Acute kidney injury and urinary drug crystals in children treated with tosufloxacin: a multicenter retrospective study

Background: Tosufloxacin (TFLX), a fluoroquinolone, is widely used in Japanese children with macrolide-resistant Mycoplasma pneumoniae infection. Acute kidney injury (AKI) associated with TFLX has been reported, often with urinary drug crystals; however, its incidence and clinical characteristics remain unclear. Methods: In this multicenter retrospective study, we included 227 children (2–15 years) who underwent blood and/or urine testing. AKI was defined according to KDIGO criteria. Kidney function and clinical characteristics were compared between patients with and without TFLX exposure at the initial visit and during follow-up. Among TFLX-treated patients, factors associated with AKI and urinary drug crystals were analyzed. Results: At the initial visit, AKI was more frequent in patients already receiving TFLX than in those not treated with TFLX (10% vs. 2.0%; p = 0.018). However, when analysis was restricted to patients in whom TFLX was newly initiated at our institutions, AKI incidence was 2.6% and not significantly different from controls. Gastrointestinal symptoms were more common in the AKI group (70% vs. 11%; p < 0.0001). Urinary drug crystals were detected with similar frequencies in the AKI and non-AKI groups (63% vs. 57%), and continuation of TFLX after crystal detection did not lead to AKI progression. Conclusions: Our findings suggest an association between TFLX exposure and creatinine elevation. We also evaluated AKI incidence among patients newly initiated on TFLX. Urinary drug crystals were frequently detected; however, crystal formation alone did not fully explain AKI development. Clinicians should be aware of the potential for AKI during TFLX therapy, particularly in patients with gastrointestinal symptoms.