What is the recommended dose of methylcobalamin syrup for sub‑acute myelopathy?

Methylcobalamin Syrup Dosing for Subacute Myelopathy

For subacute myelopathy (SAM) due to vitamin B12 deficiency with neurological manifestations, intramuscular hydroxocobalamin 1000 mcg on alternate days is the standard treatment until neurological improvement plateaus, not oral syrup formulations. 1

Critical Treatment Principles

Neurological involvement demands aggressive parenteral therapy, not oral syrup. The presence of subacute combined degeneration of the spinal cord (which defines SAM) requires immediate high-dose intramuscular treatment because:

• Neurological damage can become irreversible if treatment is delayed or inadequate 1, 2
• Oral absorption is unreliable in patients with malabsorption conditions that commonly cause B12 deficiency 1
• The loading phase for neurological symptoms requires hydroxocobalamin 1000 mcg IM on alternate days until no further neurological improvement occurs (typically several weeks to months) 1

Why Syrup Formulation Is Inappropriate for SAM

Oral syrup methylcobalamin should not be used as primary treatment for subacute myelopathy. The evidence shows:

• Oral formulations require doses exceeding 200 times the dietary allowance (647-1032 mcg daily) just to normalize mild deficiency without neurological symptoms 3
• Even high-dose oral therapy (1000-2000 mcg daily) is only recommended when severe neurological symptoms are absent 1
• Research on methylcobalamin syrup (500 mcg daily) was conducted in autism patients, not neurological emergencies like SAM 4

Proper Treatment Protocol for SAM

Loading phase:

• Hydroxocobalamin 1000 mcg intramuscularly on alternate days until neurological recovery plateaus 1
• Alternative regimen: 1000 mcg IM three times weekly for 2 weeks if neurological symptoms are less severe 1, 2

Maintenance phase:

• After neurological improvement plateaus, transition to hydroxocobalamin 1000 mcg IM every 2 months for life 1
• Monthly dosing (1000 mcg IM) may be used when metabolic needs are higher 1

Critical Safety Precautions

Never administer folic acid before ensuring adequate B12 repletion, as it can mask megaloblastic anemia while allowing irreversible subacute combined degeneration to progress 1, 2

Monitor serum potassium closely during the first 48 hours of B12 repletion and provide supplementation if hypokalemia develops 1

If Oral Therapy Is Absolutely Required

If parenteral therapy is genuinely unavailable or refused (which should be strongly discouraged in SAM), the minimum effective oral dose would be:

• Methylcobalamin 1000-2000 mcg daily orally (not syrup-specific dosing, as syrup is simply a delivery vehicle) 1, 2
• This dose is based on therapeutic equivalence: 5000 mcg methylcobalamin equals 5000 mcg cyanocobalamin on a microgram-for-microgram basis 5
• However, this approach carries significant risk of inadequate treatment and permanent neurological damage in SAM 1

Monitoring Requirements

• Recheck serum B12, complete blood count, methylmalonic acid, and homocysteine at 3 months, 6 months, and 12 months 1
• Annual monitoring once levels stabilize 1, 2
• Clinical neurological examination to assess treatment response 1