A nurse is reviewing the laboratory report of a client and identifies a serum potassium level of 6.8 mEq/L. Which of the following medications should the nurse plan to administer?

A. Sevelamer is incorrect because it is a phosphate binder used to treat hyperphosphatemia, not hyperkalemia. B. Darbepoetin alfa is incorrect because it is an erythropoiesis-stimulating agent used to treat anemia, not to lower potassium levels. C. Lactulose is incorrect because it is used to reduce ammonia levels in clients with hepatic encephalopathy, not potassium. D. Sodium polystyrene is correct because it is a cation-exchange resin that removes excess potassium from the body through the gastrointestinal tract, making it appropriate for treating hyperkalemia.