Effects of Macrolides on Asthma Control

Inclusion Criteria: * Diagnosis of asthma * Age 18-70 * Current smoker * Duration of symptoms \>1yr with stability for 4 weeks * Able to maintain asthma without exacerbations during run in period * Able to wean off other asthma medication Exclusion Criteria: * Ex-smokers or never smokers * Planning to quit smoking during duration of trial * Patients with unstable asthma * Patients with current epilepsy, psychosis or history of significant atrial or ventricular tachyarrhythmia * Corrected QT-interval greater than 450msec in women, 430msec in men * Low potassium levels. If can be corrected then screening can continue with confirmation of normal levels prior to taking study medication * Liver disease (ALT and/or AST levels 2 or more times ULN) * Significant renal disease (Creatinine or urea levels 2 or more times ULN) * Any previous severe adverse reactions to macrolides * Patients who are known to have specific IgE sensitivity or skin test positivity to grass pollen and a history of worsening of asthma due to hay fever will not be recruited from mid May to the end of July * Upper or lower respiratory tract infection in the 4 weeks prior to randomisation. Run in period can be prolonged in this situation to have 4 weeks with no respiratory infection prior to randomisation. * Patients who require medications known to interact with azithromycin * On other immunosuppressants or chronic antibiotics * Weight less than 45kg * Frequent asthma exacerbations (greater than 4) requiring oral corticosteroids in the year prior to randomisation * Current or past diagnosis of allergic-bronchopulmonary-aspergillosis * Pregnancy and breast feeding * Mental impairment or language difficulties that makes informed consent not possible