Drug cartridge, drug injection device, and drug injection system

A drug cartridge comprising:

• a pre-filled syringe including a drug, a syringe barrel having a syringe columnar space in which the drug is arranged and a syringe opening located at one end of the syringe columnar space, an injection needle located on an opposite side of the syringe barrel from the syringe opening and being in communication with the syringe columnar space, a stopper movable in the syringe columnar space and arranged on the syringe opening side, and a needle shield that covers a tip of the injection needle and is removable;
• a cassette outer sheath including a cassette front opening, a cassette rear opening and a cassette columnar space located between the cassette rear opening and the cassette front opening, wherein the cassette outer sheath holds the pre-filled syringe in the cassette columnar space so that a part of the injection needle and a part of the needle shield protrude from the cassette front opening;
• a cap mated with the needle shield and fitted into the cassette front opening so as to cover the needle shield, wherein the cap is removable from the cassette outer sheath together with the needle shield;
• a needle guard including a guard portion and movable in an axis direction of the cassette columnar space in the cassette columnar space, wherein the needle guard is movable between a first engagement position and a second engagement position, wherein in the first engagement position, a front end of the guard portion is further backward than the tip of the injection needle protruding from the cassette front opening, and in the second engagement position, the front end of the guard portion protrudes from the tip of the injection needle protruding from the cassette front opening where the cap is detached;
• a sleeve movable in the axis direction in the cassette columnar space between a first position located on the cassette rear opening side and a second position located on the cassette front opening side relative to the first position, wherein the sleeve is engaged with the cassette outer sheath in the first position;
• and
• a cassette spring that biases the needle guard toward the cassette front opening,
• wherein when the cap is fitted into the cassette front opening, the cap is capable of assuming a locked state where the cap cannot be detached from the cassette outer sheath and an unlocked state where the cap can be detached from the cassette outer sheath, and the needle guard is in contact with the cap and is located in the first engagement position against a biasing force of the cassette spring, where the cap is fitted into the cassette front opening and the sleeve is in the first position, the cap is locked;
• and,
• where the cap is fitted into the cassette front opening and the sleeve is in the second position, the sleeve renders the cap in an unlocked state and the needle guard in a locked state in which the needle guard is unmovable in the first engagement position.