This study is a randomized crossover study. COPD patients aged 40 years or older with stable disease were included. Each patient received 4 weeks of treatment with either doxofylline or procaterol followed by a 2-week washout period, and then 4 weeks of treatment with the other drug. Respiratory symptoms were assessed by modified Medical Research Council (mMRC) dyspnea scale and COPD Assessment Test (CAT). Pulmonary functions were assessed by spirometry with bronchodilator testing, and adverse events were recorded. Spirometry data including forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and forced expiratory flow at 25-75% of FVC (FEF25-75) were also collected.
