Formoterol Dose Ranging Study (ACHIEVE Duaklir USA Phase IIb)

Inclusion Criteria: * Adult male or non-pregnant, non-lactating female patients aged ≥40. * Patients with a diagnosis of COPD (GOLD guidelines, 2016) for a period of at least 6 months prior to Visit 1. * Patients with moderate to severe stable COPD: post-bronchodilator FEV1 ≥ 30% and \<80% of the predicted normal and post-bronchodilator FEV1/FVC \< 70% at Visit 1. * Patients with reversible airway obstruction defined as an increase in FEV1 of at least 12% and 200 mL over the baseline value after four inhalations of albuterol sulfate 108 µg via a pMDI at Visit 1. * Current or former-smokers, with a smoking history of ≥ 10 pack-years. * Patients able to perform acceptable and repeatable pulmonary function testing for FEV1 according to the American Thoracic Society (ATS)/European Respiratory Society (ERS) 2005 criteria at Visit 1. * Patients eligible and able to participate in the study and who had signed an Informed Consent Form prior to initiation of any study-related procedures. Exclusion Criteria: * Patients with asthma. * Any respiratory tract infection (including the upper respiratory tract) or COPD exacerbation (including the mild COPD exacerbation) within 6 weeks prior to Visit 1 or during the run-in period. * Patients hospitalized for a COPD exacerbation (an emergency room visit for longer than 24 hours is considered a hospitalization) within 3 months prior to Visit 1. * Clinically significant respiratory conditions other than COPD. * Patients who in the investigator's opinion may need to start a pulmonary rehabilitation program during the study and/or patients who started/finished it within 3 months prior to Visit 1. * Use of long-term oxygen therapy (≥ 15 hours/day). * Patients who do not maintain regular day/night, waking/sleeping cycles including night shift workers. * Clinically significant cardiovascular conditions. * Patients with uncontrolled Type I or Type II diabetes, uncontrolled hypo-or hyperthyroidism, hypokalaemia, or hyperadrenergic state, uncontrolled hypertension. * Patients with history of long QT syndrome or whose QTc (calculated according to Fridericia's Formula QTc=QT/RR1/3) \> 470 ms as indicated in the centralized reading report assessed at Visit 1. * Patients with clinically significant abnormalities in the laboratory tests, ECG parameters (other than QTc) or in the physical examination at Visit 1 that might compromise patient safety. * Patients with a history of hypersensitivity reaction to an inhaled medication or any component thereof, including paradoxical bronchospasm. * Patients with known narrow-angle glaucoma, symptomatic bladder neck obstruction, acute urinary retention or symptomatic unstable prostate hypertrophy. * History of malignancy of any organ system (including lung cancer), treated or untreated, within the past 5 years other than basal or squamous cell skin cancer. * Patients with any other serious or uncontrolled physical or mental dysfunction. * Patients with a history (within 2 years prior to screening) of drug and/or alcohol abuse that may prevent study compliance based on the Investigator judgment. * Patients unlikely to be cooperative or who cannot comply with the study procedures. * Patients treated with any investigational drug within 30 days (or 6 half-lives, whichever is longer) prior to Visit 1. * Patients who intended to use any concomitant medication not permitted by this protocol or who had not undergone the required washout period for a particular prohibited medication. * Patients unable to give consent, or patients of consenting age but under guardianship, or vulnerable patients. * Any other conditions that, in the investigator's opinion, might render the patient to be unsuitable for the study. * Involvement in the planning and/or conduct of the study (applies to AstraZeneca staff and/or site staff), or patients employed by or relatives of the employees of the site or sponsor. * Previous randomization in the present study D6571C00002.