Pharmacokinetics

Question 1

What is pharmacokinetics?

Answer 1

The effect of the body on the drug
Where does the drug go?

Question 2

ADME Meaning

Answer 2

Absorption
Distribution
Metabolism
Excretion

Question 3

What is the therapeutic window?

Answer 3

The plasma concentration of the drug with desired effects without adverse effects
Between Minimal Effect Concentration and Toxicity

Question 4

What is Cmax

Answer 4

Peak level of plasma concentration

Question 5

What is the elimination phase?

Answer 5

Post Cmax when concentration reduces

Question 6

What is Tax

Answer 6

The time at which Cmax occurs

Question 7

How does administration affect rate of absorption?

Answer 7

IV bolus - rate is instant
Directly into circulatory system
IV infusion - rate is independent on amount of drug
Zero order
Oral/intramuscular - rate is proportional to amount of drug
First order
As amount of drug at administration site decreases, rate of absorption decreases
Has to diffuse into circulatory system

Question 8

What is elimination rate?

Answer 8

Amount of drug eliminated from body per unit time
Unit is mass or moles/time

Defined as removal of parent drug not metabolites

Question 9

Where does elimination occur

Answer 9

Majority of drugs are metabolised in the liver

Question 10

How many of phases of elimination are there?

Answer 10

2 phases

Some drugs can skip phase I

Question 11

Phase I of elimination

Answer 11

Catabolic - Break down of complex molecules
Drug is made slightly more soluble via :
oxidation, reduction or hydrolysis

Question 12

Phase II of elimination

Answer 12

Anabolic -Making of new molecules
Metabolite is made more water-soluble via:
synthetic conjugations
Drug is now water soluble

Question 13

Where does excretion occur?

Answer 13

Kidneys
Hepatobiliary system
Lungs (volatile compounds)
Milk
Sweat

Question 14

How does Renal Excretion occur?

Answer 14

1 -Drug enters into kidney then into capillaries
2 - Drug can be filtered at glomerulus
○ Drugs are bound to plasma proteins
○ Only free drug can be filtered into lumen of nephron
3 - Drugs remaining in capillary has another opportunity to move into lumen of nephron via secretion on PCT cells
Organic anion and cation transporters recognise weak acid and weak basic drugs
Pumped into lumen of PCT
4 - Opportunity for drugs to be reabsorbed in DCT
Depends on lipophilicity of drug
Lipophilic can cross back over membrane

Question 15

What is drug clearance?

Answer 15

Measure of efficiency of drug elimination
Volume of blood/plasma cleared of drug per unit time
OR
Constant relating rate of elimination to blood/plasma concentration

Sum of all organ clearances

Usually expressed in units of volume per time per kg or bodyweight
Irreversible process

Question 16

How do you determine blood plasma clearance?

Answer 16

Calculate area under blood/plasma concentration - time graph

Question 17

When can you not calculate exact clearance?

Answer 17

Oral administration - don’t know how much made it to the circulatory system

Question 18

What is bioavailability?

Answer 18

Measure of the extent of absorption from administration site to measurement site
Irrelevant to time - only amount
equivalent to (IV dose/oral dose) X (AUC oral/AUC IV)
AUC - area under curve

The higher the bioavailability - the more drug is absorbed into blood

Question 19

What is volume distribution (Vd)?

Answer 19

How drugs are distributed through the body into various tissues
Calculated theoretical value - apparent volume
Represents a drug’s tendency to either remain in the plasma or redistribute to other tissue compartments
Is a reversible process

Question 20

What is half-life?

Answer 20

Time taken for concentration of a drug to halve

Question 21

How to calculate half-life?

Answer 21

Natural log (ln) of drug conc against time graph
Gradient = K
Half-life = ln2/k