Study of Fosfomycin-containing Antibiotic Regimens for the Treatment of Infective Endocarditis in Clinical Practice (FOSFO-IE)

A prospective, multicenter, non-interventional, observational cohort study on the use of a pharmacological agent, conducted within Infectious Diseases units-and, where available, as part of multidisciplinary teams for infective endocarditis-selected according to predefined feasibility criteria. Enrollment will be consecutive and will include all eligible patients for whom fosfomycin has already been initiated, or is initiated by the treating clinician, as part of routine clinical practice.

The decision to prescribe fosfomycin, the dosage, antibiotic combinations, duration of treatment, diagnostic tests, and any potential cardiac surgery strategy will remain entirely independent of the study and subject to local clinical judgment.

The study population will consist of adult patients with a diagnosis of definite or probable infective endocarditis, according to the 2023 Duke-ISCVID criteria, who have received at least one dose of intravenous (IV) fosfomycin as part of the antibiotic regimen for the clinical episode under observation. The availability of the minimum set of clinical, therapeutic, and microbiological data required by the protocol is a necessary requirement for inclusion.

Primary objective To describe the overall clinical outcomes and safety profile of fosfomycin-containing antibiotic regimens used in clinical practice for the treatment of infective endocarditis, assessed by the proportion of overall therapeutic success at a predefined 90-day follow-up and the incidence of adverse events of interest.

Secondary objectives To describe the methods of fosfomycin use in this setting, including clinical indication, timing of initiation, dosage, duration, combination agents, and the rationale behind the therapeutic choice.

To describe the clinical, microbiological, echocardiographic, and imaging characteristics of the enrolled patients.

To evaluate early and late microbiological outcomes, including blood culture clearance, persistence of bacteremia, microbiological recurrence, emergence of resistance, and relapse.

To describe the safety profile of fosfomycin, with particular attention to sodium overload, hypokalemia, electrolyte imbalances, renal toxicity, and adverse events leading to modification or discontinuation of treatment.

To explore the association between patterns of fosfomycin use and clinical or microbiological outcomes, without the intent of establishing causal inference.

To describe microbiological data related to fosfomycin in a standardized manner, specifying the raw MIC value, the antimicrobial susceptibility testing (AST) method, the interpretive criteria applied, and whether or not categorization according to applicable clinical breakpoints is possible.