A 62-year-old man with CKD stage 4 (eGFR 22 mL/min/1.73m², serum potassium 5.6 mEq/L, phosphate 5.9 mg/dL, bicarbonate 19 mEq/L) is reviewed. His iPTH is 220 pg/mL and calcium is 9.1 mg/dL. Per KDIGO 2023 guidelines on CKD-MBD, which agent is preferred for managing his hyperphosphataemia at this stage?

• A Calcium carbonate — cheapest and most available phosphate binder
• B Calcitriol — directly reduces phosphate by decreasing PTH-mediated bone resorption
• C Cinacalcet — best addresses the combined hyperkalaemia and hyperphosphataemia simultaneously
• D Sevelamer carbonate — preferred to avoid additional calcium load and arterial calcification risk ✓

Explanation

KDIGO 2017/2023 CKD-MBD guidelines recommend restricting dietary phosphate first, then using phosphate binders. In non-dialysis CKD, calcium-based binders (calcium carbonate, acetate) are traditionally first-line but KDIGO recommends limiting calcium load given risks of hypercalcaemia and vascular calcification, especially in patients with pre-existing calcification or hypercalcaemia tendency. Sevelamer (non-calcium, non-absorbed anion exchange resin) is preferred when serum calcium is at high-normal or PTH is suppressed. This patient has serum calcium 9.1 mg/dL (acceptable), but given CKD progression, sevelamer limits further calcium accumulation. Calcitriol reduces PTH but can increase phosphate absorption. Cinacalcet is a calcimimetic for secondary hyperparathyroidism, not directly for hyperphosphataemia.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.