Drug absorption and distribution

Question 1

What is drug absorption?

Answer 1

process which a drug enters the body from its sites of administration and enters the general circulation

Question 2

What is drug distribution?

Answer 2

transport of a drug by general circulation

Question 3

What is metabolism?

Answer 3

process by which tissue enzymes catalyse the chemical conversion of a frequently lipid-soluble drug to an often less active and more polar form that is more readily excreted from the body

Question 4

What is excretion?

Answer 4

the processes that remove the drug or its metabolites from the body

Question 5

4 physiochemical factors controlling drug absorption from the GI tract

Answer 5

solubility, chemical stability, lipid-to-water coefficient and degree of ionisation

Question 6

How is a drug often absorbed?

Answer 6

simple diffusion

Question 7

What increases the rate of diffusion?

Answer 7

increased with lipid solubility of the drug

Question 8

What is the partition coefficient?

Answer 8

rate of the drug concentration in the membrane and concentration in water at equilibrium

Question 9

Does an acid donate or accept protons?

Answer 9

donate protons

Question 10

Does a base donate or accept protons?

Answer 10

accept protons

Question 11

What forms only readily diffuse across the lipid bilayer?

Answer 11

unionised

Question 12

What two factors impact degree of ionisation

Answer 12

pKa and local pH

Question 13

What id pKa?

Answer 13

pH at which 50% of drug is ionised and 50% is unionised

Question 14

What does Henderson-Hasselbalch equation calculate?

Answer 14

proprotion of ionised and unionised drugs

Question 15

What is the absorption of weak acids facilitated by?

Answer 15

pH of the stomach lumen

Question 16

When are bases absorbed?

Answer 16

when they reach the small intestine

Question 17

Where does the majority of absorption occur?

Answer 17

small intestine - large surface area

Question 18

Are weak acids and bases or strong acids and bases better absorbed?

Answer 18

weak acids and bases are well absorbed

Question 19

When do acidic drugs become less ionised?

Answer 19

acidic environment

Question 20

When do basic drugs become less ionised?

Answer 20

basic environment

Question 21

Factors affecting GI absorption

Answer 21

GI motility, pH, blood flow, drug manufacturing, physiochemical interactions and presence of transporters

Question 22

What is oral availability?

Answer 22

fraction of the drug that reaches the systemic circulation after oral ingestion

Question 23

What is system availability?

Answer 23

fraction of the drug that reaches the systemic circulation after absorption

Question 24

Common routes of drug administration

Answer 24

oral, inhalation, buccal/ sublingual, transdermal/ subcutaneous, intravenous, rectal and intramuscular

Question 25

Pros and cons of oral administration

Answer 25

simple, good absorption
inactivation of some drugs by enzymes, food binding

Question 26

Pros and cons of sublingual/ buccal administration

Answer 26

rapid absorption, by passes portal system
infrequent route, few preparations available

Question 27

Pros and cons of rectal administration

Answer 27

used for local effect and nocturnal administration of some drugs
infrequent route, variable absorption

Question 28

Pros and cons of intravenous

Answer 28

rapid onset
sterile preparation required

Question 29

Pros and cons of intramuscular administration

Answer 29

rapid onset
painful

Question 30

Pros and cons of subcutaneous administration

Answer 30

ideal for drugs requiring parental administration
few disadvantages

Question 31

Pros and cons of inhalation administration

Answer 31

lungs ideally suited due to huge surface area
when used for local effect requires degree of manual dexterity

Question 32

Pros and cons of transdermal administration

Answer 32

slow absorption across skin
suitable for few drugs

Question 33

Pros and cons of topical administration

Answer 33

ideal for local effect
few disadvantages