NAPLEX (North American Pharmacist Licensure Examination) Practice Exam

What does Theophylline block to cause bronchodilation?

1. Adenosine receptors

2. Phosphodiesterase

3. Leukotriene pathways

4. Beta-2 adrenergic receptors

The correct answer is: Phosphodiesterase

Theophylline is a medication used to treat asthma and other respiratory conditions. It works by relaxing and opening up the airways, making it easier to breathe. It achieves this by inhibiting or blocking phosphodiesterase, an enzyme that breaks down cyclic nucleotides, which are important for smooth muscle relaxation. By blocking phosphodiesterase, Theophylline allows these cyclic nucleotides to accumulate and promote bronchodilation. The other options, while involved in the respiratory process, do not play a significant role in Theophylline's mechanism of action. Adenosine receptors help regulate bronchoconstriction but are not directly affected by Theophylline. Leukotriene pathways also play a role in inflammation and bronchoconstriction, but are not affected by Theophylline directly. Beta-2 adrenergic receptors are targeted by other asthma medications, such as albuterol, but are not involved in Theophylline's mechanism of action.