Macromineral·Vitamins & Minerals

Calcium carbonate

Calcium supplementation in osteoporosis, hyperphosphatemia in end-stage renal failure, hypocalcemia

MINERALCaltrate, Cal-Sup, Titralac600 mg tabletUNSCHEDULEDTGA

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At a glance

Max Dose

2500 mg/day

Caution: Absorption

ACID DEPENDENT

High risk: Binding Trap

CRITICAL

Caution: Constipation

HIGH RISK

Cautions

Avoid / Cautions

Pre-existing hypercalcemia, hypercalciuria, severe kidney stones. Pregnancy Category A. Demands increase in 3rd trimester.

Where it stands

Rapid Summary

Overview

The most common and cheapest form of calcium supplementation. Highly dependent on stomach acid to dissolve. Acts as a potent binder of other drugs in the gut.

Clinical Focus

Cannot be taken simultaneously with Thyroxine, Iron, Doxycycline, or Ciprofloxacin. It will permanently bind them in the gut, causing clinical failure.

Bottom Line

Take with food

Calcium carbonate is a first-line calcium supplement for osteoporosis prevention and phosphate binding in CKD, but requires gastric acid for absorption (take with food) and can cause constipation and hypercalcaemia.

Formulation & Access

Brand Names

Caltrate, Cal-Sup, Titralac

Oral Routes

Tablets (600 mg elemental calcium). Often combined with Vitamin D3.

Prescribing & PBS

Over The Counter (OTC).

Indications & Use

Primary

TGA

Calcium supplementation in osteoporosis, hyperphosphatemia in end-stage renal failure, hypocalcemia.

Clinical Place

Mandatory adjunct for patients on Denosumab or Bisphosphonates to provide the building blocks for bone remineralisation.

Quick reference

Class & Role

Macromineral — The most common and cheapest form of calcium supplementation.

Route / Formulation

Tablets (600 mg elemental calcium). Often combined with Vitamin D3. (Caltrate, Cal-Sup, Titralac)

Usual Dose & Max

PO 600 mg (Elemental Calcium) OD or BD. Must be taken strictly WITH FOOD to stimulate stomach acid for absorption. Max 2500 mg/day (Total elemental calcium from diet + pills).

Key Indication Doses

Osteoporosis Adjunct / Supplement: PO 600 mg (Elemental Calcium) OD or BD. Must be taken strictly WITH FOOD to stimulate stomach acid for absorption. Phosphate Binding (CKD): PO 1.25 - 2.5 g TDS (Taken strictly WITH MEALS to bind dietary phosphate before it absorbs). Renal Impairment: Can cause vascular calcification in severe CKD if overdosed.

Best Uses

Key Risks

Gastrointestinal: Severe constipation, bloating, flatulence. Metabolic: Hypercalcemia (especially if taking high-dose Vitamin D or thiazide diuretics), Milk-Alkali syndrome (metabolic alkalosis and renal failure). Renal: Nephrolithiasis (Calcium kidney stones).

Key Interactions

Levothyroxine (Oroxine), Iron, Fluoroquinolones (Ciprofloxacin), Tetracyclines (Doxycycline), Bisphosphonates. Calcium forms an indestructible physical 'brick' with these drugs in the stomach. You MUST separate doses by a minimum of 2 to 4 hours. Thiazide diuretics (HCTZ) reduce calcium excretion in the kidneys, massively increasing the risk of hypercalcemia.

Monitoring

Monitor U&E (Calcium, Phosphate, eGFR) regularly in CKD patients or those on concurrent high-dose Vitamin D. Ensure prophylactic laxatives are considered in the frail elderly, as it acts like concrete in the bowel.

Clinical Pearl

Calcium Carbonate physically requires a highly acidic stomach (pH < 2) to dissolve into an absorbable form. If a patient is taking Pantoprazole or Esomeprazole (PPI), the stomach has no acid, and the Calcium Carbonate will pass straight through the bowel unabsorbed. For patients on PPIs, you MUST switch them to Calcium Citrate (Citracal), which dissolves independent of acid.

Access

Caltrate, Cal-Sup, Titralac600 mg tablet

Brand: Caltrate, Cal-Sup, Titralac
Formulation: Tablets (600 mg elemental calcium). Often combined with Vitamin D3.

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