Intramuscular injection

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Intramuscular injection (IM)

An intramuscular injection is a shot given into a muscle. Muscles have many blood vessels, so medicines often enter the bloodstream faster than injections given under the skin. This method also avoids first-pass metabolism that can happen with oral medicines.

Common injection sites
- Deltoid: outer upper arm
- Ventrogluteal: hip area
- Vastus lateralis: outer thigh (often used for infants)
- Dorsogluteal (buttock): used less because it risks nerves and vessels

How it’s done
- Clean the skin first.
- Insert the needle quickly in a short, dart-like motion at a 72–90 degree angle.
- Inject slowly, then withdraw the needle.
- Apply gentle pressure with gauze if there’s any bleeding.

How much medicine is given
- Usually 2–5 mL total.
- Deltoid injections are typically 1 mL or less because the muscle area is small.

Special techniques
- Z-track method: the skin is pulled to the side before injection, the needle goes in, and the skin is released after the needle is out. This helps keep the medicine in the muscle and reduces irritation.
- Aspiration (pulling back the plunger to check for blood) is no longer routinely recommended for most IM injections.

Needle length
- Varies by person. Shorter needles may be used for children or thin people; longer needles (around 1 inch to 1.5 inches) may be needed for larger patients to reach the muscle.

When IM injections should be avoided
- Bleeding problems or very low blood platelets
- Active infection at the injection site
- Muscle illness or severe muscle wasting
- Severe dehydration or very low blood volume

Risks and side effects
- Common: pain, redness, swelling at the site
- Rare: nerve or blood vessel injury, abscess, or other infections if not done properly
- Difficulty with the procedure if equipment isn’t sterile or properly used

Notes
- IM injections deliver medicine quickly into the muscle and bypass some digestion processes, but absorption can still vary.
- The choice of site and needle length depends on the medicine, the amount, and the patient’s size and condition.