Lecture 3

Question 1

What are the different mechanisms of drug passage through biological membranes?

Answer 1

Passive diffusion
Facilitated diffusion
Active transport
pinocytosis
filtration

Question 2

What is the most important mechanism for drug passage?

Answer 2

Passive diffusion which applies to non-polar drugs which has concentration gradient as the major force and does not require any energy

Question 3

What does the rate of passive diffusion depend on?

Answer 3

The concentration gradient
Surface Area
Thickness of membrane
Diffusion coefficient of the molecule

Question 4

What is the equation which can be used to determine the rate of diffusion?

Answer 4

Rate= ((concentration1-Conc.2)Surface areadiffusion coefficient)/thickness of membrane

Question 5

What is a partition coefficient?

Answer 5

The ratio of a drug in oil phase:water phase

Question 6

How can the partition coefficient of a drug be determined?

Answer 6

Mix a known amount of drug in an equal mix of water and oil and then determine the concentration of the drug in each after giving time for the drug to equilibriate

Question 7

What is the clinical significance of a drugs partition coefficient?

Answer 7

A higher value means more of the drug will be absorbed as a value of one means the drug is equally water and lipid soluble while a number such as 52 would suggest the drug is 52 times more soluble in lipid than in water

Question 8

What role does ionization play in drug absorption?

Answer 8

Most drugs are weak acids or bases meaning they can become charged, however only the uncharged form will readily cross the cell membrane

Question 9

What is the generic equation that can be used to determine how much of a drug is ionized?

Answer 9

pKa - pH = Log (protonated/unprotonated)

Question 10

What is the protonated form of an acid?

Answer 10

The neutral form

Question 11

What is the protonated form of a base?

Answer 11

The charged form

Question 12

What is the non-protonated form of an acid?

Answer 12

The charged form

Question 13

What is the non-protonated form of a base?

Answer 13

The neutral form

Question 14

how can the henderson-hasselbach equation be important with the distribution of a drug into breastmilk?

Answer 14

Breast milk is at a different pH to blood plasma and as a result uncharged drug can move across the membrane and then become ionized by the pH trapping the drug in the breast milk this can lead to the accumulation of a drug in breast milk which could be harmful to the child being breastfed