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An intramuscular injection is a technique used to deliver a medication deep into the muscles. This allows the bloodstream to absorb the medication 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.
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 are not 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 cannot be located.
They may be used instead of oral delivery because some drugs are destroyed by the digestive system when you swallow them.
Intramuscular injections are absorbed faster than subcutaneous injections. This is because muscle tissue has a greater blood supply than the tissue just under your skin. Muscle tissue can also hold a larger volume of medication than subcutaneous tissue.
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 your 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.
Vastus lateralis muscle of the thigh
The thigh may be used when the other sites are not 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.
Ventrogluteal muscle of the hip
The ventrogluteal muscle is the safest site for adults and children older than 7 months. It’s deep and not close to any major blood vessels or nerves. This site is difficult for self-injection and may require the help of a friend, family member, or caregiver.
Place the heel of your hand on the hip of the person receiving the injection, with your fingers pointing toward their head. Position your fingers so your thumb points toward their groin and you feel the pelvis under your pinky finger. Spread your index and middle fingers in a slight V shape, and inject the needle into the middle of that V.
Dorsogluteal muscles of the buttocks
The dorsogluteal muscle of the buttocks was the site most commonly selected by healthcare professionals for many years. However, due to the potential for injury to the sciatic nerve, the ventrogluteal muscle is most often used instead.
This site in the dorsogluteal muscle is difficult to use for self-injection and is not recommended.
You should not 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.
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:
1. Wash your hands
Wash your hands with soap and warm water to prevent potential infection. Be sure to thoroughly scrub between your fingers, on the backs of your hands, and under your fingernails.
2. Gather all the needed supplies
Assemble the following supplies:
- needle and syringe with medication
- alcohol pads
- puncture-resistant container to discard the used needles and syringe (typically a red, plastic sharps container)
3. Locate the 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 is comfortable, provides easy access to the location, and keeps the muscles relaxed.
4. Clean the injection site
Clean the site selected for injection with an alcohol swab and allow the skin to air dry.
5. Prepare the syringe with medication
- Remove the cap. If the vial or pen is multidose, take a note about when the vial was first opened. The rubber stopper should be cleaned with an alcohol swab.
- 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 also makes it easier to draw the medication into the syringe. If you forget this step, you can still get the medication out of the vial.
- 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 of the air into the vial. Be careful to not touch the needle to keep it clean.
- 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.
- Remove air bubbles. Tap the syringe to push any bubbles to the top and gently depress the plunger to push the air bubbles out.
6. Self-inject with a syringe
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.
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. Do not put the cap back on the needle.
A sharps container is a red container that you can purchase at any pharmacy. It’s used to collect medical waste, like needles and syringes. You should not put any of these materials into the regular garbage, as needles can be hazardous to anyone who handles the trash.
9. Apply pressure to the injection site
Use a piece of gauze to apply light pressure to the injection site. You can even massage the area to help the medication be absorbed into the muscle. It’s normal to see slight bleeding. Use a bandage if necessary.
To minimize possible discomfort before your injection:
- Apply ice or an over-the-counter topical numbing cream to the injection site before cleaning it with the alcohol pad.
- Allow the alcohol to dry completely before the injection. Otherwise, it might cause stinging.
- Warm the vial of medication by rubbing it between your hands prior to drawing the medication into the syringe.
- Have someone you trust give you the injection. Some people find it difficult to inject themselves.
It’s typical 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 professional 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
You may 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.
You can ask your doctor 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.