Supplementary Material for: Potassium-Binding Resins: Associations with Serum Chemistries and Interdialytic Weight Gain in Hemodialysis Patients

Background: Although potassium-binding sodium-based resins (K resins) have been prescribed to treat hyperkalemia for 50 years, there have been no large studies of their effects among hemodialysis (HD) patients. Methods: Data from 11,409 patients in the Dialysis Outcomes and Practice Patterns Study in Belgium, Canada, France, Italy, and Sweden (nations where ≥5% of patients were prescribed a sodium- based K resin; seven other countries had <5% use) between 2002 and 2011 were analyzed. Linear mixed models examined associations between K resin use and interdialytic weight gain (IDWG) and serum electrolyte concentrations. Mortality was analyzed using Cox regression. An instrumental variable approach was used to partially account for unmeasured confounders. Results: The K resin prescription rate was 20% overall. As hypothesized, patients prescribed a K resin had greater IDWG and higher serum bicarbonate, phosphorus, and sodium (but not calcium) concentrations. Patients prescribed a K resin had higher serum K levels, but serum K levels were lower in an instrumental variable analysis limiting treatment by indication bias. K resin use was not associated with mortality risk. Conclusion: We report the first large study of K resin use and associated laboratory and clinical outcomes in HD patients. The prescription rate of K resins varied dramatically by country and dialysis center. The results suggest that K resin use may effectively lower serum K, although at the expense of somewhat higher phosphatemia and greater IDWG, and had no clear association with mortality. Further study is warranted to elucidate the optimal role for K resins in modern dialysis care.