Polystyrene sulfonates are a group of medications used to treat high blood potassium. Therapeutic effects generally appear hours to days after commencement of therapy. Oral formulations often also contain the laxative sorbitol in order to lessen the risk of constipation which can be severe.
Polystyrene sulfonates are derived from polystyrene by the addition of sulfonate functional groups. Sodium polystyrene sulfonate was approved for medical use in the United States in 1958. but it was never marketed.
Polystyrene sulfonates are also used in technical applications to remove potassium, calcium, and sodium from solutions.
Medical uses
thumb|right|[[Micrograph showing sodium polystyrene sulfonate crystals (purple – at top of the image) in the biopsy of a colonic mass. H&E stain.]]
Polystyrene sulfonate is typically supplied in the form of either a sodium or a calcium salt. It is used medically as a potassium binder in hyperkalemia (high blood potassium) occurring in the context of acute and chronic kidney disease. The medication has a delayed onset of action and is effective in sequestering potassium over the longer-term, however, its effectiveness in acute management of hyperkalemia is tenuous. Constipation can be severe, culminating in life-threatening fecal impaction.
GI injury occurs both with polystyrene sulfonate alone or in formulations containing sorbitol. It can occur with oral or rectal administration. Polystyrene sulfonate may be directly toxic to the intestinal mucosa, inducing a local inflammatory response that causes vascular injury. Co-administration of sorbitol is thought to compound the risk of GI injury by independently promoting vascular injury by causing vasospasm and prostaglandin-mediated pro-inflammatory effects.
Contraindications
Polystyrene sulfonates should not be used in people with obstructive bowel disease and in newborns with reduced gut motility.
Interactions
Polystyrene sulfonates can bind to various drugs within the digestive tract and thus lower their absorption and effectiveness. Common examples include lithium, thyroxine, and digitalis. In September 2017, the FDA recommended separating the dosing of polystyrene sulfonate from any other oral medications by at least three hours to avoid any potential interactions.
Mechanism of action
Polystyrene sulfonates release sodium or calcium ions in the stomach in exchange for hydrogen ions. When the resin reaches the large intestine the hydrogen ions are exchanged for free potassium ions, and the resin is then eliminated in the feces. The net effect is lowering the amount of potassium available for absorption into the blood and increasing the amount that is excreted via the feces. The effect is a reduction of potassium levels in the body, at a capacity of 1 mEq of potassium exchanged per 1 g of resin. The fact that the medication's site of action is the large intestine explains the delayed and prolonged effects seen with oral administration. leading to well defined linear polymers, as well as more complicated molecular architectures.
Chemical uses
Polystyrene sulfonates are useful because of their ion exchange properties. Linear ionic polymers are generally water-soluble, whereas cross-linked materials (called resins) do not dissolve in water. These polymers are classified as polysalts and ionomers. mostly commonly under the tradename Amberlyst.