Comparative Analysis of Alternative Calcium Chelators for the Treatment of Calcific Band Keratopathy

In this study, we compared clinically relevant biochemical properties of each chelator for pH, osmolarity, and calcium chelation potential.

In total, 0.2 M K 2 EDTA and K 3 EDTA (BD vacutainer tubes by Becton, Dickinson and Company) and Na 2 EDTA (Sigma Aldrich) solutions were made. The pH of each solution was measured (Mettler Toledo pH meter), and the theoretical osmolarity was calculated. Next, we determined the calcium chelation potential of each EDTA salt by titrating it with 10 μmol of calcium hydroxyapatite or CaCl 2 containing Patton-Reeder colorimetric indicator. Statistical significance was analyzed using analysis of variance.

The 0.2 M solutions of Na 2 EDTA, K 2 EDTA, and K 3 EDTA have pH values of 4.43, 5.71, and 9.191 and theoretical osmolarities of 600, 600, and 800 mOsm/L, respectively. Calcium chelation ability was similar among all 3 solutions: 0.94 to 0.98 mol of EDTA was needed to fully chelate 1 mol calcium ions of CaCl 2 ( P = 0.296), 0.100 to 0.108 mol of EDTA for 1 mol calcium ions of the hydroxyapatite aqueous suspension ( P = 0.296), and 0.992 to 0.996 mol for 1 mol calcium ions of hydroxyapatite in acidic solution ( P = 0.178). Compared with the clinical standard of 3% (30 mg/mL) Na 2 EDTA, approximately 3.3% (33 mg/mL) K 2 EDTA and 3.6% (36 mg/mL) K 3 EDTA are needed to chelate an equivalent amount of calcium.

In this article, we provide clinically relevant biochemical properties of 2 alternatives to Na 2 EDTA and demonstrate comparable calcium chelation ability among all 3 solutions. In situations where sterile sources of Na 2 EDTA are unavailable, potassium EDTA may provide a convenient and equally effective method of treatment for band keratopathy.