Expansion
Inducers speed metabolism and reduce effect; inhibitors slow it and increase effect
Expansion
Inducers (increase metabolism, so reduce drug levels) - CRAP GPS
- C - Carbamazepine
- R - Rifampicin
- A - Alcohol (chronic)
- P - Phenytoin
- G - Griseofulvin
- P - Phenobarbital
- S - Sulphonylureas, St John’s wort, smoking
Inhibitors (reduce metabolism, so increase drug levels) - AODEVICES
- A - Allopurinol, amiodarone
- O - Omeprazole
- D - Disulfiram
- E - Erythromycin and other macrolides
- V - Valproate
- I - Isoniazid
- C - Ciprofloxacin, cimetidine
- E - Ethanol (acute)
- S - Sulphonamides
Also grapefruit juice, azole antifungals and protease inhibitors.
Timing distinguishes them clinically: inhibition acts within hours, while induction requires new protein synthesis and takes days to weeks, with a similar delay on stopping. This is why the INR of a warfarinised patient started on rifampicin falls gradually, and rises dangerously weeks after rifampicin is stopped if the dose was increased.