Effectiveness of Oral Fosfomycin in the Treatment of Cystitis among Adult Cancer Patients in Outpatient Settings

Abstract Purpose Cancer patients are at increased risk of urinary tract infections (UTIs) due to malignancy- and treatment-related immunosuppression. Oral fosfomycin is a convenient option for cystitis amid rising antimicrobial resistance, but data on its effectiveness in cancer patients are limited. This study evaluated the effectiveness of oral fosfomycin for cystitis in adult cancer patients managed in outpatient settings. Methods This retrospective study was conducted at a comprehensive cancer center and included adult cancer patients (≥ 18 years) who received oral fosfomycin for cystitis in outpatient settings between January and December 2024. Clinical cure was defined as symptom resolution without additional healthcare visits within 7 days; recurrence was defined as a subsequent UTI-related healthcare encounter within 90 days. Results A total of 455 patients were included. Mean age was 58 ± 19 years, 60% were female, and 90% had solid tumors, mainly breast (29%) and bladder (18%) cancers. Active chemotherapy was ongoing in 39% of patients. Positive urine analysis was reported in 69% and urinary symptoms in 65%. Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli was the most common isolated pathogen (63%). Fosfomycin, prescribed as targeted therapy in 63% of patients, achieved an overall clinical cure rate of 89%. Subsequent UTI-related events occurred in 43% of patients within 90 days. Conclusion Oral fosfomycin achieved a high clinical cure rate in adult cancer patients treated for cystitis in outpatient settings, supporting its role as a practical treatment option. Despite favorable initial outcomes, recurrence remained common, highlighting the need for further studies to identify recurrence risk factors and optimize long-term outcomes.