Caffeine (1,3,7-trimethylxanthine) clears via three parallel N-demethylations by CYP1A2: N3-demethylation to paraxanthine (~84%, the dominant pathway), N1-demethylation to theobromine (~12%), N7-demethylation to theophylline (~4%). Paraxanthine is itself a CNS stimulant + adenosine receptor antagonist, and is partly responsible for caffeine's late-half-life effects. The 84:12:4 ratio plus a 5-7 h plasma t½ are the basis for the caffeine + paraxanthine plasma profile.
Organ Systems
digestive
Pathway Steps
caffeine → paraxanthine — via CYP1A2 (N3-demethylation; ~84% of caffeine clearance). CYP1A2 N3-demethylation to paraxanthine is ~84% of caffeine clearance, and paraxanthine carries much of the stimulant effect. CYP1A2 activity varies widely (the *1F polymorphism), is induced by smoking, and is inhibited by fluvoxamine, ciprofloxacin, and oral contraceptives.
caffeine → theobromine — via CYP1A2 (N1-demethylation; ~12%). A minor (~12%) CYP1A2 route yields theobromine (also the main cacao methylxanthine). Because one enzyme dominates, caffeine is a classic CYP1A2 phenotyping probe — and pregnancy markedly slows caffeine clearance via reduced CYP1A2.
caffeine → theophylline — via CYP1A2 (N7-demethylation; ~4%). The smallest (~4%) route gives theophylline, itself a narrow-therapeutic-index drug — so CYP1A2 inhibitors (ciprofloxacin, fluvoxamine) that also raise theophylline can cause toxicity, illustrating the shared metabolism.
Known Modulators
fluvoxamine (inhibitor) — CYP1A2. Potent CYP1A2 inhibitor — caffeine AUC ↑ ~5-10× with fluvoxamine at 100 mg/d. See fluvoxamine → caffeine edge in compounds.json.
ciprofloxacin (inhibitor) — CYP1A2. Verbatim AUC 1.59× from Healy 1989. See ciprofloxacin → caffeine edge.
modafinil (activator) — CYP1A2 (mild induction at SS). AUC ratio 0.90 at SS per Rowland 2018 cocktail study — sub-threshold but reproducible.
theacrine (inhibitor) — adenosine A1/A2A (1,3,7,9-tetramethyluric acid). kucha tea methylxanthine; longer t½ than caffeine; less tolerance development; CYP1A2 substrate
mixed amphetamine salts (inhibitor) — DAT + NET (Adderall salts mixture). amphetamine salt mixture; ADHD + narcolepsy; cross-link: dopamine_receptor_signaling
bergamottin (inhibitor) — CYP3A4 (mechanism-based inactivator). grapefruit furanocoumarin; suicide CYP3A4 inhibitor; mechanistic basis of the grapefruit-juice DDI cluster