How-to: Intramuscular injection

What are intramuscular injections?

An intramuscular injection is a technique used to deliver a medication deep into the muscles. This allows the medication to be absorbed into the bloodstream quickly. You may have received an intramuscular injection at a doctor’s office the last time you got a vaccine, like the flu shot.

In some cases, a person may also self-administer an intramuscular injection. For example, certain drugs that treat multiple sclerosis or rheumatoid arthritis may require self-injection.

What are intramuscular injections used for?

Intramuscular injections are a common practice in modern medicine. They’re used to deliver drugs and vaccines. Several drugs and almost all injectable vaccines are delivered this way.

Intramuscular injections are used when other types of delivery methods aren’t recommended. These include:

  • oral (swallowed into the stomach)
  • intravenous (injected into the vein)
  • subcutaneous (injected into the fatty tissue just under the layer of skin)

Intramuscular injections may be used instead of intravenous injections because some drugs are irritating to veins, or because a suitable vein can’t be located. It may be used instead of oral delivery because some drugs are destroyed by the digestive system when a drug is swallowed.

Intramuscular injections are absorbed faster than subcutaneous injections. This is because muscle tissue has a greater blood supply than the tissue just under the skin. Muscle tissue can also hold a larger volume of medication than subcutaneous tissue.

Intramuscular injection sites:

Intramuscular injections are often given in the following areas:

Deltoid muscle of the arm

The deltoid muscle is the site most typically used for vaccines. However, this site is not common for self-injection, because its small muscle mass limits the volume of medication that can be injected — typically no more than 1 milliliter.

It’s also difficult to use this site for self-injection. A caregiver, friend, or family member can assist with injections into this muscle.

To locate this site, feel for the bone (acromion process) that’s located at the top of the upper arm. The correct area to give the injection is two finger widths below the acromion process. At the bottom of the two fingers, will be an upside-down triangle. Give the injection in the center of the triangle.

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Vastus lateralis muscle of the thigh

The thigh may be used when the other sites aren’t available or if you need to administer the medication on your own.

Divide the upper thigh into three equal parts. Locate the middle of these three sections. The injection should go into the outer top portion of this section.

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Dorsogluteal muscles of the buttocks

The dorsogluteal muscle of the buttocks was the site most commonly selected by healthcare providers for many years. However, due to the potential for injury to the sciatic nerve, the ventrogluteal is most often used now. This site is difficult to use this site for self-injection and not recommended.

You shouldn’t use an injection site that has evidence of infection or injury. If you’ll be giving the injection more than once, make sure to rotate injection sites to avoid injury or discomfort to the muscles.

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How to administer a intramuscular injection:

Any person who administers intramuscular injections should receive training and education on proper injection technique.

The needle size and injection site will depend on many factors. These include the age and size of the person receiving the medication, and the volume and type of medication. Your doctor or pharmacist will give you specific guidelines about which needle and syringe are appropriate to administer your medication.

The needle should be long enough to reach the muscle without penetrating the nerves and blood vessels underneath. Generally, needles should be 1 inch to 1.5 inches for an adult, and will be smaller for a child. They’ll be 22-gauge to 25-gauge thick, noted as 22g on the packaging.

Follow these steps for a safe intramuscular injection:

Wash your hands. Wash your hands with soap and warm water to prevent potential infection. Be sure to thoroughly scrub between fingers, on the backs of hands, and under fingernails. The Centers for Disease Control and Prevention (CDC) recommends lathering for 20 seconds — the time it takes to sing “Happy Birthday” twice.

Assemble the following supplies:

  • needle and syringe with medication
  • alcohol pads
  • gauze
  • puncture-resistant container to discard the used needles and syringe — typically a red, plastic sharps container
  • bandages

Locate injection site. To isolate the muscle and target where you’ll place the injection, spread the skin at the injection site between two fingers. The person receiving the injection should get into a position that’s comfortable, provides easy access to the location, and keeps the muscles relaxed.

Clean injection site. Clean the site selected for injection with an alcohol swab and allow the skin to air dry.

Prepare syringe with medication. Before withdrawing medication from a vial and injecting yourself or someone else, make sure you’re using the correct medication, at the correct dose, at the correct time, and in the right manner. Use a new needle and syringe with every injection.

Preparing a syringe:

1. Remove the cap from the vial. 

If the vial is multidose, make a note about when the vial was first opened. The rubber stopper should be cleaned with an alcohol swab.

2. Draw air into the syringe.

Draw back the plunger to fill the syringe with air up to the dose that you’ll be injecting. This is done because the vial is a vacuum, and you need to add an equal amount of air to regulate the pressure. This makes it easier to draw the medication into the syringe. Don’t worry, though — if you forget this step, you can still get the medication out of the vial.

3. Insert air into the vial.

Remove the cap from the needle and push the needle through the rubber stopper at the top of the vial. Inject all the air into the vial. Be careful to not touch the needle to keep it clean.

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4. Withdraw the medication. 

Turn the vial and syringe upside down so the needle points upward and pull back on the plunger to withdraw the correct amount of medication.

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5. Remove air bubbles.

Tap the syringe to push any bubbles to the top and gently depress the plunger to push the air bubbles out.

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6. Self-injection with a syringe. Insert the needle.

Hold the needle like a dart and insert it into the muscle at a 90-degree angle. You should insert the needle in a quick, but controlled manner. Do not push the plunger in.

Check for blood.

Using the hand that’s holding the skin at the injection site, pick up your index finger and thumb to stabilize the needle. Use your dominant hand — the one that did the injection — to pull back on the plunger slightly, looking for blood in the syringe. Ask your doctor if this is needed for the type of medicine you will be injecting, as it’s not required for all injections.

  • If you see blood going into the syringe, it means the tip of the needle is in a blood vessel. If this happens, withdraw the needle and begin again with a new needle, syringe with medication, and injection site. It’s rare to have this happen.
  • If you don’t see blood going into the syringe, the needle is in the correct place and you can inject the medicine.
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7. Inject the medication.

Push the plunger slowly to inject the medication into the muscle.

8. Remove the needle

Withdraw the needle quickly and discard it into a puncture-resistant sharps container. Don’t recap the needle.

9. Withdraw the needle.

Let go of the pinched skin and withdraw the needle. Discard the used needle in a puncture-resistant sharp’s container.

10. Apply pressure to the site.

Use gauze to apply light pressure to the injection site. If there’s any bleeding, it should be very minor. You may notice a little bruising later. This is common and nothing to be concerned about.

Complications of intramuscular injections:

It’s normal to experience some discomfort after an intramuscular injection. But certain symptoms may be a sign of a more serious complication. Call your doctor or healthcare provider right away if you experience:

  • severe pain at the injection site
  • tingling or numbness
  • redness, swelling, or warmth at the injection site
  • drainage at the injection site
  • prolonged bleeding
  • signs of an allergic reaction, such as difficulty breathing or facial swelling

It’s also normal to have some anxiety about performing or receiving an injection, especially an intramuscular injection due to the long needle. Read through the steps several times until you feel comfortable with the procedure, and take your time.

Don’t hesitate to ask your provider or pharmacist to go through the procedure with you beforehand. They’re more than willing to help you understand how to perform a safe, proper injection.