Reuse prevention flush syringe

A syringe comprising:

• a barrel having a first end and a second end positioned opposite from the first end, the barrel defining an interior space;
• a stopper positioned within the interior space, the stopper is moveable within the interior space relative to the barrel;
• a plunger connected to the stopper;
• and
• a collar comprising threads configured to engage corresponding threads of a medical connector, the collar at least partially received by the barrel, one of the barrel and the collar defining a slot and the other of the barrel and the collar comprising a pin received within the slot, wherein the collar has a connection position where the collar is fixed relative to the barrel when the syringe is being connected to the medical connector, a disconnection position where the collar is fixed relative to the barrel when the syringe is being disconnected from the medical connector, and a reuse prevention position wherein the collar is axially spaced from the first end of the barrel to prevent the threads of the collar from engaging with the threads of the medical connector.