Pharmaceutics 4

Question 1

Weak acids are likely to be ________ in the stomach allowing them to be absorbed across lipophillic gastric mucosa

Answer 1

Unionised
Note: in order for the unionised drug to partition into lipophillc environment, it must have a coefficient partition that favours this partitioning

Question 2

Are weak bases ionised or unionised in the stomach?

How does this affect their absorption?

Answer 2

Ionised, making them less likely to be absorbed across lipophillic gastric mucosa
(More likely to be absorbed further down the GI tract where the pH is higher)

Question 3

What three features make the small intestine particularly good for absorption? What do these added features mean in terms of absorption?

Answer 3

Large surface area
Long residence time
Excellent blood flow
This means that even ionised drugs can be partially absorbed in the small intestines

Question 4

What is ion-pairing and how does it affect absorption?

Answer 4

Ionised drugs may combine with an oppositely charged ion in the small intestine, overall making the ion pair a neutral species that can permeate the gastric mucosa

Question 5

What kind of molecules may be absorbed via active transport that others would not have been?

Answer 5

Ionised, or highly hydrophillic drug molecules

Some drug molecules resemble vital compounds and so may be actively absorbed