Single use retractable needle syringe

Claim 1

In a syringe containing (1) a barrel having an elongated cavity, a longitudinal axis through the elongated cavity, an open proximal end, a distal end, an inner wall surface, and an outer wall surface and (2) a plunger capable of moving reciprocally and axially in the barrel, having an outer wall surface adapted to slidably engage the inner wall surface of the barrel, a proximal end, and a distal end, the improvement consisting essentially of: a) a needle assembly removably mounted on the distal end of the barrel, which needle assembly has a lateral surface, a proximal end, a distal end, and a central channel, b) the proximal end of the needle assembly and the distal end of the plunger have a corresponding engaging means selected from the group consisting of corresponding raised ring and recessed band, threads, a friction fit provided by corresponding male and female tapers, and corresponding raised tab and recessed tab wherein the engaging means of the plunger can fixedly engage the engaging means of the needle assembly so that, following engagement, when the plunger is retracted toward the proximal end of the barrel, the needle assembly is separated from the distal end of the barrel and retracted into the barrel, and c) corresponding engaging means situated on 1) the lateral surface of the needle assembly or 2) the outer wall surface of the plunger at the distal end of the plunger and the inner surface of the barrel near the proximal end of the barrel such that when the needle assembly is retracted inside the barrel, the needle assembly cannot be withdrawn from the proximal end of the barrel, but becomes locked to the inner surface of the barrel near the proximal end thereof.