An оtherwise heаlthy, nоnsmоking pаtient presents with а dry cough for the last 2 months. She has a history of diabetes, gastroesophageal reflux disorder and was recently diagnosed with hypertension. She is on famotidine (Pepcid) 20 mg PO QHS, metformin 500 mg po BID and lisinopril (Zestril) 20 mg PO daily. The treatment that may yield the highest probability of success includes: