Calcium Carbonate 1250mg Tablet Equivalency
A 1250mg calcium carbonate tablet contains 500mg of elemental calcium, which is equivalent to exactly one 500mg elemental calcium tablet. 1
Understanding the Calculation
Calcium carbonate contains 40% elemental calcium by weight. 1 This is the critical conversion factor that determines how much absorbable calcium you're actually getting from any calcium carbonate supplement.
The Math:
- 1250mg calcium carbonate × 40% = 500mg elemental calcium 1
- Therefore, one 1250mg calcium carbonate tablet = one 500mg elemental calcium tablet 2
Why This Matters Clinically
Dosing decisions must be based on elemental calcium content, not the total calcium salt weight. 1 This is a common source of confusion and dosing errors in clinical practice.
Key Points for Prescribing:
- Supplement labels should list both total calcium carbonate AND elemental calcium content 1
- The 1250mg calcium carbonate formulation (providing 500mg elemental calcium) is commercially available as products like Tums 500 2
- If you need more than 500mg of elemental calcium daily, divide the doses to improve absorption and minimize gastrointestinal side effects 1
Practical Absorption Considerations
Calcium carbonate should be taken with meals because gastric acidity is required for optimal absorption 1, 2, 3
Common Pitfalls to Avoid:
- Do not take calcium carbonate with acid-reducing medications (H2 blockers or proton pump inhibitors), as this significantly impairs absorption 1, 2
- Maximum single dose should not exceed 500mg of elemental calcium for optimal absorption 1, 3
- Calcium carbonate is more likely to cause constipation and bloating compared to other calcium formulations 1, 2
Alternative Formulations
If gastrointestinal side effects occur or if the patient takes acid-reducing medications, calcium citrate is the preferred alternative (though it contains only 21% elemental calcium, requiring larger tablets) 1