Vitamin B12 Injection Dosage and Frequency for Confirmed Deficiency
For patients with confirmed vitamin B12 deficiency, the recommended treatment is 1000-2000 μg intramuscularly daily for 6-7 days, followed by alternate-day dosing for 7 doses, then every 3-4 days for 2-3 weeks, and finally 1000 μg monthly for maintenance therapy. 1, 2
Initial Treatment Protocol
For Pernicious Anemia (Malabsorption)
- Initial loading dose: 100 mcg daily for 6-7 days via intramuscular (IM) or deep subcutaneous injection 2
- If clinical improvement and reticulocyte response are observed:
- Continue with 100 mcg on alternate days for 7 doses
- Then 100 mcg every 3-4 days for another 2-3 weeks
- Maintenance: 100 mcg monthly for life 2
For Other Causes of B12 Deficiency
- Clinical Nutrition guidelines recommend 1000-2000 μg daily IM initially 1
- The FDA label recommends following a similar protocol to pernicious anemia depending on deficiency severity 2
- Many clinicians prefer using 1000 μg doses as they provide better retention with no additional cost or toxicity 3
Maintenance Therapy Options
Intramuscular Maintenance
- Standard maintenance: 1000 μg monthly 1, 4
- According to recent research, individualized regimens may be necessary for up to 50% of patients with malabsorption, ranging from twice weekly to every 2-4 weeks to remain symptom-free 4
Oral Maintenance (For Patients with Normal Absorption)
- For patients with normal intestinal absorption, chronic treatment can transition to oral B12 preparations 2
- Oral supplementation of 1000 μg daily can be effective even in pernicious anemia through passive diffusion 5
- Patients with B12 deficiency due to dietary insufficiency can be managed with oral supplementation 4
Special Considerations
Monitoring
- Monitor platelet count until normalization 1
- Assess B12 levels periodically during maintenance therapy 1
- Do not use "titration" of injection frequency based on measuring biomarkers such as serum B12 or MMA 4
Route of Administration
- Avoid intravenous administration as most of the vitamin will be lost in urine 2
- Sublingual B12 supplementation offers comparable efficacy to intramuscular administration with better patient compliance and cost-effectiveness 1
- For severe deficiency or severe neurologic symptoms, intramuscular therapy is preferred for more rapid improvement 6
Specific Patient Populations
- Patients with ileal resection >20 cm require lifelong B12 supplementation 1
- Patients who have had bariatric surgery should receive 1 mg of oral vitamin B12 per day indefinitely 6
Common Pitfalls and Caveats
- Delaying treatment for more than 3 months may cause permanent degenerative lesions of the spinal cord 1
- Using intravenous route results in almost all of the vitamin being lost in the urine 2
- Inadequate dosing or frequency may fail to correct neurological symptoms
- For patients with malabsorption issues, oral therapy alone may be insufficient despite high doses 4
- Folic acid should be administered concomitantly if needed to avoid masking B12 deficiency symptoms 2