xanthine derivative, any one of the closely related alkaloids caffeine, theobromine, and theophylline. They are found in plants widely distributed geographically and are variously ingested as components in beverages such as coffee, tea, cocoa, and cola drinks. The xanthine derivatives or methylxanthines have pharmacological properties that stimulate the central nervous system, produce diuresis, and relax smooth muscles. Theobromine has low potency and is seldom used as a pharmaceutic. Caffeine produces greater central nervous system stimulation than theophylline or theobromine. Caffeine and theophylline also affect the circulatory system, tending to dilate the systemic blood vessels but increasing cerebrovascular resistance with an associated decrease in cerebral blood flow and the oxygen tension of the brain. The ability of the xanthine derivatives to relax smooth muscle is used in certain treatments of asthma. Theophylline is most effective in such treatment and markedly increases vital capacity. The methylxanthines reinforce the release of certain secretions of various endocrine and exocrine tissues, except for mast cells and, possibly, certain other mediators of inflammation. Consumption of xanthine beverages may cause various problems, including restlessness and inability to sleep, GI irritation, and excessive myocardial stimulation characterized by premature systole and tachycardia. See also caffeine, theobromine, theophylline.
