Vitamin B12

Water-Soluble·Vitamins & Minerals

Pernicious anemia, post-gastrectomy, strict vegan diet deficiency, severe neuropathy

VITAMINNeo-B12, Hydroxocobalamin, CyanocobalaminAmpoules (1000 mcg/1 mL) for…S4TGA

Target Level

> 200 pmol/L

Route

IM or PO

Neuro Damage

IRREVERSIBLE

Storage

HEPATIC

Rapid Summary

Overview

Cobalamin. Essential water-soluble vitamin required for red blood cell formation and myelin sheath maintenance. The liver stores massive amounts, meaning deficiency takes years to develop.

Maximum Dose

Max 1000 mcg (1 mg) per injection.

Clinical Focus

Severe B12 deficiency causes subacute combined degeneration of the spinal cord. If not treated quickly, the neurological damage is completely irreversible.

Bottom Line

Vitamin B12 is essential for treating megaloblastic anaemia and preventing irreversible neurological damage from deficiency, but IM loading is required for pernicious anaemia as oral absorption is impaired.

Formulation & Access

Brand Names

Neo-B12, Hydroxocobalamin, Cyanocobalamin

Parenteral

Ampoules (1000 mcg/1 mL) for deep IM injection. (Hydroxocobalamin is preferred as it stays in the body longer).

Oral Routes

Tablets (1000 mcg).

Prescribing & PBS

Over The Counter (PO). General Benefit PBS (IM).

Indications & Use

Primary

TGA

Pernicious anemia, post-gastrectomy, strict vegan diet deficiency, severe neuropathy.

Clinical Place

IM formulation is mandatory if the patient lacks Intrinsic Factor (Pernicious anemia), as oral absorption will be near zero.

Quick reference

Class & Role

Water-Soluble — Cobalamin.

Route / Formulation

Ampoules (1000 mcg/1 mL) for deep IM injection. (Hydroxocobalamin is preferred as it stays in the body longer). (Neo-B12, Hydroxocobalamin, Cyanocobalamin)

Usual Dose & Max

IM 1000 mcg 3 times a week for 2 weeks (Loading), then 1000 mcg every 3 months for life. Max 1000 mcg (1 mg) per injection.

Key Indication Doses

Pernicious Anemia / Severe Deficiency: IM 1000 mcg 3 times a week for 2 weeks (Loading), then 1000 mcg every 3 months for life. Dietary Deficiency (Vegans): PO 1000 mcg OD. Neurological Involvement: IM 1000 mcg on alternate days until symptoms stop improving, then every 2 months.

Best Uses

Avoid / Cautions

Known hypersensitivity to cobalt or cobalamin. Pregnancy Category A.

Key Risks

Metabolic: Hypokalemia. When you give B12 to a severely anemic patient, the bone marrow suddenly goes into overdrive making billions of new RBCs. The new cells pull massive amounts of potassium out of the blood, which can trigger fatal hypokalemia arrhythmias in the first 48 hours. Immunological: Anaphylaxis to the IM injection (very rare). Dermatological: Acne-like rash (transient).

Key Interactions

Metformin, PPIs (Pantoprazole), and Colchicine physically block the absorption of oral B12 in the terminal ileum. Patients on long-term Metformin/PPIs frequently become deficient and require IM replacement.

Monitoring

Monitor U&E (Potassium) strictly during the first week of intensive IM loading in severe anemia. Check FBC (MCV should normalize) and Reticulocyte count.

Clinical Pearl

Nitrous Oxide (used in anaesthesia and recreationally abused in 'nangs') irreversibly oxidises the cobalt atom in Vitamin B12, completely destroying it. Severe nitrous abuse causes instant, profound B12-deficiency paralysis and spinal cord degeneration.

Access

Neo-B12, Hydroxocobalamin, CyanocobalaminTablets (1000 mcg)

Brand: Neo-B12, Hydroxocobalamin, Cyanocobalamin
Formulation: Tablets (1000 mcg)