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303 MEDIMAGE > 3b. Elimination - ADME II: elimination of drugs > Flashcards

3b. Elimination - ADME II: elimination of drugs Flashcards

1
Q

what is elimination

A

processes involved in removing a drug from the body

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2
Q

what are the 2 parts of drug elimination

A 
metabolism = biotransformation of a drug
excretion = mechanism or pathway a drug leaves the body
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3
Q

what does excretion result in

A

result in irreversible loss of drug from the body

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4
Q

what are the 4 main paths of drug excretion

A

biliary excretion
kidney
respiration via lungs
tears/sweat/milk/saliva

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5
Q

what are the 2 ways drugs can be eliminated

A

a fraction can be excreted as unchanged drug and other fraction can be subjected to metabolism before excretion

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6
Q

biliary excretion involves what organ and what happens

A

liver

active secretion of drug or metabolites from hepatocyte in liver to bile. bile is conc in gall bladder and transport drug to gut for excretion in faeces so is an alternative to kidneys

drugs excreted in bile can also be reabsorbed into plasma via enterohepatic circulation

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7
Q

what is enterohepatic circualtion

A

begins with drug absorption across GI tract into portal circulation followed by uptake into liver

some drug will reach systemic circulation but some will be excreted in bile, some may be conjugated in liver and conjugated metabolites may be secreted in bile and returned to intestine via biliary duct

Conjugated metabolites are poorly absorbed in gut due to high polarity so excreted in faeces

Gut microbiota produce enzymes that can deconjugate drugs so some of parent frug molecule will be released from conjugate in intestine and reabsorbed, cross intestinal wall and taken into liver again, restarting cycle

Result in reservoir of recirculating free drug in our body. Drugs that undergo extensive enterohepatic circulation have a longer duration of action as they are recycled

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8
Q

what is the effect of enterohepatic circulation on plasma conc after single oral dose of drug

what will you see on graph plasma conc over time

A

instead of seeing decrease in plasma conc following absorption phase, will have more than one absorption phase and this prolongs drugs elimination

multiple peaks on graph

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9
Q

what does the kidney do

A

regulate volume and composition of body fluids and conserves essential compounds and removes waste products

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10
Q

what does the kidney do to water soluble drugs and metabolites

A

remove water soluble drugs and metabolites

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11
Q

what does the kidney do to lipophilic drugs and metabolites

A

usually retained as they undergo reabsorption

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12
Q

what are the 3 processes of renal excretion

A

glomerular filtration
active secretion
passive reabsorption

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13
Q

what is the nephron

A

functional unit of kidney to filter blood

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14
Q

what does a nephron consist of

A

blood supply and ducts called tubules

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15
Q

what happens to the blood filtered by glomerulus

A

blood filtered by glomerulus is caught by nephron tubule and bowmans tubule is proximal tubule that surrounds glomerulus and catches filtrate

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16
Q

what is the path that a filtrate travels through the tubules

A

Filtrate travels through the rest of the tubules such as the proximal convoluted tubule, loop of henle and distal conv tubule before exiting nephron into common collecting duct that are shared by many nephrons

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17
Q

what is the glomerular filtration rate

A

volume of filtrate formed by both kidneys per min

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18
Q

what is the normal plasma flow

A

600mL/min

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19
Q

what does it mean when people say that the renal blood flow and GFR change in parallel

A

any increases in blood flow will cause increase in GFR

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20
Q

what effect does molecular size have on GFR

A

harder to pass through if molecule is larger

21
Q

the plasma proteins will do what to molecules being filtered

A

plasma proteins will restrict molecules being filtered as they are v large molecules

22
Q

describe how the GFR is a passive process

A

Passive process depends on molecular size and ionization and conc of drug in plasma as movement will go down conc gradient

23
Q

filtered drug will pass down to where in the nephron

A

proximal tubule

24
Q

what is the path of parts of nephrons

A

proximal tubules -> loop of henle -> distal tubule -> collecting duct

25
Q

what happens to drugs not filtered in the glomerular

A

leave through efferent arteriole that runs closely to renal tubule

renal tubule cells have transporters that allows active transport of drug from plasma into tubule lumen

26
Q

what transporters transport anions

A

OAT - organic anion transporter

27
Q

what transporters transport cations

A

OCTs - organic cation transporter

28
Q

tubular transporters exhibit what feature and what is its substrate specificities

A

saturability = reach max rate of excretion

has overlapping substrate specificities

29
Q

what does overlapping substrate specificities of transporters lead to regarding excretion

A

leads to competition and inhibition so leads to decrease excretion and therefore plasma conc of drug

30
Q

what does the nephron water reabsorption do to conc gradient

what kinds of molecules are relevant to the conc gradient

A

Water reabsorbed as it passes through tubules so water leave tubule leaving drug behind increasing drug conc in renal tubule

Can create favourable conc grad for passive diffusion from high to low conc

Non-ionised/lipid soluble drugs are only relevant drugs as are only type that can cross membrane easily polar dugs will stay in tubule for excretion

31
Q

what can passive reabsorption be manipulated by

what does active secretion and reabsorption do to it

A

Can be manipulated by altering pH of tubular fluid or urine. Active secretion contributes to renal excretion whereas reabsorption conspires against it

32
Q

how does body size influence renal drug excretion

A

GFR is proportional to lean body weight

33
Q

how does age influence renal drug excretion

A

renal function decrease 50% with age

34
Q

how does pregnancy influence renal drug excretion

A

renal function increases by 50%

35
Q

how does disease influence renal drug excretion

A

renal disease and heart disease decrease renal function

36
Q

what does competitive inhibition of tubular secretion do to renal drug excretion and what does this do to the drug effects

A

decreases secretion to prolong drug effects

37
Q

what does increasing pH do to excretion

A

increase ionisation of weak acids which decreases tubular reabsorption thus increasing excretion

38
Q

what does increased urinary flow do to the rate of excretion

A

increased urinary flow rate dilutes conc in tubule therefore decreasing the conc gradient for passive reabsorption of drug increases enhanced effect

39
Q

what is the effect of pH on urinary excretion of methamphetamine

what happens if you make the urine more acidic or alkaline

A

treatment with ammonium chloride to increase excretion of amphetamine in overdose

taking baking soda to make urine more alkaline decreases excretion of amphetamine and prolong the effect

40
Q

what does low GFR do to drug and metabolites accumulation

A

leads to accumulation

41
Q

GFR is used as what for dosage adjustment of potentially toxic drugs which are excreted primarily via kidney

A

index of renal function for dosage adjustment

42
Q

what is inulin and what can it be used to do

A

used to measure GFR

intert polysaccharidde with no active secretion or reabsorption

43
Q

why is inulin impractical for measuring GFR

A

invasive and 24h collection is impractical

44
Q

why is inulin useful for measuring GFR

A

eliminated by glomerular filtration only as there is no protein binding in plasma

45
Q

what is alternative to using inulin to measure GFR

why is this method inaccurate and why is it better than inulin

A

creatine not as accurate as it undergoes bit of secretion so may overestimate GFR

only requires single blood flow to estimate GFR

46
Q

what is CrCL equation

A

(140-age) x (weight in kg) x 0.85 if female

divide whole thing by 72 x Cr

47
Q

how are many IV administered contrast agent eliminated

A

contrast agents are water soluble compounds that are renally eliminated

48
Q

what is a pro and con about elimination of contrast media

A

metabolism isnt significant enough to cause problems but downside is that renal function plays very important role for excretion and renal risk need to be indentified

303 MEDIMAGE (14 decks)

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