19.3 : 抗喘息薬：メチルキサンチン

Methylxanthines, such as theophylline, act as bronchodilators to manage asthma.

Theophylline's exact mechanism of action is complex, potentially involving phosphodiesterase enzyme inhibition, elevating intracellular cAMP and cGMP levels. This action stimulates cardiac function, relaxes airway smooth muscle, and reduces inflammation.

Another suggested mechanism is via adenosine receptor inhibition on cell surfaces to increase adenylyl cyclase activity, leading to bronchodilation.

Theophylline is typically administered orally as a sustained-release formulation to ensure a prolonged therapeutic effect. Aminophylline, a combination of theophylline and ethylenediamine, is administered intravenously in specific cases.

Despite the therapeutic benefits, theophylline yields side effects ranging from mild symptoms such as nausea, vomiting, abdominal discomfort, and headache to more severe effects such as seizures or arrhythmias.

Due to its narrow therapeutic window and adverse effects, theophylline has been replaced by β₂-agonists and corticosteroids. As a result, the FDA no longer recommends theophylline for status asthmaticus.