Vitamin B12 Supplementation Regimen for Inpatient Setting
For inpatient vitamin B12 supplementation, administer 1000 mcg intramuscularly daily for 6-7 days, followed by alternate days for 7 doses, then every 3-4 days for 2-3 weeks, and finally monthly for maintenance. 1, 2
Initial Assessment and Dosing
Severe Deficiency/Pernicious Anemia
- Initial loading dose: 1000 mcg intramuscularly daily for 6-7 days 3, 1
- Intermediate phase: 1000 mcg intramuscularly every other day for 7 doses 1
- Transition phase: 1000 mcg intramuscularly every 3-4 days for 2-3 weeks 1
- Maintenance: 1000 mcg intramuscularly monthly for life 3, 1
Mild to Moderate Deficiency
- Initial loading: 1000 mcg intramuscularly 5-6 biweekly injections 4
- Maintenance: 1000 mcg intramuscularly monthly 4
Special Considerations
Post-Surgical Patients
- For patients with ileal resection >20 cm: 1000 mcg vitamin B12 monthly indefinitely 5
- For bariatric surgery patients: 1000 mcg oral B12 daily indefinitely 3
Concomitant Medications
- For patients receiving pralatrexate: 1000 mcg intramuscular B12 to be started no more than 10 weeks prior to therapy and then every 8-10 weeks 5
- For patients on metformin: Monitor B12 levels more frequently as metformin can contribute to B12 deficiency 3
Route of Administration Considerations
While oral vitamin B12 at high doses (1000-2000 mcg daily) has shown comparable efficacy to intramuscular administration in outpatient settings 6, 7, 8, the intramuscular route is preferred for inpatient initiation, especially for:
- Patients with pernicious anemia 1, 2
- Patients with severe neurological symptoms
- Patients with malabsorption disorders
- Critically ill patients where rapid correction is needed
Monitoring
- Check B12 levels after 3 months of supplementation 3
- Monitor for clinical improvement and reticulocyte response 1
- If other deficiencies are present (particularly folate), they should be treated concurrently 1
Common Pitfalls to Avoid
- Avoid intravenous administration: This route results in most of the vitamin being lost in the urine 1, 2
- Don't underdose: Lower doses (100 mcg) are less effective than 1000 mcg for replenishing stores 4, 7
- Don't rely on oral supplementation for patients with pernicious anemia during initial treatment phase 1, 2
- Don't forget concomitant folate supplementation if needed 1
- Don't use sublingual B12 for initial inpatient treatment of severe deficiency, despite its effectiveness in maintenance therapy 3
Transition to Outpatient Care
When transitioning to outpatient care, consider:
- Continuing intramuscular injections monthly for patients with pernicious anemia or severe malabsorption 1
- Switching to high-dose oral therapy (1000 mcg daily) for patients with normal intestinal absorption 3, 6
The inpatient regimen focuses on rapid correction of deficiency with parenteral therapy, which is more reliable in the acute setting, while planning for appropriate long-term maintenance based on the underlying cause of deficiency.