Tamper Resistant Syringe Cap

This invention relates to medical equipment, and particularly to a closure for preventing tampering with a filled syringe or the like.

In a hospital, after a pharmacist has filled a syringe with a medication, the syringe is then carried to the patient. Particularly when the contents of the syringe are a narcotic such as morphine, there is a risk that the person in custody of the syringe during transportation may withdraw its contents for his or her own purposes, perhaps then refilling the syringe with another liquid such as saline, and recapping the syringe to escape detection.

This invention is intended to prevent or at least impede tampering during transportation, and provides a readily noticeable indication of tampering. More generally, an object of the invention is to prevent contamination of syringes and their contents, by barring access to their outlet ports.

Another object of the invention is to enable one to screw a sealing cap onto the end of a syringe or the like, yet to prevent the cap from being unscrewed surreptitiously.

A related object is to simplify the manufacture, and reduce the costs, of a tamper-evident syringe cap.

These and other objects are attained by a tamper-resistant closure for a medical injection device such as a syringe, the closure including a cap having both a blind bore sized to receive and seat tightly against the syringe tip, to prevent material from entering or being withdrawn from the device. The cap has a threaded connection to the syringe tip, and is entirely covered by a loose-fitting shield having a one-way drive mechanism which prevents the cap from being unscrewed from the injection device while the shield is in place. The shield has at least one internal, frangible tang protruding obliquely into the envelope of the cap, so that the shield and cap can be easily assembled, but cannot thereafter be disassembled without breaking the tang and thus providing an indication of tampering.

In the accompanying drawings,

FIG. 1 is an exploded isometric view of a syringe, and of a closure for the syringe embodying the invention;

FIG. 2 is an end view, taken in the direction 2--2 in FIG. 1, of the shield portion of the invention;

FIG. 3 is a sectional view, taken along the axial plane 3--3 in FIG. 2, showing both the shield, and the cap in its installed position;

FIG. 4 is a side elevation of the cap alone; and

FIG. 5 is an end view of the cap, viewed in the direction of FIG. 2.

FIG. 6 is an exploded view corresponding to FIG. 1, showing an alternative form of the invention.

The invention is embodied in an assembly comprising a syringe 10 including a barrel 12 and a plunger 14 telescopically received therein. A resilient piston 16 affixed at the distal end of the plunger has at least one sealing lip 18 (two are preferred) slightly compressed by the barrel, to prevent leakage around the piston. The proximal end of the plunger has and enlarged head 20 for engaging the thumb. A skirt or flange 24 at the proximal end of the barrel provides a finger hold.

A female lock 26 is provided around the slightly tapered tip 28 of the syringe. It may be molded with the syringe, and formed separately and then affixed to the syringe by ultrasonic welding or other secure methods. The luer lock comprises a tubular skirt 30 having internal, double-lead, right-hand helical threads 32 whose internal diameter substantially exceeds the outside diameter of the tip, so that an annular volume 34 is left between the threads and the tip.

To prevent contamination of the syringe interior, via the nozzle, a cap 36 is provided. The cap has a central blind bore 38 (FIGS. 3 and 5) of uniform diameter which fits over the nozzle, seating tightly against it when the nozzle is inserted sufficiently far into the bore, short of the bottom of the bore. A enlarged collar 40 extends around the center of the cap. The proximal end 42 of the cap has a reduced diameter, and two lugs 44 extend from opposite sides of the proximal end. These lugs are sized to engage the internal threads on the luer lock, serving as male threads.

The distal end 46 of the cap also has a reduced diameter, except for a thin peripheral flange 48 having a diameter slightly less than that of the collar. The distal end terminals at a short, flat blade 50 arranged along a diameter of the cap.

To prevent people from unscrewing the cap, a shield 52 is installed over it. The shield has a tubular shell 54 slightly larger, in length and diameter, than the cap, so that the whole cap can fit loosely within the shield. The proximal end of the shield is open, while the distal end is closed by a square plate 56 perpendicular to the axis of the shell, and formed integrally with it.

Inside the shield, two protruding ramps 58 (FIGS. 2-3) are formed on the plate surface, astride the axis. Each ramp has a leading edge parallel to the axis (that is, perpendicular to the plate surface), and a trailing edge forming an acute angle with the plate surface. This angle should be less than the angle of repose between the materials of the shield and cap, respectively. An angle of about 30.degree. is now preferred. The protrusions are spaced apart sufficiently, so that the cap blade 50 just spans them.

Three equally spaced semi-circular openings 60 extend through the plate. The flat edge of each opening is just outside the inside diameter of the shell 54. Each of the openings is formed during manufacture, as corresponding core pins, used to form the frangible tangs 62, are withdrawn. Each of the core pins (not shown) has a semi-cylindrical distal portion beveled at an angles corresponding to that of the tangs; the forward tip surface is provided with a recess, which forms the tang integrally with the shell 54.

Each tang 62 protrudes toward the axis of the shell, but obliquely, so that each tang, if extended, would meet the surface of the plate near its center. Tangs having a rectangular cross-section measuring 0.031 inch in the tangential direction by 0.018 have been found to perform well. The preferred inclination is 45.degree. from the axial direction, to ensure complete breakage.

As shown in FIG. 1, a slot 64 may be formed in the shield plate; the slot has lateral dimensions at least equal to those of the cap blade, whereby, once the shield has been removed, it can be used as a screwdriver for unscrewing the cap.

Each of the components of this invention is preferably formed by injection molding from thermoplastic material. The presently preferred material for the cap is polypropylene, because of its chemical compatibility and acceptability for pharmaceutical use. The shield material, on the other hand, is selected more for its mechanical characteristics, especially for its ability to produce reliable tang breakage, yet have good strength and moldability. An acrylic plastic is presently preferred, although a high-impact polystyrene is considered as an alternative.

In use, the cap and shield will normally have been pre-assembled by pushing them together until the tangs hook behind the peripheral flange of the cap. A pharmacist, having filled the syringe with a medication or other fluid, then threads the cap onto the end of the syringe, to seal off the outlet port, and prevent fluid loss and contamination, by turning the shield clockwise while the one-way drive members are engaged. Now, because the shield completely encloses the cap, the cap cannot be unscrewed directly; nor can it be turned by rotating the shield, because of the one-way driving connection between the shield and the cap. The only way the cap can be removed, to get at the contents of the syringe, it to remove the shield forcibly by pulling it off the cap. The tangs are unavoidably broken by such removal, and the fact that the shield no longer is retained on the cap, once the tangs are broken, makes tampering evident. Noticeability is improved if the cap and shield have greatly different coloration. Furthermore, we have found it advantageous to choose a transparent material for the shield, to facilitate inspection of the underlying cap.

The foregoing is a description of the best mode of practicing the invention now contemplated by the inventor. Some variations are presently contemplated as well. For example, one could reverse male and female luer locks, as shown in FIG. 6. This variation is useful where the injection device is not a syringe, but rather an injection port in a fluid infusion line, for example.

Since the invention is subject to other modifications and variations, it is intended that the foregoing description and the accompanying drawings shall be interpreted as illustrative of only one form of the invention. Such variations not presently contemplated may be suggested by this invention and within the scope of the following claims.