Comparing the Efficacy of Tiotropium + Olodaterol (5/5 µg) Fixed Dose Combination (FDC) Over Tiotropium 5µg in Reducing Moderate to Severe Exacerbations in Patients With Severe to Very Severe Chronic Obstructive Pulmonary Disease.

Inclusion criteria: * Male or female patients, 40 years of age or older. * Diagnosis of COPD with a documented post-bronchodilator Forced expiratory volume in one second (FEV1)\< 60% of predicted normal and a post-bronchodilator FEV1/ forced vital capacity (FVC) \<70% at Visit 1 * Documented history of at least one moderate to severe COPD exacerbation in the previous 12 months requiring treatment with systemic corticosteroids and/or antibiotics and/or related hospitalization. * Symptomatically stable as defined by: no evidence of COPD exacerbation requiring use of either antibiotics and/or steroids 4 weeks prior to visit 1 and no evidence of change in their usual COPD medication 4 weeks prior to visit 1. * Current or ex-smokers with a smoking history of more than 10 pack years. Exclusion criteria: * Significant disease other than COPD. * Clinically relevant abnormal baseline haematology, blood chemistry or creatinine \> x2 ULN will be excluded regardless of clinical condition. ( A repeat laboratory evaluation can be conducted if deemed necessary by the investigator.) * Current documented diagnosis of asthma. For patients with allergic rhinitis or atopy, source documentation is required to verify that the patient does not have asthma * A diagnosis of thyrotoxicosis * A history of myocardial infarction within 6 months of screening visit. * Life-threatening cardiac arrhythmia. * Known active tuberculosis. * Any malignancy unless free of disease for at least 5 years (patients with treated basal cell carcinoma or squamous cell skin cancers are allowed). * A history of cystic fibrosis. * Clinically relevant bronchiectasis. * Patients with severe emphysema requiring endobronchial interventions within 6 months prior to screening * A history of significant alcohol or drug abuse in the opinion of the investigator. * Patients who have undergone thoracotomy with pulmonary resection * Patients being treated with oral or patch ß-adrenergics. * Patients being treated with oral corticosteroid medication at unstable doses * Patients being treated with antibiotics for any reasons within 4 weeks of screening visit * Patients being treated with PDE4 inhibitors within 3 months of screening visit * Patients who have taken an investigational drug within one month or six half-lives * Pregnant or nursing women. * Women of childbearing potential not using a highly effective method of birth control.