Introduction:
Urinary tract infections (UTIs) with resistant bacterial strains are one of the most troublesome problems in children with severe congenital anomalies of the kidney and urinary tract (CAKUT). We present the results of non-standard prophylactic treatment with fosfomycin of infants with complex urinary tract malformations.

Material and methods:
It was a retrospective analysis of data of 5 male infants after urological interventions due to complex CAKUT. The frequency of UTIs, their aetiology and course, frequency and duration of hospitalisation due to UTIs, prophylaxis and treatment outcomes were analysed.

Results:
The mean follow-up period was 16 months. Mean number of UTIs during observation was 5 (2–6). Infections with multi-drug resistant strains were observed in all patients before commencing fosfomycin prophylaxis, on average 21 days after urological procedure. Due to recurrent UTIs with highly resistant or reduced susceptibility strains, despite standard prophylaxis, we introduced fosfomycin in 50–70 mg/kg dose once a day for 4–9 months what reduced frequency of infections (3.6 vs. 1.0, p = 0.01), infections with decreased susceptibility strains (3.6 vs. 0.0, p = 0.00006) and need for hospitalisations (3.6 vs. 0.2, p = 0.003). Fosfomycin was introduced after 2–5 UTIs, at the mean age of 7 months, after mean of 4 months of ineffective standard prophylaxis. We didn’t record any significant adverse effects of the treatment or bacterial resistance development.

Conclusions:
In children with urinary tract malformations, and in particular with a history of urological interventions, in the case of recurrent UTIs with strains of reduced susceptibility to antibiotics, several months of non-standard prophylactic treatment with fosfomycin may be considered.