An autoinjector (or auto-injector) is a
medical device
A medical device is any device intended to be used for medical purposes. Significant potential for hazards are inherent when using a device for medical purposes and thus medical devices must be proved safe and effective with reasonable assura ...
designed to deliver a
dose
Dose or Dosage may refer to:
Music
* ''Dose'' (Gov't Mule album), 1998
* ''Dose'' (Latin Playboys album)
* ''Dosage'' (album), by the band Collective Soul
* "Dose" (song), a 2018 song by Ciara
* "Dose", song by Filter from the album '' Short ...
of a particular
drug
A drug is any chemical substance that causes a change in an organism's physiology or psychology when consumed. Drugs are typically distinguished from food and substances that provide nutritional support. Consumption of drugs can be via insuffla ...
. The injectors were initially designed to overcome the hesitation associated with self-administration of the needle-based
drug delivery device
Drug delivery refers to approaches, formulations, manufacturing techniques, storage systems, and technologies involved in transporting a pharmaceutical compound to its target site to achieve a desired therapeutic effect. Principles related to d ...
.
Most autoinjectors are one-use,
disposable,
spring
Spring(s) may refer to:
Common uses
* Spring (season), a season of the year
* Spring (device), a mechanical device that stores energy
* Spring (hydrology), a natural source of water
* Spring (mathematics), a geometric surface in the shape of a ...
-loaded
syringe
A syringe is a simple reciprocating pump consisting of a plunger (though in modern syringes, it is actually a piston) that fits tightly within a cylindrical tube called a barrel. The plunger can be linearly pulled and pushed along the inside ...
s (prefilled syringes). By design, autoinjectors are easy to use and are intended for self-administration by patients, or administration by untrained personnel. The site of injection depends on the drug loaded, but it typically is administered into the
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 bone ...
or the
buttocks.
Autoinjectors are
sharps waste.
History
Automatic syringes are known since 1910s, and many spring-loaded devices with needle protectors were patented in the first half of the 20th century, but it was not until 1970s when they became economically feasible to mass-produce (simple
syrette
A syrette is a device for injecting liquid through a needle. It is similar to a syringe except that it has a closed flexible tube (like that typically used for toothpaste) instead of a rigid tube and piston. It was developed by the Pharmaceutic ...
s were used instead before).
Design
![Components of an Adalimumab-Humira pen - annotated](https://upload.wikimedia.org/wikipedia/commons/0/03/Components_of_an_Adalimumab-Humira_pen_-_annotated.jpg)
Designs exist for both
intramuscular
Intramuscular injection, often abbreviated IM, is the injection of a substance into a muscle. In medicine, it is one of several methods for parenteral administration of medications. Intramuscular injection may be preferred because muscles have l ...
and
subcutaneous injection
Subcutaneous administration is the insertion of medications beneath the skin either by injection or infusion.
A subcutaneous injection is administered as a bolus into the subcutis, the layer of skin directly below the dermis and epidermis, ...
. Disposable autoinjectors commonly use a pre-loaded spring as a power source. This spring and the associated mechanical components form a one-shot
linear actuator. When triggered the actuator drives a three-step sequence:
# accelerate the syringe forward, puncturing the injection site
# actuate the piston of the syringe, injecting the drug
# deploy a shield to cover the needle
Some injectors are triggered by simply pushing the nose ring against the injection site. In these designs, the protective cap is the primary safety. Other designs use a safety mechanism similar to
nail guns: The injection is triggered by pushing the nose ring against the injection site and simultaneously, while applying pressure, pushing a trigger button at the rear end of the device.
Since spent autoinjectors contain a
hypodermic needle
A hypodermic needle (from Greek ὑπο- (''hypo-'' = under), and δέρμα (''derma'' = skin)), one of a category of medical tools which enter the skin, called sharps, is a very thin, hollow tube with one sharp tip. It is commonly used w ...
, they pose a potential biohazard to waste management workers. Hence the protective cap is designed not only to protect the drug and keep the needle
sterile
Sterile or sterility may refer to:
*Asepsis, a state of being free from biological contaminants
* Sterile (archaeology), a sediment deposit which contains no evidence of human activity
*Sterilization (microbiology), any process that eliminates or ...
but also to provide adequate sharps waste confinement after disposal.
Injectors intended for application through layers of clothing may feature an adjustable injection depth. Other typical features include: A drug inspection window, a color-coded spent indicator, and an audible click after the injection has finished
Uses
![AutoinjectorMarkI](https://upload.wikimedia.org/wikipedia/commons/c/c6/AutoinjectorMarkI.jpg)
*
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 th ...
s are often prescribed to people who are at risk for
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 follow ...
. Brand names include Anapen, EpiPen, Emerade, and Auvi-Q.
* Rebiject,
Rebiject II
Interferon beta-1a (also interferon beta 1-alpha) is a cytokine in the interferon family used to treat multiple sclerosis (MS). It is produced by mammalian cells, while interferon beta-1b is produced in modified '' E. coli''. Some research indi ...
and Rebidose autoinjectors for
Rebif
Interferon beta-1a (also interferon beta 1-alpha) is a cytokine in the interferon family used to treat multiple sclerosis (MS). It is produced by mammalian cells, while interferon beta-1b is produced in modified '' E. coli''. Some research indic ...
, the drug for
interferon beta-1a
Interferon beta-1a (also interferon beta 1-alpha) is a cytokine in the interferon family used to treat multiple sclerosis (MS). It is produced by mammalian cells, while interferon beta-1b is produced in modified '' E. coli''. Some research indic ...
used to treat
multiple sclerosis
Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...
. An autoinjector for the
Avonex
Interferon beta-1a (also interferon beta 1-alpha) is a cytokine in the interferon family used to treat multiple sclerosis (MS). It is produced by mammalian cells, while interferon beta-1b is produced in modified '' E. coli''. Some research indic ...
version of this same medication is also on the market.
* SureClick autoinjector is a combination product for drugs
Enbrel or
Aranesp to treat
rheumatoid arthritis
Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are involv ...
or
anemia
Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, th ...
, respectively.
*
Subcutaneous sumatriptan
Sumatriptan, sold commonly under brand names Imitrex and Treximet among others, is a medication used to treat migraine headaches and cluster headaches. It is taken orally, intranasally, or by subcutaneous injection. Therapeutic effects gen ...
autoinjectors are used to terminate
cluster headache attacks.
* Naloxone autoinjectors are being developed and prescribed to recreational opioid users to counteract the deadly affects of opioid overdos
Military uses include:
* Autoinjectors are often used in the military to protect personnel from
chemical warfare
Chemical warfare (CW) involves using the toxic properties of chemical substances as weapons. This type of warfare is distinct from nuclear warfare, biological warfare and radiological warfare, which together make up CBRN, the military acronym ...
agents. In the
U.S. military
The United States Armed Forces are the military forces of the United States. The armed forces consists of six service branches: the Army, Marine Corps, Navy, Air Force, Space Force, and Coast Guard. The president of the United States is the ...
,
atropine
Atropine is a tropane alkaloid and anticholinergic medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate, and to decrease saliva production during surgery. It is typically given i ...
and 2-PAM-Cl (
pralidoxime chloride
Pralidoxime (2-pyridine aldoxime methyl chloride) or 2-PAM, usually as the chloride or iodide salts, belongs to a family of compounds called oximes that bind to organophosphate-inactivated acetylcholinesterase. It is used to treat organophosph ...
) are used for
first aid
First aid is the first and immediate assistance given to any person with either a minor or serious illness or injury, with care provided to preserve life, prevent the condition from worsening, or to promote recovery. It includes initial in ...
("buddy aid" or "self aid") against
nerve agents
Nerve agents, sometimes also called nerve gases, are a class of organic chemicals that disrupt the mechanisms by which nerves transfer messages to organs. The disruption is caused by the blocking of acetylcholinesterase (AChE), an enzyme that ...
. An issue item, the
Mark I NAAK
In the United States military, the Mark I NAAK, or MARK I Kit, ("Nerve Agent Antidote Kit") is a dual-chamber autoinjector: Two anti-nerve agent drugs— atropine sulfate and pralidoxime chloride—each in injectable form, constitute the kit. T ...
(Nerve Agent Antidote Kit), provides these drugs in the form of two separate autoinjectors. A newer model, the
ATNAA (Antidote Treatment Nerve Agent Auto-Injector), has both drugs in one syringe, allowing for the simplification of administration procedures. In the
Gulf War
The Gulf War was a 1990–1991 armed campaign waged by a 35-country military coalition in response to the Iraqi invasion of Kuwait. Spearheaded by the United States, the coalition's efforts against Iraq were carried out in two key phases: ...
, accidental and unnecessary use of
atropine
Atropine is a tropane alkaloid and anticholinergic medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate, and to decrease saliva production during surgery. It is typically given i ...
autoinjectors supplied to
Israel
Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...
i civilians proved to be a major medical problem.
* In concert with the
Mark I NAAK
In the United States military, the Mark I NAAK, or MARK I Kit, ("Nerve Agent Antidote Kit") is a dual-chamber autoinjector: Two anti-nerve agent drugs— atropine sulfate and pralidoxime chloride—each in injectable form, constitute the kit. T ...
,
diazepam (''
Valium'') autoinjectors, known as
CANA, are carried by US service members.
Variants
Another design has a shape and size of a
smartphone
A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, whic ...
which can be put into a pocket. This design also has a retractable needle and automated voice instructions to assist the users on how to correctly use the autoinjector. The "Auvi-Q" epinephrine autoinjector uses this design.
A newer variant of the autoinjector is the gas
jet autoinjector, which contains a cylinder of pressurized gas and propels a fine jet of liquid through the skin without using a needle. This has the advantage that patients who fear needles are more accepting of using these devices. The autoinjector can be reloaded, and various doses or different drugs can be used, although the only widespread application to date has been for the administration of
insulin
Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism o ...
in the treatment of
diabetes
Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...
.
2
See also
* Syrette
A syrette is a device for injecting liquid through a needle. It is similar to a syringe except that it has a closed flexible tube (like that typically used for toothpaste) instead of a rigid tube and piston. It was developed by the Pharmaceutic ...
References
{{Dosage forms, state=expanded
Medical equipment
Drug delivery devices