# Comparison of 24-Hour urine parameters before and after initiation of Metformin in patients with diabetes and urolithiasis: A retrospective analysis

## TL;DR

This study found that starting metformin in diabetic patients with kidney stones does not significantly change urine parameters linked to stone formation.

## Contribution

The study provides new evidence on metformin's lack of impact on urinary stone risk factors in diabetic patients.

## Key findings

- No significant changes in calcium oxalate, calcium phosphate, or uric acid supersaturation after metformin initiation.
- Urine volume increased slightly but not clinically significantly.
- Metformin use, both short- and long-term, did not alter urine chemistry to reduce stone risk.

## Abstract

This retrospective study investigated the impact of metformin initiation on 24-hour urine parameters in patients with diabetes with urolithiasis. Utilizing the Medicare-Litholink database, we analyzed 427 patients who started metformin between two 24-hour urine collections conducted less than 18 months apart. To isolate the effect of metformin on urinary parameters as a surrogate marker of stone growth, we excluded patients taking other oral hypoglycemics or medications known to alter urine composition. Our longitudinal analysis revealed no statistically significant changes in key urinary parameters, including supersaturation of calcium oxalate, supersaturation calcium phosphate, and supersaturation of uric acid. Urine volume showed a significant, albeit clinically minor, increase (2.1 to 2.2 L/day, p = 0.0074). Time-dependent analysis comparing short-term (< 100 days) and long-term (> 296 days) metformin use also showed no significant impact on urine chemistry. Similarly, when controlling dosage of metformin (\documentclass[12pt]{minimal}
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\begin{document}$$\:\le\:$$\end{document}1000 mg/day or > 1000 mg/day) we found no significant impact on urine chemistry. These findings suggest that metformin use is not significantly associated with reduced urinary stone risk factors in patients with diabetes and urolithiasis, thus, failing to support its use among urolithiasis patients with new onset diabetes.

The online version contains supplementary material available at 10.1007/s00240-025-01881-3.