PED1003/L04 Drug Absorption and Distribution

Question 1

Give 2 ways that drugs move around the body.

Answer 1

Bulk flow
Diffusion across barriers

Question 2

Give 3 ways in which a drug can cross a membrane.

Answer 2

Diffuse through layers
Through water channels
Through carrier proteins

Question 3

Give 2 types of carrier protein that can transfer drugs across a membrane.

Answer 3

Solute carrier transporters
ATP-binding cassettes

Question 4

When is intravenous injection used? (3)

Answer 4

A rapid onset of action is needed
High dose control needed
Drug poorly absorbed
Drug is unstable or metabolised in GI tract

Question 5

What does the rate of absorption of an IV drug depend on? (2)

Answer 5

Diffusion through tissue
Removal by local blood flow

Question 6

Why is the stomach a poor site for absorption?

Answer 6

High proportion of drugs are ionised - pH partitioning

Question 7

Why is the small intestine the main site of absorption for orally administrated drugs?

Answer 7

Large, highly permeable SA
Highly vascularised
pH 6-7.4
Enterocytes (epithelium) contain metabolic enzymes and transproters

Question 8

Give 2 examples of uptake transporters from gut lumen to enterocytes.

Answer 8

OATP1A2
OCT3
ASBT
PEPT1.2

Question 9

Give 1 example of uptake transporters from blood into enterocytes.

Answer 9

OCT1.2
OATP3A1

Question 10

Give 2 examples of efflux transporters from enterocytes into gut lumen.

Answer 10

O-gp
MRP2
BCRP

Question 11

Give 3 examples of efflux transporters from enterocytes into blood.

Answer 11

MRP1
MRP3
MRP4
MCT1
ENT1.2

Question 12

Where is a high proportion of drug lost? What is the process called?

Answer 12

Liver - metabolic inactivation

Question 13

What is enterohepatic recirculation (EHR)? (3)

Answer 13

Drug enters hepatic portal vein
Transported to liver then gall bladder
Secreted in bile to small intestine

Question 14

Descrie sublingual administration. Give an example (3+1)

Answer 14

Films and sprays
Network of capillaries under tongue
Bypasses first pass metabolism
E.g., Glyceryl trinitate for angina

Question 15

Describe rectal administration. Give an example. (3+1)

Answer 15

Suppositories and enemas
Useful for local effects
Avoids 2/3 first pass metabolism
E.g., managing opioid withdrawal

Question 16

Describe inhalation administration. Give an example. (3+1)

Answer 16

Powders, gases ans suspensions
Bypasses first pass metabolism
Local lung effects
E.g., anaesthetics

Question 17

Describe cornea administration. Give an example (1+1)

Answer 17

Local eye effects
E.g., Dorzolamide

Question 18

Describe nasal mucosa administration. Give an example. (1+1)

Answer 18

Nasal spray
E.g., gonadotrophin

Question 19

Describe vaginal administration. (4)

Answer 19

Gels, pessaries and rings
Avoids first pass metabolism
Useful for local drug effects
pH variance may affect absorption

Question 20

Describe transdermal administration. Give an example. (4+1)

Answer 20

Stick on patches or gels
Steady rate of delivery
Bypasses first pass metabolism
Highly lipid soluble drugs can slowly enter through skin
E.g., hormone replacement

Question 21

Give 4 factors that affect crossing membranes.

Answer 21

pH (ionisation)
Solubility
Permeability
Gastric motility
Food
Particle size
Capsules/coatings

Question 22

Give an example of where ion trapping is utilised.

Answer 22

Sodium bicarbonate in aspirin overdose

Question 23

Give 2 ways in which gastric motility may be affected.

Answer 23

Disorder
Drug treatment

Question 24

What is Tmax?

Answer 24

The time taken to get to maximum plasma concentration

Question 25

What is Cmax?

Answer 25

Maximum concentration of compound after dosing

Question 26

What is the area under a curve (AUC) equal to?

Answer 26

Total systemic exposure

Question 27

What is bioavailability (f)?

Answer 27

The fraction of the drug administered that is absorbed and available to have an effect in the body

Question 28

What is the equation for bioavailability (f)?

Answer 28

F = (AUCoral)/(AUCiv) x (doseiv)/(doseoral)

Question 29

What is Ka?

Answer 29

Rate of absorption