H.F. is a 65-year-old woman with a diagnosis of COPD (FEV1/FVC ratio 0.44 and FEV1 49%; CAT score 4). Her medical history includes allergic rhinitis, chronic bronchitis, gastroesophageal reflux disease, and osteopenia. She has never used tobacco. H.F.’s home drugs include albuterol as needed and tiotropium daily. She has had only one COPD exacerbation in the past 6 months, for which she was hospitalized. H.F. now has an acute exacerbation of COPD, requiring a second hospitalization. She has been adherent to her medications but has required albuterol three or four times per day over the past 3 days. Her blood eosinophil count is 75 cells/mm³. Which one of the following is best to recommend as escalation in H.F.’s COPD maintenance regimen?