Drug Absorption

Question 1

Name the factors that determine drug absorption across a membrane

Answer 1

• Characteristics of the membrane
• Mechanisms of passage across membrane
• Dwell time of drug-membrane interface
• Physicochemical characteristics of the drug
• pH of the microenvironment
• Surface area of absorptive surface

Question 2

Describe the mechanisms by which drugs cross biological membranes

Answer 2

Transcellular diffusion (95% of drugs)
Paracellular diffusion (small drugs)
Carrier-mediated transport mechanisms
– Facilitated diffusion
– Active transport
Endocytosis

Question 3

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

Answer 3

Facilitated diffusion → with conc gradient only
Active transport → may go against the conc gradient

Question 4

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

Answer 4

Efflux transporters facilitate movement out of the cell
Consequences
– Limited drug absorption
– Enhanced drug elimination
– Limited distribution

Question 5

Identify the mechanism by which nanoparticles cross biological membranes

Answer 5

Endocytosis