Sodium Polystyrene Sulfonate
Sodium Polystyrene Sulfonate (SPS) is a non-absorbable **cation exchange resin** used primarily as an adjunctive treatment for hyperkalemia (high blood potassium levels) in veterinary patients. > **Clinical Pearl:** Because its onset of action is slow (hours to days), SPS should **not** be used as the sole therapy for acute, life-threatening hyperkalemia. Faster-acting therapies (e.g., IV calcium gluconate, regular insulin with dextrose, or sodium bicarbonate) should be prioritized in emergencies. Key points: * It works by exchanging sodium ions for potassium ions in the gastrointestinal tract. * It is often administered with a cathartic (like sorbitol) when given orally to prevent constipation and expedite the removal of the resin-potassium complex. * The underlying cause of the hyperkalemia (e.g., acute kidney injury, urinary obstruction, hypoadrenocorticism) must always be identified and treated concurrently.
Mechanism: SPS acts as a cation exchange resin in the gastrointestinal tract. * **Mechanism:** After oral or rectal administration, the resin exchanges its **sodium ions** for hydrogen ions in the acidic environment of the stomach. As it travels into the large intestine, where potassium concentration is higher, it exchanges these ions for **potassium ions**. * **Binding Capacity:** While theoretically capable of exchanging up to 3.1 mEq of potassium per gram, in vivo it typically exchanges approximately **1 mEq of potassium per gram** of resin. * **Excretion:** The resin, now bound to potassium, is excreted unchanged in the feces, thereby physically removing potassium from the body. * **Sodium Load:** Because it releases sodium in exchange for potassium, it delivers a significant sodium load to the patient, which can be problematic in sodium-restricted individuals.
Dosing by species
- Life-threatening hyperkalemia in neonatal foals · 15 grams of resin in 100 mL of 10% dextrose · Enema · Once/As directed · As needed · Monitor serum potassium and sodium closely.
- Hyperkalemia · 2 grams of resin/kg divided into 3 daily doses (suspended in 3-4 mL water/gram or commercial suspension). Severe hyperkalemia: 3-4 times the normal amount may be given. · PO/Enema · q8h · As needed · If PO, give with a cathartic. If enema, do NOT use a cathartic (must retain in colon for at least 30 mins). Enema prep: add 15g per 100 mL of 1% methylcellulose or 10% dextrose.
- Mild hyperkalemia (<6 mEq/L) · 2 grams/kg in 3-4 divided doses with 20% sorbitol · PO/Enema · q6-8h · As needed · May also be given as an enema without sorbitol.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Patients on severely restricted sodium diets
- Severe congestive heart failure (CHF)
- Severe hypertension
- Oliguric or anuric acute kidney injury (where sodium load cannot be excreted)
- Conditions predisposing to severe constipation or bowel obstruction
Adverse effects
- Constipation (fecal impaction reported rarely)
- Anorexia
- Vomiting
- Nausea
- Hypokalemia (from overuse)
- Hypocalcemia
- Hypomagnesemia
- Sodium retention / Hypernatremia
Drug interactions
- Antacids (Calcium or Magnesium containing) · SPS may bind with magnesium or calcium, preventing bicarbonate ion neutralization and potentially leading to systemic metabolic alkalosis. Concurrent use is not recommended.
- Laxatives (Calcium or Magnesium containing) · Similar to antacids, can lead to metabolic alkalosis and reduced potassium-binding efficacy.
Monitoring
- Serum electrolytes (sodium and potassium at least once daily; calcium, magnesium)
- Acid/base status
- ECG (if warranted to monitor cardiac effects of hyper/hypokalemia)
- Fecal output and consistency (monitor for constipation/impaction)
Overdose
Overdosage or overuse may lead to severe electrolyte imbalances, including **hypokalemia** (low potassium), **hypocalcemia** (low calcium), and **hypomagnesemia** (low magnesium), as well as significant **sodium retention**. Treatment is symptomatic and supportive. Discontinue the drug immediately and correct electrolyte deficits based on frequent serum chemistry monitoring.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.