Colistin Therapy for Urinary Tract Infections Due to Multidrug-Resistant Bacteria: Experience at a Tertiary Academic Medical Center

Background: Urinary tract infections (UTIs) caused by multidrug-resistant Gram-negative bacteria (MDR-GNB) present increasing therapeutic challenges, especially in regions with limited access to novel β-lactam/β-lactamase inhibitors. Colistin remains a salvage therapy in such cases; however, data describing its real-world efficacy and nephrotoxicity in urinary infections are limited. Methods: We conducted a retrospective cohort study of adult patients who received intravenous colistin (colistimethate sodium) for culture-confirmed UTIs at a tertiary academic medical center in Riyadh, Saudi Arabia. The primary outcome was colistin-induced acute kidney injury (AKI), defined as an increase in serum creatinine of ≥ 26 μmol/L from baseline per the AKIN creatinine criterion. Secondary outcomes included microbiologic failure, clinical failure, and in-hospital mortality. Multivariable logistic regression was used to identify independent predictors of AKI. Results: Among 102 patients, the median age was 80 years (IQR, 72– 84), and 46% were male. Klebsiella pneumoniae (44.9%) and Pseudomonas aeruginosa (20.4%) were the most common pathogens. Over half (52%) were exposed to concomitant nephrotoxic agents. Colistin-induced AKI occurred in 15 patients (14.7%). Chronic kidney disease was more frequent among those who developed AKI (73% vs. 26%, p< 0.001); however, no independent predictors were identified in multivariable analysis. In a sensitivity analysis using CKD as a binary covariate, CKD was independently associated with AKI (adjusted OR 19.17; 95% CI, 3.03– 121.30; p=0.002). Clinical failure occurred in 12.7% and microbiologic failure in 2.9% of patients. Conclusion: In this cohort of patients with MDR-GNB UTIs, intravenous colistin was associated with favorable clinical and microbiological outcomes. The observed incidence of AKI was lower than previously reported in the literature, though this should be interpreted cautiously given the small number of events and the high prevalence of baseline renal impairment and nephrotoxic co-exposures. The infographic is divided into three sections: study population, treatment and outcomes. The study population section describes patients with multidrug-resistant gram-negative urinary tract infections, totaling 102 individuals. The median age is 80 years, with 33.3 percent having chronic kidney disease and 52.0 percent exposed to nephrotoxic agents. The treatment section details intravenous colistin, specifically colistimethate sodium (CMS). The median duration of treatment is 10 days, with a median loading dose of 4 mg per kg (range 2.5 to 5) and a median maintenance dose of 2.9 mg per kg per day (range 1.95 to 4.35). The outcomes section lists clinical failure at 12.7 percent, microbiological failure at 2.9 percent, culture negative results in 5 days, afebrile status in 1 day and colistin-induced acute kidney injury at 14.7 percent.Infographic on study population, treatment and outcomes of intravenous colistin for urinary tract infections. Keywords: colistin, urinary tract infection, multidrug-resistant bacteria, acute kidney injury, nephrotoxicity