Azithromycin: Increased rate of relapses of haematological malignancies and mortality in haematopoietic stem cell transplantation (HSCT) patients treated with azithromycin

Pfizer Pte Ltd would like to inform healthcare professionals about the increased rate of relapses of haematological malignancies and mortality in Haematopoietic Stem Cell Transplantation (HSCT) patients treated with azithromycin. This was based on the results of a clinical trial, ALLOZITHRO, which detected an increased risk of haematological relapses in patients treated with azithromycin compared with placebo [adjusted Hazard Ratio (95% CI) = 1.6 (1.12-2.4)]. The clinical trial investigated long-term azithromycin exposure to prevent bronchiolitis obliterans syndrome (BOS) in patients who underwent allogeneic HSCT for haematological malignancy. While it was not clear how azithromycin could have contributed to the observed higher rate of haematological relapses in the study, it was concluded that long-term azithromycin exposure following HSCT may include risks which outweigh the anticipated benefits.  In Singapore, azithromycin is not approved for the prevention of BOS. Please refer to the letter for more details.