An Early Phase 1 interventional study of Neutral Phosphate in Kidney Stones, Calcium Oxalate Kidney Stones and Hypophosphatemia, sponsored by University of Chicago. Not yet recruiting at 1 site in United States. Open to participants aged 18 Years to 70 Years. Per ClinicalTrials.gov, last updated 2026-10-29.
Sponsored by University of Chicago · Early Phase 1, Interventional, and Treatment
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 pilot tests whether a lower dose can reduce urine calcium while avoiding those negative effects. It is exploratory and will provide preliminary data for a larger grant-funded trial.
This is a single-group, open-label pilot in which all participants receive the same intervention. Before each collection, participants hold certain medications and supplements that could affect urine chemistry, in discussion with their treating physician. Participants complete a baseline 24-hour urine collection at home, followed by a fasting baseline visit at the University of Chicago Medicine Clinical Research Center with vital signs and a blood draw. A coordinator calls at one week to check for side effects and adherence. Participants then repeat the 24-hour urine collection and a fasting visit with vital signs, a blood draw, and a side effect and adherence assessment at 2 weeks.
Urine collections are analyzed by Litholink lab for a full set of stone risk chemistries, and supersaturation values are calculated. Serum is analyzed in the University of Chicago General Chemistry laboratory. Urine and serum samples are frozen and stored for possible later assays. Basic clinical variables are taken from the electronic health record and confirmed by interview. Analysis is descriptive, looking at the change in each participant from baseline to 2 weeks, and no formal hypothesis testing is planned.
509 studies on the registry are indexed under Kidney Calculi; 146 are open to participants now.
This study's planned enrollment of 5 is below the median of 86 across 391 interventional studies indexed under Kidney Calculi.
Browse Kidney Calculi studies →University of Chicago is the lead sponsor of 924 studies on the registry; 185 are open to participants now.
Of its 103 completed or terminated interventional studies of FDA-regulated products, 72 (70%) have results posted.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
GFR (glomerular filtration rate) is how much blood the kidneys filter each minute. It is usually estimated from a blood test — eGFR, by formulas such as CKD-EPI or MDRD — and some studies ask for it to be measured directly instead. Usually given in mL/min/1.73 m².
Check the method, the units and the minimum the study states. A value of 90 or above is in the normal-or-high range, but kidney damage can show in other tests too.
GFR and eGFR (kidney filtering)
GFR (glomerular filtration rate) is how much blood the kidneys filter each minute. It is usually estimated from a blood test — eGFR, by formulas such as CKD-EPI or MDRD — and some studies ask for it to be measured directly instead. Usually given in mL/min/1.73 m².
Check the method, the units and the minimum the study states. A value of 90 or above is in the normal-or-high range, but kidney damage can show in other tests too.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Participants receive 250 mg of oral neutral phosphate twice daily for 2 weeks, dispensed by the University of Chicago Investigational Drug Service. Urine calcium and related stone risk measures are collected by 24-hour urine collection and compared before and after the 2-week course. A coordinator calls at 1 week to check for side effects and adherence, and these are assessed again at the final study visit.
Drug: Neutral Phosphate
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.
Change in from urine calcium from baseline (time 0) and 2-weeks (completion) after oral phosphate (250mg twice daily) supplementation
Change in 24-hour urine calcium (mg/day) from baseline to the end of 2 weeks of oral neutral phosphate (250 mg twice daily). Urine is collected over 24 hours at home before the baseline visit and again at 2 weeks, and calcium is measured by Litholink (Labcorp). The change is calculated for each participant as the 2-week value minus the baseline value.
Time frame: 2 weeks
Change in Urine Calcium Oxalate Supersaturation
Change in 24-hour urine calcium oxalate supersaturation from baseline to the end of 2 weeks of oral neutral phosphate (250 mg twice daily). Supersaturation is calculated with the EQUIL2 program from the 24-hour urine chemistries measured by Litholink (Labcorp). The change is the 2-week value minus the baseline value for each participant.
Time frame: 2 weeks
Change in Urine Calcium Phosphate Supersaturation
Change in 24-hour urine calcium phosphate supersaturation from baseline to the end of 2 weeks of oral neutral phosphate (250 mg twice daily). Supersaturation is calculated with EQUIL2 from the 24-hour urine chemistries measured by Litholink (Labcorp). The change is the 2-week value minus the baseline value for each participant.
Time frame: 2 weeks
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is not yet recruiting, as verified in Oct 2026. You cannot join it, but the record below documents what was studied.
Get an email when the registry record changes — status, dates, results — or when someone posts here.
Sign in to followQuestions and observations about this study, from anyone following it. Not medical advice, and not a channel to the study team — their contact details are on the registry record.
Sign in to join the discussion. Reading takes no account; posting does. You choose a display name, and a pseudonym is the default.
Nothing here yet. If you are running this trial, taking part in it, or weighing whether to, this is the place to say so.