Fosfomycin Trometamol Compared With an Alternative Active Antibiotic as Step-down Therapy for the Treatment of Acute Pyelonephritis Due to Escherichia Coli in Elderly Women : a Randomized, Multicenter, Non-inferiority Trial

Acute pyelonephritis (APN) is among the most common bacterial infections in older women. Oral step-down antibiotic therapy may potentially be associated with toxicity, particularly with fluoroquinolones or trimethoprim-sulfamethoxazole, espcially in geriatric patients. The emergence of resistant strains reduces the choice of oral step-down treatment, thereby increasing the risk of nosocomial complications related to intravenous access and prolonged hospitalization. Fosfomycin trometamol (FT) has broad activity against Enterobacterales, including resistant strains. It has an excellent safety profile and moderate ecological impact, and has been used for several years to treat cystitis. Recent studies have demonstrated its efficacy as an oral step-down therapy for the treatment of E.coli APN in younger women. Its efficacy in a geriatric population remains to be demonstrated. The primary objective is to demonstrate the non-inferiority, in terms of clinical cure, of FT compared with an alternative active antibiotic as step-down therapy for E. coli APN in older women. FOSFOLD is a national, multicenter, randomised, comparative, phase 3, non-inferiority trial (1:1), open-label with two parallel treatment groups. After 3 or 4 days of appropriate empirical antibiotic therapy, women aged 75 or over with E.coli APN will be randomised to receive either 3g of FT once daily or an alternative antibiotic treatment in accordance with current french guidelines, for a total of 10 days. The primary endpoint is clinical cure at Day 17, i.e. 10 days after completion of antibiotic therapy. If non-inferiority of FT is confirmed, it could provide a new therapeutic approach for oral step-down therapy in the older patients with APN. Its favorable tolerability profile could help prevent common geriatric complications, such as delirium, falls and malnutrition. Ultimately, it could help prevent some of the iatrogenic functional decline associated with hospitalisation.

Inclusion Criteria: 1. Female. 2. Age ≥ 75 years. 3. Body temperature ≥ 38°C on at least once during the 72 hours preceding diagnosis. 4. At least one new symptom among the following : urinary urgency, dysuria, increased urinary frequency, gross hematuria, burning on urination, spontaneous of provoked flank or suprapubic pain or urinary incontinence. 5. Positive urine culture collected before initiation of antibiotic therapy defined as : ≥ 10,000 leukocytes/mL and monomicrobial culture with Escherichia coli ≥ 103 CFU/mL and susceptibility to FT,the empirical antibiotic,and at least one alternative antibiotic (active and not contraindicated), administered either orally (fluoroquinolone, amoxicillin, amoxicillin-clavulanic acid, or trimethoprim-sulfamethoxazole or, in the absence of an oral alternative, intravenously. 6. Ability to reveive oral medication 7. Favorable clinical course after 3 or 4 days of effective empirical antibiotic therapy, defined as resolution of fever (temperature \< 38°C) and regression or reduction in the intensity and/or frequency of the clinical sign(s) present at the time of APN diagnosis, without the occurrence of any new symptoms. Exclusion Criteria: 1. Presence of an infectious focus other than the urinary tract. 2. Severe infection and/or initial infectious complications, including septic shock, requirement for an emergency upper urinary tract intervention, or renal abscess. 3. Indwelling urinary catheter, including bladder, ureteral, or nephrostomy catheters. 4. Inability to take oral medication. 5. Immunosuppression, including sold-organ transplant, ongoing immunosuppressive therapy, ongoing chemotherapy. 6. Hypersensitivity to fosfomycin trometamol or to any of the excipients of the study medication 7. End-stage chronic kidney disease with an estimated glomerular filtration rate (eGFR) \< 15 mL/min/1.73 m2. 8. Lack of health insurance coverage. 9. Patient under legal protection or guardianship. 10. Absence of written informed consent from the patient or, if the patient is unable to provide consent, absence of agreement from the designated trusted person or a close relative. 11. Participation in another interventional clinical research protocole