Caffeine (1, 3, 7-trimethylxanthine) is one of the most important naturally occurring methylated xanthine alkaloids. It is a constituent of coffee, tea, sodas, chocolate, various energy drinks, and is the most widely consumed behaviorally active substance in the world. After rapid and complete absorption from gastrointestinal tract, caffeine undergoes extensive hepatic metabolism, mediated primarily by cytochrome P450 1A2 N-demethylation, to form three primary metabolites, paraxanthine (1, 7-dimethylxanthine), theobromine (3, 7-dimethylxanthine), and theophylline (1, 3-dimethylxatnhine). In humans, the formation of paraxanthine accounts for 83.9 ± 5.4% of caffeine metabolism, while theobromine and theophylline account for 12.2 ± 4.1 and 3.7
