Drug Pharmacokinetics

Question 1

What is the therapeutic index?

Answer 1

Therapeutic index: ratio between
• Concentration that achieves a therapeutic response
• Concentration that achieves a toxic effect

Question 2

Is it good to have a wide or narrow therapeutic index?

Answer 2

Wide

Question 3

What does the mnemonic ADME stand for in pharmacokinetics ?

Answer 3

Absorption
Distribution
Metabolism
Excretion

Question 4

Describe absorption in relation to drug pharmacokinetics

Answer 4

drug entering the body and reaching the systemic circulation

Question 5

Describe distribution in relation to drug pharmacokinetics

Answer 5

how the drug moves from the systemic circulation to reach the target tissues

Question 6

Describe metabolism in relation to drug pharmacokinetics

Answer 6

How the drug is chemically altered by the body - usually this alters the drug characteristics to facilitate excretion.

Question 7

Describe excretion in relation to drug pharmacokinetics. How is this most commonly achieved?

Answer 7

how the drug is removed from the body, most commonly this is achieved via concentration in bile or urine.

Question 8

What are the 2 main divisions of drug delivery routes?

Answer 8

Local administration

Systemic administration

Question 9

When is local administration of a drug used?

Answer 9

When the site of action of the drug is readily accessible

Question 10

When is systemic administration of a drug used?

Answer 10

When:
o Tissue may be inaccessible AND/OR
o Widespread distribution of drugs is necessary

Question 11

What is the most common route of drug delivery in systemic administration of a drug?

Answer 11

Oral

Question 12

List 3 principles of selecting an appropriate drug route

Answer 12

Route must provide adequate delivery of the drug
Must be acceptable for the patient
Should minimise adverse drug effects

Question 13

List advantages of IV administration

Answer 13

Absorption is instant
Absorption is trivial - can be affectively ignored
Rapid systemic delivery of drug

Question 14

Describe subcutaneous/intramuscular administration

Answer 14

Only small volume can be given
Similar to IV, but slower onset of action
May be painful/unpleasant for patient
Requires training and equipment

Question 15

What is an advantage of oral administration?

Answer 15

It is the most simple and convenient method of drug administration

Question 16

In what 3 cases would oral administration not be chosen?

Answer 16

If drug is digested or poorly absorbed
If drug is irritant to stomach
If very rapid onset of action is required

Question 17

What happens if a drug remains bound to a plasma protein? effect on volume of distribution?

Answer 17

It remains in the circulation and has a small volume of distribution

Question 18

What happens if a drug has a high degree of lipid solubility? effect on volume of distribution?

Answer 18

It is more widely distributed in the tissues.

High volume of distribution

Question 19

calculation for dose of a drug =

Answer 19

Dose of a drug = Concentration x Volume

Question 20

calculation for Loading dose of a drug =

Answer 20

Loading dose = Dose/kg x Body weight

Question 21

What is the calculation for a top up dose?

Answer 21

Top up dose = change in conc x volume of Distribution

Question 22

Define Bioavailability

Answer 22

Bioavailability = fracture of the drug reaching systemic circulation after oral administration

Question 23

In what way can absorption or distribution of drugs be improved?

Answer 23

By using pro-drugs

Question 24

What can pro-drugs allow?

Answer 24

they allow a drug that would not otherwise be suitable for oral administration to be given by this route

Question 25

What are the 2 barriers that oral administration presents to absorption into the systemic circulation?

Answer 25

absorption into the portal circulation from the intestine

passage through the liver to enter systemic circulation (first pass metabolism - reduces drug concentration)

Question 26

what is a modified release delivery system?

Answer 26

a delivery system designed to slow the absorption of a drug to provide a smoother profile of drug concentration (so no high peaks and low troughs)