theophylline (thi-off-i-leen) n. an alkaloid, occurring in the leaves of the tea plant, that has a diuretic effect and relaxes smooth muscles. Theophylline preparations, particularly aminophylline, are used mainly as bronchodilators to treat severe asthma attacks. Trade names: Nuelin SA,Slo-Phyllin,Uniphyllin Continus.

theophylline An alkaloid found in tea, chemically related to caffeine, and with similar effects; 1,3‐dimethylxanthine; caffeine is trimethylxanthine.