Which of the following medications is used to relax bronchial tubes?

Theophylline is a medication that serves to relax the bronchial tubes, which can help to improve airflow in conditions such as asthma and chronic obstructive pulmonary disease (COPD). It acts as a bronchodilator by inhibiting certain enzymes and promoting the relaxation of smooth muscles within the respiratory tract, thereby widening the airways and enhancing breathing. This mechanism of action is crucial for managing symptoms and providing relief to patients experiencing bronchoconstriction. Theophylline can also have anti-inflammatory effects, adding further benefit to respiratory management.

The other medications listed, while important in their respective categories, do not have bronchodilatory properties. IVIG (Intravenous Immunoglobulin) is primarily used for immunological conditions, Caspofungin is an antifungal medication, and Flagyl (Metronidazole) is an antibiotic used for treating various infections. None of these medications are indicated for relaxing bronchial tubes.