Intramuscular Injections

How to Cite This Chapter: Oczkowski S, Jankowski M, Szułdrzyński K. Intramuscular Injections. McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. Accessed May 22, 2024.
Last Updated: June 27, 2022
Last Reviewed: June 27, 2022
Chapter Information

Before attempting any procedures described in this chapter, wash and disinfect your hands and wear disposable gloves.


1. Absolute: Edema or inflammatory changes at the planned injection site, shock and peripheral hypoperfusion (except for the administration of epinephrine in patients with anaphylactic shock [see Anaphylaxis and Anaphylactic Shock]), patients refusing consent to the procedure.

2. Relative: Muscle atrophy (this can impair absorption). Coagulopathy, thrombocytopenia, use of anticoagulants (risk of hematoma). Avoid IM injections in patients receiving long-term renal replacement therapy.

Potential ComplicationsTop

Abscess and other infectious complications; irreversible nerve injury (most frequently of the sciatic nerve); reversible sensory abnormalities (in the area innervated by the sciatic nerve); aseptic muscle necrosis (most frequently seen after glucocorticoid injections); specific adverse effects of administered agents (eg, allergic reactions).


Nonsterile disposable gloves; skin disinfectant (single-use alcohol swabs or single-use cotton swab with disinfectant solution); syringe; needle bore 0.8 to 0.9 mm (21-20 gauge); needle for drawing drug from ampoule (or a syringe prefilled with the drug, with or without a needle); sterile gauze and bandage; sharps container for disposal.

Injection SiteTop

1. Buttock: Place the patient on one side or supine with knees slightly flexed. Determine the injection site (defining gluteal quadrants is no longer recommended): Place the tip of the index finger on the anterior superior iliac spine and spread your fingers, moving the middle finger as far posteriorly as possible without displacing the index finger. While holding the index finger firmly in place, turn the hand so that your thenar rests on the greater trochanter of the patient’s femur. The injection site should be within the lower third of the triangle formed by the index finger and the middle finger.

2. Arm: Injections into the lateral surface of the deltoid muscle are associated with a significant risk of nerve and vascular injury. If this site is chosen, have the patient relax their arm. By palpation, locate the acromion process. The injection site is 3 fingerbreadths below the acromion process, in the middle of the deltoid muscle.

3. Thigh: Place the patient supine. Place one hand on the greater trochanter and the other on the patient’s knee on the lateral surface of the thigh, thumbs pointing towards each other. The injection site should be in the middle of the imaginary line connecting the thumbs.


1. Close the curtains to ensure privacy for the patient. Explain the planned procedure to the patient and confirm consent.

2. Prepare the medication, if necessary, by drawing the medication from the ampule or vial into the syringe using a sterile needle. It is unnecessary to clean the top of a sealed vial. Remove the needle used to draw up the drug from the syringe and replace with a sterile 20-gauge or 21-gauge needle.

3. Perform hand hygiene and don nonsterile disposable gloves.

4. Disinfect the planned injection site using a single-use alcohol swab or single-use cotton swab with disinfectant solution. Start over the planned injection site and work outwards. Allow the disinfectant to dry completely.

5. Using the nondominant hand to hold the skin around the injection site, insert the needle with a syringe attached into the skin at a 90 degree angle and deep enough to make the needle tip stay within the muscle. If the needle touches the bone, withdraw the needle ~1 cm.

6. Before injecting the drug, aspirate with the plunger to avoid intravascular administration. If blood is aspirated, withdraw the needle and prepare another drug dose using a new needle and syringe.

7. Immobilize the needle by holding the needle hub with one hand and slowly inject the drug, then withdraw the needle at a 90 degree angle to the skin.

8. Immediately cover the site with a clean dry cotton gauze and apply pressure. If bleeding occurs, protect the injection site with dressing.

9. Dispose of all sharps securely in a sharps container. Do not recap needles to avoid needle-stick injuries. Remove gloves and perform hand hygiene.

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