The purpose of this study is to assess the safety and tolerability of MDT-637, when inhaled by subjects with Intermittent, or Mild-to-Moderate Persistent, Asthma.

Inclusion Criteria:

1. Documented clinical history and physician diagnosis of intermittent or mild or moderate persistent asthma for at least 6 months prior to screening OR subjects with historical record of Beta-agonist reversibility within previous 5 years
2. Subjects must demonstrate bronchial hyper-reactivity on methacholine challenge of PC20 less than 8mg/mL.
3. Visit 2 FEV1 (with no treatment change in the interim) must be within 12% of Visit 1 result
4. Males and/or females (if not surgically sterile or confirmed to be post menopausal) must agree to practice 2 barrier contraception methods until they are discharged from the study
5. Willing to give written informed consent
6. 18 to 50 years of age
7. BMI of 19-30 kg/m2
8. Non-smoker (for at least 90 days prior to screening) and willing to abstain from smoking during the course of the study
9. Good general health (excepting asthma) as determined by medical history, physical examination, ECG and clinical laboratory tests
10. Willing to abstain from alcohol, caffeine, and xanthine-containing beverages for 24 hours prior to dosing and for 24 hours after dosing.

Exclusion Criteria:

1. Uncontrolled, clinically significant disease which in the opinion of the Principal Investigator, Medical Monitor or Sponsor (MicroDose Therapeutx; MDTx) would place the subject at risk through study participation or would confound the assessment of the safety of MDT-637
2. Inability to perform acceptable and repeatable spirometry in accordance with American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines
3. Abnormal FEV1, FVC, or FEV1/FVC (FEV1 and FVC < 75% of predicted and/or FEV1/FVC ratio < 0.7)
4. FEV1 variability > 12% between Visit 1 and Visit 2
5. Evidence of current or history of additional respiratory disease (other than asthma); for instance emphysema, chronic bronchitis or cystic fibrosis.
6. Upper respiratory tract infection within 6 weeks of Visit 1
7. Use of rescue albuterol or other short acting bronchodilator (SAB) more often than five times per week
8. History of significant nasal irritation from nasal inhalation of medication
9. History of malignancy
10. History of clinically significant alcohol or drug abuse
11. Positive drug screen for drugs of abuse
12. Positive test for HIV, Hepatitis B or Hepatitis C
13. Allergy to lactose, or lactose intolerance
14. Use of prescription medication (other than SAB and/or low dose inhaled corticosteroid e.g. fluticasone propionate 44 mcg BID or budesonide 100 mcg BID or equivalent) within 14 days of Visit 2 or over-the-counter preparations, including dietary and herbal supplements, within 5 days of Visit 2
15. Positive urine pregnancy test at Visit 1 or Visit 2 or visit 4
16. Abnormal QTc interval at Visit 1(> 450 msec in males or > 470 msec in females)
17. Significant blood donation (or testing) in previous 8 weeks
18. Use of any Investigational Product in previous 6 weeks (small molecule products) or previous 3 months (biologic products)