SZC Mechanism and Use — EECC MCQ

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ModerateCardiac PharmacologySZC Mechanism and UseEECC

A 65-year-old man with HFrEF on sacubitril/valsartan and eplerenone has a potassium of 5.7 mmol/L. Sodium zirconium cyclosilicate (SZC) is started. After 48 hours of SZC, potassium falls to 4.8 mmol/L. How does SZC work?

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Correct answer: D — Gastrointestinal potassium exchange for sodium and hydrogen

Sodium zirconium cyclosilicate (SZC, Lokelma) is a non-absorbed inorganic cation exchanger that selectively traps potassium (and ammonium) ions in the GI tract, exchanging them for sodium and hydrogen. It has a rapid onset (1-2 hours — faster than patiromer which takes ~7 hours) and can be used for both acute management (10 g TDS for 24-72 hours) and chronic maintenance (5-10 g daily). Key advantages over legacy binders: (1) selective potassium binding (minimal calcium, magnesium effects); (2) palatability; (3) rapid onset; (4) no GI necrosis risk. The ESC HF Guidelines recommend potassium binders as RAAS enablers (Class IIa), allowing continuation of life-saving ACEi/ARNI and MRA therapy. SZC contains sodium (~400 mg per 5 g dose), which should be considered in fluid-sensitive HF patients.

Reference: ESC (2023): HF Guidelines; SZC Product Information: https://bnf.nice.org.uk/