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Intramuscular injection, often abbreviated IM, is the injection of a substance into a muscle. In medicine, it is one of several methods for parenteral of medications. Intramuscular injection may be preferred because muscles have larger and more numerous than subcutaneous tissue, leading to faster absorption than subcutaneous or intradermal injections. Medication administered via intramuscular injection is not subject to the first-pass metabolism effect which affects oral medications.
Common sites for intramuscular injections include the deltoid muscle of the upper arm and the gluteal muscle of the buttock. In infants, the vastus lateralis muscle of the thigh is commonly used. The injection site must be cleaned before administering the injection, and the injection is then administered in a fast, darting motion to decrease the discomfort to the individual. The volume to be injected in the muscle is usually limited to 2–5 , depending on injection site. A site with signs of infection or muscle atrophy should not be chosen. Intramuscular injections should not be used in people with myopathy or those with trouble clotting.
Intramuscular injections commonly result in pain, redness, and swelling or inflammation around the injection site. These side effects are generally mild and last no more than a few days at most. Rarely, or blood vessels around the injection site can be damaged, resulting in severe pain or paralysis. If proper technique is not followed, intramuscular injections can result in localized infections such as and gangrene. While historically aspiration, or pulling back on the syringe before injection, was recommended to prevent inadvertent administration into a vein, it is no longer recommended for most injection sites by some countries.
, especially inactivated vaccines, are commonly administered via intramuscular injection. However, it has been estimated that for every vaccine injected intramuscularly, 20 injections are given to administer drugs or other therapy. This can include medications such as , immunoglobulin, and such as testosterone and medroxyprogesterone. In a case of severe allergic reaction, or anaphylaxis, a person may use an epinephrine autoinjector to self-administer epinephrine into the muscle.
Intramuscular injections are generally avoided in people with thrombocytopenia or clotting problems, to prevent harm due to potential damage to blood vessels during the injection. They are also not recommended in people who are in hypovolemic shock, or have myopathy or muscle atrophy, as these conditions may alter the absorption of the medication. The damage to the muscle caused by an intramuscular injections may interfere with the accuracy of certain cardiac tests for people with suspected myocardial infarction and for this reason other methods of administration are preferred in such instances. In people with an active myocardial infarction, the decrease in circulation may result in slower absorption from an IM injection. Specific sites of administration may also be contraindicated if the desired injection site has an infection, swelling, or inflammation. (2015). 9781469853031, Lippincott Williams & Wilkins. ISBN 9781469853031 Within a specific site of administration, the injection should not be given directly over irritation or redness, birthmarks or moles, or areas with scar tissue.
The dorsogluteal site of injection is associated with a higher risk of skin and tissue trauma, muscle fibrosis or contracture, hematoma, nerve palsy, paralysis, and infections such as and gangrene. Furthermore, injection in the gluteal muscle poses a risk for damage to the sciatic nerve, which may cause shooting pain or a sensation of burning. Sciatic nerve damage can also affect a person's ability to move their foot on the affected side, and other parts of the body controlled by the nerve. Damage to the sciatic nerve can be prevented by using the ventrogluteal site instead, and by selecting an appropriate size and length of needle for the injection.
The injection site is first cleaned using an antimicrobial and allowed to dry. The injection is performed in a quick, darting motion perpendicular to the skin, at an angle between 72 and 90 degrees. The practitioner will stabilize the needle with one hand while using their other hand to depress the plunger to slowly inject the medication – a rapid injection causes more discomfort. The needle is withdrawn at the same angle inserted. Gentle pressure may be applied with gauze if bleeding occurs. (2025). 9781975121365, Wolters Kluwer. ISBN 9781975121365 Pressure or gentle massage of the muscle following injection may reduce the risk of pain.
Aspiration was recommended by the Danish Health Authority for COVID-19 vaccines for a time to investigate the potential rare risk of blood clotting and bleeding, but it is no longer a recommendation.
The ventrogluteal site on the hip is used for injections which require a larger volume to be administered, greater than 1 mL, and for medications which are known to be irritating, viscous, or oily. It is also used to administer narcotic medications, Antibiotics, and Antiemetic. The ventrogluteal site is located in a triangle formed by the anterior superior iliac spine and the iliac crest, and may be located using a hand as a guide. The ventrogluteal site is less painful for injection than other sites such as the deltoid site.
The vastus lateralis site is used for infants less than 7 months old and people who are unable to walk or who have loss of muscular tone. The site is located by dividing the front thigh into thirds vertically and horizontally to form nine squares; the injection is administered in the outer middle square. This site is also the usual site of administration for epinephrine autoinjectors, which are used in the outer thigh, corresponding to the location of the vastus lateralis muscle. Last revised 03/15/2017
The dorsogluteal site of the buttock site is not routinely used due to its location near major and , as well as having inconsistent depth of adipose tissue. Many injections in this site do not penetrate deep enough under the skin to be correctly administered in the muscle. While current evidence-based practice recommends against using this site, many healthcare providers still use this site, often due to a lack of knowledge about alternative sites for injection.
This site is located by dividing the buttock into four using a cross shape, and administering the injection in the upper outer quadrant. This is the only intramuscular injection site for which aspiration is recommended of the syringe before injection, due to higher likelihood of accidental intravenous administration in this area. However, aspiration is not recommended by the US CDC, which considers it outdated for any intramuscular injection.
To help infants and children cooperate with injection administration, the Advisory Committee on Immunization Practices in the United States recommends using distractions, giving something sweet, and rocking the baby side to side. In people who are overweight, a 1.5-inch needle may be used to ensure the injection is given below the subcutaneous layer of skin, while a -inch needle may be used for people who weigh under . In any case, the skin does not need to be pinched up before injecting when the appropriate length needle is used.
Intramuscular injections began to be used for administration of vaccines for diphtheria in 1923, pertussis in 1926, and tetanus in 1927. By the 1970s, researchers and instructors began forming guidance on injection site and technique to reduce the risk of injection complications and side effects such as pain. Also in the early 1970s, botulinum toxin began to be injected into muscles to intentionally paralyze them for therapeutic reasons, and later for cosmetic reasons. Until the 2000s, aspiration after inserting the needle was recommended as a safety measure, to ensure the injection was being administered in a muscle and not inadvertently in a vein. However, this is no longer recommended as evidence shows no safety benefit and it lengthens the time taken for injection, which causes more pain.
Special populations
Some populations require a different injection site, needle length, or technique. In very young or weak elderly patients, a normal-length needle may be too long to inject properly. In these patients, a shorter needle is indicated to avoid injecting too deeply. It is also recommended to consider using the anterolateral thigh as an injection site in infants under one year old.
History
Injections into muscular tissue may have taken place as early as the year 500 AD. Beginning in the late 1800s, the procedure began to be described in more detail and techniques began to be developed by physicians. In the early days of intramuscular injections, the procedure was performed almost exclusively by physicians. After the introduction of antibiotics in the middle of the 20th century, nurses began preparing equipment for intramuscular injections as part of their delegated duties from physicians, and by 1961 they had "essentially taken over the procedure". Until this delegation became virtually universal, there were no uniform procedures or education for nurses in proper administration of intramuscular injections, and complications from improper injection were common.
Veterinary medicine
In animals common sites for intramuscular injection include the quadriceps, the lumbodorsal muscles, and the triceps muscle.
See also
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