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

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.

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 degrees 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 degrees C for 0.5 hour. The vitamin concentrations in the recovered filtrate were quantified by HPLC.

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.

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.