Paraxanthine is an inhibitor of phosphodiesterase 9 (PDE9) and an antagonist of adenosine receptors A1 and A2 (Kis = 35 and 22 μM, respectively in equine forebrain tissues). It is the main metabolite of caffeine in humans, making up 80% of the three dimethylxanthine metabolites produced by caffeine demethylation. Paraxanthine increases locomotor activity and counteracts adenosine receptor agonist-induced motor depression in rats not habituated to caffeine. At a dose of 30 mg/kg, paraxanthine induces a significant increase in striatal cGMP and extracellular striatal dopamine concentrations in vivo. It also promotes wakefulness and increases locomotor activity and core temperature in narcoleptic transgenic mice without increasing behavioral anxiety.
