Medicine:Autoinjector

An autoinjector (or auto-injector) is a medical device for injection of a premeasured dose of a particular drug. Most autoinjectors are one-use, disposable, spring-loaded syringes (prefilled syringes). By design, autoinjectors are easy to use and are intended for self-administration by patients, administration by untrained personnel, or easy use by healthcare professionals; they can also overcome the hesitation associated with self-administration using a needle. The site of injection depends on the drug, but it typically is administered into the thigh or the buttocks.

History

Automatic syringes are known since the 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 syrettes were used instead before). In 2023 an open source autoinjector was developed that could be digitally replicated with a low cost desktop 3D printer. It was tested against the then current standard (ISO 11608–1:2022) for needle-based injection systems and found to cost less than mass manufactured systems.

Design

Components of a Humira autoinjector pen

Designs exist for both intramuscular and subcutaneous injection. 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:{{Citation needed|date=August 2024}

1. accelerate the syringe forward, puncturing the injection site
2. actuate the piston of the syringe, injecting the drug
3. deploy a shield to cover the needle

Uses

A variety of autoinjectors in use with the US Armed Forces

• Subcutaneous sumatriptan autoinjectors are used to terminate cluster headache attacks.
• Naloxone autoinjectors are being developed and prescribed to recreational opioid users to counteract the deadly effects of opioid overdose.[1]

Military uses include:

• Autoinjectors are often used in the military to protect personnel from chemical warfare agents. In the U.S. military, atropine and 2-PAM-Cl (pralidoxime chloride) are used for first aid ("buddy aid" or "self aid") against nerve agents. An issue item, the Mark I NAAK (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, accidental and unnecessary use of atropine autoinjectors supplied to Israeli civilians proved to be a major medical problem.

Variants

File:Auvi-Q Injection.webm

Another design has a shape and size of a smartphone 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 in the treatment of diabetes.

See also

• Syrette
• Injector pen