A syringe assembly (400) configured to prevent reuse is disclosed. The syringe assembly comprises a barrel (420), plunger rod (440) and stopper (460). The plunger rod comprises a stopper engaging portion (446) and flexible protrusion (444). In use, once the stopper has reached the end of its travel in the distal direction, the plunger rod may continue travelling such that the stopper engaging portion occupies a gap in the stopper and the flexible protrusion engages an internal rib (423), thereby locking the plunger rod within the barrel. The plunger rod further includes a frangible portion (443), located on a support portion (445) and proximate the flexible protrusion. The frangible portion includes at least four point connections (see 572-575, figures 46C, 47 & 48)； whereby a first, second, third and fourth point connection are disposed adjacent to the edge of the support member. The flexible protrusion further includes four leaves (see 551-554, figures 48 & 49) disposed equidistant from each other, which provide structural reinforcement to the flexible protrusion to inhibit the flexible protrusion from flexing inwardly after the plunger rond has been locked in the barrel. The third point connection and the fourth point connection of the frangible portion are misaligned with a third and a fourth leaf. In use, once the plunger has been locked in the barrel the point connections of the frangible portion break when reuse is attempted.
