What are the recommended sites for intramuscular (IM) injections?

Recommended Intramuscular Injection Sites

The deltoid muscle is the preferred site for routine intramuscular injections in adults, while the anterolateral thigh is recommended for infants and young children. 1

Age-Specific Site Selection

Infants (<12 months)

• Use the anterolateral aspect of the thigh as the primary site, which provides the largest muscle mass in this age group 1
• Needle specifications: 7/8 to 1 inch length, 22-25 gauge 1

Toddlers and Children (>12 months to 18 years)

• The deltoid muscle is preferred if muscle mass is adequate 1
• The anterolateral thigh remains an acceptable alternative, particularly for toddlers with insufficient deltoid development 1
• Needle specifications: 7/8 to 1¼ inches length, 22-25 gauge, based on muscle size 1
• For toddlers using the thigh, use a longer needle (typically 1 inch) 1

Adults (>18 years)

• The deltoid muscle is the recommended site for routine intramuscular vaccinations and injections 1
• The anterolateral thigh is an acceptable alternative site 1
• Needle specifications: 1 to 1½ inches length, 22-25 gauge 1

Critical Sites to Avoid

Gluteal/Buttock Region

• The buttock should NOT be used for routine injections due to risk of sciatic nerve injury 1, 2
• Gluteal injections are associated with decreased immunogenicity of hepatitis B and rabies vaccines in adults, likely from inadvertent subcutaneous or deep fat tissue injection rather than true intramuscular delivery 1, 2

Proper Injection Technique

Needle Insertion

• Insert at a 90-degree angle for all intramuscular injections 1
• The needle must be long enough to penetrate muscle without seeping into subcutaneous tissue, but not so long as to risk injury to underlying nerves, blood vessels, or bone 1, 2

Aspiration Considerations

• No data exist documenting the necessity of aspiration (pulling back the plunger before injection) 1
• If aspiration is performed and blood appears in the needle hub, withdraw and select a new site 1

Multiple Injections Protocol

• When administering more than 2 injections, use different anatomic sites 1
• If multiple injections must be given in a single limb, the thigh is preferred due to greater muscle mass 1
• Separate injection sites by more than 1 inch to allow differentiation of any local reactions 1
• Document the location of each injection in the medical record 1

Anatomical Refinements Based on Recent Research

Deltoid Muscle Specifics

• The safest deltoid injection site is at the intersection of the anteroposterior axillary line and the perpendicular line from the mid-acromion, which is distant from the axillary nerve and posterior circumflex humeral artery 3
• A more conservative approach recommends injecting 4 fingerbreadths (approximately 9 cm) below the mid-acromion point to avoid neurovascular structures 4
• Never inject in the upper half of the deltoid muscle 4

Thigh Muscle Specifics

• When using the thigh, the middle of the vastus lateralis is safer than the rectus femoris due to lower risk of vascular or nerve damage 5
• The rectus femoris contains the descending branch of the lateral circumflex femoral artery and muscle branches of the femoral nerve, making it a higher-risk site 5

Common Pitfalls to Avoid

• Inadequate needle length results in subcutaneous rather than intramuscular administration, potentially reducing vaccine efficacy and increasing local reactions 2
• Using the dorsogluteal site risks sciatic nerve injury and reduced vaccine immunogenicity 1, 2
• Failing to individualize needle selection based on patient age, muscle size, and subcutaneous tissue thickness can lead to improper medication delivery 1
• Injecting too high on the deltoid increases risk of axillary nerve and posterior circumflex humeral artery injury 3, 4