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metabolism Flashcards

1
Q

Biotransformation

A

the sum if all processed whereby a compound is transformed chemically within a living organism

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2
Q

what does primary transformation do?

A

makes a lipophilic compound more hydrophilic

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3
Q

are detoxification and biotransformation the same thing?

A

NO

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4
Q

biotransformation products

A

may get more or less potent/ biologically active

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5
Q

detoxification products

A

always get less potent

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6
Q

what is phase one of metabolism called?

A

oxidation step known as bioconversion

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7
Q

what happens in phase 1 of metabolism?

A

polar functioning group such as a hydroxyl group introduced into the lipophilic drug making it more hydrophilic

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8
Q

what enzyme normally carries out phase 1?

A

cytochrome P450 mono oxygenases

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9
Q

what happens in phase 2 of metabolism?

A
  • Metabolites produced in phase 1 are covalently linked to naturally occurring endogenous species – eg sugars, peptides and sulfides
  • Makes the metabolites quite water soluble and non toxic – readily excreted
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10
Q

what happens to the molecular weight of drugs as they exit phase 2?

A

it increases as theyre being added to

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11
Q

where does the name cytochrome P450 come from

A

Cytochrome: it is a coloured intracellular protein
P: it is pink
450: its absorption spectrum has a maximum at 450 nm

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12
Q

what are the Cytochrome P450 Monooxgenases involved in?

A

in the liver, they’re in the smooth ER, drug metabolism

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13
Q

what are Cytochrome P450 Monooxgenases also known as?

A

microsomal enzymes, this is because of the fraction that they are found in when you homogenise the cell

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14
Q

what is the main function of the Cytochrome P450 Monooxgenases in phase 1 of metabolism?

A

give the drug 1 oxygen from molecular oxygen, and the other oxygen is released as water – makes the drug more hydrophillic

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15
Q

equation for phase 1

A

R-H + O2 + H+ – NADPH/Enzyme –> R-OH + NADP+ + H2O

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16
Q

Hydroxylation

A

is a chemical process that introduces a hydroxyl group (-OH)

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17
Q

Epoxidation

A

a conversion of a usually unsaturated compound into an epoxide

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18
Q

Dealkylation

A

removal of an alkyl groups

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19
Q

Deamination:

A

removal of an amino group

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20
Q

Sulfoxidation

A

reaction with, or conversion to a sulfoxide

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21
Q

Desulfuration

A

the process of removing sulphur

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22
Q

what is Epoxie

A

cyclic ether with 3 rings

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23
Q

what is Epoxie

A

cyclic ether with 3 rings

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24
Q

different levels of CYP2D6 which catalyse the reaction of iodine to morphine depend on?

A

genetic polymorphisms

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25
people who are poor metabolisers of codine
coding is ineffective as they don't break down enough coding into morphine
26
ultra rapid metabolisers of coding are at risk of
morphine toxicity
27
ultra rapid metabolisers of coding have how many copies of the gene CYP2D6?
2 or more
28
why are there reports of children dying from having coding?
they don't have the correct levels of CYP2D6 in their livers, so break down too much coding and get poised from the high levels of morphine can overdose even from receiving the milk of mothers containing codine
29
if the enzyme that breaks down a drug is inhibited what is the effect on the drug?
increased activity of the drug
30
which drug would increase the activity of the enzyme which breaks down warfrin? effect?
carbemazepine | reduces the activity of warfarin due to enhanced metabolism
31
which drug would decrease the activity of the enzyme which breaks down warfrin? effect?
erythromycin increase the activity of warfarin due to impaired metabolism
32
a safer drug has a ...
high therapeutic index, large lethal dose and a small effective dose
33
dangerous drugs have
lower therapeutic index, requires regular monitoring, minor modification could cause toxic effects
34
which drugs could be toxic with minor adjustments?
warfarin, lithium, digoxin
35
what is the equation for therapeutic index?
LD50/ED50
36
ED50 -
the effective dose in 50% of the population
37
when would 2 drugs reacting be dangerous when affecting the theraputic index?
when they make the therapeutic index smaller
38
what enzymes are requires for phase 2 of metabolism?
transferase enzymes
39
what are also required for phase 2 metabolism>
cofactors
40
what are the 2 important things required for phase 2?
cofactors and transferase enzymes
41
what is glutathione important in?
cofactor which is important in phase 2 of metabolism
42
what is glutathione made of?
glutamic acid, cysteine, glycine
43
what are the 2 important cofactors required for conjugation in phase 2?
UDP-GA and PAPS
44
which transferase enzyme add glutaronic acid? using which cofactor?
glucuronyl transferase using UDP cofactor
45
which transferase enzyme add sulphate groups to amino or hydroxyl compounds? using which cofactor?
Sulphotransferase – requires PAPS to be a sulfur donor
46
what does Glutathione S transferase do?
conjugates electrophilic metabolites
47
what is the issue with first pass metabolism?
Drugs extracted so efficiently by the liver or gut wall – amount reaching systemic system much less than that is absorbed
48
how does individual variation affect first pass metabolism?
in the activities of drug-metabolising enzymes and also as a result of variation in hepatic blood flow.
49
some drugs which undergo substantial elimination through first pass
aspirin, salbutamol, morphine,
50
Zero-order elimination kinetics
Elimination of a constant quantity per time unit of the drug quantity present in the organism - straight line
51
First order elimination kinetics
Elimination of a constant fraction per time unit of the drug quantity present in the organism. The elimination is proportional to the drug concentration
52
which order of kinetics do most drugs follow
first order
53
which drugs follow zero order kinetics? why?
alcohol, aspin, phenytoin | when saturated and drug one excess
54
why would a drug follow zero order kinetics?
limited number of enzymes available for metabolism of drug – limit reached – metabolism happens at constant rate – always a straight line - alcohol
55
Half-life
Time it takes for the plasma concentration or the amount of drug in the body to be reduced by 50%.
56
how much drug should be remaining after 3 half lives?
12.5%
57
Elimination rate constant (K):
Fractional rate of drug removal from the body
58
what should the elimination rate constant be in first order kinetics
constant
59
Clearance
The volume of plasma in the VASCULAR COMPARTMENT cleared of drug per unit time by the processes of metabolism and excretion
60
clearances are addictive - what is the CLtotal equation
CL renal + CL non renal | could be different for other organs???
61
clearance as a product of first order elimination...
constant (k) and Volume distribution
62
what is the CLtotal equation
k+Vd
63
what is the CLtotal equation
k+Vd
64
(O1) rate of elimination is proportional to
plasma concentration
65
zero order alcohol metabolism is
linear not exponential
66
why in zero order does conc. of drug become a constant value?
enzymes are saturated and cannot metabolise any more alcohol
67
doesn't matter how much you have in your body elimination will be
approximately 4mili mol / litre / hour
68
what is the oxidation factor in alcohol metabolism?
alcohol dehydrogenase – requires cofactor NAD+ that isnt produced constantly – produced over period of time – enzymes cant work without
69
slow elimination means ... half life | because
long half life | - large Vd, large fraction of drug located in tissues not accessible to organs of elimination, long HL
70
rapid elimination means ... half life | because
short half life | - small Vd, small fraction in the tissues, more assemble to organs elimination, short HL
71
Most drugs follow first order kinetics
Metabolism rate is proportional to drug plasma concentration | Drug concentration drops by fixed percentage in a given time
72
A few drugs follow zero order kinetics
Metabolism removes a fixed amount of drug in a given period Drug concentration drops linearly Overdoses take longer to clear Example: alcohol
73
Repeated administration
Drug administration of a fixed dose at a regular time interval, through a given route
74
Loading dose
In urgent situations, the steady state plasma concentration must be reached more rapidly. A higher dose can then be administered on treatment initiation, to compensate for accumulation.
75
accumulation occurs when
the drug is administered before the previous dose is completely eliminated
76
concentration steady state av equation
= (f x dose) / (CL x J)
77
what guides maintenance dosage intervals/
drug half life
78
warren half life
37 hours, so should be taken daily
79
drugs with 1/2 life less than 30 mins should be given
by infusion
80
Drugs ½ life 30 min should be taken
every 8 hours but should consult the therapeutic index
81
if the drug has a low therapeutic index, must be given every
1/2 life by INFUSION
82
½ life 8-24 hours
give every ½ life
83
total clearance of a drug is the fundamental parameter describing
its elimination
84
the rate of elimination equals
CLtotal x plasma conc
85
CL total determines
steady stat plasma conc. (CLss)
86
CLss =
rate drug administration/ CLtot
87
most dugs follow
1st order kinetics - exponential
88
Vd
where the body is treated as one well stirred compartment. Vd is the parent volume linking the amount of drug in the body at any time to the plasma conc.
89
elimination half life is
directly proportional to Vd and inversely proportional to CLtot
90
within how many half lives with repeated dosing does plasma conc. reach a steady value?
3-5 HLs
91
how would a therapeutic dose be reached rapidly in urged situations?
by giving a loading dose
92
Loading dose is achieved in plasma conc. determined by
L = Ctarget x vd
93
what would a 2 compartment model mean for kinetics
they become biexponential
94
what do the 2 compartment in the 2compartment model represent?
process of transfer between plasma and tissues (a phase) elimination from the plasma (B phase)
95
some drugs show non-exponential kinetics - important clinical consequences ...
disproportionate increase in steady state plasma conc. when daily dose inc.

Pharmacology (18 decks)

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