Abstract: A single-use syringe having a barrel and a plunger is provided. The plunger at least one vane, and the vane is provided with serrations or ratchet teeth. The serrations each have a vertical rear wall and a sloped top edge. A barbed clip is provided that fits on the serrated vane. The barbs on the clip engage the inner wall of the barrel. When the plunger is initially withdrawn, the barbs of the clip engage the inner wall of the barrel and the clip remains in position with respect to the barrel. Because the tops of the serrations are sloped, the ridged/serrated vane of the plunger passes easily under the clip. When the plunger is re-inserted into the barrel, the clip engages one of the vertical rear walls of the serrations and moves along with the plunger deeper into the barrel. If one attempts to re-retract the plunger, the distal wall of the plunger strikes the clip, and the clip is immobilized because the barbs engage the inner wall of the barrel.

Abstract: This invention is a single-use syringe (10) having a rd-like plunger (14) and made with a plurality of frusto-conical or bead-like ratchet teeth (28). A radially resilient, spring locking clip (40) dangles on the ratchet portion of the plunger. The location of the clip determines the maximum dosage which can be administered by the syringe. Aspirating gaps (114) can be provided on the plunger rod to allow selective aspiration prior to loading and dispensing medication. In use, a first withdrawal of the plunger with respect to the barrel (12) allows, for aspiration, then medication can be drawn into the cavity of the barrel since the cam tooth (83) of the locking spring clip glides, by radial flexing, over the surface of the ratchet teeth and, yet, the locking spring is maintained in relative position along the barrel by outwardly directed contact points embedding into the interior sidewall of the barrel.

Abstract: An economical hypodermic syringe is provided. A retractable needle head is provided to slide along longitudinal grooves in the barrel of the syringe. Notches in the grooves engage teeth provided on tabs of the needle head, and lock the needle head in a predetermined position. The tabs are resilient, and if squeezed against the resilient bias, will disengage from the notches in the grooves. In this way, the needle may be partially or fully withdrawn into the barrel. In addition or alternatively, a needle cover is included which is adapted to serve as the plunger of the syringe. The outer diameter of the needle cover is narrower than the inner diameter of both the barrel and an ampoule.

Abstract: A single use syringe is provided having a rod-like plunger comprising a plurality of cylindrical ratchet teeth. A resilient locking spring dangles on the ratchet teeth of the plunger. The original location of the locking spring determines the maximum dosage which may be administered by the syringe. A first withdrawal of the plunger with respect to the barrel allows medication to be drawn into the barrel. The tab of the locking spring resiliently cams over the surface of the ratchet teeth. The locking spring is maintained in position along the barrel by outwardly directed contact points which embed into the interior side wall of the barrel. During administration of the medication, i.e., when the plunger is distally pushed with respect to the barrel, the locking spring tab cooperates with the base of the ratchet teeth and causes the spring to move along with the plunger. A second attempted withdrawal of the plunger is blocked once the locking spring has been moved to its full distal position.