17.01.4.4 Theophylline

Theophylline was discussed in eChapter 3. Theophylline is a phosphodiesterase inhibitor. As a result of inhibiting phosphodiesterase, theophylline causes an increase in the levels of cAMP in the bronchial smooth muscle. The levels of cAMP determine the degree of bronchodilation, and when the levels are increased, there is an increased relaxation of smooth muscle. By inhibiting phosphodiesterase, theophylline inhibits the breakdown of cAMP, to cause an increased bronchodilation Theophylline is used clinically as a bronchodilator, mainly in the emergency treatment of asthma, especially when asthma is continuing despite the use of a β₂-adrenoceptor agonist.