Calcium binding by radiopaque media

This study quantified the binding of ionic calcium by contrast media with disodium edetate and trisodium citrate versus those with only calcium disodium edetate. First, calcium binding by sodium diatrizoate with calcium disodium edetate was measured using an ion-selective electrode at ionic strengths of .08, .16, and .80 molal. Significant binding of calcium was observed, and the probable reaction product is calcium chloride diatrizoate. Second, solutions were mixed containing Renografin 76 (or Hypaque 76) and NaCl at a physiologic ionic strength. The Renografin, which contains disodium edetate and trisodium citrate, caused significantly more binding than did the Hypaque. However, 60% of the drop in ionic calcium was observed with Hypaque and is related to the diatrizoate anion. The nonionic agent iopamidol produced no decrease in ionic calcium. Significant reductions in ionic calcium are produced by both the diatrizoate anion and by edetate and citrate additives.