Single-use syringe

An operable single-use syringe comprising:

• a barrel having an inside surface defining a chamber for retaining fluid, an open proximal end and a distal end having a distal wall with a tip extending distally therefrom having a passageway therethrough in fluid communication with said chamber;
• a plunger rod including an elongate body portion defining a longitudinal axis, a proximal end and a distal end, a stopper at said distal end slidably positioned in fluid-tight engagement in said barrel, said body portion extending outwardly from said open proximal end of said barrel, said body portion including two parallel longitudinal slots, at least one of said slots including a plurality of inwardly facing axially spaced discontinuities;
• a locking element positioned in said barrel between said elongate body portion of said plunger rod and said inside surface of said barrel, said locking element having a proximal end, a distal end, a base and two leg members in substantially parallel relationship extending from said base into each of said longitudinal slots, said locking element having an outwardly and proximally directed distal end barb and an outwardly and proximally directed proximal end barb for engaging said inside surface of said barrel to prevent proximal motion of said locking element with respect to said barrel, said legs including at least one outwardly facing deflectable resisting element for engaging said discontinuities on said axial slot for moving said locking element in a distal direction along said inside surface when said plunger rod is advanced in a distal direction and allowing proximal motion of said plunger rod with respect to said locking element for filling said chamber.