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The effect of the addition of a buffer to an ethylenediaminetetracetic acid (EDTA) litholytic solution on the solubility of calcium oxalate monohydrate and hydroxyapatite is investigated. The experiments show that the addition of triethanolamine as a buffer to EDTA solutions at pH 8 and 8.5 enhances the solubility of these salts, confirming theoretical predictions. The solubility of calcium oxalate monohydrate at 25C in solutions with varying ratios of buffer to EDTA concentrations and an osmolality of 0.9 was determined. The solutions resulting in the highest solubility were finally tested for their litholytic ability at 37C. At pH 8 solubilities of 22.5 g X l-1 for calcium oxalate monohydrate and 20.2 g X l-1 for hydroxyapatite were obtained. The corresponding solubilities at pH 8.5 were respectively 24.5 g X l-1 and 19.2 g X l-1.

The toxicity to the urothelium of bipotassium ethylene-diaminetetraacetic acid (K2-EDTA) buffered with 0.2 M triethanolamine (TEA) at pH 8 and 8.5 was tested in rats and dogs. Even at a low concentration of 3.125 mM, K2-EDTA is very noxious to the bladder mucosa. This toxicity is not due to the buffer TEA, which is well tolerated. Although buffered K2-EDTA, at pH 8.5 is an excellent chemolytic agent for calcium-containing stones, its clinical use is limited by this toxicity.

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