J.A. Kastelik and colleagues propose early use of azithromycin for cystic fibrosis (CF) based on subgroup analysis of 24 adult “responders” in their clinic who had lower Pseudomonas aeruginosa antibodies and less respiratory exacerbation prior to starting azithromycin compared to 12 nonresponders. Would these adult responders with mild respiratory disease have experienced a mean 0.3 L improvement in forced expiratory volume in one second with placebo? Subgroup post hoc analysis of retrospective data is fraught with bias and interpretation must be circumspect. The bottom line is we do not know why azithromycin improves respiratory function in people with CF and we do not know when to prescribe it. There is no clinical evidence, as yet, of an indirect anti-pseudomonal effect and, furthermore, the data of Kastelik et al. 1 do not appear to support this assertion.
Is it possible that the widespread use of azithromycin in CF clinics throughout the world represents long-term anti-staphyloccocal chemoprophylaxis being introduced via the back door? If so, we need to be cautious, as azithromycin has potential for generating resistance. This may have profound long-term effects on our choice of antimicrobials. There are probably better long-term anti-staphylococcal agents with a narrower spectrum of action and less tendency to promote resistance.
It is important that cystic fibrosis teams introduce azithromycin in a structured manner and audit their results, as J.A. Kastelik and colleagues have done. Close liaison with the microbiology department to monitor clinic resistance patterns is essential.
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