What is the appropriate treatment for a vegan patient with vitamin B12 deficiency, presenting with fatigue, nausea, pallor, and glossitis, and having a low serum vitamin B12 level and mild anemia?

Treatment of Vitamin B12 Deficiency in a Vegan Patient with Severe Deficiency

This patient requires immediate intramuscular hydroxocobalamin 1 mg three times weekly for 2 weeks, followed by lifelong maintenance injections every 2-3 months, as this is a severe deficiency (B12 level 75 pg/mL) with clinical manifestations in a vegan patient who cannot obtain B12 from dietary sources. 1

Initial Treatment Protocol

Determining Neurological Involvement

First, assess whether neurological symptoms are present beyond the glossitis already noted 1:

• Check for: paresthesias, numbness, gait disturbances, cognitive impairment, memory problems, or peripheral neuropathy 1, 2
• If neurological symptoms present: Administer hydroxocobalamin 1 mg intramuscularly on alternate days until no further improvement, then transition to maintenance 1, 2
• If no neurological involvement (only hematologic/mucosal symptoms): Administer hydroxocobalamin 1 mg intramuscularly three times weekly for 2 weeks, then maintenance 1, 2

Why Intramuscular Route is Essential

Intramuscular administration is mandatory for this patient because 2:

• The severity of deficiency (B12 = 75 pg/mL, well below 150 pmol/L threshold) requires rapid correction 1
• Vegan diet indicates ongoing lack of dietary B12 source, making absorption optimization critical 1
• Oral supplementation, even at high doses, is unreliable in severe deficiency and should not be used initially 3, 4

Maintenance Therapy

After initial loading, lifelong maintenance with hydroxocobalamin 1 mg intramuscularly every 2-3 months is required 1, 2:

• This patient will never obtain adequate B12 from diet due to vegan lifestyle 3
• Monthly injections (1000 mcg) are an acceptable alternative if the patient requires more frequent dosing to remain symptom-free 1
• Some patients (up to 50%) require individualized schedules ranging from every 2-4 weeks based on symptom resolution, not laboratory values 4

Critical Safety Considerations

Folic Acid Warning

Never administer folic acid before or without adequate B12 treatment 1, 2, 3:

• Folic acid can mask the anemia while allowing irreversible neurological damage (subacute combined degeneration of the spinal cord) to progress 1, 2, 3
• Check folate levels and treat only after B12 therapy is established 2

Choice of B12 Formulation

Hydroxocobalamin is the preferred formulation over cyanocobalamin 1:

• Established dosing protocols with superior tissue retention 1
• All major guidelines provide specific evidence-based regimens for hydroxocobalamin 1
• Cyanocobalamin (as mentioned in FDA labeling) requires renal clearance and may be problematic in renal dysfunction 1

Monitoring Strategy

Initial Follow-up

Recheck at 3 months after starting treatment 1:

• Measure serum B12, complete blood count (to assess hemoglobin improvement), and homocysteine (target <10 μmol/L) 1
• Assess for resolution of fatigue, nausea, pallor, and glossitis 1
• Methylmalonic acid (MMA) can be checked if B12 levels remain borderline or symptoms persist 1

Ongoing Monitoring

• Second check at 6 months, then at 12 months to ensure stabilization 1
• Annual monitoring thereafter once levels stabilize 1
• Do not stop monitoring after one normal result, as patients with dietary insufficiency can relapse if injections are discontinued 1

Common Pitfalls to Avoid

Never discontinue B12 supplementation even if levels normalize 1:

• This vegan patient requires lifelong therapy due to complete absence of dietary B12 3
• Stopping injections will lead to recurrence of deficiency and potentially irreversible neurological damage 1

Do not rely on oral supplementation as primary therapy in severe deficiency 3, 4:

• While recent evidence suggests oral B12 (1000-2000 mcg daily) may work in some cases of pernicious anemia 5, intramuscular therapy remains the guideline-recommended approach for severe deficiency with clinical manifestations 1, 2
• Oral therapy may be considered for long-term maintenance only after initial parenteral correction in carefully selected patients 6

Do not "titrate" injection frequency based on serum B12 levels 4:

• Treatment decisions should be based on symptom resolution, not laboratory values 4
• Up to 50% of patients require more frequent injections than standard protocols to remain symptom-free 4

Expected Timeline for Improvement

• Hemolysis/reticulocyte response: 1 month 5
• Mucosal symptoms (glossitis, nausea): 4 months 5
• Neurological symptoms (if present): Variable, may take months and can be incomplete if treatment delayed 3, 7
• Anemia correction: Typically within 2-3 months with appropriate therapy 3