Pharmacokinetics

Question 1

Pharmacokinetics

Answer 1

What the body does to the drug.
Relationship between concentration and time.
Defines time course of drug ADME and provides mathematical basis for assessing therapeutic and toxic effects of drug in body.

Question 2

Pharmacodynamics

Answer 2

What the drug does to the body.
Relationship between concentration and effect.

Question 3

PK/PD

Answer 3

Relationship between effect and time

Question 4

ADME

Answer 4

Absorption
Distribution
Metabolism
Excretion
- Active amount of drug is not the same as the dose given -> dose should be decided to produced the desired plasma concentration

Question 5

What affects absorption?

Answer 5

Properties of the drug, pH
Rate of gastric emptying
Intestinal motility
Drug interactions
Passage through gut wall

Question 6

Bioavailability (F)

Answer 6

Fraction of administered dose reaching systemic circulation
- 100% for i.v., <100% for non i.v.
- determines what dose will produce desired effect
- explains differences in toxicity/therapeutic effects in different routes of administration

Question 7

Cmax

Answer 7

Highest plasma concentration after a single dose is given

Question 8

Tmax

Answer 8

Time for a drug to reach Cmax

Question 9

Half-life

Answer 9

Time taken for the concentration to fall to half of its original value

Question 10

Steady state

Answer 10

When the amount of drug being given is equal to the amount of drug being washed away -> equilibrium
- Gives best effect of drug
- Achieved by maintenance dosing

Question 11

Accumulation to steady state

Answer 11

1 t1/2 = 50% plasma conc
2 t1/2 = 75
3 t1/2 = 87.5
4 t1/2 = 93.75
5 t1/2 = 96.875

Question 12

Vd

Answer 12

How a drug spreads through the body after entering the bloodstream.
Not a physical volume.
Amount of drug in body / concentration of drug in blood.
Low Vd = high conc in blood
High Vd = low conc in blood

Question 13

Clearance

Answer 13

Volume of blood cleared of drug per unit time.
L/hr
Determines maintenance dose for target drug concentration
Inversely proportional to plasma concentration

Question 14

AUC

Answer 14

Area under curve after a single dose measures clearance

Question 15

Hepatic metabolism

Answer 15

A proportion of drug is metabolised each time it goes through the liver.
If liver is not working properly, the drug cannot be extracted in the same way, the drug conc can rise to higher doses.
Major cause of drug interactions from cytochrome p450.

Question 16

Grapefruit

Answer 16

Inhibits CYP3A
Potentiates effect of drug as drug is not metabolised

Question 17

St John’s Wort

Answer 17

Induces CYP3A
Decreases effect of drug as there is greater metabolism

Question 18

Renal clearance

Answer 18

Elimination rate constant describes how quickly a drug is removed from the body

Question 19

Zero order of elimination

Answer 19

Constant rate of elimination irrespective of plasma conc

Question 20

First order of elimination

Answer 20

Rate of elimination proportional to plasma concentration
Constant fraction of drug eliminated per unit time

Question 21

Maintenance Dose Rate

Answer 21

Calculated to keep a constant drug conc over time.
(Cl x Css)/F