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Injection (often referred to as a "shot" in US English, or a "jab" in UK English) is the act of putting a liquid, especially a drug, into a person's body using a needle (usually a hypodermic needle) and a syringe. Injection is a technique for delivering drugs by parenteral administration, that is, administration via a route other than through the digestive tract. Parenteral injection includes subcutaneous, intramuscular, intravenous, intraperitoneal, intracardiac, intraarticular and intracavernous injection.
Injection is generally administered as a bolus, but can possibly be used for continuous drug administration as well. Even when administered as a bolus, the medication may be long-acting, and can then be called depot injection. Administration by an indwelling catheter is generally preferred instead of injection in case of more long-term or recurrent drug administration.
Injections are among the most common health care procedures, with at least 16 billion administered in developing and transitional countries each year. 95% of injections are administered in curative care, 3% are for immunization, and the rest for other purposes, such as blood transfusions. In some instances the term injection is used synonymously with inoculation even by different workers in the same hospital. This should not cause confusion; the focus is on what is being injected/inoculated, not the terminology of the procedure.
Since the process inherently involves a small puncture wound to the body (with varying degrees of pain depending on injection type and location, medication type, needle gauge and the skill of the individual administering the injection), fear of needles is a common phobia.
Intravenous injections involve needle insertion directly into the vein and the substance is directly delivered into the bloodstream. In medicine and drug use, this route of administration is the fastest way to get the desired effects since the medication moves immediately into blood circulation and to the rest of the body. This type of injection is the most common and often associated with drug use.
Intramuscular injections (IM injections) deliver a substance deep into a muscle, where they are quickly absorbed by blood vessels. Common injections sites include the deltoid, vastus lateralis, and ventrogluteal muscles. Most inactivated vaccines, like influenza, are given by IM injection. Some medications are formulated for IM injection, like Epinephrine autoinjectors. Medical professionals are trained to give IM injections, but patients can also be trained to self-administer medications like epinephrine.
In a subcutaneous injection, the medication is delivered to the tissues between the skin and the muscle. Absorption of the medicine is slower than that of intramuscular injection. Since the needle does not need to reach the muscles, often a bigger gauge and shorter needle is used. Usual site of administration is fat tissues behind the arm. Certain intramuscular injection medicine such as EpiPen® can also be used subcutaneously. Insulin injection is a common type of subcutaneous injection medicine. Certain vaccines including MMR (Measles, Mumps, Rubella), Varicella (Chickenpox), Zoster (Shingles) are given subcutaneously.
In an Intradermal Injection, medication is delivered directly into the dermis, the layer just below the epidermis of the skin. The injection is often given at a 5 to 15 degree angle with the needle placed almost flat against the patient's skin. Absorption takes the longest from this route compared to intravenous, intramuscular, and subcutaneous injections. Because of this, intradermal injection are often used for sensitivity tests, like tuberculin and allergy tests, and local anesthesia tests. The reactions caused by these tests are easily seen due to the location of the injections on the skin.
Common sites of intradermal injections are the forearm and lower back.
A depot injection is an injection, usually subcutaneous, intradermal, or intramuscular, that deposits a drug in a localized mass, called a depot, from which it is gradually absorbed by surrounding tissue. Such injection allows the active compound to be released in a consistent way over a long period. Depot injections are usually either solid or oil-based. Depot injections may be available as certain forms of a drug, such as decanoate salts or esters. Examples of depot injections include Depo Provera and haloperidol decanoate. Prostate cancer patients receiving hormone therapy usually get depot injections as a treatment or therapy. Zoladex is an example of a medication delivered by depot for prostate cancer treatment or therapy. Naltrexone may be administered in a monthly depot injection to control opioid abuse; in this case, the depot injection improves compliance by replacing daily pill administration.
The advantages of using a long-acting depot injection include increased medication compliance due to reduction in the frequency of dosing, as well as more consistent serum concentrations. A significant disadvantage is that the drug is not immediately reversible, since it is slowly released.
The pharmaceutical injection type of infiltration involves loading a volume of tissue with the drug, filling the interstitial space. Local anesthetics are often infiltrated into the dermis and hypodermis.
The pain of an injection may be lessened by prior application of ice or topical anesthetic, or simultaneous pinching of the skin. Recent studies suggest that forced coughing during an injection stimulates a transient rise in blood pressure which inhibits the perception of pain. Sometimes, as with an amniocentesis, a local anesthetic is given. The most common technique to reduce the pain of an injection is simply to distract the patient.
Proper needle technique and hygiene is important to avoid skin irritation and injection-site infections. A new, sterile needle should be used each time, as needles get duller and more damaged with each use and reusing needles increases risk of infection. Needles should not be shared between people, as this increases risk of transmitting blood-borne pathogens. This can lead to infections and even lifelong disease.
40% of injections worldwide are administered with unsterilized, reused syringes and needles, and in some countries this proportion is 70%, exposing millions of people to infections.
Another risk is poor collection and disposal of dirty injection equipment, which exposes healthcare workers and the community to the risk of needle stick injuries. In some countries, unsafe disposal can lead to re-sale of used equipment on the black market. Many countries have legislation or policies that mandate that healthcare professionals use a safety syringe (safety engineered needle) or alternative methods of administering medicines whenever possible.
According to one study, unsafe injections cause an estimated 1.3 million early deaths each year.
To improve injection safety, the WHO recommends:
- Changing the behavior of health care workers and patients
- Ensuring the availability of equipment and supplies
- Managing waste safely and appropriately
A needle tract infection is an infection that occurs when pathogenic micro-organisms are seeded into the tissues of the body during an injection. Such infections are also referred to as needlestick infections.
Many species of animals, and some stinging plants, have developed poison-injecting devices for self-defence or catching prey, for example:
- Venomous snakes
- Stinging insects
- Weevers (a fish)
- Sting rays
- Bloodsucking insects: some of them first inject an anticoagulant to make feeding easier
- Cnidocyte cells in the animals called cnidaria
- Stinging nettles
- Dart injection
- Jet injector
- Injection port
- Lethal injection
- Needlestick injury
- Needle remover
- Safety syringe
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