Where is a vitamin B12 (B12) injection typically administered?

Vitamin B12 Injection Administration Sites

For adults, vitamin B12 injections should be given in the deltoid muscle of the upper arm, while infants and young children should receive injections in the anterolateral aspect of the thigh. 1, 2

Site Selection by Age Group

Adults (>18 years)

• The deltoid muscle is the preferred site for intramuscular vitamin B12 injections in adults 1, 3
• Use a 1 to 1½ inch, 22-25 gauge needle to ensure proper muscle penetration 1, 2
• Insert the needle at a 90-degree angle perpendicular to the skin surface 2
• The anterolateral thigh can be used as an alternative site when multiple injections are needed 2, 3

Infants (<12 months)

• The anterolateral aspect of the thigh is the preferred site, as it provides the largest muscle mass in infants 1, 2
• Use a 7/8 to 1 inch, 22-25 gauge needle 2
• This site minimizes risk of neurovascular injury in this age group 4

Toddlers and Older Children (12 months to 18 years)

• The deltoid muscle may be used if adequate muscle mass is present 1, 2
• The anterolateral thigh remains an appropriate alternative, particularly for children with less developed deltoid muscles 1
• Use a 7/8 to 1¼ inch, 22-25 gauge needle depending on muscle size 2

Critical Sites to Avoid

Never use the buttock for routine vitamin B12 injections due to two major concerns: 1, 2, 3

• Risk of sciatic nerve injury, which can cause permanent neurologic damage 4, 1
• Decreased medication efficacy from inadvertent subcutaneous or deep fat tissue injection rather than true intramuscular administration 1, 2

If the buttock must be used in exceptional circumstances (such as when administering large volumes of immune globulin), only the upper outer quadrant should be used with the needle directed anteriorly, not inferiorly or perpendicular to the skin 4, 1

Proper Injection Technique

Needle Insertion

• Insert the needle at a 90-degree angle to ensure intramuscular rather than subcutaneous delivery 2
• The needle must be long enough to reach muscle mass but not so long as to endanger underlying nerves, blood vessels, or bone 1, 2

Pre-Injection Check

• Before injecting, pull back on the plunger to check for blood return 1
• If blood appears in the needle hub, withdraw the needle and select a new site 4, 1
• Repeat this process until no blood appears 4

Multiple Injections

• When administering multiple injections in the same limb, separate injection sites by more than 1 inch (2.5 cm) to differentiate any local reactions 2, 3
• Document the location of each injection in the medical record 3

Route of Administration Options

Both intramuscular and subcutaneous routes are effective for vitamin B12 administration: 5

• Intramuscular injection results in peak plasma levels within 1 hour and is the traditional route 5
• Subcutaneous injection is also rapidly and quantitatively absorbed, providing comparable bioavailability 5
• For subcutaneous injections in adults, use the deltoid area; in infants, use the thigh 4
• Subcutaneous injections require a 5/8 to 3/4 inch, 23-25 gauge needle inserted into tissues below the dermal layer 4

Common Pitfalls to Avoid

• Using inadequate needle length results in subcutaneous rather than intramuscular delivery, reducing medication efficacy 2
• Failing to aspirate before injection may result in inadvertent intravascular administration 1
• Injecting into the buttock, which carries both safety and efficacy concerns 1, 2
• Using a one-size-fits-all approach without considering age, muscle mass, and injection volume 2