POS is a particular form of chronic rhinosinusitis described in 2% of the general population. They lead to an alteration in the quality of daily life with a significant impact on the professional life of 70% of patients. They can be of idiopathic or of secondary origin. The most frequent secondary forms are those observed in cystic fibrosis and immune deficiencies. The pathophysiology of primary POS remains poorly understood, involving Th1-type inflammation and various bacteria (with Staphylococcus Aureus in the forefront). Bacteria could impair the ciliary beat, perpetuating infection and mucosal inflammation. There is no established recommendation for the treatment of primary POS Long-term low-dose macrolides are currently proposed for these forms of chronic rhinosinusitis when conventional treatments (local corticosteroids, saline rinsing, iterative short courses of antibiotics adapted to the germs found, and surgical drainage) have failed. This treatment with macrolides is currently used off label.

Macrolides are effective on most gram-positive and gram-positive bacteria. Macrolides also have immunomodulatory properties on the Th1 immune response. This effect is maintained even in the presence of macrolide-resistant bacteria. In chronic obstructive pulmonary disease, daily administration of half-dose macrolides over the long term (HDLT) has been shown to be effective in reducing the frequency of infectious exacerbations. Uncontrolled trials have described an improvement in symptom scores in chronic rhinosinusitis with or without polyps. The results observed in randomized trials versus placebo are contradictory. A meta-analysis published in 2013 based on these 2 randomized studies was inconclusive regarding the efficacy of HDLT macrolides. The heterogeneity of the inclusion criteria with rhinosinusitis of a different proTh-2 inflammatory profile corresponding to that usually observed in nasal polyposis could explain this lack of result. A review of the literature published in 2017 on HDLT macrolides based on 52 publications observed a very wide diversity of antibiotic protocols in terms of the molecule chosen, the administration scheme and the duration of treatment (8 to 24 weeks). The number of patients studied was often small, which affected the statistical power of the results obtained. The authors of this review conclude by stressing the need to conduct placebo-controlled studies on large populations of patients selected on the phenotypic level.

This study propose to evaluate the value of HDLT macrolides in this specific etiological setting. This project plans to exclude all chronic rhinosinusitis of Th2 inflammatory origin (allergy, nasosinusal polyposis) or those due to cystic fibrosis or immune deficiency. In addition, the inclusion centers selected in Ile de France have the necessary expertise to evaluate the impact of azithromycin on mucociliary clearance, notably with the development of innovative tools to measure the efficiency of the ciliary beat (high-speed video microscopy and particle tracking).At the same time, the tolerance of HDLT macrolides measured in patients with cystic fibrosis or chronic obstructive pulmonary disease (COPD) is excellent, provided that the well-documented contraindications are respected. No serious adverse effects have been reported, apart from cases of transient or permanent moderate hearing loss requiring audiometric monitoring.

No specific study regarding the treatment of primary POS is available to date, even tough POS is very prevalent and its management is still associated with poor patient-reported outcomes.