Subjects will undergo pulmonary function testing (spirometry) and complete a respiratory symptom score [Chronic Respiratory Infection Symptom Score (CRISS)] at initiation of IV treatment (Baseline/ Visit 1) and at Day 7-10 (Visit 2). At Visit 2, subjects will be allocated to groups ERR or NERR based on their initial clinical response as determined by the change in forced expiratory volume in 1 second (FEV1; percent of predicted) and CRISS from Baseline and then randomized to an IV treatment duration (nested within group).