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Phosphate Binder (Calcium-Based)

Calcium Acetate 667mg (PhosEx)

Brand names: PhosEx, Phoslo

Adult dose

Dose: 667mg (1 tablet) with each meal initially; titrate to 3–4 tablets per meal based on serum phosphate. Usual range: 4–8 tablets/day (2668–5336mg/day).
Route: Oral
Frequency: With each meal (three times daily)
Max: 12 tablets/day (8004mg calcium acetate) — limited by hypercalcaemia risk
Each 667mg tablet contains approximately 169mg elemental calcium (less calcium per mg than calcium carbonate). More effective phosphate binder per mg calcium than calcium carbonate — lower hypercalcaemia risk than carbonate. Must be taken WITH meals.

Paediatric dose

Route: Oral
Frequency: With meals
Max: Specialist paediatric nephrology guidance required
Concentration: 667mg tablets N/A/ml
Off-label paediatric use — doses vary by body weight and phosphate level; specialist paediatric nephrology.

Dose adjustments

Renal

Designed for CKD and dialysis — no dose adjustment required; monitor calcium closely in advanced CKD

Hepatic

No dose adjustment required

Clinical pearls

  • Cheapest phosphate binder available — cost-effective for patients without hypercalcaemia; first-line in many UK renal units when serum calcium is normal
  • Avoid when calcium >2.55 mmol/L — switch to non-calcium binder (sevelamer, lanthanum, or sucroferric oxyhydroxide)
  • Calcium load consideration: multiple calcium-based binder tablets plus active vitamin D can cause significant hypercalcaemia; monitor calcium × phosphate product weekly initially
  • KDIGO CKD-MBD 2017: limit use of calcium-based binders in patients with persistent or recurrent hypercalcaemia, arterial calcification, adynamic bone disease, or low PTH
  • Patient counselling: must take WITH food — taking on empty stomach reduces phosphate binding and increases GI side effects

Contraindications

  • Hypercalcaemia (calcium >2.55 mmol/L — do not use calcium-based binders)
  • Hypercalciuria
  • Nephrolithiasis (calcium-based stones — relative contraindication)
  • Digitalis toxicity (hypercalcaemia risk)

Side effects

  • Hypercalcaemia (dose-dependent — especially with concurrent active vitamin D)
  • Constipation
  • Nausea
  • Metastatic calcification (if calcium × phosphate product >4.4 mmol²/L²)

Interactions

  • Active vitamin D analogues (calcitriol, alfacalcidol) — additive hypercalcaemia risk
  • Digoxin — hypercalcaemia increases toxicity
  • Tetracyclines/fluoroquinolones — reduced absorption (separate by 2h)
  • Thiazide diuretics — additive hypercalcaemia

Monitoring

  • Serum calcium (every 1–4 weeks when adjusting dose; monthly when stable)
  • Serum phosphate
  • Calcium × phosphate product (target <4.4 mmol²/L²)

Reference: BNFc; BNF; KDIGO CKD-MBD Guidelines 2017; PhosEx SPC; NICE TA117. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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