A 23-year-old man with a childhood history of eczema presents to your office for the first time complaining of a non-productive cough that started 4 months ago after a respiratory tract infection during the winter. He generally has the cough roughly once or twice a week, usually after strenuous exercise. He has not had any fevers at home and denies any hemoptysis. He smokes socially, roughly 1 pack a week, and binge drinks on the weekends. He denies any intravenous drug use, but has had several unprotected heterosexual relationships this past year. His temperature is 37.0 C (98.6 F), blood pressure is 110/80 mm Hg, pulse is 65/min, and respirations are 15/min. His physical examination is remarkable only for end expiratory wheezes on bilateral lower lung fields. At this time the most effective treatment about his condition is: