US Patent 7004929 Safety pre-filled cartridge injector

A device is provided for injecting fluid from a pre-filled cartridge. The device includes a needle and a hollow barrel that holds a pre-filled cartridge. A needle retainer releasably retains the needle in an extended position so the needle can be inserted into a patient. A plunger in the rear of the barrel cooperates with the cartridge to expel fluid from the cartridge during an injection. After an injection, the needle is automatically retracted into the barrel when pressure is released from the plunger. A locking mechanism locks the contaminated needle and cartridge in the barrel after needle retraction. After use, the device may be safely disposed of in a sharps container.