intramuscular injections
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Intramuscular injection, often abbreviated IM, is the
injection Injection or injected may refer to: Science and technology * Injective function, a mathematical function mapping distinct arguments to distinct values * Injection (medicine), insertion of liquid into the body with a syringe * Injection, in broadca ...
of a substance into a muscle. In
medicine Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pr ...
, it is one of several methods for
parenteral administration A route of administration in pharmacology and toxicology is the way by which a drug, fluid, poison, or other substance is taken into the body. Routes of administration are generally classified by the location at which the substance is applied. ...
of medications. Intramuscular injection may be preferred because muscles have larger and more numerous
blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...
s than subcutaneous tissue, leading to faster absorption than subcutaneous or
intradermal injection Intradermal injection, often abbreviated ID, is a shallow or superficial injection of a substance into the dermis, which is located between the epidermis and the hypodermis. For certain substances, administration via an ID route can result in a ...
s. Medication administered via intramuscular injection is not subject to the
first-pass metabolism The first pass effect (also known as first-pass metabolism or presystemic metabolism) is a phenomenon of drug metabolism whereby the concentration of a drug, specifically when administered orally, is greatly reduced before it reaches the system ...
effect which affects oral medications. Common sites for intramuscular injections include the
deltoid muscle The deltoid muscle is the muscle forming the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle', particularly in other animals such as the domestic cat. Anatomically, the deltoid muscle appears to be made up o ...
of the upper arm and the gluteal muscle of the buttock. In infants, the
vastus lateralis muscle The vastus lateralis (), also called the vastus externus, is the largest and most powerful part of the quadriceps femoris, a muscle in the thigh. Together with other muscles of the quadriceps group, it serves to extend the knee joint, moving the l ...
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
milliliter The litre (international spelling) or liter (American English spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metre (m3). ...
s, 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
myopathies In medicine, myopathy is a disease of the muscle in which the muscle fibers do not function properly. This results in muscular weakness. ''Myopathy'' means muscle disease (Greek : myo- ''muscle'' + patheia '' -pathy'' : ''suffering''). This mean ...
or those with trouble clotting. Intramuscular injections commonly result in pain, redness, and swelling or
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...
around the injection site. These side effects are generally mild and last no more than a few days at most. Rarely, nerves 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 abscesses 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.


Uses

Intramuscular injection is commonly used for medication administration. Medication administered in the muscle is generally quickly absorbed in the bloodstream, and avoids the first pass metabolism which occurs with oral administration. The medication may not be considered 100%
bioavailable In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. Ho ...
as it must still be absorbed from the muscle, which occurs over time. An intramuscular injection is less invasive than an intravenous injection and also generally takes less time, as the site of injection (a muscle versus a vein) is much larger. Medications administered in the muscle may also be administered as
depot injection A depot injection is a term for an injection formulation of a medication which releases slowly over time to permit less frequent administration of a medication. They are designed to increase medication adherence and consistency, especially in ...
s, which provide slow, continuous release of medicine over a longer period of time. Certain substances, including
ketamine Ketamine is a dissociative anesthetic used medically for induction and maintenance of anesthesia. It is also used as a recreational drug. It is one of the safest anesthetics, as, in contrast with opiates, ether, and propofol, it suppresses ...
, may be injected intramuscularly for
recreational Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is an essential element of human biology and psychology. Recreational activities are often done for enjoyment, amusement, or pleasur ...
purposes. Disadvantages of intramuscular administration include skill and technique required, pain from injection, anxiety or fear (especially in children), and difficulty in self-administration which limits its use in outpatient medicine.
Vaccine A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. The safety and effectiveness of vaccines has been widely studied and verified.
s, especially
inactivated vaccine An inactivated vaccine (or killed vaccine) is a vaccine consisting of virus particles, bacteria, or other pathogens that have been grown in culture and then killed to destroy disease-producing capacity. In contrast, live vaccines use pathogens ...
s, 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 antibiotics, immunoglobulin, and
hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...
s such as testosterone and
medroxyprogesterone Medroxyprogesterone (MP), is a progestin which is not used medically. A derivative, medroxyprogesterone acetate (MPA), is used as a medication in humans, and is far more widely known in comparison. ''Medroxyprogesterone'' is sometimes used as a ...
. In a case of severe allergic reaction, or
anaphylaxis Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the foll ...
, a person may use an epinephrine autoinjector to self-administer epinephrine in the muscle.


Contraindications

Because an intramuscular injection can be used to administer many types of medications, specific
contraindication In medicine, a contraindication is a condition that serves as a reason not to take a certain medical treatment due to the harm that it would cause the patient. Contraindication is the opposite of indication, which is a reason to use a certain tre ...
s depend in large part on the medication being administered. Injections of medications are necessarily more invasive than other forms of administration such as by mouth or topical and require training to perform appropriately, without which complications can arise regardless of the medication being administered. For this reason, unless there are desired differences in rate of absorption, time to onset, or other pharmacokinetic parameters in the specific situation, a less invasive form of drug administration (usually by mouth) is preferred. Intramuscular injections are generally avoided in people with low platelet count 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 A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may ...
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. 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.


Risks and complications

As an injection necessitates piercing the skin, there is a risk of infection from
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
or other organisms present in the environment or on the skin before the injection. This risk is minimized by using proper
aseptic technique Asepsis is the state of being free from disease-causing micro-organisms (such as pathogenic bacteria, viruses, pathogenic fungi, and parasites). There are two categories of asepsis: medical and surgical. The modern day notion of asepsis is deri ...
in preparing the injection and sanitizing the injection site before administration. Intramuscular injections may also cause an abscess or gangrene at the injection site, depending on the specific medication and amount administered. There is also a risk of nerve or vascular injury if a nerve or blood vessel is inadvertently hit during injection. If single-use or sterilized equipment is not used, there is the risk of transmission of infectious disease between users, or to a practitioner who inadvertently injures themselves with a used needle, termed a
needlestick injury A needlestick injury is the penetration of the skin by a hypodermic needle or other sharp object that has been in contact with blood, tissue or other body fluids before the exposure. Even though the acute physiological effects of a needlestick i ...
.


Site-specific complications

Injections into the deltoid site in the arm can result in unintentional damage to the
radial Radial is a geometric term of location which may refer to: Mathematics and Direction * Vector (geometric), a line * Radius, adjective form of * Radial distance, a directional coordinate in a polar coordinate system * Radial set * A bearing f ...
and
axillary nerve The axillary nerve or the circumflex nerve is a nerve of the human body, that originates from the brachial plexus ( upper trunk, posterior division, posterior cord) at the level of the axilla (armpit) and carries nerve fibers from C5 and C6. Th ...
s. In rare cases when not performed properly, the injection may result in shoulder dysfunction. The most frequent complications of a deltoid injection include pain, redness, and inflammation around the injection site, which are almost always mild and last only a few days at most. The dorsogluteal site of injection is associated with a higher risk of skin and tissue trauma, muscle fibrosis or contracture, hematoma, nerve
palsy Palsy is a medical term which refers to various types of paralysisDan Agin, ''More Than Genes: What Science Can Tell Us About Toxic Chemicals, Development, and the Risk to Our Children;; (2009), p. 172. or paresis, often accompanied by weakness a ...
, paralysis, and infections such as abscesses 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.


Technique

An intramuscular injection can be administered in multiple different muscles of the body. Common sites for intramuscular injection include: deltoid, dorsogluteal,
rectus femoris The rectus femoris muscle is one of the four quadriceps muscles of the human body. The others are the vastus medialis, the vastus intermedius (deep to the rectus femoris), and the vastus lateralis. All four parts of the quadriceps muscle attach ...
,
vastus lateralis The vastus lateralis (), also called the vastus externus, is the largest and most powerful part of the quadriceps femoris, a muscle in the thigh. Together with other muscles of the quadriceps group, it serves to extend the knee joint, moving the ...
and ventrogluteal muscles. Sites that are bruised, tender, red, swollen, inflamed or scarred are generally avoided. The specific medication and amount being administered will influence the decision of the specific muscle chosen for 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. Pressure or gentle massage of the muscle following injection may reduce the risk of pain.


Aspiration

Aspirating for blood to rule out injecting into a blood vessel is not recommended by the US
CDC The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
,
Public Health Agency of Canada The Public Health Agency of Canada (PHAC; french: Agence de la santé publique du Canada, ASPC) is an agency of the Government of Canada that is responsible for public health, emergency preparedness and response, and infectious and chronic dis ...
, or Norway Institute of Public Health, as the injection sites do not contain large blood vessels and aspiration results in greater pain. There is no evidence that aspiration is useful to increase safety of intramuscular injections when injecting in a site other than the dorsogluteal site. However, aspiration is recommended by the Danish Health Authority for
COVID-19 vaccines A COVID19 vaccine is a vaccine intended to provide acquired immunity against severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2), the virus that causes coronavirus disease 2019 (COVID19). Prior to the COVID19 pandemic, an est ...
to reduce the potential rare risk of blot clotting and bleeding.


Z-track method

The Z-track method is a method of administrating an IM injection that prevents the medication being tracked through the subcutaneous tissue, sealing the medication in the muscle, and minimizing irritation from the medication. Using the Z-track technique, the skin is pulled laterally, away from the injection site, before the injection; then the medication is injected, the needle is withdrawn, and the skin is released. This method can be used if the overlying tissue can be displaced.


Injection sites

The deltoid muscle in the outer portion of the upper arm is used for injections of small volume, usually equal to or less than 2 ml. This includes most intramuscular vaccinations. It is not recommended to use the deltoid for repeated injections due to its small area, which makes it difficult to space out injections from each other.The Joanna Briggs Institute. Recommended Practice. Injection: Intramuscular. The Joanna Briggs Institute EBP Database, from the JBI@Ovid database, published 2019; JBI2138. Accessed on 12 September 2020. The deltoid site is located by locating the lower edge of the
acromion process In human anatomy, the acromion (from Greek: ''akros'', "highest", ''ōmos'', "shoulder", plural: acromia) is a bony process on the scapula (shoulder blade). Together with the coracoid process it extends laterally over the shoulder joint. The acr ...
, and injecting in the area which forms an upside down triangle with its base at the acromion process and its midpoint in line with the
armpit The axilla (also, armpit, underarm or oxter) is the area on the human body directly under the shoulder joint. It includes the axillary space, an anatomical space within the shoulder girdle between the arm and the thoracic cage, bounded superior ...
. An injection into the deltoid muscle is commonly administered using a 1-inch long needle, but may use a -inch long needle for younger people or very frail elderly people. 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, sedatives and
anti-emetic An antiemetic is a drug that is effective against vomiting and nausea. Antiemetics are typically used to treat motion sickness and the side effects of opioid analgesics, general anaesthetics, and chemotherapy directed against cancer. They may b ...
s. The ventrogluteal site is located in a triangle formed by the
anterior superior iliac spine The anterior superior iliac spine (abbreviated: ASIS) is a bony projection of the iliac bone, and an important landmark of surface anatomy. It refers to the anterior extremity of the iliac crest of the pelvis. It provides attachment for the ing ...
and the
iliac crest The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superiolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the poster ...
, 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 The vastus lateralis (), also called the vastus externus, is the largest and most powerful part of the quadriceps femoris, a muscle in the thigh. Together with other muscles of the quadriceps group, it serves to extend the knee joint, moving the ...
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 In human anatomy, the thigh is the area between the hip ( pelvis) and the knee. Anatomically, it is part of the lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of ...
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 autoinjector An epinephrine autoinjector (or adrenaline autoinjector, also known by the trademark EpiPen) is a medical device for injecting a measured dose or doses of epinephrine (adrenaline) by means of autoinjector technology. It is most often used for t ...
s, which are used in the outer thigh, corresponding to the location of the vastus lateralis muscle. The dorsogluteal site of the buttock site is not routinely used due to its location near major
blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...
s and nerves, as well as having inconsistent depth of
adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular ...
. 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 Evidence-based practice (EBP) is the idea that occupational practices ought to be based on scientific evidence. While seemingly obviously desirable, the proposal has been controversial, with some arguing that results may not specialize to indiv ...
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
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
, which considers it outdated for any intramuscular injection.


Special populations

In some populations, a change in injection site, needle length, or technique is necessary. For example, in very young people or frail elderly people, a normal length needle may be too long to safely inject in the desired muscle. For this reason, in these people, a shorter needle is recommended to decrease the risk of injecting too deep. It is also recommended to consider using the anterolateral thigh as an injection site in infants under one year old. To help infants and children cooperate with injection administration, the
Advisory Committee on Immunization Practices The Advisory Committee on Immunization Practices (ACIP) is a committee within the United States Centers for Disease Control and Prevention (CDC) that provides advice and guidance on effective control of vaccine-preventable diseases in the U.S. c ...
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.


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 An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention o ...
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. Intramuscular injections began to be used for administration of vaccines for
diphtheria Diphtheria is an infection caused by the bacterium '' Corynebacterium diphtheriae''. Most infections are asymptomatic or have a mild clinical course, but in some outbreaks more than 10% of those diagnosed with the disease may die. Signs and s ...
in 1923,
whooping cough Whooping cough, also known as pertussis or the 100-day cough, is a highly contagious bacterial disease. Initial symptoms are usually similar to those of the common cold with a runny nose, fever, and mild cough, but these are followed by two or t ...
in 1926, and
tetanus Tetanus, also known as lockjaw, is a bacterial infection caused by ''Clostridium tetani'', and is characterized by muscle spasms. In the most common type, the spasms begin in the jaw and then progress to the rest of the body. Each spasm usually ...
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.


Veterinary medicine

In animals common sites for intramuscular injection include the
quadriceps The quadriceps femoris muscle (, also called the quadriceps extensor, quadriceps or quads) is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large ...
, the lumbodorsal muscles, and the triceps muscle.https://ouv.vt.edu/content/dam/ouv_vt_edu/sops/small-animal/sop-dogs-and-cats-injections.pdf


See also

* Subcutaneous injection *
Intradermal injection Intradermal injection, often abbreviated ID, is a shallow or superficial injection of a substance into the dermis, which is located between the epidermis and the hypodermis. For certain substances, administration via an ID route can result in a ...
* Intravenous injection


References


External links

*
Prevention and Control of Influenza, Recommendations of ACIP
{{Authority control Medical treatments Routes of administration Dosage forms Injection (medicine) Muscular system