week 3: principles of drug absorption

as per the Fick’s first law of diffusion, the rate of absorption of a drug through the gastrointestinal tract is higher if ____________

a) area of the absorbing membrane is lower

b) diffusion coefficient (D) of the drug is higher

c) diffusion coefficient (D) of the drug is lower

d) the thickness of the membrane is higher

b

which of the following best explains why the duodenum is primary site of drug absorption via passive diffusion?

a) the duodenum contains abundant villi and microvilli increasing surface area

b) the duodenum exhibits an alkaline pH favoring both weak acids and bases

c) the duodenum has higher blood perfusion than other intestinal segments

d) the duodenum has the lowest metabolic enzyme activity in the GI tract

a

a drug with high permeability but existing primarily in ionized form at intestinal pH would likely exhibit:

a) increased distribution

b) rapid passive diffusion

c) poor absorption

d) enhanced absorption

c

for a poorly water soluble drug that is primarily absorbed by passive diffusion, which of the following is the best approach for increasing the drug absorption from the GI tract?

a) making minor structure modifications to increase the drug lipophilicity

b) using the crystalline form of the drug

c) converting the drug into a salt form (e.g. Na salt)

d) decreasing the particle size of the drug

d

cell membranes are more permeable to the unionized form of a drug than to its ionized form. this is mostly because:

a) unionized forms are lipophilic

b) ionized forms are amphiphilic

c) unionized forms are hydrophilic

d) ionized forms are lipophilic

a

which of the following drugs is most likely to rely on active transport?

a) large, lipid soluble drug

b) large lipid insoluble drug

c) small, lipophilic, unionized drug

d) a volatile anesthetic gas

b

which of the following is most accurate for transport of hydrophilic molecules (e.g. glucose, amino acids) across the biological cell membranes.

a) a concentration gradient is required

b) diffusion occurs spontaneously from a region of low concentration to a region of high concentration

c) a concentration gradient is not required

d) energy via ATP breakdown is required

a

which of the following correctly contrasts facilitated diffusion and active transport?

a) facilitated diffusion occurs against a concentration gradient, while active transport follows it

b) facilitated diffusion is passive and requires a concentration gradient, whereas active transport requires energy to move against a gradient

c) active transport is nonspecific, whereas facilitated diffusion is highly specific

d) both require ATP hydrolysis for transport across membranes

b

which of the following will increase drug absorption by passive diffusion from the GI tract?

a) increasing the ionization of the drug

b) decreasing the diffusion coefficient of the drug

c) decreasing the partition coefficient of the drug

d) increasing the partition coefficient of the drug

d

based on the Noyes-Whitney equation for drug dissolution, rate of drug dissolution will be fastest from ____________, because of its _____________.

a) granules; higher surface area

b) fine particles; higher surface area

c) tablet; higher surface area

d) tablet; lower surface area

b