Can I give an adult with vitamin D deficiency and no hypercalcemia, severe renal impairment, or granulomatous disease ergocalciferol (vitamin D₂) 50,000 IU every two weeks?

Can You Give Ergocalciferol 50,000 Units Every 2 Weeks?

No, ergocalciferol 50,000 IU every 2 weeks is not a standard evidence-based regimen and should not be used. The established protocols are either 50,000 IU weekly for 8-12 weeks during the loading phase, or 50,000 IU monthly for maintenance therapy. 1, 2

Why Every-Two-Week Dosing Is Not Recommended

The guideline-supported regimens are based on pharmacokinetic principles and clinical trial data that demonstrate efficacy and safety:

• For active treatment of deficiency (<20 ng/mL): The standard loading dose is ergocalciferol 50,000 IU once weekly for 8-12 weeks, which effectively raises 25(OH)D levels to target ranges. 1, 2, 3

• For maintenance after correction: The recommended regimen is 50,000 IU once monthly (equivalent to approximately 1,600 IU daily), which sustains adequate levels without excessive accumulation. 1, 2

• The every-two-week interval falls between these two regimens and lacks supporting evidence for either efficacy or safety, creating uncertainty about whether it provides adequate repletion or appropriate maintenance. 2

The Evidence-Based Dosing Algorithms

For Vitamin D Deficiency (<20 ng/mL)

Loading Phase:

• Ergocalciferol 50,000 IU orally once weekly for 8 weeks (moderate deficiency) or 12 weeks (severe deficiency <10 ng/mL). 1, 2, 3
• This regimen typically raises 25(OH)D levels by 40-70 nmol/L (16-28 ng/mL) over the treatment period. 2

Maintenance Phase:

• After achieving target levels ≥30 ng/mL, transition to 50,000 IU monthly OR 800-2,000 IU daily. 1, 2
• Recheck 25(OH)D levels 3 months after completing the loading phase to confirm adequate response. 2, 4

For Vitamin D Insufficiency (20-30 ng/mL)

• Add 1,000 IU daily to current intake and recheck in 3 months, OR
• Use 50,000 IU monthly as maintenance dosing. 2

Important Formulation Considerations

Cholecalciferol (D3) is strongly preferred over ergocalciferol (D2) for maintenance therapy because:

• D3 maintains serum levels significantly longer than D2, particularly with intermittent dosing schedules. 2, 5
• D3 demonstrates superior bioavailability and may be 3-5 times more potent at raising 25(OH)D levels. 5
• A single 600,000 IU dose of D2 actually decreased 25(OH)D3 levels by an average of 4 ng/mL in one study, while D3 regimens effectively normalized levels. 5

However, for the standard weekly loading regimen (50,000 IU weekly for 8-12 weeks), both ergocalciferol and cholecalciferol are acceptable. 1, 2

Alternative Regimens for Special Circumstances

If weekly dosing presents adherence challenges, consider these evidence-based alternatives:

• Twice-weekly dosing: Ergocalciferol 50,000 IU twice weekly achieves the most rapid correction, reaching target levels within 1 month and plateauing at 60 ng/mL by 7 months. 6
• Daily high-dose: 7,000 IU daily is safe and effective for patients with obesity, malabsorption, or multi-drug regimens affecting vitamin D metabolism. 7
• Weekly high-dose for high-risk patients: 30,000 IU weekly (or twice weekly for 6-8 weeks) for obese patients or those with malabsorption. 7

Critical Pitfalls to Avoid

• 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 hypercalcemia risk. 1, 2

• Avoid single ultra-high loading doses (>300,000 IU) as they may be inefficient or potentially harmful for fall and fracture prevention. 2

• Do not create non-standard dosing intervals without evidence, as vitamin D has a long half-life and requires specific dosing schedules validated by clinical trials. 2

Essential Co-Interventions

• Ensure adequate calcium intake of 1,000-1,500 mg daily from diet plus supplements if needed. 2, 3
• Calcium supplements should be taken in divided doses of no more than 600 mg at once for optimal absorption. 2
• Take vitamin D with the largest, fattiest meal of the day to maximize absorption. 2

Monitoring Protocol

• Recheck 25(OH)D levels 3 months after initiating treatment to allow levels to plateau. 2, 4
• Target level is ≥30 ng/mL for anti-fracture efficacy, with optimal range 30-44 ng/mL. 2
• Monitor serum calcium every 3 months during treatment, discontinuing therapy if corrected calcium exceeds 10.2 mg/dL (2.54 mmol/L). 2