drug handling processes

Question 1

define first pass metabolism

Answer 1

Metabolism which takes place before the drug

reaches the systemic circulation after oral administration.

Question 2

define bioavailability

Answer 2

the fraction of drug that reaches the systemic

circulation

Question 3

define Apparent volume of distribution

Answer 3

The volume of plasma into which a drug appears to be dissolved.

Question 4

define The elimination half life

Answer 4

The time taken for the amount of drug in

the plasma [or body] to decrease by half.

Question 5

define clearance

Answer 5

the VOLUME of plasma cleared of drug per unit time e.g. Litres/hour. Total body clearance is the sum of clearance of all eliminating organs (hepatic, renal, lung etc.)

Question 6

roughly how many half lives are required before a drug is eliminated

Answer 6

5

Question 7

describe zero order half life and describe what its graph would look like

Answer 7

straight line graph - not curved

For some drugs, elimination processes can saturate (can’t cope with the elimination) in the therapeutic concentration range – this is a ‘zero order process’ in which drug is cleared at a fixed rate regardless of plasma concentration, being potentially more dangerous.

The concept of half-life is inappropriate – zero-order rate constant (k0) is used.

Question 8

describe first order pharmacokinetics and what its graph would look like

Answer 8

The exponential decline in plasma concentration found for most drugs is a ‘first order process’ – the higher the concentration, the more quickly the drug is eliminated

curved line in graph