solubility of weak acids and bases

Question 1

What are some examples of weakly acidic drugs?

Answer 1

phenobarbital
(phenobarbitone), phenytoin, warfarin, NSAIDs
* These drugs will be more polar and therefore have a
greater aqueous solubility at higher pH values

Question 2

What are some examples of weakly basic drugs?

Answer 2

diazepam, codeine
* These drugs will be more polar and therefore have a
greater aqueous solubility at lower pH values

Question 3

What are some examples of amphoteric drugs?

Answer 3

oxytetracycline, nitrazepam, norfloxacin
* Contain both acidic and basic groups so these drugs will
have two (or more) pKa values, e.g. “pKa1” and “pKa2

Question 4

When will amphoteric drugs become ionised?

Answer 4

Amphoteric drugs will be ionised at all pH values – the
overall charge, i.e. whether positive or negative, depends
on whether the acidic group or the basic group is
predominantly ionised