Is the initial loading phase for vitamin D (Vitamin D) supplementation oral or another route?

Vitamin D Loading Phase: Route of Administration

The initial loading phase for vitamin D supplementation is oral, not parenteral, for the vast majority of patients. 1, 2

Standard Oral Loading Protocol

For vitamin D deficiency (<20 ng/mL), the guideline-recommended approach is oral ergocalciferol (vitamin D2) or cholecalciferol (vitamin D3) 50,000 IU once weekly for 8-12 weeks. 1, 2

Key Implementation Details:

• Vitamin D3 (cholecalciferol) is strongly preferred over D2 (ergocalciferol) because it maintains serum levels longer and has superior bioavailability, particularly important for intermittent dosing schedules 2, 3

• The Endocrine Society guidelines specifically recommend oral vitamin D for the loading phase in bariatric surgery patients, with doses ranging from 50,000 IU 1-3 times weekly, escalating to 50,000 IU 1-3 times daily in cases of severe malabsorption 1

• After the 8-12 week loading phase, transition to maintenance therapy of 800-2,000 IU daily or 50,000 IU monthly to maintain target levels ≥30 ng/mL 2

When Parenteral (IM) Administration Is Indicated

Intramuscular vitamin D should be reserved for specific malabsorption conditions where oral supplementation has failed. 2

Specific Indications for IM Route:

• Post-bariatric surgery patients with malabsorptive procedures (Roux-en-Y gastric bypass, biliopancreatic diversion) who fail oral supplementation—IM administration results in significantly higher 25(OH)D levels and lower rates of persistent deficiency 2

• Inflammatory bowel disease with documented malabsorption 2

• Short-bowel syndrome 2

• Pancreatic insufficiency 2

• Patients not responding to adequate oral supplementation trials 2

IM Dosing Protocol:

• The standard IM formulation is cholecalciferol 50,000 IU, though availability varies significantly by country 2

• IM administration should only be considered after documented failure of oral therapy, not as first-line treatment 2

Critical Pitfalls to Avoid

• Do not initiate with single ultra-high loading doses (>300,000-540,000 IU) as they have been associated with increased falls and fractures in clinical trials 2, 3

• Do not use active vitamin D analogs (calcitriol, alfacalcidol, doxercalciferol, paricalcitol) to treat nutritional vitamin D deficiency—these do not correct 25(OH)D levels and are reserved for advanced CKD with impaired 1α-hydroxylase activity 2

• Ensure adequate calcium intake of 1,000-1,500 mg daily during the loading phase, as vitamin D enhances calcium absorption and adequate dietary calcium is necessary for clinical response 2

• For patients with contraindications to IM injections (anticoagulation, infection risk), substantially higher oral doses (4,000-5,000 IU daily for 2 months) should be used rather than attempting IM administration 2

Monitoring Protocol

• Recheck 25(OH)D levels 3 months after initiating loading therapy to confirm adequate response and guide transition to maintenance dosing 2

• If using intermittent dosing (weekly or monthly), measure levels just prior to the next scheduled dose 2

• Target 25(OH)D level is ≥30 ng/mL for anti-fracture efficacy, with an upper safety limit of 100 ng/mL 2