Paraxanthine, or 1,7-dimethylxanthine, is a dimethyl derivative of xanthine, structurally related to caffeine. Like caffeine, paraxanthine is a psychoactive central nervous system (CNS) stimulant. It possesses a potency roughly equal to that of caffeine and is likely involved in the mediation of the effects of caffeine itself.
Paraxanthine is not produced by plants and is only observed in nature as a metabolite of caffeine in animals. The compound is produced from caffeine (1,3,7-trimethylxanthine) breakdown. After intake, roughly 84% is demethylated at the 3-position to yield paraxanthine. The drug is by far the chief metabolite of caffeine in the body.
Certain proposed synthetic pathways of caffeine make use of paraxanthine as a bypass intermediate. However, its absence in plant alkaloid assays implies that these are infrequently, if ever, directly produced in nature.
Paraxanthine has a number of physiological effects on animals. In humans, the compound acts as a nonselective, competitive inhibitor of adenosine receptors. As a result, paraxanthine triggers an elevated diastolic blood pressure and an increase in plasma epinephrine levels. Furthermore, the compound is responsible for the lipolytic properties of caffeine, and its presence in the blood causes an increase in serum free fatty acid concentration. Paraxanthine, unlike caffeine, acts as an enzymatic effector of Na+/K+ ATPase. As a result, it is responsible for increased transport of potassium ions into skeletal muscle tissue. Similarly, the compound also stimulates increases in calcium ion concentration in muscle.
Paraxanthine is believed to exhibit a lower toxicity than caffeine. While blood levels commensurate with average intake appear to be fairly innocuous, high blood concentrations of paraxanthine have been linked to spontaneous abortion in pregnant mothers.