Sodium polystyrene sulfonate (SPS) potassium binding resins increase colonic potassium excretion and are approved by the U.S. Food and Drug Administration (FDA) for the treatment of hyperkalemia. In 2009, the FDA recommended that sorbitol, a cathartic often given with SPS to prevent obstipation, not be added to SPS powder because of associated colonic necrosis. A premixed oral suspension of SPS in 33% sorbitol was not included in this warning. SPS resins increase stool potassium excretion in normokalemic subjects, but proportionately more potassium is excreted due to cathartics when the two are combined. In hyperkalemic patients, oral SPS mixed in water significantly decreases serum potassium within 24 hours. SPS/sorbitol-associated colonic necrosis is most commonly seen in patients who have received enemas in the setting of recent abdominal surgery, bowel injury, or intestinal dysfunction. It is a rare event, on the order of 0.2 to 0.3%, almost exclusively present in patients at risk. The agent most likely associated with colonic necrosis is 70% sorbitol, and animal data support that etiology. There is very little data to suggest that oral SPS given with 33% sorbitol (in the premixed form) or SPS powder in water orally or as an enema causes colonic necrosis. SPS ion-exchange resins are the only agents, other than dialysis and diuretics, available to increase potassium excretion in hyperkalemia, and when used appropriately, they appear to be clinically effective and reasonably safe.

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Regardless of sampling frame, standard task-based inclusion criteria to define caregivers may enhance validity.