Effects and Safety of Different Dose of Bambuterol on Chinese COPD Patients

Patients with COPD who meet the inclusion criteria will enter the 7-days washout baseline period. After the baseline period, patients will be randomly assigned to one of the following treatment sequences: * Sequence I: bambuterol 10mg (21 days) -washout (7 days) - bambuterol 5mg (21 days) - washout (7 days) - placebo (21 days); * Sequence II: bambuterol 5mg (21 days) -washout (7 days) - placebo (21 days) - washout (7 days) - bambuterol 10mg (21 days) ; * Sequence III: placebo (21 days) -washout (7 days) - bambuterol 10mg (21 days) - washout (7 days) - bambuterol 5mg (21 days). During the treatment period patients will record their adverse events and use of rescue medication (Ipratropium bromide) in a diary. At each visit, pulmonary function tests will be performed. At V2, V4 and V6, forced expiratory volume at one second (FEV1) and forced vital capacity (FVC) are measured at following times: immediately before tablet treatment, and at 0.5, 1, 2, 3, 4, 6, 9, 12hrs after administration of tablets, FEV1 and FVC area under curve (AUC) 0\~12 hours will be analyzed. At V1, V3, V5 and V7, and FVC are measured a time in the morning. Peak expiratory flow rate (PEFR) is measured by Mini-Wright peak flow meter in the morning before treatments. All other data will be evaluated as safety status, and monitoring of adverse events.