Vitamin B12 (Methylcobalamin) Injection

Vitamin B12 (Methylcobalamin) Injection

Available presentation(s): 5, 30 mL. Verify the exact concentration and total active quantity on the prescription and dispensing label.

Introduction: Methylcobalamin is an active form of vitamin B12. Compounded injection may be used for replacement when a prescriber selects this form, although most formal dosing guidance is based on hydroxocobalamin or cyanocobalamin.

Dosage: For deficiency, determine dose and schedule from diagnosis, severity, neurologic involvement, cause and maintenance needs. The 1 mg/mL and 25 mg/mL products are not dose-equivalent by volume; prescribe in milligrams and verify concentration. There is no established high-dose wellness regimen.

Mechanisms of Action: Acts as a cofactor for methionine synthase, supporting methylation and conversion of homocysteine to methionine; B12 also supports DNA synthesis and neurologic function.

Contraindications & Precautions: Avoid in cobalamin/cobalt hypersensitivity. Establish diagnosis where possible before treatment. Monitor potassium in severe megaloblastic anaemia and clinical/biochemical response. The 25 mg/mL strength presents a substantial dosing-error risk.

Interactions: Chloramphenicol may reduce haematologic response. Metformin, acid suppressants and nitrous oxide can contribute to functional deficiency. Biotin-containing combinations may interfere with laboratory tests.

Adverse Reactions / Side Effects: Injection-site pain, rash, pruritus, headache, diarrhoea and acneiform eruptions may occur; anaphylaxis is rare. Hypokalaemia can occur during rapid haematopoietic response.

Pregnancy & Breastfeeding: Treat confirmed deficiency during pregnancy and breastfeeding. Avoid unsupported supraphysiologic dosing.

Storage: Store under the conditions stated on the Optimus dispensing label and product-specific worksheet. Protect from light where labelled. Do not freeze unless explicitly validated. Maintain cold chain if the label requires refrigeration. Do not use after the assigned beyond-use date or if there is visible particulate matter, precipitation, colour change, loss of container integrity or evidence of improper storage. Once entered, follow the validated in-use time; do not assume a compounded vial is multi-dose.

References

• New Zealand Formulary (NZF), current online edition; product-specific approved data sheets where available; USP Pharmaceutical Compounding—Sterile Preparations; and Optimus Healthcare validated formulation, sterility/endotoxin controls and assigned beyond-use date.
• DailyMed. Thiamine Hydrochloride, Pyridoxine Hydrochloride, Hydroxocobalamin and Levocarnitine injection labels, current editions. https://dailymed.nlm.nih.gov/
• NIH Office of Dietary Supplements. Health Professional Fact Sheets (vitamins and minerals), current online editions. https://ods.od.nih.gov/factsheets/list-VitaminsMinerals/
• US FDA. Compounding and the FDA: Questions and Answers. Updated 16 September 2025. https://www.fda.gov/drugs/human-drug-compounding/compounding-and-fda-questions-and-answers