Bronchiolitis obliterans syndrome (BOS), an obstructive airway disease as a result of chronic rejection, is one of the major causes of morbidity and mortality in long-term survivors of allogeneic bone marrow transplantation (BMT). Although augmentation of immunosuppressive treatment might help but the only effective treatment for BOS is by lung transplantation.

Macrolide antibiotics, which have been licensed to use as antibacterial agents for decades, have been found to have immunomodulatory properties in addition to their antibacterial activity. Low dose Azithromycin, an antibiotic of the macrolide family, has been shown to have promising result in a pilot study in treating BOS associated with lung transplantation. We propose to perform a prospective, randomised, double blind study to test the efficacy of Azithromycin in treating BOS after BMT. Patients with proven BOS after BMT will be randomised into two groups based on lung function parameters. One group will receive low dose Azithromycin while placebo will be provided for the other group. Lung function will be serially monitored at 3 month, 6 months and 12 months after commencement of treatment with drug/placebo. If Azithromycin was proven effective in treating BOS then all patient with proven BOS should be treated with this drug.