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10 Cards in this Set

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Phase 1
Catabolic reactions - oxidation, reduction and hydrolysis most common.

Aim to prepare drug for phase to by adding or forming a chemically reactive functional frouip (OH, NH2, OOH)

Mostly occur in the liver.

Oxidation is a major route which is catalysed by chtochrome p450 family of mixed oxidases.
Other enzymes
Plasma esterases
monoamine oxidases
decarboxylases
Most important isotypes in liver (cytochrome p450)?
CYP1, 2 &3
Most common cytochrome p450 reaction?
monooxygenase reaction - insertion of one oxygen atom to a drug while the other is reduced to water
Monooxygenase reaction requires?
Cytochrome p450 haeme protein

O2

Cytochrome p450 reductase

NADPH
Phase 2 aim?
Enhancing water solubility (ionised or polar) to aid excretion through a series of conjugation reactions.
Major conjugation reaction?
Glucuronidation (morphine)
glycosidation
sulfation (paracetemol) ->highly ionised
methylation ->more polar
acetylation ->more polar
amino acid conjugation ->more polar
glutathione conjugation
Monooxygenase oxidation reaction?
O-dealkylation
Alpihatic hydroxylation
Deamination
N-dealkylation
N-oxidation
S-oxidation
Aromatic hydroxylation
Enzyme inhibition +example
Two drugs are metabolised by the same p450 enzyme they will inhibit eachothers metabolism therefore there is a risk of overdosing.

terfenadine & cimetidine (CYP3A4)
Enzyme induction
Enzyme induces its own metabolism leading to tolerance.
(Phenobarbitone reduces effectiveness of digitoxin by enhancing its metabolism)