enzyme induction

Question 1

Rifampicin induces CYP3A4 → What happens to OCP?

Answer 1

Faster metabolism → ↓ blood level → Contraceptive failure → Unwanted pregnancy 😱

Question 2

Fix for OCP + Rifampicin?

Answer 2

Use condoms / IUCD during + 28 days after rifampicin

Question 3

Paracetamol → toxic metabolite?

Answer 3

NAPQI

Question 4

Inducers that ↑ NAPQI?

Answer 4

Chronic alcohol, Phenytoin, Carbamazepine → ↑ CYP2E1

Question 5

Risk of paracetamol in alcoholics?

Answer 5

> 4g → glutathione depleted → fulminant liver failure

Question 6

Antidote for paracetamol overdose?

Answer 6

N-acetylcysteine (NAC) = glutathione donor

Question 7

Phenytoin → effect on Vitamin D?

Answer 7

↑ CYP24A1 → ↓ active 1,25-OH Vit D

Question 8

Phenytoin long-term → bone disease?

Answer 8

Adults: Osteomalacia | Kids: Rickets

Question 9

Fix for phenytoin-induced rickets?

Answer 9

Vitamin D + Calcium supplements

Question 10

Key inducers mnemonic?

Answer 10

PC RGS C → Phenytoin, Carbamazepine, Rifampicin, Griseofulvin, Smoking, Chronic alcohol

Question 11

Enzyme induction = ?

Answer 11

↑ metabolism = ↓ drug effect (except paracetamol toxicity ↑)

Question 12

Phenobarbitone in neonatal jaundice?

Answer 12

Benefit! ↑ glucuronyl transferase → ↓ bilirubin → prevents kernicterus

Question 13

Autoinduction example?

Answer 13

Carbamazepine → tolerance → dose ↑ needed

Question 14

Porphyria trigger?

Answer 14

Barbiturates → ↑ porphobilinogen → acute attack

Question 15

Warfarin + cabbage/spinach?

Answer 15

Rapid elimination → ↓ INR → bleeding risk ↓