Svensson Lec 2

Question 1

Name the factors that determine drug absorption across the membrane.

Answer 1

1. Characteristics of the membrane
2. Mechanisms of passage across membranes
3. Dwell time of drug-membrane interface
4. Physicochemical characteristics of the drug
5. pH of the microenvironment
6. Surface area of absorptive surface

Question 2

Identify the site in the GI tract where most drug absorption occurs.

Answer 2

small intestine
- SA is increased with folds

Question 3

Identify the mechanism by which nanoparticles cross biological membranes.

Answer 3

endocytosis

Question 4

what is FICK’s law of diffusion?

Answer 4

when it undergoes passive diffusion, the transport rate should increase as the concentration increases

Question 5

in contrast to simple diffusion, carrier-mediated transport is ___

Answer 5

both saturable and subject to competitive inhibition

Question 6

Differentiate the two forms of carrier-mediated absorption: facilitated diffusion and active transport.

Answer 6

a. facilitated diffusion
– With concentration gradient only
– Conformational change
– No energy and involves transport proteins
b. Active transport
– May go against gradient
– Needs energy

Question 7

Describe the impact of efflux transporters on drug absorption from the small intestine.

Answer 7

1. Efficiently remove drugs from cells that have entered via passive diffusion
2. Can reduce the amount of drug that accumulates in certain tissues, such as brain
3. Increases the amount of drug absorbed with pgp
4. Can either move solutes in or facilitate their movement out of the cell
5. in to out

Question 8

what are the mechanisms by which drugs cross the biological membranes

Answer 8

transcellular, paracellular, carrier-mediated transport (facilitated diffusion and active transport)

Question 9

what is transcellular diffusion

Answer 9

→ driven by conc. gradient
- 95% drugs absorbed here
- Can be increased by
1. Removing ionized groups
2. Increasing lipophilicity
3. Reducing size
- Compromise between solubility and permeability necessary

Question 10

what is paracellular diffusion

Answer 10

→ driven by conc. gradient
- Tight junctions between cells
–> Small channels
–> MW <180 Da (polar mol.)
–> Very few drugs
–> Toxins can open junctions
–> Selective openings can active oral absorption of insulin and other proteins