Peak Bronchoprotection Conferred by Levosalbutamol and Racemic Salbutamol

Inclusion Criteria: 1. Mild to moderate stable asthmatics on ≤ 2000μg BDP or equivalent 2. Methacholine responsive PC20\< 4 mg/ml 3. \>1dd change in methacholine PC20 after the administration of racemic Salbutamol. 4. Male or female 18-65 5. Informed Consent 6. Ability to comply with the requirements of the protocol Exclusion Criteria: 1. Severe asthmatics as defined by an FEV1≤ 60% or PEF variability \> 30% or with continual daytime or nocturnal symptoms. 2. The use of oral corticosteroids within the last 3 months. 3. Recent respiratory tract infection (2 months). 4. Significant concomitant respiratory disease such as COPD, CF, ABPA, bronchiectasis and active pulmonary tuberculosis. 5. Any other clinically significant medical condition such as unstable angina, acute myocardial infarction in the preceding 3 months, recent TIA/ CVA,that may endanger the health or safety of the participant, or jeopardise the protocol. 6. Any significant abnormal laboratory result as deemed by the investigators 7. Pregnancy, planned pregnancy or lactation 8. Known or suspected contra-indication to any of the IMP's 9. Concomitant use of medicines (prescribed, over the counter or herbal) that may interfere with the trial.