Cystic fibrosis (CF), a life-shortening genetic disease, is marked by acute episodes during which symptoms of lung infection increase and lung function decreases. These pulmonary exacerbations are treated with varying antibiotics for varying time periods based on needs determined by individual patients, their families, and the health care providers. Cystic fibrosis pulmonary guidelines for the treatment of pulmonary exacerbation published by the Cystic Fibrosis Foundation (CFF) in 2009 provided recommendations for treatment and also identified key questions for which additional studies were needed. A strong desire among clinicians to reduce treatment durations (and reduce cost, inconvenience, and potential toxicities) is in conflict with belief that patients not responding robustly to treatment might benefit from extending treatment. This randomized, controlled, open-label study is designed to evaluate the efficacy and safety of differing durations of IV treatment, given in the hospital or at home for a pulmonary exacerbation in adult patients with CF.

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.