What is the proper technique for administering an intramuscular or subcutaneous injection in an adult?

Proper Injection Technique for Adults

Subcutaneous Injections

For subcutaneous injections in adults, use a 4-mm pen needle inserted at 90 degrees into healthy subcutaneous tissue at recommended sites (abdomen, thigh, buttock, or upper arm), avoiding the area within 2 fingerbreadths of the umbilicus, scars, and lipohypertrophic areas. 1

Needle Specifications and Angle

• Use 4-mm pen needles for all adults regardless of age, sex, ethnicity, or BMI 1
• Insert at 90 degrees for standard 4-mm needles 1
• If using needles >4 mm or syringes, lift a skinfold to avoid intramuscular injection 1
• For thin individuals, pinch the skin and consider a 45-degree angle to prevent intramuscular injection 1

Recommended Injection Sites

The four acceptable sites are 1:

• Abdomen: 2 adult fingerbreadths (approximately 2 inches) away from the umbilicus, avoiding a 2-inch radius circle around the navel 1, 2
• Thigh: Upper third anterior lateral aspect of both thighs 1
• Buttock: Posterior lateral aspect of both upper buttocks and flanks 1
• Upper arm: Middle third posterior aspect 1

Critical Site Rotation

• Rotate systematically within one anatomical area (e.g., different quadrants of the abdomen) rather than switching between different body regions with each injection 1
• This practice decreases variability in absorption while preventing lipohypertrophy 1
• Maintain at least 1 cm between injection sites 2

Technique Steps

1. Ensure hands and injection site are clean 1
2. For suspensions (except rapid-acting insulin and insulin glargine), gently roll the vial or pen between palms to resuspend 1
3. Lightly grasp a fold of skin if needed 1
4. Release the pinch before injecting 1
5. Insert needle at 90 degrees (or 45 degrees if thin) 1
6. Routine aspiration is not necessary 1
7. Keep needle embedded in skin for 5 seconds after complete delivery when using pens 1

Common Pitfalls to Avoid

• Never inject within 2 fingerbreadths of the umbilicus due to reduced subcutaneous tissue thickness and risk of intramuscular injection 1, 2
• Avoid areas with scars or lipohypertrophy, as these interfere with absorption 1, 2
• Do not inject into bony prominences 1

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Intramuscular Injections

For intramuscular injections in adults, use a 1 to 1½ inch, 22-25 gauge needle inserted at 90 degrees perpendicular to the skin, with the deltoid muscle as the preferred site and the anterolateral thigh as an alternative—never use the buttock. 3

Needle Specifications

• Length: 1 to 1½ inches (25-38 mm) 3
• Gauge: 22-25 gauge 3
• The needle must be long enough to reach muscle but not so long as to involve underlying nerves, blood vessels, or bone 3

Injection Angle

• Always use 90 degrees perpendicular to the skin surface 3
• Deviating from this angle can reduce medication efficacy or increase local adverse reactions 3

Recommended Sites for Adults

• Deltoid muscle (preferred): Maximum volume 1-2 mL 3
• Anterolateral thigh: Use for volumes >2 mL or when deltoid is not suitable 3
• Vastus lateralis (middle portion): Safest thigh site with low risk of vascular or nerve damage 4

Critical Safety Warnings

• Never use the buttock due to risk of sciatic nerve injury and decreased immunogenicity from inadvertent subcutaneous or deep fat tissue injection 3, 5
• When administering multiple IM injections in the same limb, separate sites by more than 1 inch (2.5 cm) to differentiate local reactions 3

Technique Steps

1. Verify medication label before injection 1
2. Ensure hands and injection site are clean 1
3. Select appropriate site based on volume and patient anatomy 3
4. Insert needle at 90 degrees 3
5. Aspiration is not necessary according to current CDC guidance 3, 5
6. Inject medication steadily 6
7. Withdraw needle and apply gentle pressure if needed 6

Volume Considerations

• Deltoid: Maximum 1-2 mL for routine injections 3
• Thigh or ventrogluteal: Use for volumes >2 mL 3
• For large volumes (e.g., 2 grams ceftriaxone), divide dose between two sites 5

Common Pitfalls to Avoid

• Using inadequate needle length results in subcutaneous rather than intramuscular delivery and reduced efficacy 3
• Injecting into the buttock carries both safety risks (sciatic nerve injury) and efficacy concerns (decreased absorption) 3, 5
• Failing to individualize needle selection based on patient muscle mass increases risk of improper administration 3
• Avoid the middle of the rectus femoris in the thigh due to presence of major blood vessels and nerves 4