Phentermine/Topiramate in Obese, Diabetic Uric Acid Stone Formers: An Open-Label Randomized Feasibility Trial

The purpose of this study was to determine whether medical treatment of obesity, diabetes, and low urine pH with combination phentermine/topiramate affects uric acid (UA) kidney stone burden.

Individuals with obesity, diabetes mellitus, normal renal function, urine pH < 5.8, and stone analysis ≥ 80% UA were block randomized (2:1 ratio) to phentermine 18.75 mg/topiramate 100 mg vs pragmatic controls for an 18-month, prospective, open-label feasibility study with dose escalation. The primary outcome was change in CT stone volume. Secondary outcomes included medication adherence; patient safety; and change in anthropometrics, laboratory studies, and body composition.

Nineteen participants (age 62.1 ± 9.8 years; 68% male; mean BMI = 36.3 ± 2.9 kg/m²) were randomized, and 15 completed the study with 73% pill adherence and no serious adverse events. Stone volume by intention-to-treat analysis fell by 52% in the intervention group and rose by 8.6% in the control group (P = .10), with per-protocol analysis demonstrating statistically significant stone volume reduction (P = .02). At study end and compared with means of controls, the intervention group had greater weight loss (-10.2 vs +2.9 kg), reduction in HgbA1c levels (-0.2 vs +0.5), lower 24-hour urine citrate (309 ± 81 vs 951 ± 782 mg), and lower UA supersaturation (0.7 ± 1.1 vs 1.8 ± 1.0), along with higher 24-hour urine pH (6.2 ± 0.5 vs 5.5 ± 0.4) and calcium phosphate supersaturation (0.9 ± 0.8 vs 0.2 ± 0.1) (all P < .05).

Among obese individuals with diabetes mellitus and UA nephrolithiasis, phentermine/topiramate was well tolerated and demonstrated significant stone burden reductions by per-protocol analysis. The intervention group also had greater weight loss, higher urinary pH, and lower HgbA1c and urinary citrate levels. These data provide a framework to study the impact of this novel alternative UA therapy on a wider range of patients with obesity and diabetes.