Preferred Site for Intramuscular Vitamin B12 Injections

Site Selection by Age Group

The Centers for Disease Control and Prevention (CDC) recommends using the deltoid muscle as the preferred site for intramuscular vitamin B12 injections in adults, including vitamin B12 administration 1, 2, 3, 4
For infants and young children, the American Academy of Pediatrics recommends using the anterolateral thigh as the preferred site for intramuscular vitamin B12 injections 1, 2, 3, 5
The CDC recommends using a 1 to 1½ inch, 22-25 gauge needle to ensure proper muscle penetration in adults 2, 3, 4
For toddlers and older children with adequate deltoid muscle mass, the deltoid can be used for intramuscular vitamin B12 injections 2, 3

The CDC explicitly advises against using the buttock for routine intramuscular injections due to risk of sciatic nerve injury 2, 3, 4
Gluteal injections are associated with decreased immunogenicity of certain medications, likely due to inadvertent subcutaneous or deep fat tissue injection rather than true intramuscular administration 2

Insert the needle at a 90-degree angle for all intramuscular injections 2, 3
The needle must be long enough to reach muscle mass but not so long as to involve underlying nerves, blood vessels, or bone 2, 3
Inadequate needle length results in subcutaneous rather than intramuscular administration, potentially reducing medication efficacy 2

The Centers for Disease Control and Prevention recommends the anterolateral aspect of the thigh as the injection site for infants and young children under 12 months, using a 7/8 to 1 inch, 22-25 gauge needle 6
For toddlers and older children, the deltoid muscle may be used if muscle mass is adequate, with a needle size ranging from 22-25 gauge and 5/8 to 1¼ inches based on muscle size 6
The anterolateral thigh remains an option for toddlers and older children with longer needles (7/8 to 1¼ inches) 6

The buttock should not be used routinely for vitamin B12 injections due to significant risks, including risk of sciatic nerve injury and decreased medication efficacy 7
If the buttock must be used, only the upper outer quadrant should be used with the needle directed anteriorly, not inferiorly or perpendicular to the skin 6, 7

Before injecting, pull back on the plunger to check for blood return; if blood appears, withdraw and select a new site, as recommended by the MMWR Recommendations and Reports 7