Calcium Replacement Therapies

Calcium replacement therapies restore total and ionised calcium in hypocalcaemia and supply dietary calcium for bone health. Oral salts treat deficiency and hypoparathyroidism, and intravenous calcium treats symptomatic hypocalcaemia, hyperkalaemia with ECG changes, magnesium toxicity and calcium channel blocker overdose.

Mechanism. Calcium raises extracellular ionised calcium, restoring neuromuscular and cardiac membrane stability and acting as a cofactor in bone mineralisation and coagulation.

Pharmacokinetics. Oral absorption is about 30% and falls at doses over 500 mg of elemental calcium, so split the doses. Calcium carbonate needs gastric acid and food. Calcium citrate does not.

Salt	Elemental calcium	Notes
Calcium carbonate	40%	Cheapest, take with meals
Calcium citrate	21%	Preferred with proton pump inhibitors or achlorhydria
Calcium gluconate	9%	Intravenous 10% solution: 10 mL contains 2.2 mmol (about 90 mg)
Calcium chloride	27%	Intravenous 10% solution: 10 mL contains 6.8 mmol (about 270 mg); irritant, central line preferred

Differences. Gluconate is used peripherally; chloride has three times the elemental calcium but causes tissue necrosis on extravasation.

Dietary supplement: 500 to 1000 mg elemental calcium daily in divided doses of no more than 500 mg, to reach total intake of 1000 to 1200 mg.
Hypoparathyroidism and hungry bone syndrome: 1 to 2 g elemental calcium daily in divided doses, with calcitriol or alfacalcidol.
Symptomatic acute hypocalcaemia (tetany, seizures, QT prolongation): 10 mL of 10% calcium gluconate intravenously over 10 minutes with ECG monitoring, repeated if symptoms persist, then an infusion: 100 mL of 10% calcium gluconate in 1 litre of 5% dextrose or 0.9% sodium chloride at 50 mL/h, titrated to calcium. Correct magnesium at the same time.
Hyperkalaemia with ECG changes: 10 mL of 10% calcium gluconate over 2 to 5 minutes, repeated after 5 to 10 minutes if ECG changes persist.
Calcium channel blocker overdose and cardiac arrest from hyperkalaemia: calcium chloride 10% 10 mL via a central line, or gluconate 30 mL peripherally.
Children: 10% calcium gluconate 0.5 mL/kg (maximum 10 to 20 mL) slowly over 10 to 30 minutes with monitoring.

Special groups. Pregnancy: where dietary intake is low, 1.5 to 2 g elemental calcium daily from 20 weeks reduces pre-eclampsia. Breastfeeding: compatible. Children: rickets need calcium 500 mg daily. Older adults: constipation and stone risk. Kidney impairment: limit calcium-based products with hyperphosphataemia. Liver impairment: no adjustment. Regional: dietary calcium is low where maize is the staple and dairy intake is low, so nutritional rickets and osteomalacia are common.

Adverse effects. Constipation, bloating, hypercalcaemia, hypercalciuria and kidney stones, milk-alkali syndrome with antacid excess. Intravenous: bradycardia, arrhythmia with rapid infusion, extravasation necrosis, digoxin toxicity.

Contraindications. Hypercalcaemia, hypercalciuria, and calcium given within a line carrying ceftriaxone in neonates (fatal precipitation).

Interactions. Calcium reduces absorption of levothyroxine, quinolones, tetracyclines, bisphosphonates and iron (separate by 2 to 4 hours). Thiazides raise calcium. Intravenous calcium precipitates with bicarbonate and phosphate.

Monitoring. Corrected or ionised calcium, magnesium, phosphate and creatinine; ECG during intravenous therapy; urinary calcium in long-term therapy.

Referral and escalation. Refractory hypocalcaemia, hypoparathyroidism, and calcium over 2.8 mmol/L.

Calcium Replacement Therapies

Class Overview And Mechanism

Members And Differences

Clinical Use And Selection

Class Safety And Monitoring