What is the recommended dose and administration of methylcobalamin solution for vitamin B12 supplementation?

Methylcobalamin Weekly Dosing for Vitamin B12 Supplementation

For weekly methylcobalamin administration, the recommended dose is 1500 mcg intramuscularly once per week, though this regimen produces lower serum cobalamin levels compared to more frequent dosing schedules. 1

Evidence-Based Dosing Comparison

The most direct evidence comparing weekly versus more frequent methylcobalamin dosing comes from a head-to-head trial:

• 500 mcg three times weekly produced significantly higher serum cobalamin levels (1892.08 ± 234.50 pg/mL) compared to 1500 mcg once weekly (1438.5 ± 460.32 pg/mL), with p=0.028 1
• Both regimens improved neuropathy symptoms similarly, but the three-times-weekly schedule achieved superior biochemical correction 1

Guideline-Recommended Dosing Protocols

For patients requiring parenteral B12 therapy, current guidelines favor monthly rather than weekly administration:

Standard Maintenance Regimen

• 1000 mcg intramuscularly monthly is the preferred maintenance dose for patients with malabsorption, including those with >20 cm ileal resection 2, 3, 4
• This monthly schedule is more effective than the previously recommended 3-monthly injections 3, 4

Initial Treatment Phase

• For deficiency with neurological symptoms: 1000 mcg IM on alternate days until improvement, then transition to monthly maintenance 3, 4
• For deficiency without neurological symptoms: 1000 mcg IM three times weekly for 2 weeks, then monthly maintenance 3, 4

Clinical Considerations for Weekly Dosing

If weekly administration is specifically required for your clinical situation:

• Weekly dosing produces suboptimal serum levels compared to more frequent administration, though it remains clinically effective for symptom control 1
• Consider using 1500 mcg weekly as the minimum effective dose based on available evidence 1
• Monthly dosing of 1000 mcg is preferred over weekly schedules according to current guidelines, as it provides adequate maintenance with less frequent administration 2, 3, 4

Important Caveats

• Methylcobalamin or hydroxocobalamin are preferred over cyanocobalamin in patients with renal dysfunction, as cyanocobalamin requires renal clearance of the cyanide moiety 3, 4
• Never administer folic acid before treating B12 deficiency, as it may mask deficiency and precipitate subacute combined degeneration of the spinal cord 3, 4
• Individual variation is substantial: up to 50% of patients may require more frequent injections (ranging from twice weekly to every 2-4 weeks) to remain symptom-free 5

Monitoring Parameters

• Check serum B12 and homocysteine every 3 months until stabilization, then annually 3, 6
• Target homocysteine <10 μmol/L for optimal outcomes 3, 6
• Do not titrate injection frequency based on serum B12 or methylmalonic acid levels—base adjustments on clinical symptoms and patient quality of life 5

Practical Algorithm

1. If starting therapy: Use 1000 mcg IM three times weekly for 2 weeks (or alternate days if neurological symptoms present) 3, 4
2. For maintenance: Transition to 1000 mcg IM monthly rather than weekly 2, 3, 4
3. If weekly dosing is mandated: Use minimum 1500 mcg IM weekly, recognizing this produces lower serum levels 1
4. If symptoms recur on monthly dosing: Increase frequency to every 2-4 weeks based on symptom control 5