Background: intravenous Fosfomycin (ivFO) is an antibiotic with a broad antimicrobial spectrum, covering both Gram- and Gram+ pathogens. Literature proves it to be a valid option in pulmonary exacerbations (PEx) in patients (pt) with Cystic Fibrosis (pwCF). Pt with bronchiectasis of other aetiology (pwNCFB) have not been previously studied.

Aim: describe effectiveness and safety of ivFO for PEx in pwCF and pwNCFB.

Methods: a retrospective analysis on pwCF and pwNCFB treated for PEx in hospital with ivFO in our adult CF Centre from 1.1.18 to 31.12.22 was performed. 49 pt were included (32 pwFC; mean age 42 ys (19-85), mean FEV1pp 50 (19-109), receiving a total of 107 courses (mean courses/pt 2.18 (1-11)). All had P. aeruginosa chronic infection and many had coinfections: S. aureus Methicillin-Sensitive (19) and Resistant (8), Achromobacter spp (8), E. coli (7), S. maltophilia (1), Acinetobacter spp (4), P. mirabilis (3). In all ivFO was associated with another antibiotic: Piperacillin/Tazobactam (35), Ceftazidime (21), Tobramycin (13), Meropenem (23), Imipenem/Cilastatin (8), Ceftazidime/Avibactam (13), Cefepime (2), Linezolid (3).

Results: treatment was effective in all pt with no evidence of emerging resistance. Mean course duration was 13 days (6-30). In 21 cases (19.6%) mild side effects occurred: asymptomatic increase of liver enzymes (5.6%), nausea (5.6%), peripheral edema (3.7%), diarrhea (2.8%), hypokalemia (1.9%). One anaphylactic reaction occurred.

Conclusions: ivFO proved to be effective in PEx in pwCF and pwNCFB even after repeated courses. Treatment was well tolerated, with fewer side effects than in previous literature, despite an older population.