Drug Absorption

Question 1

what is pharmokinetics?

Answer 1

what the body does to drugs

Question 2

what is absorption?

Answer 2

it is the process where unchanged drug enters the circulation

Question 3

what is distribution?

Answer 3

the dispersion of a drug among fluids and tissues of the body

Question 4

what is metabolism?

Answer 4

it is the transformation of a drug into it’s daughter compounds

Question 5

what is excretion?

Answer 5

the removal of the drug/metabolites form the body

Question 6

what is the importance of ADME?

Answer 6

• key factor in determining the speed of a drug’s effects, duration and potential for problems in special cases
• essential for safe and intelligent use of medicine by drs
• designing dosing regimens
• monitoring treatment compliance
• medicine licensing requirement
• substance abuse monitoring

Question 7

what are drugs in circulation determined by?

Answer 7

supply rate, distribution and removal from body

Question 8

what are the key principles of absorption?

Answer 8

• medicines need to be absorbed unless given directly into the circulation
• diff routes of administration presents diff barriers to absorption
• diff routes of administration results in diff bioavailability and onset

Question 9

what is considered when a delivery route is chosen?

Answer 9

• the speed of onset
• convenience: IV or oral?
• bioavailabiltiy: proportion of administrated drug reaching the systemic circulation (100% of drugs administered by IV is bioavailable)
• side effects and specificity of action

Question 10

what are the different ways a drug can be administered?

Answer 10

• subcutaneous
• intravenous
• intramuscular

-orally

Question 11

how does absorption occur?

Answer 11

• by active transport through cells (very few medicines)
• by facilitated diffusion (few medicines)
• by simple diffusion (most medicines)

Question 12

what is Fick’s law?

Answer 12

rate of diffusion = SA x [C] difference x permeability

Question 13

what is permeability determined by?

Answer 13

• molecular size
• lipid solubility
• presence of charged groups

Question 14

most drugs are weka acids or bases so they are ionisable

what is the extent of ionisation dependent on?

Answer 14

pH, acid/base constant

Question 15

what must the state of the medicine be in order for it to diffuse across the cell membrane?

Answer 15

uncharged

Question 16

what is the Henderson-Hasselbalch equation and what does it do?

Answer 16

for acids:
pH = pKa - log[non-ionised] / [ionised]

for bases:
pH = pKa + log[non-ionised] / [ionised]

-it is used to predict the extent of ionisation

Question 17

when does the pH =pKa?

Answer 17

earn the drug is 50% ionised

Question 18

what is the concept of ion-trapping?

Answer 18

the idea that drugs are absorbed more efficiently when the pH of the environment is similar to the pH of the drug

• eg: acidic drugs are better absorbed in the stomach
• eg: basic drugs are better absorbed in the intestine

Question 19

what are the Lipinski’s rules and what are they used for?

Answer 19

-used to approach ADME optimisation

1) molecular weight < 500Da
2) drug must have no more than 5 H bond donors
3) no more than 10 H bond acceptors
4) log P < 5 (partition coefficient)