Single-use syringe

An operable single-use syringe comprising:

• an elongate cannula made of thermoplastic material, said cannula having an outside surface, a proximal end, a distal end and a lumen therethrough defining a longitudinal axis, said outside surface at said proximal end including at least one discontinuity, said distal end having a stopper piercing tip;
• a thermoplastic 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, said tip being formed in intimate contact around the proximal end of said cannula engaging said at least one discontinuity so that said lumen is in fluid communication with said chamber, said cannula projecting distally from said distal wall for a distance of at least 23 mm (0.9 inch), said thermoplastic material of said cannula having a higher flexural modulus than said thermoplastic material of said barrel;
• 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, each of said slots including a plurality of axially spaced discontinuities;
• and
• 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 two outwardly and distally directed distal end barbs and two outwardly and distally directed proximal end barbs for engaging said inside surface of said barrel to prevent proximal motion of said locking element with respect to said barrel, said legs each including a deflectable proximal resisting element for engaging said discontinuities on said longitudinal slots 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 drawing fluid into said chamber.