Study subjects will be randomized to receive either study drug or placebo (1.5% NaCl) by inhalation via a PARI eFlow nebulizer. Each subject will complete 28 days of daily dosing. All study patients will be followed for safety, pharmacokinetics, clinical and microbiologic activity for 56 days post completion of study treatment. The total study period will be up to 84 days, with screening visit occurring within the preceding 14 days prior to study day 1. Patients will be clinically evaluated during the first 48 hours post first study dose and weekly for the 28 day treatment period and during the follow up visits at study days 35, 42, 49, 56, 70 and 85 days to determine safety and tolerability, pharmacokinetics (PK) and clinical and microbiologic activity.