A syringe assembly comprising: a barrel (120) including a cylindrical side wall (110) having an interior surface (126) defining a chamber (128) for retaining fluid, an open proximal end (129), and an open end Distal (121) including a distal wall (122) having an opening (111) therethrough in fluid communication with said chamber (128), chamber (128) further having a first internal diameter, a rib (123) adjacent to the open proximal end (129) having a second internal diameter, wherein the second internal diameter is less than the first internal diameter, a region of increased diameter located proximally from the locking rib (123) having a third internal diameter greater than the first and second internal diameters, and a diameter transition region (127) extending between the locking rib (123) and the increased diameter region； an elongated plunger stem (140) including a proximal end (149), a distal end (141), a plug engaging portion (146) located at the distal end (141) of the plunger stem (140), a thumb rest (142) on the proximal end (149) of the plunger stem (140), a main body portion (148) extending between the proximal and distal ends of the plunger stem (140), a protrusion (144 ) annular radially extending from the plunger stem (140) having an outer diameter greater than the second inner diameter of the plunger stem (140) further including at least one brittle portion (143)； a plug (160) having a proximal end (169) and a distal end (161), the plug (160) attached to the plug-engaging portion (146) of the plunger stem (140), the plug (160 ) distally and proximally movable relative to the plug engaging portion (146) for a preselected axial distance such that when the distal end (161) of the plug (160) is in contact with the distal wall (122) of the cylinder ( 120), the annular protrusion (144) is allowed to advance distally past the locking rib (123) in the cylinder (120) and lock the plunger rod (140) in the cylinder (120) to prevent reuse of the syringe assembly,
