Gastroenterological Enzymes

Question 1

What is the function of cytochrome P450 enzymes?

Answer 1

Phase I drug metabolism in the liver (reduces concentrations before reaches systemic circulation)
- oxidation
- reduction
- hydrolysis

Question 2

Which drugs are affected by P450 enzymes?

Answer 2

• clopidogrel
• statins
• warfarin
• POP/COCP

Question 3

When giving statins with a P450 inhibitor, how must the dosage be adjusted?

Answer 3

Reduced
(Less metabolism, higher dose)

Question 4

When giving statins with a P450 inducer, how must the dosage be adjusted?

Answer 4

Increased
(More metabolism, lower dosage)

Question 5

What substances act as P450 inhibitors?

Answer 5

• sodium valproate (antiepileptic)
• SSRIs (sertraline)
• acute alcohol intake
• amiodarone (VTs)
• omeprazole (PPI)
• allopurinol (gout)
• ciprofloxacin (abx)

Question 6

What substances act as P450 inducers?

Answer 6

Longer exposure:
- St John’s Wort (depression, menopause, ADHD, OCD)
- smoking
- rifampicin (ulcer, H2 HIST)
- phenytoin (epilepsy, trigeminal neuralgia)
- carbamazepine (epilepsy, diabetic neuropathy pain, trigeminal neuralgia)
- chronic alcohol intake

Question 7

If you take a P450 enzyme inducer (i.e. smoking) with the COCP, what are the risks?

Answer 7

• pregnancy (lower dose due to metabolism)
• thrombosis