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
what is Ka a measure of
how strong or weak an acid or base is relative to water
26
rule of two - ACIDS
if you go 2 pHs below it will be 0% ionised and if you go 2 pHs above it will be 100% ionised
27
rule of two - bases
if you go 2 pHs below it will be 100% ionised and if you go 2 pHs above it will be 0% ionised
28
pKa of carboxylic acid
4.5
29
pKa of R-OH
4-11
30
pKa of R-NH2
3.5
31
pKa of R-N
5
32
what is logD
the distribution coefficient
33
log is logD dependent on
pH
34
is logD greater or less than logP
less
35
what happens with drugs in the fed state
liquid and disintegrated tablets empty with food controlled release retained for longer
36
what happens with drugs in the fasted state
little discrimination between formulation types
37
how do high carb meal impact pH
they have little change
38
how do high protein meal affect pH
elevates pH
39
how does liquid mixed meal impact pH
it elevates it but returns to base levels
40
what happens above pH 5 in stomach
pepsin is denatured and gastric acid production is reduced