Screening of chelating agents for chemolysis.

The solubility of calcium oxalate monohydrate and calcium hydroxyapatite was calculated as a function of pH in the presence of different chelating agents and was compared with the solubilities in EDTA- or CDTA-containing solutions. An analysis of the solubility curves for 19 chelating agents showed that 5 of the complexing agents considered result in a high solubility for calcium phosphate and oxalate at pH 8 or higher. For these complexing agents the solubility curves of struvite were also calculated. EGTA and HEDTA showed rather low solubilities for struvite due to their low tendency to form complexes with magnesium. On the basis of the calculated solubility curves, the expected litholytic effectiveness for the inorganic kidney stone compounds could be classified in the following decreasing order: CDTA approximately equal to EDTA approximately equal to EGTA greater than EEDTA greater than DTPA greater than UDA approximately equal to HEDTA. With the exception of EGTA and HEDTA for struvite stones, solutions based on these compounds show high solubilities for all the inorganic kidney stone compounds at a solution pH of 8 or higher and therefore have good prospects as litholytic agents.