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pharmacology exam > drug metabolism > Flashcards

drug metabolism Flashcards

1
Q

in order for a drug to work what needs to be achieved

A

an adequate concentration in tissues

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2
Q

what name is given to administration via the skin

A

topical administration

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3
Q

what name is given to administration into the body

A

systemic administration

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4
Q

what are the 2 types of systemic administration and what route do they take

A
  1. enteral administration - GI tract route
  2. parenteral administration - non GI tract route
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5
Q

give the 3 forms of enteral administration

A
  • oral
  • rectal
  • sublingual
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6
Q

give the 5 forms of parenteral administration

A
  • injection
  • bolus injection
  • I.V.
  • inhalation
  • cutaneous
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7
Q

how does a drug reach the target organ

A

it must cross the cell membrane from GI tract to blood plasma

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8
Q

what are the 3 sites of absorption

A
  • stomach
  • small intestine
  • large intestine (colon)
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9
Q

why is the small intestine the the main site of absorption

A
  1. large surface area due to microvilli
  2. high blood flow
  3. bile helps solubilise some drugs
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10
Q

what is the mechanism of diffusion for non-polar chemicals (transcellular)

A

passive diffusion

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11
Q

what is the mechanism of diffusion for polar chemicals (transcellular)

A

facillitated diffusion

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12
Q

what is the mechanism of diffusion for polar chemicals with no concentration gradient (transcellular)

A

active transport

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13
Q

what type of drugs enter the blood capillary via paracellular absorption

A

non-lipophilic drugs

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14
Q

how does food interat with the effect of tetracycline

A

it can bind to calcium in milk, forming an insoluble complex that cannot be absorbed by the GI tract therefore, reducing the drugs bioavailability making it less effective

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15
Q

what do anticholinergics do

A

slows down stomach emptying time, delyaing the drugs passage to the intestine

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16
Q

what do laxatives do?

A

increase gut motility, reducing the contact time of the drug with the absorption site

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17
Q

what do cardiovascular drugs do?

A

reduce blood flow to GI tract, decreasing the rate and efficiency of absorption

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18
Q

what happens when a drug interacts with an antacid

A

drugs may bind to antacids reducing their absorption

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19
Q

give 2 ion exchange resins

A
  • cholestyramine - used to lower cholesterol
  • charcoalw
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20
Q

what effect does cholestyramine have on other drugs

A

it can absorb other drugs prevent their effect

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21
Q

what is charcoal used for

A

used in poinsoning cases to absorb toxins and prevent their absorption

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22
Q

give 5 factors that affect passage of drug through the cell membrane

A
  1. water soluility
  2. lipid solubility
  3. degree of ionisation
  4. active transport
  5. molecular weight
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23
Q

what does the partition coefficient measure

A

distribution of unionised molecules

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24
Q

what does it mean is Log p>0

A
  • drug is more lipophilic
  • rapidly absorbed via the cell membrane (transcellular route)
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25
Q

what does it mean is Log p<0

A
  • drug is more hydrophilic
  • slowly absorbed between cells (paracellular route)
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26
Q

what does it mean if pH>pKa in acidic conditions in a weak acidic drug

A

more unionised so better absorption

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27
Q

what does it mean if pH>pKa in basic conditions in a weak acidic drug

A

more ionised so less absorption

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28
Q

what does it mean if pH>pKa in basic conditions in a weak basic drug

A

more unionised so well absorbed

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29
Q

what are the 3 main proteins that drugs bind to

A
  1. albumin
  2. b-globulin
  3. acid glycoprotein
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30
Q

what drugs does albumin bind to

A
  • acidic drugs
  • most abundant plasma region
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31
Q

what drugs does b-globulin bind to

A
  • some basic drugs
  • e.g. hormones/steroids
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32
Q

what drugs does acid glycoprotein bind to

A
  • binds to some basic drugs
  • levels increase during inflammation
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33
Q

what are the effects of proteins binding to drugs

A
  1. reduced excretion
  2. reduced pharmacological effect
  3. potential displacement of other drugs already bound
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34
Q

what does the amount drug bound depend on

A
  1. drug concentration
  2. affinity for the protein
  3. protein concentration
  4. competition
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35
Q

what administration route is best for a high affinity drug and why

A

I.V. injection - single dose, drug can diffuse out of the plasma

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36
Q

define drug metabolsim

A

the enzyme catalysed conversion of a drug into a chemically distinct product (metabolite)

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37
Q

why do drug need to be metabolised to a metabolite

A

most drugs are non-polar (lipophilic) and require conversion to a polar chemical (hydrophilic for excretion

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38
Q

where is the main site of metabolism

A

liver

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39
Q

how many phases of metabolism are there and what do they do

A
  1. phase i - functionalisation, small chemical modifcations e.g. oxidation
  2. phase ii - conjugation, addition of large charged groups to increase water solubility and excretion
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40
Q

what is the consequence of phase i reactions

A
  • small decrease in lipophilicity
  • slight increase in excretion
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41
Q

what is the consequence of phase ii reactions

A
  • large decrease in lipophilicity
  • increase in excretion
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42
Q

give 4 reaction types in phase i

A
  1. oxidation by cytochrome P450
  2. non-P450 oxidation
  3. reduction
  4. hyrdolysis
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43
Q

where is CYP450 found

A
  • smooth endoplasmic recticulum of liver cells
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44
Q

what does CYP450 require

A
  • molecular oxygen and NADPH as co-factors
  • cytochrome P450 reductase
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45
Q

give the 12 different oxidation reactions of CYP450

A
  1. aliphatic hydroxylation
  2. aromatic hydroxylation
  3. epoxidation
  4. N-dealkylation
  5. O-dealkylation
  6. S-dealkylation
  7. oxidative deamination
  8. N-oxidation
  9. S-oxidation
  10. alcohol oxidation
  11. dehydrogenation
  12. dehalogenation
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46
Q

what is the prosthetic group in all P450s

A

ferriprotoporphyrin IX

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47
Q

where does oxidation occur

A

in the heme group

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48
Q

explain the P450 cycle

A
  1. drugs bind to the active site
  2. molecular oxygen (O2) interacts with the iron the heme group
  3. one oxygen atom is used to form water and the other is incorporated into the drug to form the oxidised product
  4. drug leaves the active site
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49
Q

give an example of a molecule that goes through aliphatic hydroxylation

A
  • tolbutamide
  • hypoglycaemic agent used to treat diabetes
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50
Q

give an example of a molecule that goes through aromatic hydroxylation

A
  • salicylic acid
  • treatment for psoriasis
51
Q

give an example of a molecule that goes through epoyxidation

A
  • carbamazepine
  • anticonvulsant used to treat epilepsy
52
Q

give an example of a molecule that goes through O-dealkylation

A
  • phenacetin
  • analgesic related to aldehyde paracetamol
53
Q

give an example of a molecule that goes through N-dealkylation

A

diazepam, treatment for anxiety

54
Q

give an example of a molecule that goes through deamination

A
  • amphetamine
  • indirectly acting sympathomimetic
55
Q

give an example of a molecule that goes through N-oxidation

A

clozapine
antipsychotic used for schizophrenia

56
Q

how is alcohol oxidation mediated and where does it occur

A
  • alcohol dehydrogenase
  • primary and secondary alcohols
57
Q

what mediates N-, S-oxidation reactions

A

flavin monooxygenase

58
Q

where is FMO found and what is its necessary co factor

A
  • in liver microsomes smooth E.R
  • NADPH
59
Q

what are the 2 types of monoamine oxidase

A

MAO-A and MAO-B

60
Q

where is MAO-A found

A
  • found in the liver
  • pulmonary vascular endothelial
  • GI tract
  • placenta
61
Q

where is MAO-B found

A
  • blood platlets
62
Q

what is the role of MAO

A
  • inactivates endogenous neurotramitters
63
Q

give 2 inhibitors of MAO

A
  • caffeine
  • antidepressants
64
Q

give an example of a molecule that goes through metabolisation via MAO

A
  • sumatriptan
  • treatment in headaches
65
Q

what does aldehyde oxidation

A

aldehydes into carboxylic acid

66
Q

give an example of a molecule that goes through xanthine oxidation

A

6-mercaptopurine
anti-tumour drug

67
Q

give an example of a molecule that goes through azo reduction

A
  • prontosil (inactive) to sulphanilamide (active)
68
Q

give an example of a molecule that goes through nitro reduction

A

clonazepam
used to prevent seizures

69
Q

give an example of a molecule that goes through sulfoxide reduction

A

sulindac
non-steroidal anti-inflammatory drug

70
Q

give an example of a molecule that goes through quinone and epoxide reduction

71
Q

give an example of a molecule that goes through amine hydrolysis

A

procainamide
anti-arrythmic

72
Q

where does hydrolysis occur

A

plasma tissue

73
Q

give an example of a molecule that goes through lactone hydrolysis

A

activation of lavastatin
choleterol lowering drug

73
Q

give an example of a molecule that goes through ester hydrolyis

A

activation of morphine

74
Q

give an example of a molecule that goes through alkaline phosphate hydrolysis

A

activation of phenytoin - antiepileptic

75
Q

what is a phase ii reaction

A

reaction catalysed by a transferase enzyme that transfer a polar group from a donor to the phase i metabolite

76
Q

what are the 2 exceptions in phase ii reactions

A

acetylation and methylation in which polar groups are masked

77
Q

where does glucuronidation occur

A

in the liver

78
Q

what is he donor molecule for glucuronidation and what does it do

A

uridine diphosphate glucuronic acid (UDPGA) - transfers the glucuronyl group to nucleophillic O, N or S

78
Q

what is glucuronidation catalysed by

A

UDP-glucuronoyltransferase

78
Q

give an example of a molecule that goes through O-glucuronidation

A

salicylic acid

79
Q

give an example of a molecule that goes through N-glucronidation

A

sulphanilamide

79
Q

what enzyme catalyses sulphation

A

sulphaeotransferase

79
Q

what is the donor molecule for sulphation

A

3’phosphoadenosine-5’phosphosulfate (PAPS)

80
Q

sulphation and glucuronidation compete for some pathways, who predominates

A

sulphation predominates at low substrate concentrations, glucuronidation predominates at higher concentration

81
Q

give an example of a molecule that goes through sulphation

A

paracetamol

82
Q

where does glycine conjugation occur

A

in the mitochondria

83
Q

which enzyme catalyses glycine conjugation

A

N-acyl transferase

84
Q

give an example of a molecule that goes through glycine conjugation

A

salicylic acid

85
Q

what enzyme catalyses glutathione conjugation

A

glutathione S-transferase

86
Q

give an example of a molecule that goes through glutathione conjugation

A

paracetamol

87
Q

what enzyme catalysis acetylation

A

N-acetyl-tranferase (NAT)

88
Q

what is the donor for acetylation

A

acetylene coA

89
Q

what is the risk with acetylation

A
  • decreases water solubility
  • no increase in excretion
  • can precipitate out into kidney tubules leading to renal toxicity
90
Q

give an example of a molecule that goes through acetylation

A

sulfanilimide

91
Q

what is the enzyme that catalyses methylation

A

methyltranferase

92
Q

what is the donor molecule for methylation

A

S-adenosyl methionine (SAM)

93
Q

what enzyme catalyses O-methylation

A

catechol-O-methyltransferase (COMT)

94
Q

what enzyme catalyses S-methylation

A

thiopurine-S-methyltransferase (TPMT)

95
Q

give an example of a molecule that goes through S-mthylation

A

6-mercaptopurine

96
Q

give an example of a molecule that goes through O-methylation

A

L-DOPA - parkinsons disease treatment

97
Q

what is the phase ii metabolism reactions for functional group OH

A
  • glucuronidation
  • sulphation
  • methylation
98
Q

what is the phase ii metabolism reactions for functional group COOH

A
  • glucuronidation
  • glycine conjugation
99
Q

what is the phase ii metabolism reactions for functional group NH2

A
  • acetylation
  • glucuronidation
    -sulpahation
100
Q

give 5 causes of variabilty in drug metabolsim

A
  1. drug-drug interaction
  2. drug-diet interaction
  3. genetic variation
  4. underlying disease
  5. environment/lifestyle
101
Q

what is enzyme inhibition?

A

when a drug blocks the active site of a metabolising enzyme, reducing its ability to metabolise other drugs

102
Q

what is a non-competitive inhibitor

A

the inhibitor binds to a site other than the active site - altering enzyme activity

103
Q

what is a competitive inhibitor

A

drugs that compete for the same binding site on an enzyme

104
Q

what is irreversicle inhibition

A

inhibitor (drug) forms a permamnent bond with the enzyme deactivating it

105
Q

what is enzyme induction

A

when a drug stimulates the production of enzymes, this leads to increased metabolsim of the drug reducing efficacy

106
Q

why is it bad to eat grapefruit when you are on certain medication?

A

it contains a compound called furanocoumarin which acts as an inhibitor of CYP3A4 (enzyme responsible for drug metabolism

107
Q

what is irinotecan

A

a pro-drug used in colorectal cancer treatment

108
Q

what is the phase i metabolism of irrontecan

A

conversion of irinotecan to its active SN-38 variant via carboxylesterase

109
Q

what is the phase ii metabolism of irrontecan

A

glucuronidation of SN-38 to its inactive form by UGT1A1 - build up of active SN-38 can be toxic

110
Q

give 4 examples of toxic phase i metabolites

A
  1. epoxides
  2. hydroxyl amines
  3. quinoneimines
  4. free radicals
111
Q

how is paracetamol overdoes toxic

A

normally paracetamol can be metabolised by either glucuronidation or sulfation, in overdose situations these pathways become saturated leading to increased production of NAPQI (highly toxic) which binds to the liver causing hepatitis

112
Q

explain isoniazid hepatoxcitiy

A

the phase ii metabolism is acetylation - converts isoniazid into inactive metabolites
- NAT responsible for metabolism has variations in its genes leading to different acetylation rates - slow acetylation means active isoniazid persists longer in the body

113
Q

what is a type A ADR

A
  • on target
  • exaggeration o drugs normal pharmacological effect
  • dose deendent
114
Q

what is a type B ADR

A
  • off-target
  • novel unexpected responses
  • may only be discovered after a drug is available for general use
115
Q

what is a type C ADR

A
  • continuing
  • presists for long time after withdrawal
116
Q

what is a type D ADR

A
  • delayed
  • become apparent sometime after the use of the medicine
117
Q

what is a type E ADR

A
  • end of use
  • associated with withdrawal of medicine

pharmacology exam (2 decks)

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