate of elimination of drug/plasma drug concentration

Unit: volume/time

Question 9

First order elimination

Answer 9

Rate of elimination = CL * C

CL is constant

Question 10

Rate of elimination =

Answer 10

Vmax * C/(Km+C)

Question 11

First order kinetics

Rate of elimination =

Answer 11

Vmax * C/Km

CL = Vmax/Km

Question 12

Log of C vs. t gives a

Answer 12

Straight line

Question 13

Half-life is a _________ for drugs eliminated by first-order kinetics

Answer 13

Constant

Question 14

Steady-state concentration

Css

Answer 14

The plasma concentration when the amount administrated per unit time is equal to the amount eliminated per unit time

Question 15

Steady state is attained after ____ half-lives

Answer 15

4

Question 16

Equation for half-life

Answer 16

t1/2= 0.693*Vd/CL

Question 17

Doubling the infusion rate

Answer 17

Doubles the Css

But same 4 half-lives to reach Css

Question 18

Saturation kinetics of elimination when C exceeds Km

Answer 18

Rate of elimination = Vmax * C/C=Vmax

Question 19

Examples of zero order = saturation kinetics

Answer 19

Aspirin at high doses
Ethanol
Phenytoin

Question 20

Properties of saturation kinetics

Answer 20

Rate of elimination is maximal and independent of drug concentration

Zero-order elimination

A constant amount of drug is eliminated per unit time

Plot of C vs. t is linear

Drug is removed at a constant rate

CL is not constant. CL = Vmax/(Km+C)

Hal-life is not constant. No longer 4 half-life

Question 21

Properties of first order kinetics

Answer 21

The concentration at a later time will depend on the rate of elimination of the drug

The drug concentration decays exponentially

Rate of elimination is directly proportional to drug concentration

A constant fraction of the drug is eliminated per unit of time