BACKGROUND AND OBJECTIVES: Sodium thiosulfate (STS) reduced calcium stone 
formation in both humans and genetic hypercalciuric stone forming (GHS) rats. We 
sought to measure urine chemistry changes resulting from STS administration in 
people. DESIGN SETTING PARTICIPANTS MEASUREMENTS: STS was given to healthy and 
hypercalciuric stone forming adults. Five normal non-stone forming adults (mean 
age 33 years), and 5 people with idiopathic hypercalciuria and calcium kidney 
stones (mean age 66 years) participated. Two baseline 24-hour urine collections 
were performed on days 2 and 3 of 3 days of self-selected diets. Subjects then 
drank STS 10 mmol twice a day for 7 days and did urine collections while 
repeating the self-selected diet. Results were compared by non-parametric 
Wilcoxon signed rank test. The primary outcome was the resulting change in urine 
chemistry.
RESULTS: STS administration did not cause a significant change in urinary 
calcium excretion in either group. In both groups, 24 hour urinary ammonium (P = 
0.005) and sulfate excretion (P = 0.007) increased, and urinary pH fell (P = 
0.005); citrate excretion fell (P<0.05) in hypercalciuric participants but not 
in non-stone formers. Among stone formers with hypercalciuria, 3 of 5 patients 
had measurement of serum HCO3 concentration after the STS period: it did not 
change. The net effect was an increase in supersaturation of uric acid, and no 
change in supersaturation of calcium oxalate or calcium phosphate.
CONCLUSIONS: The basis for studies demonstrating that STS prevented stones in 
rats and people was not reflected by the changes in urine chemistry reported 
here. Although serum HCO3 did not change, urine tests suggested an acid load in 
both non-stone forming and hypercalciuric stone-forming participants. The long 
term safety of STS needs to be determined before the drug can be tested in 
humans for long-term prevention of stone recurrence.