pH and ionisation

Question 1

many drugs are weak acids or bases, what 2 forms can these drugs be in

Answer 1

ionised or un-ionised

(for many drugs un-ionised form can permeate membrane

Question 2

what 2 things does the ionisation proportion of a drug depend on

Answer 2

the pKa of the drug and the local pH

Question 3

describe what pKa is

Answer 3

pKa = pH at which 50% is ionised and 50% is un-ionised

Question 4

give the name of and the equation that can be used to determine the proportions of ionised and un-ionised drugs in a given pH environment

Answer 4

the Henderson-Hasslebach equation
for acids: pH - pKa = log(A-/AH)

for bases: pH - pKa = log(B/BH+)

Question 5

describe the relationship between the accumulation of weak acids/bases and pH

Answer 5

weak acids = accumulate in areas of high pH

weak bases = accumulate in areas of low pH