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MD3002 post MSA > drug metabolism > Flashcards

drug metabolism Flashcards

1
Q

where does metabolism happen (biotransformation)

A 
gut lumen and wall
plasma
lungs
kidneys
nerves 
liver
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2
Q

what is phase one metabolism

A

usually oxidation, reduction or hydrolysis

introduce/reveal a chemical group
‘functionalisation’
products are usually more reactive

prepares for phase 2

e.g. adds OH, NH2, -SH, -COOH

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3
Q

what is phase 2 metabolism

A

synthetic or conjugative
usually hydrophilic or inactive compounds

adding something on!

e.g. sulfation
acetylation
amino acid conjugation
fatty acid conjugation
condensation

requires something to conjugate with

can then be excreted in bile or urine

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4
Q

what are the possible results of metabolism

A

deactivation/ activation
type of pharmacological response
drug uptake/ distribution
hydrophilicity

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5
Q

what enzymes are responsible for oxidation

A

mixed functional oxidases- cytochrome P450
alcohol dehydrogenase
xanthine oxidase

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6
Q

name some reduction reactions

A

ketone reduction

anaerobic cytochrome P450 metabolism

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7
Q

name some hydrolysis reaction

A

ester hydrolysis

amide hydrolysis

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8
Q

what does cytochrome p450 require

A

oxygen

NADPH

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9
Q

what are the problems with drug metabolism

A 
overlapping substrate specificities
drugs for same enzyme
different enzymes for same substrate
enzyme can be saturated
conjugate can be depleted
variation between people
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10
Q

what are the sources of excretion

A 
breath
urine
saliva
perspiration
faeces
milk
bile
hair

remember that drug or metabolite could be excreted

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11
Q

how are substances transfered from plasma to bile

A

organic cation transporters
organic anion transporters
p glycoproteins

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12
Q

describe entero hepatic recirculation

A

hydrophilic conjugates e.g. glucuronides are delivered to intestine

hydrolysis can occur in intestine by gut microbiota (depends on person) - will affect half life and efficacy - think of antibiotics and oral synthetic oestrogens

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13
Q

what drugs can be filtered

A

below 20 kDa

not if bound to plasma albumin

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14
Q

describe tubular secretion of drugs

A

OATs and OCTs
OATs transport against a chemical gradient
cleared even if bound to albumin

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15
Q

how do you change urine pH in order to favour excretion of weak acids

A

make urine more alkaline

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16
Q

what is zero order kinetics

A

straight line
constant rate of drug removal

eg alcohol - 1 unit per hour approx

few drugs
does not vary with amount of drug present
enzyme saturation

17
Q

what is first order kinetics

A

curvey graph

able to calculate a half life

most drugs
constant fraction metabolised per unit time
increases proportionately to drug
more drug, faster metabolism

eg aspirin

18
Q

how do you calculate the apparent volume of distribution of a drug

A

total amount of drug in the body /

blood plasma concentration of the drug

19
Q

what is the sum of all routes of elimination equal to (l/h)

A

clearance

20
Q

what is the half life dependent on

A

ln2 x Vd/

Cl

21
Q

what factors affect drug metabolism

A 
age
genetic variation 
race
disease
other medications
22
Q

where are microsomal CYP450s found

A

in endoplasmic reticulum, mostlly in kidney but also lung, liver and intestine

23
Q

describe the metabolism of aspirin

A

first undergoes hydrolysis to produce salicylic acid

some salicylic acid is excreted in urine

the rest is conjugated to from glucoronide

24
Q

what is ion trapping

A

more ionised drug

is less able to be reabsorbed from the nephron so is eliminated

25
Q

if urine is acidic what substances are more likely to be excreted

A

weak bases

26
Q

what is optimum pH for salicylic acid elimination in the urine

A

8 (slightly basic)

27
Q

what does a low Vd suggest

A

there is a high amount of drug in the plasma
probs water soluble
the drug is able to get to where its needed

28
Q

what does a high Vd suggest

A

probs fat soluble
there is a low amount of drug in the plasma
drug is not able to go where it is needed and stays in fatty tissue

29
Q

you start an infusion of 30 mg of hydrocodone
the plasma concentration is 1.07

the clearance is 0.5

what is the half life

A

38.8

Vd= total amount / plasma concentration

half life = Ln2 x Vd/ Cl

type in as Ln2 = x

x times vd = y

y / CL

ln2 = 0.69

30
Q

describe elimination for a drug which has an easily saturable enzyme at or near the therapeutic concentration

A

zero order kinetics.

clearance is not variable with plasma concentration

31
Q

describe clearance for a drug which does not have an easily saturable enzyme

A

first order kinetics

clearance varies with plasma concentration

MD3002 post MSA (66 decks)

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