Learning Objective
Understand the major inducers, inhibitors, and substrates of CYP450 enzymes to predict drug-drug interactions and avoid adverse effects.
CYP450 Inducers (↑ enzyme activity → ↓ substrate levels)
Mnemonic: “St. John’s Phen Phen Mom Never Refuses Greasy Carbs & Chronic Alcohol”
- St. John’s wort
- Phenytoin
- Phenobarbital
- Modafinil
- Nevirapine
- Rifampin
- Griseofulvin
- Carbamazepine
- Chronic alcohol overuse
Effect: ↓ plasma concentration of substrates like theophylline, oral contraceptives (OCPs), warfarin
CYP450 Inhibitors (↓ enzyme activity → ↑ substrate levels)
Mnemonic: “SICK FACES Come Over For Grapefruit Juice”
- Sodium valproate
- Isoniazid
- Cimetidine
- Ketoconazole
- Fluconazole
- Chloramphenicol
- Erythromycin/clarithromycin
- Sulfonamides
- Ciprofloxacin
- Omeprazole
- Fluoxetine / amiodarone
- Grapefruit juice
- Juice
Effect: ↑ plasma concentration of substrates → risk of toxicity
Activity
Common Substrates to Remember
- Theophylline
- OCPs
- Warfarin
- Anti-epileptics (e.g., phenytoin, carbamazepine)
Step 1 High-Yield Tip
- Inducers → decrease drug levels → possible therapeutic failure
- Inhibitors → increase drug levels → possible toxicity
- Use mnemonics to quickly recall multiple CYP450 interactions.
