D4 Medicines: physiochemical properties 4

Question 1

Which are absorbed across the lipophilic gastric mucosa, weak acid or weak base?

Answer 1

Weak acid as it is unionised

weak base ionised not absorbed- further down GI tract pH lower

Question 2

What are the limitations of the pH partitioning?

Answer 2

small intestines designed for absorption
large surface area
long residence time
excellent blood flow
means some ionised drugs can be absorbed to an extent in small intestines

Question 3

What is ion pairing?

Answer 3

ionised drug may combine with an oppositely charged ion, now becomes unionised and permeate the gastric mucosa

Question 4

What does active transport allow?

Answer 4

means molecules maybe absorbed even if they are ionised or highly lipophilic