Which of the following is a bronchodilator?

Theophylline is classified as a bronchodilator, which means it is effective in relaxing the muscles of the airways and increasing airflow to the lungs. It works by inhibiting phosphodiesterase, leading to an increase in cyclic AMP levels within cells, thereby causing bronchodilation. This mechanism makes theophylline particularly useful in the management of respiratory conditions like asthma and chronic obstructive pulmonary disease (COPD).

In contrast, the other options listed serve different medical purposes. Cephalosporin is an antibiotic, used to treat bacterial infections but does not have any bronchodilating effects. Prednisone, a corticosteroid, is primarily used to reduce inflammation, particularly in conditions like asthma, but it does not directly relax airway muscles. Sulfonamide is also an antibiotic and does not play a role in bronchodilation. Theophylline, therefore, stands out as the bronchodilator among the options provided.