The US Food and Drug Administration (FDA) has released a safety announcement regarding the administration of sodium polystyrene sulfonate, available in Australia under the brand name Resonium A®. In vitro binding studies were conducted with amlodipine, metoprolol, amoxicillin, furosemide, phenytoin, and warfarin. Significant binding to all six of these commonly prescribed medications was observed. On the basis of these findings, the FDA considers that sodium polystyrene sulfonate is likely to bind to many other oral medications.

The FDA now recommends that patients avoid taking sodium polystyrene sulfonate within at least three hours of other orally administered medications. For patients with gastroparesis or other conditions that delay gastric emptying, a six hour separation should be allowed.

Sodium polystyrene sulfonate is a non-absorbable cation exchange resin indicated for the treatment of hyperkalaemia. It predominantly exerts its effects in the large intestine where it removes potassium from the body by exchanging it with sodium. While there is some individual variability, the in vivo exchange capacity is around 1mmol of potassium per gram of resin administered.

Due to this mechanism of action, Resonium A® has the potential to interact with digoxin even if the doses are separated appropriately. If hypokalaemia is allowed to develop during therapy with Resonium A®, the toxic effects of digoxin are likely to be increased. All patients undergoing treatment with Resonium A® should be monitored for electrolyte disturbances, especially those taking digoxin.

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