Inclusion Criteria:

1. Male or female;
2. Have self-reported history of physician-diagnosed and treated asthma for ≥ 3 months;
3. Have a diagnosis of an acute exacerbation of asthma upon presentation at the ED as defined by dyspnea and evidence of bronchospasm in an individual with a known history of asthma;

4. Upon presentation to the ED the treatment provided included:

   • A brief history and physical examination that includes vital signs, auscultation, assessments of accessory respiratory muscle usage and the level of dyspnea the subject is experiencing;
   • Supplemental oxygen given to maintain oxygen saturation as measured by pulse oximetry of ≥ 90%;
   • Two doses of inhaled beta2-agonist (defined as albuterol 5 mg) via nebulizer (each dose given sequentially up to approximately every 20 minutes); simultaneously with
   • Two doses of an inhaled anti-cholinergic agent (defined as ipratropium 0.5 mg) via nebulizer (each dose given sequentially up to approximately every20 minutes);
   • One dose of corticosteroid of at least 60 mg given orally (prednisone) or intravenously (methylprednisolone); and
5. Have a FEV1 ≤ 55% within 10 minutes of completing the treatment described in Inclusion Criterion #4;
6. Have a negative urine pregnancy test if you are females of childbearing potential;
7. Have ECG with no dysrhythmias (except sinus tachycardia);
8. Have no clinical or electrocardiographic signs of ischemic heart disease as determined by the Investigator; and
9. Have signed the informed consent obtained prior to starting any study procedures.

Exclusion criteria:

1. Have a current or prior diagnosis or suspected diagnosis of COPD or other chronic lung disease other than asthma;
2. Have presence of pneumonia;
3. Have presence of significant other respiratory dysfunction such as pneumothorax, pneumomediastinum, or pulmonary edema;
4. Have known or suspected vocal cord dysfunction syndrome;
5. Have presence of aspirated foreign body (known or suspected);
6. Have a history or any current clinical evidence suggesting cardiomyopathy or congestive heart failure;
7. Have a history or presence of tachyarrhythmias, with the exception of sinus tachycardia;
8. Have a heart rate ≥ maximum heart rate: (maximum predicted HR [220-age]-30); OR Heart rate ≥ 150 bpm;
9. Have hypokalemia, defined as a potassium level ≤ 3.0 mg/dL according to the point-of-care device level obtained at Screening;
10. Have significant cardiac, renal, hepatic, endocrine, metabolic, neurologic or other systemic disease. A significant disease will be defined as one which, in the opinion of the Investigator, may either put the subject at risk because of participation in the study, or may influence the results of the study or the subject's ability to participate in the trial;
11. Have a self-reported history of greater than 15 pack-yr smoking history;
12. Have a fever ≥ 101.5º F;
13. Have uncontrolled hypertension defined as a blood pressure ≥ 170/100 mm Hg;
14. Have the need for immediate intubation as determined by the Investigator;
15. Are a pregnant or lactating female;
16. Have participated in another clinical study with an investigational drug within 30 days of randomization;
17. Have a positive urine drug screen for cocaine, methamphetamine or PCP;
18. Have a known allergy to MN-221 or any of the other components of the MN-221 drug product ;
19. Have a known allergy to other beta agonists;
20. Have had previous exposure to MN-221; or
21. Have used of theophylline, beta blockers, diuretics, digoxin, MAO inhibitors, or tricyclic antidepressants within 2 weeks prior to randomization.