Standardized Treatment of Pulmonary Exacerbations II

The study will assess the non-inferiority of 10 days versus 14 days treatment duration among patients who have an early robust improvement (ERR subjects) and the superiority of 21 days versus 14 days treatment duration among the subjects who do not meet the definition of ERR (non-ERR; NERR). 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). ERR subjects \[≥8% predicted improvement in FEV1 from Visit 1 to Visit 2 and CRISS reduction of ≥11 points from Visit 1 to Visit 2\] will be randomized 1:1 to either 10 days or 14 days total IV antibiotic treatment duration. Remaining (NERR) subjects will be randomized 1:1 to receive either 14 or 21 days total IV antibiotic treatment duration. All subjects will be evaluated again at Visit 3, 14 days following scheduled completion of IV antibiotic treatment.