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Exchange resins (sodium polystyrene sulfonate, Kayexalate) are useful for elimination of potassium from the body in the setting of hyperkalemia, though they work slowly. When given orally, the onset of action is at least 2 hours and peak effect may take > 6 hours. SPS normally produces constipation so it is almost always given with sorbitol. Patients that cannot tolerate oral SPS can receive the therapy as a retention enema, though the magnitude of effect is lower. There is controversy regarding exactly how much SPS will decrease the potassium level, so it seems best to recheck levels to be certain that it's achieving the desired results. Don't rely on this as the sole therapy in moderate to severe cases of hyperkalemia. There are rare case reports of patients receiving SPS + sorbitol that developed intestinal necrosis. The reports seem to indicate that is is a bit more common in post-operative patients and perhaps renal transplant patients. I'm not certain of the mechanism or if there's another way of predicting which patients are at high risk. [Weisberg LS. Management of severe hyperkalemia. Crit Care Med 2008;36:3246-3251.]