Mineral content of infant formula after treatment with sodium polystyrene sulfonate or calcium polystyrene sulfonate

Options for the management of infants with hyperkalemia secondary to renal insufficiency are limited for infants not maintained on dialysis. Precipitation of potassium (K+) from infant formula with sodium polystyrene sulfonate (KX) prior to feeding has been reported. However, its effect on calcium (Ca2+) and sodium (Na+) has not been quantitatively defined. The purpose of this study was to examine the effects of two K+ exchange resins: KX and calcium polystyrene sulfonate (RC) on Na+, K+, and Ca2+. Infant formula powder (Similac PM 60/40, Ross Laboratories, Columbus, OH, USA) was prepared with deionized water (DW) and KX or RC (1 g/mEq of K+) was added. The formula was decanted after 50 minutes and Na+, K+, and Ca2+ were assayed in the supernatant. Na+ and K+ were also assayed in ready-to-feed PM 60/40 (RTF). KX decreased the K+ concentration by 4.5 fold (P < 0.001) and increased the Na+ content by 3.8 fold (P < 0.001). In RC there was a 1.6-fold increase in Ca2+ content (P < 0.001), and a 13% decrease in K+ concentrations (P < 0.05). Preparation of the formula with DW reduced the K+ concentration by 30% compared to ready-to-feed formula (P < 0.001). We conclude that, although KX significantly reduces the K+ content of formulas, DW may be a more practical and convenient method of preparing formula for the hyperkalemic infant.