theophylline
(thē-of'ĭ-lĭn 
)
[L. thea, tea + Gr. phyllon, plant + -ine]
A white crystalline powder used as an oral agent for reactive airway diseases such as asthma. The drug has a narrow therapeutic index, and toxicity to this agent, marked by gastrointestinal upset, tremor, cardiac arrhythmias, and other complications, is common in clinical practice. Other drugs for reactive airway diseases, such as inhaled beta-agonists and inhaled steroids, are often prescribed instead of theophylline to avoid its toxicities.
SEE: aminophylline.