What are the P450 inhibitor and inducer drugs?

P450 inhibitor drugs 

  • Acute alcohol intake
  • Allopurinol
  • Amiodarone
  • Cimetidine, omeprazole
  • Co-trimoxazole
  • Dapsone
  • Imidazoles: ketoconazole, fluconazole
  • INH (Isoniazid)
  • Macrolides [Azithro-Clarithro-Erythromycins(CYP3A4)]
  • Metronidazole
  • Methylprednisolone (high dose)
  • Quinolones (ciprofloxacin/Levofloxacin)
  • Quinupristin
  • Sodium valproate
  • Spironolactone
  • SSRIs: fluoxetine, sertraline
  • SNRIs: Venlafaxine
  • Grapefruit juice (a potent inhibitor of the cytochrome P450 enzyme CYP3A4. It alters the metabolism of statins. Concomitant  use  of  atorvastatin  and  large  amounts  of  grapefruit  juice  should  be avoided  as it  contributed  to  ↑  statin-associated myotoxicity  )
  • Protease inhibitors (indinavir, nelfinavir, ritonavir, saquinavir)
  • Cranberry Juice (inhibitors of P450 enzyme CYP2C9; alter warfarin metabolism and it may increase INR )
  • Verapamil & Diltiazem

P450 inducer drugs

  • Antiepileptics: phenytoin, carbamazepine (note that valproate is an inhibitor)
  • Barbiturates
  • Chronic alcohol intake
  • Griseofulvin
  • Quinidine
  • Rifampicin
  • Smoking (affects CYP1A2, reason why smokers require more aminophylline)
  • St John's Wort
  • Sulfa drugs
  • Tetracycline
  • Nevirapine (NNRTI)


What is the autoinduction of carbamazepine?

Ans: Carbamazepine is an inducer of the P450 system. This, in turn, increases the metabolism of carbamazepine itself.


  • [Images are reproduced from the information taken from Step Up To MRCP (Review Note For Part I & Part II) By Dr Khaled El Magraby]

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