Some key facts before you watch the video on aspirin absorption:
- Aspirin is a weak acid (pKa 3.4).
- Acidic drugs in an acidic environment (like gastric lumen) are most likely to be in their neutral form ( non-ionized )
- Non-ionized drugs are more lipid soluble. Hence, they can be readily absorbed
- Since aspirin is a weak acid and gastric pH is an acidic environment, it can be readily absorbed.
- Bloodstream has a pH of around 7.4, therefore aspirin tends to be ionized. This prevents the drug from diffusing back to the stomach.
Now, watch again the video paying attention to the following details.
Deprotonated form = ionized = non-lipid soluble.
Now,since the drug is ionized it can’t diffuse back to the stomach and remains in the bloodstream.
This is ion trapping!