P450 enzyme system

Induction usually requires prolonged exposure to the inducing drug, as opposed to P450 inhibitors, where effects are often seen rapidly

Inducers of the P450 system include

• antiepileptics: phenytoin, carbamazepine
• barbiturates: phenobarbitone
• rifampicin
• St John's Wort
• chronic alcohol intake
• griseofulvin
• smoking (affects CYP1A2, reason why smokers require more aminophylline)

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Carbamazepine Rifampicin Alcohol (chronic) Phenytoin

Griseofulvin Phenobarbitone St. John’s Wort, Sulfonylurea, smoking

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Inhibitors of the P450 system include

• antibiotics: ciprofloxacin, erythromycin
• isoniazid
• cimetidine, omeprazole
• amiodarone
• allopurinol