What is the recommended dose of Vitamin B12 (Vit B12) for treating deficiency?

Vitamin B12 Dosing for Deficiency Treatment

For treating vitamin B12 deficiency, administer 1000 mcg (1 mg) of hydroxocobalamin or cyanocobalamin intramuscularly every other day for one week, then 1000 mcg monthly for life. 1

Initial Treatment Protocol

For Deficiency WITH Neurological Symptoms

• Administer hydroxocobalamin 1 mg intramuscularly on alternate days until no further neurological improvement occurs 2
• After neurological stabilization, transition to maintenance dosing of 1 mg intramuscularly every 2 months for life 2
• This aggressive initial approach is critical because neurological damage can become irreversible if not treated promptly 3

For Deficiency WITHOUT Neurological Symptoms

• Give hydroxocobalamin 1 mg intramuscularly three times weekly for 2 weeks 2
• Then switch to maintenance treatment of 1 mg intramuscularly every 2-3 months lifelong 2
• Alternative loading regimen: 1000 mcg intramuscularly 5-6 times over 2 weeks 4

Maintenance Therapy

The standard maintenance dose is 1000 mcg (1 mg) intramuscularly monthly for life, though some guidelines suggest every 2-3 months may be sufficient 1, 2

Key Maintenance Considerations

• Up to 50% of patients require more frequent injections (ranging from every 2-4 weeks) to remain symptom-free, based on clinical response rather than laboratory values 5
• Never titrate injection frequency based on serum B12 or methylmalonic acid levels alone—base adjustments on symptom resolution and clinical response 5
• Patients with pernicious anemia require monthly injections for the remainder of their lives; failure to continue will result in anemia recurrence and irreversible spinal cord nerve damage 3

Oral Therapy Alternative

High-dose oral vitamin B12 (1000-2000 mcg daily) is as effective as intramuscular therapy for correcting anemia and neurological symptoms 6, 7

When to Consider Oral Therapy

• Oral therapy may be used in patients with dietary deficiency or mild malabsorption 6
• Intramuscular therapy should be prioritized in patients with severe deficiency, severe neurological symptoms, or documented malabsorption 6
• For post-bariatric surgery patients: 1000-2000 mcg daily oral OR 1000 mcg monthly intramuscular 2
• Oral supplementation effectiveness in Crohn's disease has been demonstrated (1200-2400 mcg daily), but parenteral remains the reference standard 1

Special Population Dosing

Ileal Resection or Crohn's Disease

• Patients with >20 cm of distal ileum resected require prophylactic 1000 mcg intramuscularly monthly indefinitely 1
• Resection <20 cm typically does not cause deficiency 1
• Resection >30 cm puts patients at definite risk for B12 deficiency 1
• Screen yearly for B12 deficiency in all Crohn's patients with ileal involvement or resection 1

Post-Bariatric Surgery

• After Roux-en-Y gastric bypass or biliopancreatic diversion: 1000-2000 mcg daily sublingual OR 1000 mcg monthly intramuscular 2
• After sleeve gastrectomy or gastric banding: 250-350 mcg daily oral OR 1000 mcg weekly sublingual 2

Critical Safety Warning

Never administer folic acid before treating vitamin B12 deficiency—folic acid may mask B12 deficiency anemia while allowing progression of subacute combined degeneration of the spinal cord, causing irreversible neurological damage 2, 3

Monitoring Parameters

• Check serum B12 and homocysteine every 3 months until stabilization, then annually 2
• Monitor for resolution of neurological symptoms (paresthesias, gait disturbances, cognitive changes) 2
• Hematocrit and reticulocyte counts should be monitored daily from days 5-7 of initial therapy, then frequently until hematocrit normalizes 3
• Serum potassium must be monitored closely during the first 48 hours of treatment in pernicious anemia patients and replaced if necessary 3

Common Pitfalls to Avoid

• Do not discontinue B12 supplementation even if levels normalize—patients require lifelong therapy 2
• Do not use serum B12 levels alone to adjust injection frequency in patients on maintenance therapy 5
• Do not assume oral therapy is adequate for malabsorption conditions without documented clinical response 1
• Consider methylcobalamin or hydroxocobalamin over cyanocobalamin in patients with renal dysfunction 2