Recommended Dosage for Vitamin D Injection
For vitamin D intramuscular (IM) injection, dosage must be individualized under close medical supervision with a range of 50,000 to 200,000 IU for hypoparathyroidism and 12,000 to 500,000 IU for vitamin D resistant rickets. 1
General Dosing Guidelines for IM Vitamin D
The dosing of vitamin D injections varies significantly based on the indication:
- Hypoparathyroidism: 50,000 to 200,000 IU daily (with concurrent calcium lactate) 1
- Vitamin D Resistant Rickets: 12,000 to 500,000 IU daily 1
Important Monitoring Requirements
When administering IM vitamin D, close monitoring is essential due to the narrow therapeutic window:
- Blood calcium and phosphorus determinations must be made every 2 weeks or more frequently if necessary 1
- X-rays of bones should be taken monthly until the condition is corrected and stabilized 1
- Target 25(OH)D levels should be 30-80 ng/mL 2
Special Considerations for Different Patient Populations
Different patient groups may require adjusted dosing approaches:
- Patients with recurrent deficiency: 4,000-5,000 IU daily for 2 months to achieve blood levels of 25(OH)D between 40-60 ng/mL 3
- Patients on dialysis: 50,000 IU monthly or 12,000 IU weekly 2
- Patients with obesity: May require 2-3 times higher doses (up to 7,000 IU daily) 2, 4
- Patients with severe malabsorption: 50,000 IU 1-3 times weekly 2
- Patients with liver disease: Higher doses due to impaired hepatic 25-hydroxylation 2
Repletion Strategies
For patients with documented vitamin D deficiency, a cumulative dose of at least 600,000 IU administered over several weeks appears necessary to replenish vitamin D stores 5. However, single large doses of 300,000-500,000 IU should be avoided 5.
When using IM injection of a large bolus (600,000 IU), research shows that serum 25(OH)D levels peak at approximately 4 weeks post-injection and generally remain below 125 ng/mL, which is the upper limit recommended by the U.S. Institute of Medicine 6.
Safety and Monitoring
- Vitamin D toxicity is rare but has been described with true overdoses, manufacturing errors, or increased vitamin D sensitivity 3
- Toxicity symptoms are mediated by high calcium levels and include hypercalcemia, hypercalciuria, dizziness, and renal failure 3
- Serum calcium and phosphorus levels should be monitored monthly for the first 3 months, then every 3 months thereafter 2
- If serum calcium exceeds normal levels, therapy should be held until calcium returns to normal, then resumed at half the dose 2
Important Caveats
- The range between therapeutic and toxic doses of vitamin D is narrow 1
- IM administration is more complicated and may be contraindicated in many patients due to anticoagulation or infection risk 3
- In some countries, oral calcifediol [25(OH)D] is available and may be a good alternative, especially in cases of decreased intestinal absorption capacity 3
- For most adults with vitamin D deficiency not requiring IM administration, daily oral doses of 5,000 IU are usually needed to correct deficiency, with maintenance doses of ≥2,000 IU/day 7, 8
Remember that IM vitamin D administration should be reserved for specific clinical scenarios where oral supplementation is not feasible or effective, and requires careful monitoring due to its potency and potential for toxicity.