Calcium Citrate Formulations
Calcium citrate is available as oral tablets and powder formulations, with common brand names including Citracal™, and typically comes in tablet strengths providing 200-250 mg of elemental calcium per tablet (from approximately 950-1000 mg of calcium citrate salt). 1
Available Forms and Strengths
- Tablet formulations are the most common presentation of calcium citrate supplements 1
- Calcium citrate contains approximately 21% elemental calcium by weight, which is lower than calcium carbonate (40% elemental calcium) but offers distinct absorption advantages 2, 3
- Citracal™ is the most commonly referenced brand name in clinical guidelines 1
- Typical dosing involves one or two 950-mg or 1000-mg tablets taken two or three times daily to achieve adequate calcium supplementation 2
Key Absorption Characteristics
- Calcium citrate does not require gastric acid for absorption, making it uniquely suitable for patients taking proton pump inhibitors or H2-blockers 1, 2, 3
- It can be taken between meals or with food, providing dosing flexibility compared to calcium carbonate which must be taken with meals 1
- Calcium citrate demonstrates superior bioavailability compared to calcium carbonate, with studies showing 46% greater peak-basal variation and 94% higher area under the curve for serum calcium when taken with meals 4
Optimal Dosing Strategy
- Divide doses into increments of 500-600 mg elemental calcium or less to maximize absorption and minimize gastrointestinal side effects 1, 2
- To achieve 1,500 mg of elemental calcium daily from calcium citrate alone would require multiple tablets throughout the day due to its lower elemental calcium content 1
- The maximum single dose of elemental calcium that should be taken at one time is 500 mg 3
Clinical Advantages Over Other Calcium Salts
- Preferred for patients with achlorhydria, GERD, or those on acid-reducing medications because absorption is independent of gastric acidity 1, 2, 3, 5
- Lower risk of gastrointestinal irritation including constipation and bloating compared to calcium carbonate 2
- May be beneficial for hypocitraturic patients at risk of nephrolithiasis, as citrate salts have shown inhibitory effects on kidney stone formation 5
Important Caveats
- Despite superior absorption, calcium citrate is more expensive and requires more tablets to achieve the same elemental calcium dose compared to calcium carbonate 2, 3
- The safe upper limit for total daily calcium intake is 2,500 mg per day from all sources (food and supplements combined) 1
- Calcium citrate should not be used as a phosphate binder in children with CKD due to concerns about aluminum absorption and metabolic complications 1