What is the appropriate weekly dose of vitamin D (ergocalciferol or cholecalciferol) to replace in patients with vitamin D deficiency?

Weekly Vitamin D Replacement Dosing for Deficiency

For vitamin D deficiency (25(OH)D <20 ng/mL), the standard treatment is 50,000 IU of cholecalciferol (vitamin D3) or ergocalciferol (vitamin D2) once weekly for 8-12 weeks, followed by maintenance therapy of 800-2,000 IU daily or 50,000 IU monthly. 1, 2

Treatment Protocol Based on Deficiency Severity

Standard Deficiency (10-20 ng/mL)

• Administer 50,000 IU weekly for 8 weeks 1, 2
• This regimen typically raises 25(OH)D levels by approximately 40-70 nmol/L (16-28 ng/mL) 1
• Expected to achieve target levels of at least 30 ng/mL in most patients 1, 2

Severe Deficiency (<10 ng/mL)

• Administer 50,000 IU weekly for 12 weeks 1
• Particularly important for patients with symptoms, high fracture risk, or secondary hyperparathyroidism 1
• Levels below 10-12 ng/mL significantly increase risk for osteomalacia and nutritional rickets 1

Cholecalciferol (D3) vs Ergocalciferol (D2)

Cholecalciferol (vitamin D3) is strongly preferred over ergocalciferol (vitamin D2) because it maintains serum levels longer, has superior bioavailability, and is more effective with intermittent dosing schedules 1, 2. When using weekly dosing regimens, D3 maintains serum 25(OH)D concentrations for longer periods compared to D2 1.

Maintenance Phase After Loading

After completing the 8-12 week loading phase:

• Transition to 800-2,000 IU daily (preferred for most patients) 1, 2
• Alternative: 50,000 IU monthly (equivalent to approximately 1,600 IU daily) 1, 2
• Target 25(OH)D level should be at least 30 ng/mL for optimal health benefits, particularly for anti-fracture efficacy 1, 2

Monitoring Protocol

• Recheck 25(OH)D levels 3 months after initiating treatment to allow sufficient time for levels to plateau and accurately reflect response 1, 2
• If using intermittent dosing (weekly or monthly), measure levels just prior to the next scheduled dose 1
• After achieving target levels, recheck annually once stable 1
• Monitor serum calcium every 3 months during treatment to detect hypercalcemia 1

Essential Co-Interventions

• Ensure adequate calcium intake of 1,000-1,500 mg daily from diet plus supplements if needed 1, 2
• Calcium supplements should be taken in divided doses of no more than 600 mg at once for optimal absorption 1
• Take vitamin D with the largest, fattiest meal of the day to maximize absorption, as it is a fat-soluble vitamin 1

Special Populations Requiring Modified Dosing

Malabsorption Syndromes

• Intramuscular vitamin D3 50,000 IU is the preferred route for patients with documented malabsorption (post-bariatric surgery, inflammatory bowel disease, celiac disease, pancreatic insufficiency) 1
• IM administration results in significantly higher 25(OH)D levels and lower rates of persistent deficiency compared to oral supplementation 1
• When IM is unavailable, use substantially higher oral doses: 4,000-5,000 IU daily for 2 months or 50,000 IU 2-3 times weekly 1, 3

Chronic Kidney Disease (CKD Stages 3-4)

• Use standard nutritional vitamin D replacement with cholecalciferol or ergocalciferol 1, 2
• Never use active vitamin D analogs (calcitriol, alfacalcidol, doxercalciferol, paricalcitol) to treat nutritional vitamin D deficiency, as they bypass normal regulatory mechanisms and carry higher risk of hypercalcemia 1, 2

Elderly Patients (≥65 years)

• Minimum of 800 IU daily for maintenance, though higher doses of 700-1,000 IU daily are more effective in reducing fall and fracture risk 1, 2
• May require higher maintenance doses due to decreased skin synthesis 1

Obese Patients

• May require higher doses due to vitamin D sequestration in adipose tissue 1, 3
• Consider 7,000 IU daily or 30,000 IU twice weekly for 6-8 weeks without monitoring 3

Critical Safety Considerations

• Daily doses up to 4,000 IU are generally safe for adults without risk of toxicity 1, 2, 4
• Avoid single ultra-high loading doses (>300,000 IU) as they may be inefficient or potentially harmful, particularly for fall and fracture prevention 1, 2
• Upper safety limit for 25(OH)D is 100 ng/mL 1, 2
• Toxicity typically only occurs with prolonged daily doses exceeding 10,000 IU or serum levels above 100 ng/mL 1
• If serum calcium exceeds 10.2 mg/dL (2.54 mmol/L), discontinue all vitamin D therapy immediately 1

Common Pitfalls to Avoid

• Do not use active vitamin D analogs for nutritional deficiency - they are reserved for advanced CKD with PTH >300 pg/mL 1, 2
• Verify patient adherence before increasing doses for inadequate response, as poor compliance is a common reason for treatment failure 1
• Ensure total 25-hydroxyvitamin D (D3 and D2) is measured if the patient is on ergocalciferol supplements 1
• Do not measure levels too early - wait at least 3 months to allow steady-state levels to be reached 1, 2

Expected Response

Using the rule of thumb: an intake of 1,000 IU vitamin D daily increases serum 25(OH)D by approximately 10 ng/mL, though individual responses vary due to genetic differences in vitamin D metabolism 1. The standard 50,000 IU weekly regimen for 8-12 weeks typically raises levels by 40-70 nmol/L (16-28 ng/mL) 1.