What is the standard treatment for vitamin B12 deficiency?

Standard Treatment for Low Vitamin B12

For patients with vitamin B12 deficiency, the standard treatment is 1000 mcg of vitamin B12 administered intramuscularly every other day for one week, followed by monthly injections for life, though high-dose oral supplementation (1000-2000 mcg daily) may be effective in many cases. 1, 2

Diagnosis of Vitamin B12 Deficiency

• Diagnosis is based on low serum cobalamin levels (<148 pM) along with functional biomarkers such as elevated homocysteine (>15 mM) or methylmalonic acid (>270 mM) 1
• Clinical B12 deficiency further requires macrocytosis and/or neurological symptoms 1
• For borderline B12 levels (180-350 pg/mL), methylmalonic acid measurement should be used to confirm deficiency 3

Treatment Protocol Based on Etiology

For Pernicious Anemia

• Parenteral vitamin B12 is the recommended treatment and will be required for the remainder of the patient's life 2
• Initial treatment: 100 mcg daily for 6-7 days via intramuscular injection 2
• If clinical improvement occurs: 100 mcg on alternate days for seven doses, then every 3-4 days for 2-3 weeks 2
• Maintenance: 100 mcg monthly for life 2
• Oral therapy with high doses (1000 μg/day) has shown efficacy in recent studies but is not yet standard practice 4

For Crohn's Disease with Ileal Resection

• When more than 20 cm of distal ileum is resected: 1000 mg of vitamin B12 prophylactically every month indefinitely 1
• When more than 30 cm of distal ileum is resected: Patients are at higher risk and should be monitored more closely 1

For Normal Intestinal Absorption

• Where oral route is adequate: High-dose oral vitamin B12 (1-2 mg daily) is as effective as intramuscular administration 5, 6
• For severe deficiency: Initial treatment similar to pernicious anemia protocol may be indicated 2
• Chronic treatment can then transition to oral B12 preparation 2

Route of Administration Considerations

Intramuscular Administration

• Preferred for patients with severe deficiency or severe neurologic symptoms 5, 3
• Leads to more rapid improvement of symptoms 5
• Bypasses intestinal absorption issues 4
• Avoid using the intravenous route as most of the vitamin will be lost in urine 2

Oral Administration

• High-dose oral vitamin B12 (1000-2000 mcg daily) is effective for most patients 5, 3
• Absorption occurs through passive diffusion, even in patients with malabsorption 4
• More convenient for patients and avoids injection-related complications 5
• May become standard practice in coming years, even for conditions like pernicious anemia 1, 4

Special Populations

Patients on Certain Medications

• Those treated with sulphasalazine and methotrexate should also receive vitamin B9/folic acid supplementation 1
• Patients on metformin, proton pump inhibitors, or histamine H2 blockers for extended periods should be monitored for B12 deficiency 5, 3

Vegetarians and Older Adults

• Adults over 50 years and vegans/strict vegetarians should consume foods fortified with vitamin B12 or take supplements 5, 6
• Crystalline formulations are better absorbed than naturally occurring vitamin B12 6

Monitoring and Follow-up

• CD patients with ileal involvement and/or resection should be screened yearly for vitamin B12 deficiency 1
• Monitor clinical response and hematologic values during treatment 2
• Assess for improvement in neurological symptoms, which may take longer to resolve than hematologic abnormalities 4

Common Pitfalls and Caveats

• Oral therapy is not dependable for pernicious anemia according to traditional guidance, though recent research challenges this 2, 4
• Measurement of serum B12 alone may not reliably detect deficiency; consider measuring homocysteine and methylmalonic acid in borderline cases 5, 3
• Supplementation with vitamin B12 in patients with elevated homocysteine levels has not been shown to reduce cardiovascular outcomes 5, 6
• Avoid using vitamin B12 intravenously as most will be lost in the urine 2