Syringe plunger system with self-locking threaded geometry

1. A plunger rod useful for supporting and sliding a stopper in a syringe barrel, the plunger rod comprising:

a first end and a second end;

the first end comprising a user-interface portion having a flange;

the second end comprising a threaded portion adapted for interconnection to a stopper;

wherein the threaded portion comprises a shaft having an external male thread and a predetermined thread geometry;

the external male thread comprising a locking element, wherein the locking element comprises a planar surface and a projection having a point, wherein the projection extends at an angle relative to the planar surface and terminates at the point, and wherein the locking element departs from a general path of the threaded portion, wherein the projection and the point extend over the external male thread, and wherein the external male thread provides enhanced pull-out resistance of the stopper; and

wherein the locking element comprises a deviation from the external male thread wherein a thread angle of the locking element is greater than a thread angle of the external male thread.

2. The plunger rod of claim 1 , wherein the external male thread comprises at least 15 threads per inch.

3. The plunger rod of claim 1 , wherein the external male thread comprises a thread pitch of between approximately 0.050 inches and 0.075 inches.

4. The plunger rod of claim 1 , wherein the plunger rod is integrally formed with at least one resin selected from the group consisting of cyclic olefin resins, radiation-resistant polypropylenes, polypropylene, polycarbonates and polystyrene.

5. The plunger rod of claim 1 , wherein the external male thread comprises a thread angle of between approximately 5.0 and 10.0 degrees and the locking element comprises a thread angle of between approximately 15.0 and 25.0 degrees.

6. The plunger rod of claim 1 , wherein the locking element comprises a thread angle of between approximately 18.0 and 20.0 degrees.

7. The plunger rod of claim 1 , wherein the external male thread comprises a thread angle of between approximately 7.0 and 8.0 degrees.

8. A plunger rod useful for supporting and sliding a stopper in a syringe barrel, the plunger rod comprising:

a first end and a second end;

the first end comprising a user-interface portion;

the second end comprising a threaded portion adapted for interconnection to a stopper;

wherein the threaded portion comprises an external male thread and a predetermined thread geometry having a first thread angle;

the external male thread comprising a locking element, wherein the locking element comprises a planar surface and at least one projection departing from a general path of the threaded portion, the projection comprising a second thread angle and terminating at a point and wherein the second thread angle is greater than the first thread angle;

wherein the projection and the point extend over a portion of the external male thread;

wherein the point is operable to extend at least partially into a stopper in an assembled state;

wherein the locking element permits threaded insertion of the external male thread into a stopper by rotation in a first direction and inhibits a reverse rotation, and wherein the external male thread provides enhanced pull-out resistance of the stopper, and wherein removal of the stopper from the plunger rod by rotation is inhibited by the locking element.

9. The plunger rod of claim 8 , wherein said threaded portion comprises a thread pitch of between approximately 0.050 inches and 0.075 inches.

10. The plunger rod of claim 8 , wherein the plunger rod comprises a length of between approximately 0.50 inches and 1.00 inches.

11. The plunger rod of claim 8 , wherein the second thread angle comprises a thread angle of between approximately 18.0 and 20.0 degrees.

12. The plunger rod of claim 8 , wherein the first thread angle comprises a thread angle of between approximately 7.0 and 8.0 degrees.

13. The plunger rod of claim 8 , further comprising a stopper provided in force-transmitting communication with the external male thread.

14. The plunger rod of claim 13 , further comprising a syringe having a barrel, and wherein the plunger rod and the stopper are provided within the barrel and comprise selectively removable elements relative to the syringe.

15. A syringe including a barrel, a plunger rod, and a stopper, the plunger rod comprising:

a first end and a second end;

the first end comprising a user-interface portion;

the second end comprising a threaded portion;

wherein the threaded portion comprises an external male thread and a predetermined thread geometry having a first thread angle;

a stopper connected to the second end of the plunger rod;

the external male thread comprising a locking element, wherein the locking element comprises a planar surface and at least one projection extending at an angle relative to the planar surface, and wherein the at least one projection departs from a general path of a pitch of the threaded portion, the projection comprising a second thread angle and a point, the projection and point extending over a portion of the external male thread;

wherein the second thread angle is greater than the first thread angle; and

wherein the point extends at least partially into the stopper, the plunger rod provides enhanced pull-out resistance of the stopper, and a removal rotation of the plunger rod is operable to force the locking element further into the stopper.

16. The syringe of claim 15 , wherein the plunger rod comprises right-handed threads operable to be inserted into the stopper by a clockwise rotation.

17. The syringe of claim 16 , wherein the locking element opposes a counter-clockwise rotation and enables a clockwise rotation.

18. The syringe of claim 15 , wherein the syringe comprises a pre-filled syringe.

19. The syringe of claim 18 , wherein the syringe comprises leuprolide acetate.