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: 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.