FDA: Drug for Treating High Blood Potassium Levels Should Not Be Combined with Other Medications

On Sept. 6, 2017, the Food and Drug Administration (FDA) issued a warning on the risk of sodium polystyrene sulfonate (KAYEXALATE, KALEXATE, KIONEX, SPS) decreasing the absorption and effectiveness of many oral prescription medications.[1] Sodium polystyrene sulfonate is approved to treat high levels of potassium in the blood, a problem that most commonly occurs in patients with severe kidney failure.

The FDA based its alert on a laboratory study showing that sodium polystyrene sulfonate binds to six different oral medications that are frequently taken by patients who also are taking sodium polystyrene sulfonate, thus decreasing their absorption and therefore their effectiveness: the blood pressure medicines amlodipine (NORVASC) and metoprolol (LOPRESSOR, TOPROL-XL), the antibiotic amoxicillin (AMOXIL, AUGMENTIN, LAROTID, MOXATAG), the water pill furosemide (LASIX), the seizure medicine phenytoin (DILANTIN, PHENYTEK) and the blood thinner warfarin (COUMADIN, JANTOVEN). The agency concluded that sodium polystyrene sulfonate likely binds to many other oral medications.

Based on the probable time it takes sodium polystyrene sulfonate to pass through the stomach, the FDA has recommended that all other oral prescription and over-the-counter medications be taken at least three hours before or three hours after taking a dose of sodium polystyrene sulfonate. Doing so will make it less likely that sodium polystyrene sulfonate will interfere with any other oral medicines. For patients with conditions resulting in delayed emptying of the stomach (such as occurs in some patients with diabetes), the agency recommended increasing this interval to six hours before or after taking a dose of sodium polystyrene sulfonate.

Disturbingly, the FDA’s safety announcement came nearly two years after the agency announced that it had ordered the manufacturer of one of the sodium polystyrene sulfonate products, Kayexalate, to conduct studies on interactions between sodium polystyrene sulfonate and other commonly used drugs. At the time, the drug was already known to bind to lithium (LITHOBID) and thyroxine (LEVO-T, LEVOXYL, SYNTHROID, TIROSINT, UNITHROID).[2] These laboratory studies are not complex and can be done relatively quickly, so it is unclear why it took two years for the FDA to finally warn the public about these dangerous drug-drug interactions.

What You Can Do

If you have high levels of potassium in your blood and are prescribed sodium polystyrene sulfonate, talk with your doctor about taking the medicine at least three hours before or three hours after your other oral medications. If you are diabetic or have been diagnosed with slow emptying of your stomach, ask your doctor whether you should take your other oral medications at least six hours before or after you take sodium polystyrene sulfonate.

References

[1] Food and Drug Administration. FDA drug safety communication: FDA recommends separating dosing of potassium-lowering drug sodium polystyrene sulfonate (Kayexalate) from all other oral drugs. September 6, 2017. https://www.fda.gov/Drugs/DrugSafety/ucm572484.htm. Accessed November 14, 2017.

[2] Food and Drug Administration. FDA drug safety communication: FDA requires drug interaction studies with potassium-lowering drug Kayexalate (sodium polystyrene sulfonate). October 22, 2015. https://www.fda.gov/Drugs/DrugSafety/ucm468035.htm. Accessed November 14, 2017.