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Calcium Supplement Pregnancy: Safe in pregnancy — calcium requirements increase; supplement at 1–1.5g elemental calcium daily if dietary intake insufficient.

Calcium Carbonate

Brand names: Calcichew, Adcal, Calcichew D3 (with colecalciferol)

Adult dose

Dose: Calcium supplementation (osteoporosis prevention/treatment): 1–1.5g elemental calcium daily in divided doses. Calcichew 500mg tab: 2 tabs BD. Calcichew D3 Forte (500mg calcium + 400 IU D3): 1–2 tabs BD. Hypocalcaemia (mild): 1–2g elemental calcium daily orally.
Route: Oral (chew or swallow whole depending on formulation)
Frequency: Twice daily with meals (calcium carbonate requires acid for absorption — give with food)
Max: 2.5g elemental calcium daily (renal stones risk above this)
Calcium carbonate: 1250mg tablet = 500mg elemental calcium. Take with meals — requires gastric acid for dissolution and absorption. Separate from iron, bisphosphonates, levothyroxine, quinolones, and tetracyclines by at least 2 hours. Calcichew D3 Forte is the most commonly prescribed combined product in the UK for corticosteroid-induced osteoporosis.

Paediatric dose

Route: Oral
Frequency: Twice to three times daily with meals
Max: Varies by age
BNFc: Neonatal hypocalcaemia: IV calcium gluconate first-line (specialist). Oral supplementation: 1 month–4 years: 250mg BD; 5–11 years: 500mg BD; 12–17 years: 500–1000mg BD. Seek specialist paediatric opinion for hypoparathyroidism or complex metabolic bone disease.

Dose adjustments

Renal

eGFR <30: calcium carbonate used as phosphate binder (taken with meals); risk of hypercalcaemia — monitor calcium levels. Avoid if hypercalcaemia present.

Hepatic

No specific adjustment required.

Clinical pearls

  • Prescribe with vitamin D for all patients on long-term corticosteroids (NICE CG146) — calcium alone is insufficient without adequate vitamin D for absorption
  • Patients on PPI or H2RA: consider calcium citrate instead of carbonate — better absorbed in achlorhydria (no acid dependence for dissolution)
  • Monitor serum calcium every 6 months if on combined calcium + vitamin D supplementation — hypercalcaemia risk particularly in renal impairment
  • Calcichew D3 Forte is a phosphate binder in CKD — monitor phosphate as well as calcium

Contraindications

  • Hypercalcaemia
  • Hypercalciuria
  • Calcium-containing renal stones (nephrolithiasis)
  • Severe renal impairment with hypercalcaemia

Side effects

  • Constipation (common)
  • Nausea, GI upset
  • Hypercalcaemia (if excessive dose)
  • Milk-alkali syndrome (large doses with absorbable alkali)
  • Renal stones (long-term high doses)

Interactions

  • Bisphosphonates — chelation; separate by ≥2 hours
  • Levothyroxine — reduces absorption; separate by ≥4 hours
  • Iron supplements — reduces absorption of both; separate by 2 hours
  • Quinolones, tetracyclines — chelation; separate by 2 hours
  • Thiazide diuretics — additive hypercalcaemia risk

Monitoring

  • Serum calcium (every 6 months on supplementation)
  • Urinary calcium (24h collection if recurrent renal stones)
  • Renal function
  • Phosphate (in CKD)

Reference: BNFc; BNF 90; NICE CG146 (Osteoporosis); NICE CG182 (CKD). Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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