# From Needle to Sachet: Fosfomycin Versus Amikacin for Cystoscopy Prophylaxis

## TL;DR

This study compares two antibiotics for preventing infections after cystoscopy, finding that fosfomycin is as effective as amikacin but safer.

## Contribution

Demonstrates that oral fosfomycin is a safer alternative to parenteral amikacin for cystoscopy prophylaxis.

## Key findings

- Fosfomycin and amikacin had similar rates of symptomatic and culture-positive UTIs.
- Fosfomycin had fewer kidney injuries and injection-related reactions compared to amikacin.
- Gastrointestinal adverse effects were more common with fosfomycin than amikacin.

## Abstract

Background: Antibiotic prophylaxis is commonly administered before outpatient cystoscopic procedures (CPE). This study compared the efficacy and safety of parenteral amikacin and oral fosfomycin used as prophylactic agents before outpatient cystoscopy.

Methods: This retrospective comparative observational study included adult patients undergoing outpatient CPE at a tertiary care center between October 2024 and November 2025. Patients received either a single intravenous dose of amikacin (15 mg/kg) or a single oral dose of fosfomycin trometamol (3 g) before the procedure, according to institutional practice. The primary outcome was the incidence of symptomatic urinary tract infection (UTI) within 14 days following CPE. Secondary outcomes included culture-positive UTI and adverse drug reactions (ADRs). Categorical variables were compared using the chi-square or Fisher’s exact test, and continuous variables were compared using the independent t-test.

Results: A total of 2914 patients were included, of whom 2083 received amikacin, and 831 received fosfomycin. Symptomatic UTI occurred in 6.7% of patients in the amikacin group and 8.2% in the fosfomycin group (p = 0.18). Culture-positive UTI rates were comparable (2.1% vs 2.0%, p = 0.91). Acute kidney injury was significantly more frequent with amikacin (2.6% vs 0.1%, p < 0.001), while gastrointestinal adverse effects were more common with fosfomycin (8.3% vs 2.3%, p < 0.001). Injection-related reactions occurred only in the amikacin group.

Conclusions: Fosfomycin demonstrated efficacy comparable to amikacin for preventing post-cystoscopy UTI, with a more favorable safety profile. Oral fosfomycin represents a safe and effective alternative to aminoglycosides for prophylaxis before outpatient cystoscopic procedures, particularly in patients at risk for aminoglycoside-related toxicity.