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Pharmocokinetics > Drug metabolism by liver > Flashcards

Drug metabolism by liver Flashcards

1
Q

how can drugs cross the epithelium/ endothelium?

A

paracellular (inbetween cells)
Transcellular (through the cells - diffusion,active transport, pinocytosis)

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2
Q

solute carriers

A

organic anion transporters (drugs that are weak acids)
organic cation transporters (drugs that are weak bases)

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3
Q

which epithelium/endothelium is easiest for drugs to cross?

A

kidney (glomerulus)

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4
Q

what affect permeability?

A

cell type, number of cell layers, junction between cells

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5
Q

SLC carrier that moves in same direction

A

symporter

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6
Q

SLC carrier that moves in the opposite direction?

A

antiporter

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7
Q

Example of ATP-binding cassesttes

A

P-glycoprotein (P- gp) transporters
symport vs antiport

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8
Q

certain barriers are more permeable

A
  • to allow substances to be metabolised (liver endothelium)
  • and eliminated (renal endothelium in glomerulus)
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9
Q

examples of barrier that are less permeable

A

blood-brain barrier

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10
Q

why are other barriers less permeable?

A

to protect sensitive organs from circulating chemicals or pathogens

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11
Q

simple epithelium has how many layers?

A

one

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12
Q

stratified has how many layers?

A

multiple

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13
Q

Warfarin (acidic drug) has a pKa of 5.
If blood pH of blood increases from 7 to 7.5, what effect would this have on diffusion of warfarin across cell membranes and why?

A

becomes more ionised

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14
Q

ionised is lipid?

A

insoluble

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15
Q

unionised is lipid?

A

soluble

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16
Q

what crosses the barrier more easily : ionised or unionised?

A

unionised

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17
Q

if a drug is a weak acid and you add it in area that is more acidic what happens?

A

it will bind and become more unionised
( A- + H+ gives AH)

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18
Q

at pKa = pH, what is the % of drug ionised and unionised?

A

50%

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19
Q

medication such as proton pump inhibitors are used for?

A

treat conditions like reflux disease or gastric ulcers to increase gastric pH
-in theory might change absorption of drugs but insufficient to impact clinically

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20
Q

weak acid, increase alkaline conditions what happens?

A

less H+ ions so more of it ionised

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21
Q

most common plasma protein

A

albumin 55%

22
Q

Percentage of plasma proteins

A

globulin- 38%
fibrinogen- 7%
others <1%

23
Q

in blood drugs can bind to plasma proteins therefore can exists in what forms?

A

bound and unbound

24
Q

reversible reaction between bound and unbound drugs means?

A

it is in equilibrium
etc can have more binding if increase in protein

25
Q

importance of protein binding (2)

A

protein are too large to pass through
only free drugs can bind to site of action

26
Q

implications of protein binding

A

-typically remain in the blood
-cant be metabolised or excreted
-becomes stored in reservoir and can impact volume of distribution
-cant exert their pharmacological effect

27
Q

what effect does protein binding have on a drugs half-life?

A

longer half life b/c of reservoir effect

28
Q

factors affecting protein binding

A

affinity of drug to protein binding sites
drug concentration
drug charge (ionised form more likely to bind)
plasma protein concentration

29
Q

albumin is negatively charged what does this mean to its affinity of drug to protein binding sites?

A

high affinity for acidic drugs but has low capacity
low affinity for basic drugs but has high capacity

30
Q

what is warfarin

A

a blood thinner

31
Q

what is trimethroprim and amoxicillin

A

antibiotic

32
Q

in most cases drug & protein concentrations dont affect ratio of bound to free drugs but can at higher doses why?

A

plasma proteins become more saturated (increase of unbound fraction as drug increases (
plasma proteins all taken up)

33
Q

information of tissue binding is limited why?

A

because it requires solid tissue samples to test

34
Q

some drugs bind readily to substances outside of the bloodstream like?

A

fat, bone, muscle

35
Q

which drug can travel more easily across a cell membrane? highly lipophilic or highly hydrophilic?

A

highly lipophilic

36
Q

lipophilic

A

like lipids

37
Q

hydrophilic

A

likes water

38
Q

highly lipophilic will bind extensively to?

A

fat stores

39
Q

if someone is overweight what happens to plasma concentration and why?

A

plasma concentration is less because the drug goes to store within the fatty tissues and not within the plasma

40
Q

osteoporosis leads to increased risk of fractures why?

A

increase resorption causing thinning of the bones

41
Q

bisphosphonates work by?

A

binding to calcium in bones and inhibits resportion

42
Q

resorption

A

process in which a substance, such as tissues, is lost by being destroyed and then absorbed by the body

43
Q

what do osteoclasts do?

A

break down the tissue and release the minerals, resulting in a transfer of calcium from bone tissue to the blood

44
Q

what is volume of distribution?

A

apparent volume into which a drug disperses in order to produce the observed plasma concentation

45
Q

equation of vd

A

total amount of drug in body/ plasma concentration of drug

46
Q

if a drug remains in the plasma will vd be low or high?

A

low

47
Q

Vd is a theoretic number to…

A

help describe how well drugs distribute, rather than actual real-life volume

48
Q

how does protein binding affect Vd?

A

-Bound drugs cant leave circulatory system
-higher proportion remains in the plasma
-so, total plasma concentration will be higher
hence vd will be lower

49
Q

drug factors affecting Vd

A

plasma protein binding
tissue binding
physiochemical properties of drug

50
Q

patient factors affecting vd

A

age
sex
body muscle
level of hydration
water distribution

51
Q

examples of physiochemical properties of drug

A

size, charge, pKa, lipid/water solubility

Pharmocokinetics (22 decks)

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