University of Chicago
Kidney stones are common and often come back. One reason may be that some people with calcium stones have low phosphate levels in the blood and lose too much phosphate through the kidneys. They may also have high calcium in the urine, which raises the chance of forming stones. In older studies, high doses of phosphate supplements lowered urine calcium and appeared to reduce stone formation, but they sometimes caused stomach and bowel side effects, and phosphate is no longer used for stone prevention. This small pilot study will test a much lower dose of neutral phosphate (250 mg twice daily) for 2 weeks in adults with recurrent calcium oxalate kidney stones, high urine calcium, and low blood phosphate. Participants will collect a 24-hour urine sample and have blood drawn before and after the 2-week period. The study will look at whether the low dose reduces urine calcium and the risk of stone formation in urine. The results will help decide whether a larger study is warranted.
Patients who form kidney stones often have lower serum phosphate and higher kidney phosphate losses, largely due to reduced tubular reabsorption. Earlier trials of high-dose phosphate supplementation in patients with idiopathic hypercalciuria reduced urine calcium, and several showed fewer stones. Use of phosphate for stone prevention later declined after a randomized trial of acid phosphate found no difference in stone formation despite lower urine calcium. Studies of neutral or alkaline phosphate, in contrast, did show benefit. Higher doses can also cause gastrointestinal side effects. This…
Inclusion Criteria: * Age 18-70 * History of at least one calcium oxalate stone * Hypercalciuria (\>250mg/day) * Hypophosphatemia (\<3mg/dL) Exclusion Criteria: * History of primarily brushite, uric acid, cysteine, or struvite stones. * History of severe acid-base abnormality, very low (less than 100mg/day) or very high (greater than 1500mg/day) urine phosphate. * Any participants who cannot stop diuretic medication or alkali supplementation for the course of the study period. * Use of drugs that can directly affect proximal tubule function (i.e. topiramate). * Diagnosis of complete distal…
250 mg of oral neutral phosphate taken twice daily for 2 weeks (500 mg total per day). The study drug is dispensed by the University of Chicago Investigational Drug Service. Participants take it at home and are assessed for side effects and adherence by a 1-week phone call and again at the 2-week study visit.