For each dose evaluation period, subjects will be domiciled in the clinical research unit (CRU) for 2 nights, beginning on Day -1, one day before dosing. Determination of continued study eligibility will be made on Day -1 for each dose level. Day 1 will include study drug infusion and approximately a 24-hour observation period into Day 2 to allow safety monitoring, serial spirometry, and serum PK measurements. Subjects will be discharged from the CRU on Day 2. They will return to the CRU approximately 2-4 weeks later to participate in the subsequent dose group.