The solitary kidney (SK) undergoes adaptive phenomena of hyperfunction and hyperfiltration. These secondary adaptive phenomena can make it more vulnerable to potentially nephrotoxic therapies. Adverse reactions of the kidneys to ciprofloxacin are rare, but sometimes severe. Therefore, our study sought to assess the reactions to ciprofloxacin of patients with solitary kidney (SK) and urinary tract infection (UTI) by means of urinary biomarkers.

We studied 19 patients with SK and urinary tract infection (UTI) who had been administered a 7-day treatment with intravenous ciprofloxacin.

Urinary N-acetyl-beta-d-glucosaminidase, alpha 1-microglobulin, and estimated glomerular filtration rate (eGFR) of these patients were measured at the initiation and at the end of treatment.

In 47.37% patients NAG diminished under ciprofloxacin treatment. This observation has the significance of favourable evolution of the tubulointerstitial lesions caused by UTI and lack of nephrotoxic effects; 52.63% cases presented an increase of urinary NAG, a fact that suggests a nephrotoxic effect of ciprofloxacin.

The evolution of urinary alpha 1-microglobulin was similar to that one of urinary NAG.

Only one of three cases with chronic kidney disease (CKD) stage 5 presented acute kidney injury, associated with increase in the tubular markers.

In spite of the high variability of the urinary biomarkers, UTI evolved favourably in these cases; eGFR increased in 16 out of 19 patients, a fact which is indicative of a good outcome of renal function, even in patients with elevated levels of the tubular damage biomarkers. This observation supports the hypothesis that eGFR may be dissociated from the biomarkers which assess tubular injury.

In SK patients the occurrence of AKI is not frequent, although the urinary biomarkers rise in some patients treated with ciprofloxacin. This is related not only to the nephrotoxic effect of the drug, but probably to the association of other factors (allergy, individual susceptibility).

In SK patients, renal tubular biomarkers, especially NAG, allow monitoring of tubular injury and impose caution in prescribing ciprofloxacin treatment, mainly to patients at risk.

Ciprofloxacin is relatively safe regarding its nephrotoxicity, while caution is required in vulnerable patients.