Physicochemical effects of a new slow‐release potassium phosphate preparation (UroPhos‐K) in absorptive hypercalciuria

A new slow‐release, neutral potassium phosphate salt (UroPhos‐K) has been formulated in order to minimize gastrointestinal side effects and avoid sodium‐induced calciuria. It was tested in a prospective randomized, double‐blind trial in a group of 21 kidney stone patients with absorptive hypercalciuria type I (AH). Twelve patients allocated to the UroPhos‐K group received four tablets twice daily with breakfast and an evening snack providing 1240 mg of phosphorus and 63.5 mEq of potassium daily. Nine patients assigned to the placebo group received placebo tablets of the same appearance containing excipient only. Subjects were studied during a 3‐day period in the hospital while consuming a constant metabolic diet containing 400 mg Ca, 100 mEq Na, and 800 mg P per day before and after 3 months of treatment. Treatment with UroPhos‐K did not cause any significant gastrointestinal side effects; nor did it raise fasting serum K or phosphorus, or reduce hemoglobin or creatinine clearance. It was associated with a rise in urinary K from 46 ± 7 to 98 ± 9 mEq per day and phosphorus from 744 ± 185 to 1535 ± 112 mg per day (p < 0.001 each). UroPhos‐K treatment reduced urinary Ca from 288 ± 63 to 171 ± 49 mg/day (p < 0.001), without altering oxalate excretion. It reduced the urinary saturation of calcium oxalate without altering that of brushite. Moreover, by increasing urinary excretion of inhibitors (citrate and pyrophosphate), it reduced the propensity for spontaneous nucleation of brushite (increased formation product of brushite) and inhibited crystal agglomeration of calcium oxalate. None of these changes were seen in the placebo‐treated group. It is concluded that treatment with UroPhos‐K reduces urinary stone‐forming potential without causing gastrointestinal side effects.