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SOM 3 > E in ADME > Flashcards

E in ADME Flashcards

1
Q

what is a one compartment model?

A

single IV bolus admin. = fast drug distrib. = rapid equilibrium established = proportional clearance of drug eliminated from blood

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2
Q

how do you work out the conc. of drug in a one compartment model?

A

conc = dose/Vd

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3
Q

where is majority of drugs eliminated/cleared?

A

mainly in the kidney or liver

less importantly - excretion via lung/saliva/sweat

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4
Q

how does pulmonary drug excretion occur?

A

excretes gaseous and volatile substances

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5
Q

how can pulmonary drug excretion be tested?

A

alcohol breathalysers tests - excretion of ethanol

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6
Q

how does salivary drug excretion occur?

A

bind to saliva - depending on pH partition and protein binding

saliva drug conc. could be used to indicate drug plasma conc.

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7
Q

how does renal drug excretion occur?

A

main excretion

via urine thru the kidneys during regulation of fluid volume and composition within the body

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8
Q

what is an issue with swallowed saliva in terms of excretion?

A

saliva bound to drug depending on pH partition and protein binding = drug reabsorption

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9
Q

how do the kidneys eliminate drug substances?

A
  1. metabolism (sometimes)
  2. excretion in the urine
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10
Q

what processes handle renal excretion?

A
  1. glomerular filtration
  2. tubular secretion
  3. tubular reabsorption - active/passive
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11
Q

what molecules are excreted in glomerular filtration?

A

free drug - unbound drug
small, water soluble drugs
depends on size - fit thru pores

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12
Q

what molecules are excreted in tubular secretion?

A

secreted molecules
specialised active transport systems

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13
Q

what molecules are excreted in tubular reabsorption?

A

lipophilic and unionised drug crosses
Hydrophilic and ionised drugs cannot cross
influenced by drug lipophilicity

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14
Q

what is GFR?

A

Rate of blood filtering in the glomeruli = glomerular
filtration rate

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15
Q

what is the GFR in a normal adult male?

A

125 mL/min in normal adult male

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16
Q

what can lower GFR?

A

impaired kidney functions

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17
Q

what drugs are excreted via tubular secretion?

A

weak acids
penicillins

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18
Q

how can we alter renal eliminiation?

A

change urine pH

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19
Q

what happens when reduce urine pH?

A

acidic urine

  1. weakly acidic drugs = unionised + reabsorbed = reduced elimination
  2. weakly basic drugs = ionised = increased elimination
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20
Q

how can you get acidic urine?

A

protein rich diets
ascorbic acid co-administration

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21
Q

what happens when increase urine pH?

A

basic urine

  1. weakly basic drugs = unionised + reabsorbed = reduced elimination
  2. weakly acidic drugs = ionised = increased elimination
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22
Q

how can you get basic urine?

A

co-administer bicarbonates

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23
Q

how do you calculate the renal excretion?

A

glomerular filtration + tubular secretion - tubular reabsorption

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24
Q

how is the rate of renal elimination calculated?

A

determining the renal clearance of creatinine

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25
Q

what is creatinine?

A

calculates rate of renal elimination
endogenous compound
eliminated by the kidney only - tests kidney function

26
Q

how are drugs excreted in the liver?

A

mainly via drug metabolism. - phase

27
Q

how are drugs excreted in the liver?

A

mainly via drug metabolism. - phase1 AND phase 2 reactions

28
Q

what drug metabolism reactions undergo in the liver?

A

phase 1 - drug oxidised/reduced/hydrolysed polar groups
phase 2 - couples the drug to an endogenous molecule to form a metabolite to become pharmacologically inactive and highly water soluble

29
Q

pathology of drugs eliminated in the liver

A

must enter hepatocytes, may be metabolised, secreted into the blood or bile

bile enters the small intestine ( some material may resorb into the blood) or excreted in faeces

30
Q

what is enterohepatic circulation?

A

material reabsorbed into the blood from the bile in the small intestine

31
Q

what drugs enter enterohepatic circulation?

A

NSAIDs
opioids
digoxin
warfarin
some antibiotics

32
Q

how does drugs MW impact excretion route in the liver?

A

Drugs with MW <300 are excreted almost exclusively into urine
Drugs with MW 300-500 are excreted in both urine and bile
Drugs with MW >500 are excreted almost exclusively into bile

33
Q

what is drug clearance influenced by?

A

dose
blood flow
function of liver/kidney
plasma protein binding

34
Q

how do you work out the clearance of a drug?

A

(ELIMINATION RATE CONSTANT)/fraction of drug cleared per unit time x Vd

35
Q

what drugs bind to albumin?

A

acidic drugs

36
Q

what reduces albumin binding?

A

disease state e.g. cancer
competition e.g. presence of a second acidic drug

37
Q

what does reduce albumin binding mean?

A

more free drug = more drug able to be excreted

38
Q

describe the total body clearance?

A

overall clearance of a drug by all eliminating organs

39
Q

describe the organ body clearance?

A

clearance of a drug by a specific organ e.g. renal clearance = volume of plasma/blood cleared of drug per unit time by the kidney

40
Q

how do you calculate total body clearance?

A

renal Cl+ hepatic Cl+ other organs Cl

renal Cl (CLr) + metabolic Cl (CLm)
blood flow to the organ (Q) X extraction rate of the organ (E)

41
Q

how do you work out the renal elimination rate constant?

A

renal clearance/ Vd

42
Q

how do you work out the metabolic elimination rate constant?

A

metabolic clearance/Vd

43
Q

what is Fe?

A

fraction of the (bioavailable) drug dose that is unchanged in urine

44
Q

how do you workout Fe?

A

CLr/CLt

kR/ke

45
Q

what is hepatic extraction?

A

Hepatic extraction = the rate at which the liver extracts drug from the blood – by metabolism and removal into bile

46
Q

what does the hepatic extraction rate depend on?

A

hepatic blood flow (HBF)
intrinsic ability of the liver to handle (e.g. metabolise) the drug

47
Q

how do you workout the maximum hepatic extraction rate?

A

drug conc x HBF (hepatic blood flow)

48
Q

what is the extraction ratio (E)?

A

Fraction of drug amount presented to the organ which is eliminated during a single pass through the organ

49
Q

what do the extraction values (E) mean?

A

0 - most of the drugs escapes elimination during a single pass through the organ
1 - most of the drug is eliminated during a single pass through the organ

50
Q

how do you workout the extraction rate (E)?

A

(conc in - conc out)/ conc in

51
Q

what is the value for hepatic blood flow?

A

1.5L/min

52
Q

what are low extraction drugs?

A

diazepam, warfarin, salicylic acid, phenytoin, and procainamide

53
Q

what are high extraction drugs?

A

lidocaine, propranolol, morphine, verapamil

54
Q

what does it mean if the hepatic extraction ratio <0.3?

A

low extraction ratio drugs

55
Q

what does it mean if the hepatic extraction ratio >0.7?

A

high extraction ratio drugs

56
Q

what does it mean if the hepatic extraction ratio 0.3-0.7?

A

intermediate extraction ratio drugs

57
Q

what are low extraction ratio drugs affected by?

A

unchanged by changes in blood flow

58
Q

what are high extraction ratio drugs affected by?

A

greatly affected by changes in blood flow

hepatic blood flow increase = during meal digestion
hepatic blood flow decrease = exercise/ cirrhosis/ heart failure/ old age

59
Q

when does hepatic blood flow increase?

A

during meal digestion

60
Q

when does hepatic blood flow decrease?

A

exercise/ cirrhosis/ heart failure/ old age

SOM 3 (26 decks)

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