- Reassessment of signs and symptoms. If the subject does not improve to FEV1 ≥ 70% of predicted during the study treatment period, the subject may continue to receive further treatment including hospital admission at the discretion of the Investigator. The study will be approximately 6.5 hours in length (Hour -1.5 to Hour 5) while the subject remains in the ED. Safety, efficacy and PK parameters will be monitored throughout the treatment period. An initial 24-hour post-randomization follow-up visit will be completed to evaluate the subject's health status as well as for safety and PK parameters. A second follow-up contact will be completed by telephone seven days post-randomization for safety purposes and to evaluate the subject's health status.