What is the dose of methylcobalamin for B12 deficiency?

For B12 deficiency with neuropathy: Methylcobalamin 500 mcg IM or IV three times weekly for 4 weeks (loading), then 500 mcg orally three times daily (maintenance). Oral doses of 1000–1500 mcg/day are effective for food-cobalamin malabsorption without intrinsic factor deficiency.

What is the difference between methylcobalamin and cyanocobalamin?

Methylcobalamin is the active, bioavailable form that directly participates in neurological repair and methionine synthesis. Cyanocobalamin is a synthetic stable form that must be converted to active cobalamins in the body. Methylcobalamin is preferred for neuropathy; cyanocobalamin is preferred for replacement therapy due to stability and lower cost.

What is the dose of cyanocobalamin injection for pernicious anaemia?

Cyanocobalamin 1000 mcg IM daily for 7 days (loading), then weekly for 4 weeks, then monthly for life (maintenance) in pernicious anaemia. In India, hydroxocobalamin 1000 mcg IM is also widely used and is retained longer in the body.

Can high-dose oral B12 replace injections?

Yes. High-dose oral cyanocobalamin (1000–2000 mcg/day) can be as effective as IM injections for most causes of B12 deficiency because ~1% of oral B12 is absorbed passively without intrinsic factor. However, IM injections are preferred in severe deficiency, neurological involvement, or confirmed intrinsic factor deficiency.

What is the B12 dose for peripheral neuropathy?

Methylcobalamin 500 mcg IM three times weekly for 4–8 weeks is recommended for B12 deficiency neuropathy. Oral methylcobalamin 1500 mcg/day (500 mcg three times daily) is used for maintenance and mild neuropathy. Some Indian neurologists use 1000 mcg IM weekly for 3 months in severe cases.

Vitamin B12 Dose Calculator – Methylcobalamin, Cyanocobalamin, Hydroxocobalamin

Vitamin B12 Forms — Clinical Overview

Form	Active?	Half-life / Retention	Best For	India Availability
Methylcobalamin	✅ Yes (active)	Moderate; tissue retention moderate	Neuropathy, diabetic neuropathy, oral supplementation	Widely available (tablets, IM)
Cyanocobalamin	⚙️ Prodrug	Short plasma; good body stores	Deficiency replacement, pernicious anaemia	Most common injection form
Hydroxocobalamin	⚙️ Active precursor	Long (weeks); best retained	Pernicious anaemia, cyanide poisoning, less frequent dosing	Available (government hospitals)
Adenosylcobalamin	✅ Yes (active)	Intracellular; cofactor in mitochondria	Metabolic disorders, combined with methylcobalamin	Limited (specialty brands)

Routes of Administration

Intramuscular (IM): Gold standard for pernicious anaemia and malabsorption. Bypasses GI absorption completely. All forms available as IM injections in India (most commonly 500 mcg/mL and 1000 mcg/mL vials).

Oral: Effective for dietary deficiency and food-cobalamin malabsorption. High-dose oral B12 (1000–2000 mcg) achieves adequate levels even without intrinsic factor via passive absorption (~1%). Not recommended for pernicious anaemia as primary treatment.

Intravenous (IV): Used in hospitalised patients with severe deficiency or when IM is not feasible. Rapid correction but shorter retention. Methylcobalamin IV (500 mcg in slow IV push) used in acute neurological B12 deficiency.

Sublingual: High bioavailability, useful alternative to oral tablets. Popular in compliance-challenged patients. Available as 1000–2000 mcg sublingual strips/tablets.

Intranasal: Cyanocobalamin nasal gel/spray (500 mcg/dose) approved in some countries for maintenance in pernicious anaemia after loading with IM injections.

When to Prefer Each Form

Methylcobalamin over Cyanocobalamin when: peripheral neuropathy, diabetic neuropathy, patients who smoke (avoid cyanocobalamin — small cyanide load), renal impairment (cannot clear cyanide).

Hydroxocobalamin over Cyanocobalamin when: less frequent IM dosing needed (retained for weeks), cyanide poisoning treatment, smokers.

Cyanocobalamin remains first-choice in most national essential medicine lists due to stability, cost, and extensive evidence base for deficiency reversal.

Normal & Target B12 Levels (Indian Labs)

Normal serum B12: 180–914 pg/mL (most Indian labs). Deficiency: <200 pg/mL. Borderline: 200–300 pg/mL. Target on treatment: >400 pg/mL (functional adequacy). In neuropathy, aim >500 pg/mL for neurological recovery.

Frequently Asked Questions

What is the standard methylcobalamin dose for diabetic neuropathy?

Methylcobalamin 500 mcg IM three times weekly for 4 weeks, then 1500 mcg/day orally (500 mcg three times daily) is the most widely used regimen in India for diabetic peripheral neuropathy. Some protocols use 1000 mcg IM weekly for 3 months. The oral maintenance phase is crucial for sustained neurological benefit.

How often should cyanocobalamin injection be given for B12 deficiency?

For moderate-severe deficiency: 1000 mcg IM daily for 7 days (loading), then weekly for 4 weeks, then monthly for life if the cause is pernicious anaemia. For dietary deficiency or food-cobalamin malabsorption: 1000 mcg IM monthly or high-dose oral 1000–2000 mcg/day are both acceptable.

Is oral B12 as effective as injections?

For most causes of deficiency (dietary, food-cobalamin malabsorption), high-dose oral B12 (1000–2000 mcg/day) is equally effective as IM injections — studies confirm this. However, IM injections are preferred for: pernicious anaemia (intrinsic factor deficiency), severe neurological involvement, malabsorption syndromes, non-compliant patients, and initial rapid correction in severe deficiency.

What is the B12 dose during pregnancy?

RDA during pregnancy: 2.6 mcg/day; lactation: 2.8 mcg/day. Therapeutic supplementation if deficient: oral methylcobalamin or cyanocobalamin 500–1000 mcg/day is safe and preferred over IM during pregnancy. Severe deficiency: IM cyanocobalamin 1000 mcg weekly until levels normalise, then maintenance oral dose. Vegans/vegetarians require supplementation throughout pregnancy.

What is the dose of B12 for a child?

Paediatric oral dose for deficiency: 25–100 mcg/day (infants), 500–1000 mcg/day (older children). IM cyanocobalamin for severe deficiency: 1 mcg/kg/day for 7 days, then weekly for 4 weeks, then monthly. For confirmed pernicious anaemia in children: IM treatment for life with monthly 1000 mcg injections. Dietary supplementation: as per RDA (0.4–2.4 mcg/day by age).

Can B12 be given intravenously?

Yes. Cyanocobalamin and methylcobalamin can be given IV, though IM is preferred for most indications. IV is used in hospitalised patients, those with bleeding disorders, or in ICU settings. Methylcobalamin 500 mcg IV (diluted in 100 mL NS, given over 15–30 minutes) is used in acute B12 neuropathy. IV B12 has rapid plasma distribution but is less retained than IM.

How is hydroxocobalamin different from cyanocobalamin injections?

Hydroxocobalamin is retained in the body for 4–6 weeks after a single IM injection, allowing less frequent dosing (quarterly after loading in stable pernicious anaemia). Cyanocobalamin needs monthly injections. Hydroxocobalamin is preferred in smokers, renal failure, and cyanide poisoning. It does not contain cyanide and is now often considered superior to cyanocobalamin in terms of safety profile.