Review Question - QID 210580

A 12-year-old boy is brought to the emergency department by his mother because he has been having difficulty breathing. He started having symptoms about 3 days ago when he started experiencing persistent coughing, runny nose, and a low grade fever. Since then he has been experiencing dyspnea that grew worse until he felt that he could no longer breathe. His mom says that this has happened many times before. On presentation, physical exam reveals an anxious, thin boy who is using his accessory muscles to breathe. Prolonged expiratory wheezes are heard on auscultation of his lungs bilaterally. During stabilization, he is prescribed a drug for treatment of his condition. The patient's mother recognizes the drug since her father, a 40-pack-year smoker, also takes the medication and she is told that the drug is able to beneficially inhibit a receptor on smooth muscle in both cases. Which of the following drugs most likely has a similar mechanism of action as the drug prescribed to this patient?