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gi tract - year one > absorption of molecules 2 > Flashcards

absorption of molecules 2 Flashcards

1
Q

meaning of bioavailability

A

the amount of drug that enters the systemic circulation and is accessible at the site of action

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2
Q

what is required for absorption

A

the drug to be in a solution

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3
Q

what must occur for a drug to be in a solution

A

dissolution

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4
Q

what factors affect the concentration drugs in solution in the GI

A
  • complexation
  • adsorption
  • chemical stability
  • micellar solubilisation
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5
Q

complexation in the GI

A

mucin which is present in the GI fluids forms complexes with some drugs and reduces absorption and bioavailability

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6
Q

what does complexation lead to

A

reduction in absorption as its no longer a single molecule

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7
Q

meaning of adsorption

A

becoming part of, sticking to the surface

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8
Q

what can the co-administarion of drugs and molecules containing solid absorbents cause

A

the adsorbents interfering with the adsorption of drugs from the GI tract

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9
Q

what causes reduced chemical stability

A
  • stomach pH (acidic hydrolysis)
  • enzyme degradation
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10
Q

does micellar solubilisation increase or decrease solubility in GIT

A

increase

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11
Q

what depends on the ability of bile salts to solubilise drugs

A

mainly the lipophilicity of the drug

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12
Q

what does a micelle have

A

a hydrophobic tail (hates water)

a hydrophilic head (loves water)

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13
Q

what are surfactants designed specifically for

A

their surface-activity, they are pharmacologically inert excipients

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14
Q

what is a common feature in many surfactants

A

a long non polar hydrocarbon chain

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15
Q

what does the non polar hydrocarbon chain do on a surfactant

A

it attempts to escape contact with water, this drives molecules to accumulate at interface

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16
Q

what happens once surfactants can’t stay at the top anymore

A

they are forced to enter the water and in order to satisfy interaction processes they self associate

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17
Q

what happens when the surfactants self associate

A

the hydrophilic heads interact with eachother and the hydrophobic tails interact with eachother

18
Q

step 1 of drug absorption from GIT

A

partitioning of molecules between the GIT fluid (aqueous) and the GIT membrane (non aqueous)

19
Q

step 2 of drug absorption from GIT

A

diffusion occurs across the membrane from high C to low C

low C is due to constant removal of drug into bloodstream

20
Q

step 3 of drug absorption from GIT

A

partioning of molecules between the GIT membrane (non aqueous) and extracellular fluid (aqueous)
before entering the bloodstream

21
Q

is it the ionised or non-ionised form the drug that partitions into the membrane

A

the non-ionised form

22
Q

what depends on the extent of ionisation in the pH-partition hypothesis

A

the pH of the GIT fluid and the pKa of the drug

23
Q

how does the amount of non-ionised drug influence extent of absorption

A

as only this portion of the drug is available to diffuse across the membrane

24
Q

Ka meaning

A

the dissociation constant

25
Q

what is Ka a measure of

A

how strong or weak an acid or base is relative to water

26
Q

rule of two - acids

A

if you go 2 pHs below it will be 0% ionised and if you go 2 pHs above it will be 100% ionised

27
Q

rule of two - bases

A

if you go 2 pHs below it will be 100% ionised and if you go 2 pHs above it will be 0% ionised

28
Q

pKa of carboxylic acid

A

4.5

29
Q

pKa of R-OH

A

4-11

30
Q

pKa of R-NH2

A

3.5

31
Q

pKa of R-N

A

5

32
Q

what is logD

A

the distribution coefficient

33
Q

log is logD dependent on

A

pH

34
Q

is logD greater or less than logP

A

less

35
Q

what happens with drugs in the fed state

A

liquid and disintegrated tablets empty with food

controlled release retained for longer

36
Q

what happens with drugs in the fasted state

A

little discrimination between formulation types

37
Q

how do high carb meal impact pH

A

they have little change

38
Q

how do high protein meal affect pH

A

elevates pH

39
Q

how does liquid mixed meal impact pH

A

it elevates it but returns to base levels

40
Q

what happens above pH 5 in stomach

A

pepsin is denatured and gastric acid production is reduced

gi tract - year one (25 decks)

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