By Stacey Butterfield
It's time for hospitalists to bust out some new tools for hyperkalemia, nephrologist Andrew J. King, MD, told attendees at Wednesday's hospital medicine precourse.
Now is also the time to put away some old ones, specifically polystyrene sulfonate, he added. "Kayexalate needs to die. There is now a black box warning on cases of colonic necrosis and other serious GI events."
Dr. King, a clinical professor of medicine at the Scripps Clinic in La Jolla, Calif., first saw the fatal effects of the drug during his nephrology fellowship. "Three days post-kidney transplant, [a patient] died of necrotic bowel," he said. "Thank God I wasn't the fellow who wrote the order, but I could have been."
Avoiding polystyrene sulfonate is particularly important in certain patients, including those who are recovering from surgery, take opioids, have ileus or any bowel obstruction, or have a bowel disease, he noted.
New FDA-approved alternatives are zirconium cyclosilicate and patiromer. The former exchanges potassium with sodium and protons and the latter with calcium. Another significant distinction is that they work in different parts of the GI system.
For hospitalists, zirconium cyclosilicate might be the more exciting option, according to Dr. King. "It works throughout the intestine," he said. "I really think this is the drug for the inpatient setting, because it's relatively rapid onset." The 2014 HARMONIZE trial found that patients' mean serum potassium dropped from 5.6 to 5.0 mEq/L four hours after receiving 10 g of the drug.
Edema is a side effect, and there could be others that have not yet been discovered—for either of these drugs, Dr. King said. "I've always felt we understand a drug after 15 years. We're about five years into these drugs, so we may learn some underbellies."
In contrast, patiromer works only in the colon. "Therefore, it's not a rapid effect," said Dr. King. Research on the drug so far has focused mostly on patients with chronic hyperkalemia and showed its effects over weeks, rather than hours or days.
For example, the 2015 OPAL-HK trial "didn't give any data on day one and day two," he said. "The first data point is day three, so we don't know how rapidly this works." Side effects included constipation and hypomagnesemia.
Dr. King also offered some quick tips on use of the older options for hyperkalemia, including calcium, insulin and glucose, bicarbonate, loop diuretics, and hemodialysis. Calcium's advantage is speed, since it "acts within minutes and lasts 30 to 60 minutes. That early effect "gives you a chance to use some of these other agents," he said.
His pearl for "insulin and glucose, your old friend" was that you can repeat it after four to six hours. For bicarbonate, he advised caution, especially at the start. "Bicarbonate doesn't reduce potassium levels; it actually transiently increases them," Dr. King said. While loop diuretics plus saline can make sense for patients with "decent renal function," remember that "kaliuresis depends on diuresis," he said.
Finally, hemodialysis is a well known, reliable, and effective way to remove potassium, with obvious downsides, Dr. King noted. "You know it's hard to wrestle up dialysis like that, and it's getting harder," he said. â–