Is metformin use associated with changes in urinary parameters in stone formers?

Introduction: Diabetes mellitus (DM) is associated with an increased risk of nephrolithiasis and is often treated with metformin. The relationship between metformin and nephrolithiasis formation remains unclear as studies have demonstrated conflicting results. Methods: We conducted a cross-sectional analysis of stone-forming patients at our stone clinic prior to the initiation of stone-directed medical management. Patients were grouped based on diabetic status and diabetic medication regimen. Outcomes evaluated were 24-hour urinary parameters and specimen stone type using univariate Kruskal-Wallis and Chi-squared analyses. Multivariate analyses controlling for metabolic syndrome components and HbA1c were performed. Results: Data were available for 505 patients, of whom 147 were diabetic and 358 were not. On multivariate analyses controlling for HbA1c and other comorbidities, diabetic patients on metformin still had worse urinary parameters, including urine pH, than non-diabetic patients (pH = -0.33, -0.37, p0.05 for all urinary parameters). Conclusions: Stone-forming patients with DM on metformin were associated with urinary abnormalities similar to those not on metformin. Cohort studies comparing urinary parameters of patients prospectively started on metformin are necessary to further elucidate metformin’s role, if any, in combatting nephrolithiasis.