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An injection (often referred to as a "shot" in US English, or a "jab" in UK English) is an infusion method of putting fluid into the body, usually with a syringe and a hollow needle which is pierced through the skin to a sufficient depth for the material to be administered into the body. An injection follows a parenteral route of administration; that is, administration via a route other than through the digestive tract.
There are several methods of injection or infusion, including intradermal, subcutaneous, intramuscular, intravenous, intraosseous, and intraperitoneal. Long-acting forms of subcutaneous/intramuscular injections are available for various drugs, and are called depot injections.
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.
Intramuscular injection 
In an intramuscular injection, the medication is delivered directly into a muscle. Many vaccines are administered intramuscularly, as are codeine, metoclopramide, and many other medications. Many drugs injected intramuscularly are absorbed into the muscle fairly quickly, while others are more gradual. Injections to the buttocks are known to reach the bloodstream quickly due to the large amount of muscular tissue and corresponding blood supply.
Generally, intramuscular injections are administered by a trained medical professional; however, prescribed self-administered intramuscular injections are becoming more common for patients who require these injections routinely.
Depot injection 
A depot injection is an injection, usually subcutaneous or intramuscular, of a pharmacological agent which releases its active compound in a consistent way over a long period of time. 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.
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. In psychiatric nursing, a short acting depot, zuclopenthixol acetate (Clopixol Acuphase), which lasts in the system from 24 – 72 hours, is now more regularly used for rapid tranquillisation.
Hypodermic injections in nature 
Various animals, and some plants, have been injecting for various reasons long before humans began doing so in a process commonly called stinging. Some examples include:
- Snakes, wasps, scorpions: poison, to kill prey and self-defense.
- Some bees: poison, to defend themselves and their nests.
- Cnidaria (jellyfish, etc.): poison, to kill prey.
- Stinging nettles: poison, to try to avoid being eaten.
Injection pain 
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.
Injection safety 
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:
1. Changing the behavior of health care workers and patients.
2. Ensuring the availability of equipment and supplies.
3. Managing waste safely and appropriately.
See also 
- Intracardiac injection
- Intraarticular injection
- Intraosseous infusion
- Dart injection
- Jet injector
- Injection port
- Needlestick injury
- Needle remover
- Safety Syringe
- "Injection safety". Health Topics A to Z. World Health Organization. Retrieved 2011-05-09.
- David Healy. Psychiatric Drugs Explained: Page 19.
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- Anesthesia and Analgesia 2004;98:343-5
- Harrison, D; Stevens B, Bueno M, Yamada J, Adams-Webber T, Beyene J, Ohlsson A. (2010). "Efficacy of sweet solutions for analgesia in infants between 1 and 12 months of age: a systematic review.". Archives of Disease in Childhood 95 (6): 406–13. doi:10.1136/adc.2009.174227. PMID 20463370.
- M.A. Miller & E. Pisani. "The cost of unsafe injections". Bulletin of the World Health Organization 77 (10): 1808–811.
- "Injection Safety, First do no harm". Advocacy brochure. World Health Organization. Retrieved 2011-05-09.
- Connor, JP; Edelson, JG (1988 Apr). "Needle tract infection. A case report.". Oral surgery, oral medicine, and oral pathology 65 (4): 401–3. PMID 3163131.
|Wikimedia Commons has media related to: Injection (medicine)|
- Information about injections from the Merck Manual
- FDA Center for Drug Evaluation and Research Data Standards Manual: Route of Administration
- Revolutions Medical Corp Retractable Syringe
- Revolutions Medical Corp RevVac™ Retracting Safety Syringe Demonstration