What is Calcium carbonate (CaCO3) used for in medical applications?

What is Calcium Carbonate (CaCO3)?

Calcium carbonate is a calcium salt supplement that provides 40% elemental calcium and serves multiple medical roles: as a phosphate binder in chronic kidney disease, a calcium supplement for deficiency states and preeclampsia prevention, and an antacid for gastrointestinal conditions. 1, 2, 3

Primary Medical Applications

Phosphate Binding in Chronic Kidney Disease

• Calcium carbonate functions as a first-line phosphate binder in CKD patients to control hyperphosphatemia, though it carries higher risk of hypercalcemia compared to calcium acetate 4
• The K/DOQI guidelines note that calcium carbonate demonstrates equivalent efficacy to other phosphate binders in lowering serum phosphorus, but meta-analyses show it produces more hypercalcemic events than alternative binders 4
• Gastrointestinal side effects are actually lowest with calcium carbonate compared to other phosphate binders, though the effect size is small 4
• For CKD patients, calcium carbonate should be taken 10-15 minutes before or during meals to optimize phosphate binding 4
• The choice between calcium carbonate and other calcium-based binders depends on patient tolerance, cost, and ability to maintain calcium-phosphorus product below 55 while limiting total calcium intake 4

Calcium Supplementation

• Calcium carbonate provides the most cost-effective calcium supplementation when taken with meals, delivering approximately 200 mg elemental calcium per 500 mg tablet 4, 2, 3
• Absorption requires gastric acid, making meal-time administration essential—this is the critical limitation distinguishing it from calcium citrate 1, 2
• Divide total daily doses into increments of ≤500-600 mg elemental calcium per administration to maximize fractional absorption, as larger single doses result in decreased absorption efficiency 1, 2

Preeclampsia Prevention

• For pregnant women in low-calcium-intake populations, administer 1.5-2.0 g elemental calcium daily in divided doses for preeclampsia prevention 4, 1
• Calcium carbonate remains the WHO-recommended formulation due to cost-effectiveness, despite requiring multiple daily doses with meals 4

Critical Administration Requirements

Timing and Gastric Acid Dependency

• Patients with GERD, achlorhydria, or those taking proton pump inhibitors should NOT use calcium carbonate—prescribe calcium citrate instead, as carbonate absorption is severely impaired in low-acid environments 1, 2
• The New England Journal of Medicine explicitly states that calcium carbonate supplements must be taken with meals to optimize absorption 2

Drug Interactions

• Space calcium carbonate and iron supplements 2 hours apart, as calcium inhibits iron absorption 1
• Never administer calcium carbonate with sodium bicarbonate or through the same IV line 1

Common Pitfalls to Avoid

• Never exceed 2,000-2,500 mg total daily calcium intake (from all dietary and supplemental sources combined) due to increased risk of kidney stones and potential cardiovascular events 1, 2
• Do not administer calcium during symptomatic hyperphosphatemia without addressing phosphate levels first—risk of tissue calcification and calcium-phosphate precipitation 1
• Avoid calcium citrate while patients receive aluminum-based phosphate binders, as citrate increases aluminum absorption and may precipitate acute aluminum toxicity 4
• In CKD patients with elevated phosphate, increased calcium administration may precipitate calcium phosphate in tissues and cause obstructive uropathy 1

Special Populations

Post-Bariatric Surgery Patients

• After RYGB or sleeve gastrectomy, ensure adequate calcium intake with consideration for combined vitamin D and calcium supplementation if PTH is elevated 1
• These patients may require calcium citrate rather than carbonate due to altered gastric acid production 1

Pediatric Emergency Use

• For hypocalcemia, hyperkalemia, or calcium channel blocker toxicity in children, calcium chloride (not carbonate) is the preferred IV formulation, administered at 20 mg/kg IV/IO 1

Formulation Characteristics

• Each chewable tablet typically contains 750 mg calcium carbonate, providing 300 mg elemental calcium 3
• Store between 20-25°C (68-77°F) in a dry place 3
• Calcium carbonate exists in different polymorphic forms and porous morphologies, with recent pharmaceutical research exploring functionalized porous calcium carbonate for improving dissolution rates of poorly soluble drugs 5, 6