L9 - Absorbtion 2 - pH Partition Hypothesis and Log D Flashcards
1
Q
what are the steps in drug absorbtion in the blood stream from the GIT
A
- partioning of molecules between the GIT fluid (aq) and GIT membrane (non-aq)
- diffuses across membrane from high conc to low conc
- concentration on the side of blood is constantly low due to removal of drug into blood stream
- partioning of molecules between the GIT membrane (non-aq) and extracellular fluid (aq) prior to entering bloodstream
2
Q
pH-partition hypothesis
A
- it is the non-ionised form of the drug (not the ionised form) which partitions into the membrane, with the extent of ionise ation dependent on the pH of the GIT fluid
3
Q
what does the amount of non-ionised drug influenced
A
- extent of absorption as only this portion of the drug is available to diffuse across the membrane
4
Q
how is the extent of ionisation determined
A
- pH of the GIT fluid
- pKa of the drug
5
Q
Å2
A
total polar surface area
6
Q
what is the Å2 value of permeable drugs
A
<130
any higher would not be soluluble in lipid phase
7
Q
log D
what is it
what is it used for
what does it depend on
A
- distribution coefficien
- takes into account all forms of the drug
- both ionised and unionised
- log D is pH dependant
- always less than log P
*
8
Q
what is equation for log D
A
9
Q
what is the equation for log D using log P
A
10
Q
passive transport
A
- conc drivien
- diffusion is key
- size matter
11
Q
migrating myoelectric complex
A
12
Q
How does the body react to different formulations in fed and fast state
A
empty with food
controlled release retained for longer
13
Q
food effect on pH of stomach
A
- stomach varies in pH
- ingested foodstuff have different effects on pH
- carb meal - little change
- protein - elevates pH
- liquid mixed meal - elevates but returns to base levels
- above pH 5
- pepsin denatures
- gastric acid prodution reduced
14
Q
A
