Editing Autoinjector (section)

== Design ==
[[File: Components of an Adalimumab-Humira pen - annotated.jpg|thumb|upright|Components of a [[Humira]] autoinjector pen]]

Designs exist for both [[intramuscular injection|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]].{{Citation needed|date=August 2024}} When triggered the actuator drives a three-step sequence:{{Citation needed|date=August 2024}}

# 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 gun]]s: 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.{{Citation needed|date=August 2024}}

Since spent autoinjectors contain a [[hypodermic needle]], 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 [[Sterilization (microbiology)|sterile]] but also to provide adequate sharps waste confinement after disposal.{{Citation needed|date=August 2024}}

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.{{Citation needed|date=August 2024}}