Theophylline is used to relieve and prevent bronchospasm, or narrowing of the airways, in patients who have asthma. It is also prescribed for prevention of emphysema, chronic bronchitis, and other lung diseases, controlling wheezing, shortness of breath, and difficulty breathing. It is a methylxanthine, a long-acting bronchodilator medication that relaxes and opens up the air passages in the lungs, making it easier for the patient to breath. After first being isolated in 1888, it remains to be the most commonly used medication in the world for asthma prevention. It decreases the need to take acute asthma relief medications and is an effective steroid-sparing agent. Theophylline is sold under several trade names: Theo-Dur, Respbid, Slo-Bid, Theo-24, Theolair, Uniphyl, and Slo-Phyllin. It is available in the following formulations: Tablets (100mg, 200mg 300mg, 400mg, 450mg), syrups, and solutions. Only a physician can determine the correct dosage for each individual based on their weight, age, and the theophylline blood level. Compared with other bronchodilators, theophylline is effective and is a safer option.