What is the proper technique for administering vitamin B12 (cobalamin) intramuscularly (IM)?

How to Administer Vitamin B12 Intramuscularly

Administer hydroxocobalamin 1 mg (1000 mcg) intramuscularly using proper IM injection technique, with the deltoid or vastus lateralis as preferred sites, avoiding the buttock due to sciatic nerve injury risk. 1

Injection Site Selection

• Use the deltoid muscle (upper arm) or vastus lateralis (anterolateral thigh) as the primary injection sites for vitamin B12 administration. 1
• Avoid the buttock as a routine injection site due to potential sciatic nerve injury risk; if the buttock must be used, only inject in the upper outer quadrant with the needle directed anteriorly. 1
• For patients with thrombocytopenia (platelet count 25-50 × 10⁹/L), use smaller gauge needles (25-27G) and apply prolonged pressure (5-10 minutes) at the injection site after administration. 1

Injection Technique

• The medication is quantitatively and rapidly absorbed from intramuscular sites, with plasma levels peaking within 1 hour after injection. 2
• Standard intramuscular injection technique applies: clean the site with alcohol, insert the needle at a 90-degree angle into the muscle, aspirate to ensure you're not in a blood vessel (though this is increasingly considered optional), inject slowly, and withdraw the needle. 2
• Monitor injection sites for hematoma formation after administration, particularly in patients with bleeding disorders or thrombocytopenia. 1

Dosing Protocols Based on Clinical Presentation

For Patients WITH Neurological Involvement

• Administer hydroxocobalamin 1 mg intramuscularly on alternate days until no further improvement is observed, then transition to maintenance therapy of 1 mg intramuscularly every 2 months for life. 1, 3

For Patients WITHOUT Neurological Involvement

• Give hydroxocobalamin 1 mg intramuscularly three times weekly for 2 weeks, followed by maintenance treatment of 1 mg intramuscularly every 2-3 months lifelong. 1, 3

Maintenance Therapy

• The standard maintenance regimen is hydroxocobalamin 1 mg intramuscularly every 2-3 months for life, though some patients may require monthly dosing (1000 mcg IM monthly) to meet metabolic requirements. 1

Special Considerations for High-Risk Populations

Post-Bariatric Surgery Patients

• Administer 1 mg intramuscularly every 3 months indefinitely, or alternatively use oral supplementation at 1000-2000 mcg daily. 1, 3

Patients with Ileal Resection

• Those with >20 cm of distal ileum resected should receive prophylactic vitamin B12 injections (1000 mcg) monthly for life. 1

Patients with Severe Thrombocytopenia

• For platelet counts <10 × 10⁹/L, consider platelet transfusion support before IM administration. 1
• For platelet counts <25 × 10⁹/L with neurological symptoms, prioritize treatment despite low platelets, as neurological damage can be irreversible. 1

Formulation Selection

• Hydroxocobalamin is the preferred formulation due to established dosing protocols and superior tissue retention. 1
• In patients with renal dysfunction, use methylcobalamin or hydroxocobalamin instead of cyanocobalamin, as cyanocobalamin requires renal clearance of the cyanide moiety and is associated with increased cardiovascular events (hazard ratio 2.0) in diabetic nephropathy. 1
• Cyanocobalamin is the most widely available form in the United States and has hematopoietic activity identical to hydroxocobalamin, but hydroxocobalamin is preferred when available. 2, 1

Critical Pitfalls to Avoid

• Never administer folic acid before treating vitamin B12 deficiency, as it may mask underlying B12 deficiency while allowing irreversible neurological damage (subacute combined degeneration of the spinal cord) to progress. 1, 3
• Do not discontinue B12 supplementation even if levels normalize, as patients with malabsorption will require lifelong therapy. 1, 3
• Do not stop injections after symptoms improve, as this can lead to irreversible peripheral neuropathy. 1

Monitoring After Administration

• Recheck serum B12 levels at 3 months after initiating supplementation, then at 6 and 12 months in the first year, followed by annual monitoring. 1
• Monitor for improvement in neurological symptoms (pain, paresthesias, numbness, motor weakness), as improvement indicates effective therapy. 1
• Target homocysteine level should be <10 μmol/L for optimal outcomes. 1