Introduction
Calcium carbonate is an inorganic salt commonly used as a calcium supplement and antacid. It is one of the most widely available and frequently prescribed calcium preparations, serving both therapeutic and nutritional purposes. As a fundamental mineral supplement, calcium carbonate plays a crucial role in maintaining bone health and treating various acid-related gastrointestinal conditions.
Mechanism of Action
Calcium carbonate exerts its effects through two primary mechanisms:
- As an antacid: It neutralizes gastric acid by reacting with hydrochloric acid in the stomach to form calcium chloride, water, and carbon dioxide (CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂)
- As a calcium supplement: It provides elemental calcium, which is essential for bone mineralization, neuromuscular function, cardiac contractility, and blood coagulation
The neutralization capacity is approximately 20-22 mEq of acid per 1 gram of calcium carbonate.
Indications
FDA-approved indications:- Treatment of symptoms associated with gastroesophageal reflux disease (GERD)
- Management of dyspepsia and heartburn
- Prevention and treatment of calcium deficiency
- Adjunctive therapy in osteoporosis management
- Management of hyperphosphatemia in chronic kidney disease
- Prophylaxis against osteoporosis in high-risk populations
Dosage and Administration
Antacid dosing:- Adults: 1-2 tablets (500-1000 mg) as symptoms occur, maximum 7 tablets/day
- May be taken between meals and at bedtime
- Adults: 1000-1500 mg elemental calcium daily in divided doses
- Postmenopausal women: 1200-1500 mg daily
- Maximum single dose: 500-600 mg elemental calcium
- Renal impairment: Use with caution; monitor serum calcium
- Hepatic impairment: No dosage adjustment required
- Elderly: Consider reduced dosing if renal function impaired
- Pediatric: Safety and efficacy not established for antacid use
Pharmacokinetics
Absorption: Requires acidic environment for optimal absorption; primarily in duodenum and proximal jejunum. Bioavailability ranges from 25-35% under fasting conditions. Distribution: Calcium distributes primarily to bone (99%) with the remainder in extracellular fluid. Crosses placenta and enters breast milk. Metabolism: Not metabolized hepatically. Elimination: Primarily renal excretion (20%) with fecal elimination of unabsorbed calcium (80%). Renal clearance approximately 0.5-1.5 mL/min/1.73 m².Contraindications
- Hypercalcemia (serum calcium >10.5 mg/dL)
- Severe renal impairment (eGFR <30 mL/min)
- History of nephrolithiasis or nephrocalcinosis
- Hypersensitivity to calcium carbonate or any component
- Patients with hypochlorhydria or achlorhydria
Warnings and Precautions
Black Box Warning: None Important precautions:- Risk of milk-alkali syndrome with chronic high-dose use
- May cause constipation or gastrointestinal obstruction
- Use caution in patients with sarcoidosis
- Monitor for hypercalcemia in patients with renal impairment
- May interfere with absorption of other medications
- Not recommended for treatment of peptic ulcer disease
Drug Interactions
Significant interactions:- Bisphosphonates: Reduced absorption - separate administration by at least 2 hours
- Tetracycline antibiotics: Formation of insoluble complexes - separate by 2-4 hours
- Levothyroxine: Reduced absorption - separate by at least 4 hours
- Quinolones: Reduced antibiotic absorption - separate by 2 hours
- Iron supplements: Decreased iron absorption - separate by 2 hours
- Thiazide diuretics: Increased risk of hypercalcemia
- Digoxin: May potentiate digitalis toxicity
Adverse Effects
Common (≥1%):- Constipation (10-15%)
- Flatulence (5-10%)
- Abdominal discomfort (3-5%)
- Nausea (2-4%)
- Hypercalcemia
- Nephrolithiasis
- Milk-alkali syndrome
- Hypophosphatemia
- Renal impairment
Monitoring Parameters
Baseline:- Serum calcium, phosphorus, magnesium
- Renal function (BUN, creatinine, eGFR)
- Assessment of dietary calcium intake
- Serum calcium every 3-6 months with chronic use
- Monitor for symptoms of hypercalcemia (fatigue, nausea, polyuria)
- Renal function annually in patients with risk factors
- Bone density monitoring in osteoporosis patients
Patient Education
Key points for patients:- Take with meals for better absorption as calcium supplement
- For antacid use, take 1 hour after meals and at bedtime
- Do not exceed recommended dosage without medical supervision
- Report symptoms of hypercalcemia (nausea, vomiting, constipation, confusion)
- Maintain adequate fluid intake
- Separate calcium carbonate from other medications by 2-4 hours
- Dietary calcium sources should be considered in total calcium intake
- Notify healthcare provider if pregnant, planning pregnancy, or breastfeeding
References
1. National Institutes of Health. Calcium Fact Sheet for Health Professionals. Office of Dietary Supplements. 2023. 2. Lexicomp Online. Calcium carbonate monograph. Wolters Kluwer Clinical Drug Information. 2023. 3. Micromedex Solutions. Calcium carbonate drug information. IBM Watson Health. 2023. 4. Bo-Linn GW, et al. An evaluation of the importance of gastric acid secretion in the absorption of dietary calcium. J Clin Invest. 1984;73(3):640-647. 5. Carr AJ, et al. Calcium supplementation in clinical practice: a review of forms, doses, and indications. Nutr Clin Pract. 2017;32(2):180-196. 6. FDA-approved product labeling for various calcium carbonate preparations. 7. Cosman F, et al. Clinician's Guide to Prevention and Treatment of Osteoporosis. Osteoporos Int. 2014;25(10):2359-2381.