Metal ion and vitamin adsorption profiles of phosphate binder ion-exchange resins

Aims: To determine the metal ion and vitamin in vitro adsorption profile of sevelamer hydrochloride (sevelamer-HCl) and colestilan(INN)/ colestimide(JAN), a novel ion-exchange resin being developed as a phosphate binder for end-stage renal disease (ESRD) patients undergoing hemodialysis, adsorption of metal ions (iron, cobalt, copper and zinc) and vitamins (B6, B12, C,K and folic acid) essential for hematopoiesis/ blood coagulation was assessed. Methods: Mixtures of each resin (colestilan or sevelamer-HCl, 4 mg/ml) and metal ions (Fe(III), Fe(II), Co(II), Cu(II), and Zn(II), 1 microg/ ml) were adjusted to pH 1.2 or 6.8 and incubated at 37 °C for 1 hour. Metal ions in the recovered filtrate were detected by inductively coupled plasma optical emission spectrometry. In addition, the mixtures of each resin (4 mg/ml) and vitamins (B6, B12, C, K and folic acid, 0.5 - 250 microg/ml) were adjusted to pH 6.8 and incubated at 37 °C for 0.5 hour. The vitamin concentrations in the recovered filtrate were quantified by HPLC. Results: Colestilan did not adsorb any metals tested at either pH level, whereas sevelamer-HCl adsorbed copper(II) and zinc(II) ion at pH 6.8 with adsorption ratios of 99% and 38%, respectively. Both resins showed almost complete adsorption of vitamin C, vitamin K, and folic acid, but weak adsorption of vitamin B6, and no adsorption of vitamin B12. Conclusions: The differing adsorption profiles for metal ions and vitamins between sevelamer-HCl and colestilan may be of importance for the individualized management of anemia and malnutrition in chronic hemodialysis patients receiving phosphate binding ion-exchange resins for the control of hyperphosphatemia.