A syringe assembly (100, 400, 500) comprising: a barrel including a cylindrical sidewall having an interior surface with a first cross-sectional width defining a chamber (428, 528) for retaining fluid, an open proximal end and a distal end including a distal wall having an opening therethrough in fluid communication with said chamber (428, 528), said sidewall including a rib adjacent said proximal end defining a second cross-sectional width that is less than the first cross-sectional width; an elongate plunger rod including a proximal end, a distal end, and a main body extending between the proximal and distal end, the plunger rod being distally and proximally movable within said chamber (428, 528), the proximal end including a thumb press, the distal end including a stopper-engaging portion, the plunger rod further including a flexible protrusion between the thumb press and the main body, the protrusion having a cross-sectional width greater than the cross-sectional width of the barrel at the rib and the plunger rod further including a support member; a stopper having a proximal end and a distal end, the stopper attached to the stopper-engaging portion of the plunger rod such that when the distal end of the stopper is in contact with the distal wall of the barrel, the flexible protrusion is permitted to advance distally past the rib in the barrel and lock the plunger rod in the barrel to prevent reuse of the syringe assembly; and a gap between the distal end of the stopper and the distal wall of the barrel prior to an injection cycle characterized by the support member including an outer edge disposed proximally adjacent to the flexible protrusion and at least one frangible portion comprising disposed proximally adjacent to the support member and comprising four point connections which are disposed adjacent to the edge of the support member, the four point connections being disposed in a staggered pattern. a barrel including a cylindrical sidewall having an interior surface with a first cross-sectional width defining a chamber (428, 528) for retaining fluid, an open proximal end and a distal end including a distal wall having an opening therethrough in fluid communication with said chamber (428, 528), said sidewall including a rib adjacent said proximal end defining a second cross-sectional width that is less than the first cross-sectional width; an elongate plunger rod including a proximal end, a distal end, and a main body extending between the proximal and distal end, the plunger rod being distally and proximally movable within said chamber (428, 528), the proximal end including a thumb press, the distal end including a stopper-engaging portion, the plunger rod further including a flexible protrusion between the thumb press and the main body, the protrusion having a cross-sectional width greater than the cross-sectional width of the barrel at the rib and the plunger rod further including a support member; a stopper having a proximal end and a distal end, the stopper attached to the stopper-engaging portion of the plunger rod such that when the distal end of the stopper is in contact with the distal wall of the barrel, the flexible protrusion is permitted to advance distally past the rib in the barrel and lock the plunger rod in the barrel to prevent reuse of the syringe assembly; and a gap between the distal end of the stopper and the distal wall of the barrel prior to an injection cycle characterized by the support member including an outer edge disposed proximally adjacent to the flexible protrusion and at least one frangible portion comprising disposed proximally adjacent to the support member and comprising four point connections which are disposed adjacent to the edge of the support member, the four point connections being disposed in a staggered pattern.