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.

Relevant in asthma and psychiatry: ciprofloxacin + theophylline is one of the classic interactions with seizure risk and requires theophylline dose reduction.