Pharmacokinetics

Question 1

Do weak acids in low pH readily dissociate?
Good absorption in low pH?

Answer 1

No
Abundance of H+ in low pH, equilibrium shifts to left to associated form (HA)
Yes good absorption- remains non-charged molecule so can cross plasma membranes

Question 2

Do weak bases in low pH dissociate?
Good absorption?

Answer 2

Yes
Abundance H+, equilibrium shifts to left to charged form
No bad absorption- charged form is trapped and cannot cross plasma membranes

Question 3

Can ionised or large molecules cross the blood brain barrier easily?
How treat meningitis?

Answer 3

No
Lipophobic molecules cannot cross the BBB
I.V infusion of penicilin due to leaky tight junctions of BBB- drug can cross barrier

Question 4

What does increasing drug metabolism do?
Example

Answer 4

Increases break down of drugs in liver, reducing conc. in the plasma (possible elimination)
Can produce more toxic reactive intermediates/derivatives
Brussel sprouts increase metabolism of paracetamol-> produce toxic NAPQI (have to eat loads lol)

Question 5

What does decreasing drug metabolism do?
Example

Answer 5

Decrease-> no catabolism of drugs
Leads to accumulation of drug
Can be toxic
Grapefruit juice inhibits some p450 enzymes (if taken with warfarin -> toxic accumulation)