6 - Drug metabolism

Question 1

phase 1 and phase 2

Answer 1

1 - metabolsm by cytocrhome P450 enzymes mainly in liver or gut wall

2 - Conjugation - by transferases, e.g glucouronyl, sylphate, acetate

Question 2

CYP1A2

Answer 2

Marker drug - main drug metabolised by this - theophylline
inducer - tobacco
-inhibitor - cimetidine

Question 3

CYP2E1

Answer 3

ethanol
relevant drugs - paracetamol, in overdose - forms a metbolight NAPQ1 - very reactive
Inducer - ethanol - so can make more of the metabolight from paracetamol form

Question 4

CYP2C9

Answer 4

warfarin
risk - lower dose increase risk of bleeding increased dose - increase amount of bleeding

ethnicity - caucasian - 25% , asian 1%
-some people have lower activity of this enzyme - less clearance (increase bleeding)

Question 5

CYP2C19

Answer 5

s-mephenytoin

• omeprazole *acid pump inhibitor- and also is an inhibitor of CYP2C19

Interactions
-there is decrease effectiveness of clopidogrel (prodrug) andtiplatelet agent when combined with omeprazole

Ethnicity - caucasians and asians

Question 6

CYP3A4

Answer 6

-in GUT

Simvastatin (lipid lowering medication)
-lopomavir - HIV treatment

Drug interaction
-grapefruit juice - inhibitor (in gut)
St johns wart - inducer