Issar- Drug Transport

Question 1

what is first order diffusion?

Answer 1

when rate of diffusion is proportional to the concentration at the site of absorption.

Question 2

Fick’s Law allows us to calculate rate of diffusion. What variables in the equation equal the permeability constant (P)?

Answer 2

DAK/ h

Question 3

Facilitated diffusion plays a limited role in drug diffusion. Is energy needed to carry out this process?

Answer 3

nope

Question 4

In facilitated diffusion what order kinetics exemplifies low drug concentrations and why?

Answer 4

first order kinetics. the affinity of the drug to the transport carrier (Km) is greater than the concentration at the absorption site (Cabs)

Question 5

High drug concentrations indicate, which type of kinetic order?

Answer 5

zero order kinetics. the concentration at the absorption site (Cabs) is greater than the affinity of the drug to the transport carrier (Km)

Question 6

active transport uses energy to move molecules against concentration gradients. But can active transport sites be saturable and competitive?

Answer 6

yes

Question 7

what five molecular structural features affect drug transport?

Answer 7

molecular weight, partition coefficient, hydrogen-bond donor/ acceptor, chirality and number of rotatable bonds

Question 8

what physicochemical properties affect drug transport?

Answer 8

pH-partition theory, drug solubility and drug dissolution

Question 9

what indicates a drugs dissolution?

Answer 9

surface area, viscosity of dissolution medium, solubility at site of absorption and stability

Question 10

what does the extent of ionization of a weak electrolyte depend on?

Answer 10

pKa of the drug

pH of the solvent

Question 11

would ionizable drugs (electrolytes) follow Fick’s Law?

Answer 11

no. because there would not be equal drug concentrations on both sides at equilibrium, since there is a pH gradient across the membrane

Question 12

if a weak acid has a pKa of 3.2 and pH of 1.2, solve for the ratio [A-]:[HA]

Answer 12

10^-2

Question 13

if pH differs from one side of the membrane to the other, which drug compartment will contain the greater total drug concentration?

Answer 13

more highly ionized compartment

Question 14

what is ion trapping?

Answer 14

buildup of a higher concentration of a chemical across a cell membrane due to the pKa value of the chemical and difference of pH across the membrane

Question 15

if a basic drug of pKa= 10 is unionized in the blood (pH=7.4) what form will it be in gastric acid (pH=2)?

Answer 15

ionized. the basic drug would be rapidly ionized which would restrict it from being reabsorbed by the blood

Question 16

Phenobarbital is a weak acid with a pKa of 7.2 and will be largely unionized in plasma (pH=7.4) and gastric acid (pH=2). What would it take to get the ionized form?

Answer 16

alkalinizing procedures (adding sodium bicarbonate) would trap the drug in its ionized form

Question 17

in what medium would a weakly acidic drug be more ionized?

Answer 17

basic medium

Question 18

what is the ionization of the drug if pH=pKa?

Answer 18

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