An intramuscular injection delivers medication into a muscle. Doctors frequently use intramuscular injections to administer vaccines and certain other drugs. Injection sites include the upper arm, hip, thigh, and buttocks.
In this article, we explain where and how to administer an intramuscular injection.
Intramuscular injections offer some benefits over other types of delivery methods, such as oral, intravenous injections into a vein, and subcutaneous injections into fatty tissue under the skin.
A doctor may use an intramuscular shot if:
- they cannot locate an appropriate vein
- the particular drug would irritate the veins
- the digestive system would render pills ineffective
Intramuscular injections have other advantages too. The muscles have a plentiful supply of blood, which helps ensure that the body absorbs the medication quickly. The tissue in the muscles can also hold more medication than fatty tissue.
People can receive intramuscular injections in the following areas:
The upper arm
The deltoid muscle is the most common site for vaccines. This muscle is in the upper arm near the shoulder.
It can only receive small volumes of medication, usually 1 milliliter or less. Therefore, doctors do not use it for drugs that require larger quantities.
People self-administering medication rarely use the deltoid, as an injection site, because it is difficult for them to reach.
To find the deltoid muscle, a person feels for the bone at the top of the upper arm. Two finger-widths below this, there is a triangular muscle. The needle should enter the triangle’s center.
Healthcare professionals often give intramuscular injections into the ventrogluteal muscle of the hip.
This muscle is a very safe injection site for adults and infants more than 7 months old because it is thick and located away from major nerves and blood vessels. But it can be challenging to self-administer medication into the hip.
To locate the ventrogluteal muscle on someone else, place the heel of the hand on the hip, with the fingers pointing toward the head. The thumb should point toward the groin.
Position the index and middle fingers into a V then administer the shot in the middle of the V.
Typically, people who need to self-administer injections use the vastus lateralis muscle in the thigh.
To locate the correct spot, imagine dividing the thigh vertically into three equal parts.
Give the injection into the outer top part of the middle section.
Before doctors began using the hip as an injection site, they used the dorsogluteal muscles in the buttocks. They tend to avoid using these muscles now because of the potential risk of injury to the sciatic nerve.
People should avoid self-administering medications into the dorsogluteal muscles.
A healthcare professional should provide people with training and education before asking them to administer intramuscular injections to themselves or another person.
The following steps can help people deliver a safe injection into a muscle:
1. Wash the hands
Wash the hands thoroughly with soap and warm water. Pay careful attention to the area between the fingers and under the fingernails.
2. Gather supplies
Before giving the shot, get the following items ready:
- an alcohol wipe
- a sterile gauze pad
- a cotton ball
- a bandage
- a puncture-resistant container to dispose of the needle
- the medication
- a new needle and syringe
A doctor should provide advice on the type of needle to use. It needs to be long enough to reach deep into the muscle tissue.
Most adults will require a 1-inch needle, but the exact size depends on the person’s weight. It is essential to ask a doctor or pharmacist which size needle to use before giving an injection.
3. Prepare the injection site
Locate the injection site according to the instructions above. Gently spread the skin between two fingers and keep the muscles relaxed. Clean the skin with the alcohol swab and allow to air-dry.
4. Prepare the vial and syringe
If using a multidose vial, note the date you first opened it. Clean the rubber stopper with an alcohol swab.
Remove the cap from the syringe. Draw air into the syringe by pulling back the plunger. Fill the syringe with air up to the same level as the medication dose.
Remove the cap from the needle and push it through the top of the vial. Inject all the air into the vial.
Turn the vial and syringe upside down so that the needle points upward. Draw back the plunger to fill the syringe with the correct amount of medication.
Remove air bubbles by gently tapping the syringe and pressing the plunger. Avoid touching the needle to ensure it stays clean.
5. Inject the medication
Insert the needle into the muscle at a 90-degree angle. Use the index finger and thumb to stabilize the syringe while using the other hand to pull back on the plunger slightly to look for blood.
If there is blood, it means the needle is in a blood vessel and not a muscle. Withdraw and start over with a new needle, syringe, and injection site.
If there is no blood, the needle is in the correct position. Press down on the plunger of the syringe to inject the medication.
6. Remove the needle
Quickly remove the needle from the skin and dispose of it in a puncture-resistant container.
7. Press on the injection site
Using gauze, apply light pressure to the injection site. Light bleeding at the injection site is normal, but a person can use a bandage if necessary.
The following tips may reduce discomfort before and after the injection:
- Numb the injection site with ice or a numbing cream before cleaning the skin with the alcohol swab.
- To avoid stinging, ensure the alcohol dries completely.
- Before putting medication into the syringe, warm the vial up by rubbing it between the hands.
- Relax the muscles, as much as possible, when receiving the injection.
- Discuss changing injection sites with a doctor. Too many injections in the same location can cause scarring and skin changes.
People who find injecting themselves difficult should ask a friend, family member, or caregiver to help them.
Minor discomfort after an intramuscular injection is normal. Less commonly, more serious complications can arise, including:
- an abscess, or collection of pus
- tissue necrosis, or tissue death
- granuloma, or inflammation in the tissue
- muscle fibrosis, or scarring of muscle tissue
- hematoma, where blood seeps out of blood vessels into the surrounding tissue
- injury to blood vessels and nerves
People who notice the following symptoms should call a doctor immediately:
- severe pain at the injection site
- prolonged or excessive bleeding
- tingling or numbness around the muscle
- redness, swelling, or warmth at the injection site
- drainage at the injection site
- signs of an allergic reaction, such as swelling or breathing problems
Intramuscular injections are a common and effective way to deliver medication. There are several possible locations for administering intramuscular injections, including the shoulder, hip, and thigh.
People who need to self-administer an injection should ask their doctor for advice and guidance, and familiarize themselves with the process before they inject themselves. Alternatively, a trained family member or caregiver can deliver the shot.
It is essential to seek medical assistance if a person experiences prolonged or severe side effects after their injection.