Cytochrome P450 1A2
Also known as: CYP1A2
Cytochrome P450 enzyme that metabolises theophylline, caffeine, clozapine and olanzapine. It is induced by tobacco smoke and grilled meat, and inhibited by ciprofloxacin and fluvoxamine.
CYP1A2 inhibition (e.g. ciprofloxacin + theophylline) increases the risk of theophylline toxicity (nausea, tachycardia, seizures); smokers who quit may accumulate substrates metabolised by this enzyme.
Substrates: theophylline, caffeine, clozapine, olanzapine, duloxetine, tizanidine, melatonin.
Inhibitors: ciprofloxacin, fluvoxamine, cimetidine, oral contraceptives.
Inducers: tobacco smoke, omeprazole (weak), rifampicin, broccoli/cabbage (weak).
Relevant in asthma and psychiatry: ciprofloxacin + theophylline is one of the classic interactions with seizure risk and requires theophylline dose reduction.
DailyMed/FDA (NIH/NLM) — approved labels (theophylline, ciprofloxacin); EMC-UK (MHRA) — SmPC
