What vitamin D formulation and dosing should I prescribe for a patient on romosozumab (Evenity) with a serum 25‑hydroxy‑vitamin D level of 32 ng/mL to keep the level in the optimal range?

Vitamin D Supplementation for Patients on Romosozumab (Evenity)

For a patient on Evenity with a current vitamin D level of 32 ng/mL, prescribe vitamin D₃ (cholecalciferol) 800–1,000 IU daily as maintenance therapy to sustain levels in the optimal range of 30–44 ng/mL. 1

Understanding the Current Vitamin D Status

Your patient's level of 32 ng/mL is classified as sufficient and falls within the optimal therapeutic range for bone health (30–44 ng/mL). 1 This level exceeds the minimum threshold of 30 ng/mL required for anti-fracture efficacy and is appropriate for patients receiving anabolic osteoporosis therapy. 1, 2

Rationale for Maintenance Dosing in Evenity Patients

• Evenity (romosozumab) requires adequate vitamin D and calcium to support new bone formation and prevent hypocalcemia, making maintenance of sufficient vitamin D levels critical throughout treatment. 3
• The 30–44 ng/mL range maximizes musculoskeletal benefits without providing additional advantage at higher concentrations, and levels above 50 ng/mL offer no incremental benefit. 1
• Maintenance dosing of 800–1,000 IU daily reliably sustains levels in the target range for postmenopausal women and elderly patients with osteoporosis. 1, 2, 3

Specific Vitamin D Formulation Recommendation

Prescribe cholecalciferol (vitamin D₃) rather than ergocalciferol (vitamin D₂) because D₃ maintains serum 25-hydroxyvitamin D concentrations longer and has superior bioavailability, particularly with daily dosing regimens. 1

Practical Prescribing Options:

• Cholecalciferol 1,000 IU tablet once daily (most common and convenient)
• Cholecalciferol 800 IU tablet once daily (alternative if 1,000 IU formulation unavailable)
• Advise taking with the largest, fattiest meal of the day to maximize absorption of this fat-soluble vitamin 1

Essential Calcium Co-Supplementation

Ensure total calcium intake of 1,000–1,200 mg daily from diet plus supplements because vitamin D and calcium work synergistically for bone health, and Evenity's efficacy depends on adequate substrate availability. 1, 2, 3

• If dietary calcium is insufficient, prescribe calcium carbonate or citrate supplements
• Divide calcium supplements into doses ≤600 mg taken at separate times for optimal intestinal absorption 1
• Separate calcium from the vitamin D dose by at least 2 hours if both are supplemented 1

Monitoring Protocol

Recheck serum 25-hydroxyvitamin D in 3–6 months to confirm the maintenance dose sustains levels ≥30 ng/mL, as individual response to supplementation varies due to genetic differences in vitamin D metabolism. 1, 4

• Target range: 30–44 ng/mL for optimal bone health and fracture prevention 1
• Once stable in the target range, annual reassessment is sufficient 1, 5
• Monitor serum calcium every 3 months during Evenity therapy to detect hypercalcemia early 1

Safety Considerations

• Daily doses up to 4,000 IU are completely safe for adults, so the recommended 800–1,000 IU carries no toxicity risk. 1, 6
• Vitamin D toxicity is exceedingly rare and typically occurs only with prolonged daily doses >10,000 IU or serum levels >100 ng/mL. 1
• Discontinue vitamin D immediately if serum calcium rises above 10.2 mg/dL (2.54 mmol/L), as this indicates vitamin D-mediated hypercalcemia. 1

Common Pitfalls to Avoid

• Do not use active vitamin D analogs (calcitriol, alfacalcidol, doxercalciferol, paricalcitol) for nutritional vitamin D maintenance, as they bypass normal regulatory mechanisms and dramatically increase hypercalcemia risk. 1
• Standard multivitamins providing only 400 IU are insufficient for maintaining optimal levels in osteoporosis patients. 4
• Do not prescribe high-dose weekly regimens (e.g., 50,000 IU) for patients already in the sufficient range, as this is unnecessary and may push levels too high. 1
• Avoid relying on sun exposure alone due to skin cancer risk and impracticality, especially in elderly patients with reduced cutaneous synthesis. 1

Dose Adjustment Algorithm

If the 3-month follow-up level is:

• <30 ng/mL: Increase to 2,000 IU daily and recheck in 3 months 1, 7
• 30–44 ng/mL: Continue current dose of 800–1,000 IU daily 1
• 45–75 ng/mL: Reduce to 800 IU daily or every other day and recheck in 3 months 1
• >75 ng/mL: Discontinue supplementation temporarily and recheck in 3 months 1