What are the fundamentals of calcium replacement in terms of body requirements, oral supplementation and intravenous (IV) supplementation with doses and indications?

Fundamentals of Calcium Replacement: Requirements, Oral and IV Supplementation

Dietary calcium intake should be the primary source of calcium (1,000-1,200 mg/day for adults), with supplements used only when dietary intake is inadequate, and IV calcium reserved for acute, symptomatic hypocalcemia. 1

Body Requirements

• Daily calcium requirements vary by age and physiological state:

  • Infants: 400-600 mg/day (0-12 months) 2, 3
  • Children: 800 mg/day (1-5 years), 800-1,200 mg/day (6-10 years) 2, 3
  • Adolescents and young adults: 1,200-1,500 mg/day (11-24 years) 2, 3
  • Adults (25-50 years): 1,000 mg/day 2, 3
  • Pregnant/lactating women: 1,200-1,500 mg/day 2, 3
  • Postmenopausal women on estrogen: 1,000 mg/day 2, 3
  • Postmenopausal women not on estrogen: 1,500 mg/day 2, 3
  • Men (25-65 years): 1,000 mg/day 2, 3
  • Adults over 65 years: 1,500 mg/day 2, 3

• Most dietary calcium (>70%) comes from dairy products, with the average intake in the US being 900-1,200 mg in men and 750-850 mg in women 1

• Adequate vitamin D (600-800 IU/day; serum level ≥20 ng/ml) is essential for optimal calcium absorption 1

Oral Calcium Supplementation

Forms and Characteristics

• Calcium carbonate:

  • Provides 40% elemental calcium (highest concentration) 1, 4
  • Most cost-effective option 5
  • Requires gastric acidity for absorption (must be taken with meals) 1, 4
  • More likely to cause constipation and bloating 1, 4

• Calcium citrate:

  • Provides 21% elemental calcium 1, 4
  • Can be taken without food 1, 4
  • Preferred for patients with achlorhydria or those taking acid-reducing medications 4, 5
  • Causes fewer gastrointestinal side effects 4

• Less common forms:

  • Calcium lactate and calcium gluconate: Less concentrated forms, not practical for oral supplementation 5

Dosing Recommendations

• Maximum dose of elemental calcium should not exceed 500 mg at one time for optimal absorption 5
• If daily supplementation exceeds 500 mg, divided doses are recommended 1
• Total calcium intake (diet plus supplements) should not exceed 2,000-2,500 mg/day due to potential risks 4, 2
• For patients with GERD or on acid-reducing medications, calcium citrate is preferred despite its lower elemental calcium content 4

Intravenous Calcium Supplementation

Indications

• IV calcium is indicated for acute, symptomatic hypocalcemia 6, 7
• Not recommended for long-term use or routine supplementation 6

Forms and Characteristics

• Calcium gluconate:

  • Contains 9.3 mg (0.465 mEq) of elemental calcium per 100 mg 6
  • Preferred for peripheral administration due to less tissue irritation 6

• Calcium chloride:

  • Contains 27 mg (1.4 mEq) of elemental calcium per 100 mg 7
  • More concentrated form (approximately 3 times more elemental calcium than gluconate) 7
  • Should be administered via central or deep vein due to risk of tissue necrosis 7

Dosing and Administration

• Calcium gluconate:

  • For bolus administration: Dilute to 10-50 mg/mL in 5% dextrose or normal saline 6
  • Maximum infusion rate: 200 mg/minute in adults, 100 mg/minute in pediatric patients 6
  • For continuous infusion: Dilute to 5.8-10 mg/mL 6
  • Monitor serum calcium every 4-6 hours during intermittent infusions and every 1-4 hours during continuous infusion 6

• Calcium chloride:

  • Adult dosage: 200 mg to 1 g (2-10 mL) at intervals of 1-3 days based on response 7
  • Pediatric dosage: 2.7-5.0 mg/kg 7
  • Administer by slow IV injection (not exceeding 1 mL/min) 7
  • Preferably administer via central or deep vein 7

Important Considerations and Precautions

• Dietary sources of calcium are preferred over supplements when possible 1

• Calcium supplements should not be used as a substitute for hormone replacement therapy in postmenopausal women 8

• Excessive protein and fiber intake may increase calcium requirements due to negative calcium balance 8

• Monitor for potential side effects of calcium supplementation:

  • Gastrointestinal complaints (constipation, bloating) 5
  • Risk of kidney stones (though most studies have not shown an association) 5
  • Potential cardiovascular risks with high supplemental intake, though evidence is inconsistent 1

• For IV administration, monitor vital signs and ECG during infusion due to risk of hypercalcemia and cardiac effects 6, 7

• Avoid mixing IV calcium with ceftriaxone (risk of precipitation), especially in neonates 6