Lec 2 LOS

Question 1

what ionizable groups have a pH <7?

Answer 1

aryl carboxylic acid, aryl amine, aromatic amine, alkyl carboxylic acid

Question 2

what ionizable groups have a pH >7?

Answer 2

alkyl amines, phenol, guanidine

Question 3

how do you predict the ionizable form of the drug?

Answer 3

through Henderson-hasselbach equation

Question 4

how do you estimate the degree of ionization using the Henderson-Hasselbach Equation?

Answer 4

pH < pKa = protonated
pH > pKa = deprotonated
pH = pKa ; A- = HA = 1

Question 5

what is the range in pH where a drug will become more soluble in water?

Answer 5

” like dissolves like”
- better solubility achieved by changing pH > 7
- polar molecules dissolve better due to H bond and ionic groups

Question 5

what is the range of efficiency of passive diffusion

Answer 5

ionized drugs can’t cross lipid bilayer
- passive diffusion is most efficient when the drug is mostly neutral
- if the drug is mostly ionized it diffuses slowly
– the un-ionized portion is at equilibrium with the ionized drug
– diffusion rate is proportional with the amount of neutral

Question 6

how do you know where the drug will be absorbed in the digestive tract based on pKa?

Answer 6

• drugs are best @ a pH where it is mostly neutral ( or closest to )
  – jejunum has most of the drugs and has a pH range of 5-7
  – the stomach has mostly acidic drugs and has a pH range of 1-3

Question 7

how are drug properties affected by pH?

Answer 7

1. solubility
2. extent of absorption (bioavailability)