Theophylline is a prescription drug that has been used to treat asthma (a chronic inflammation of the airway tissues) for decades. In recent years, concern over side effects associated with the drug has lessened its use. Many physicians turned instead to alternative asthma treatments, such as inhaled beta2-agonists (medications that relax muscles in the air passageways to prevent narrowing and to open the airways) and inhaled corticosteroids (medications that prevent the inflammation associated with asthma attacks). While theophylline is still widely prescribed in poorer countries (due to its affordability), its popularity has decreased in industrialized nations.

However, new discoveries about theophylline have led to renewed interest in the drug as an asthma treatment. For many years, the process by which theophylline affects asthma symptoms was unknown. Recent studies now show that theophylline inhibits the release of histamine, a chemical that plays a key role in triggering an asthma attack. In addition, theophylline appears to suppress airway inflammation, another major cause of asthma symptoms.

Theophylline has a powerful effect on the late-phase allergic reaction of allergic asthma (inflammation of the lung's airways that is caused by an allergic reaction), which is believed to be the key reaction in the development of airway hyperreactivity (an exaggerated constriction of the airways in response to stimuli). This is important, because hyperreactive airways go into spasm from many irritants, including cold air and strong perfumes.

In addition, theophylline relaxes smooth muscles in the airway, allowing more air into the body. Theophylline may also increase the strength of a weakened diaphragm (allowing it to draw more air into the lungs) and stimulate the brain’s breathing control centers. Finally, it may reduce the volume of gas trapped in the lungs. All of these effects help improve the breathing ability of patients with asthma and other lung diseases.

Those who take theophylline must be aware that there is a very small difference between a proper dose of the drug and a toxic overdose. For this reason, many physicians reject using theophylline and instead prescribe newer medications with fewer or less serious potential side effects.