Drugs and Membrane Transport

Question 1

What are the 4 pharmacokinetic processes?

Answer 1

Absorption, Distribution, Metabolism and Excretion

Question 2

What properties effect the ability of something diffusing through lipids?

Answer 2

Drug size, lipid solubility, concentration gradient, Surface area, and Degree of ionization ( pKa of drug and pH of medium determine rate of passage)

Question 3

Are drugs able to diffuse through pores in lipid bilayers?

Answer 3

No; Usually too large to diffuse through pores and gaps, and must pass through lipid bilayer

Question 4

Discuss passive diffusion through lipids.

Answer 4

Only lipid soluble drugs cross by diffusion. The driving force is the concentration gradient of the free non-ionizing drug. Protein-bound and ionized drugs don’t affect the gradient.

Question 5

Discuss the degree of ionization for drugs.

Answer 5

Only non-ionized form diffuses across lipid membranes; pKa and pH influence diffusion

Question 6

Relate the ionization of a drug to the pH and the pKa.

Answer 6

If the pH is equal to the pKa, the ionized and non-ionized forms are in equal amounts. At low pH, there is more non-ionized drug. At high pH, there is more ionized drug. For weak bases: there is more non-ionized drug when the pH is greater than the pKa

Question 7

Describe Facilitated Diffusion

Answer 7

The driving force is the concentration gradient. It is selective and saturable; Competition among chemically related compounds.

Question 8

Describe Active Transport

Answer 8

Energy is necessary; Transport is against concentration gradient. Energy dependency, selectivity, saturation, and competition are all features.

Question 9

Describe Pino/Endocytosis

Answer 9

Large and/or lipid insoluble molecules can pass through biological membranes through membrane invagination; Requires energy.