Single-use syringe.

0001The present invention is a syringe of a type intended for disposal after it has been used to deliver a single injection.

0002A range of syringes have been developed over recent years in which one or more parts of the syringe assembly are designed to be discarded after use. Thus the hypodermic needle itself, usually contained within a protective sheath or guard, may alone be discarded or the syringe assembly overall may be formed of a relatively cheap material allowing its complete disposal after a single use.

0003The original purpose of such developments was to obviate the need to clean and re-sterilise such equipment and thus to avoid the danger of inadequately re-sterilised devices inadvertently being used on subsequent patients. However, more recently, it has been recognised that medical syringes discarded after legitimate use may be retrieved for subsequent illicit use, for example for self-injection by drug users. The emphasis has therefore switched from designing syringes which are merely disposable to producing syringes which subsequent re-use is positively prevented.

0004One approach to designing a non-reusable syringe has been to devise a syringe in which the plunger is captured within the syringe barrel after use, so that withdrawal of the plunger in order to refill the syringe is made very difficult. See, for example, UK Patent Specification No. 2184657. However such an approach has not been adapted for syringes of the type which are designed to receive a pre-filled ampoule containing the material to be injected. In addition, this approach entails discarding the plunger with the syringe.

0005It is an object of the present invention to provide a syringe of the ampoule-loaded type which may safely be discarded after a single use without any significant risk of illicit re-use.

0006The syringe according to the present invention comprises a generally tubular syringe body which is closed at a first end thereof, a double-ended hollow needle extending through said closed end generally axially with respect to the syringe body, the second end of said syringe body being generally open so as to permit the insertion of a liquid container into said syringe body, a resilient retaining means extending from said second end of said syringe body in a generally radially inward direction so as to allow the insertion of a said liquid container but to prevent its removal by engaging the adjacent end of said container, and a plunger rod adapted to reversibly enter a said container within said syringe body.

0007Liquid containers conventionally used in hypodermic injection syringes take the form of tubular ampoules, closed at one end by a cap which can be pierced by the inward end of a double-ended needle and closed at the other end by a bung which is slidable within the ampoule to expel its contents via the needle. The syringe according to the invention is designed to receive such conventional ampoules without them needing modifying in any way. Thus the plunger rod may freely abut the bung within such an ampoule to enable the liquid to be injected into a patient, but may then be withdrawn before the syringe and ampoule are discarded. If desired, the plunger rod may be removably attachable to the adjacent end of the syringe body, in the manner of a dental injection syringe handle.

0008The double-ended needle may be irreversibly attached to the syringe body before use but it is preferred that the needle be incorporated in the syringe body during the manufacture of the latter, for example by moulding the syringe body around the needle. Preferably the syringe is provided with a sheath for the needle, slidably mounted for movement between a first position in which the needle is exposed for use and a second position in which the needle is enclosed therein. It is preferred that the sheath be retained in said second position in a manner which renders subsequent re-exposure of the needle very difficult. Such a slidable sheath may be mounted upon the syringe body but in a particularly preferred form of the invention the needle is disposed within an axial projection extending from the closed end of the syringe body and the sheath is slidably mounted upon that projection.

0009At the open end of the syringe body, a resilient retaining means extends in a generally radially inward direction. The resilient retaining means may take the form of one or more inwardly projecting spigots. Such a spigot may, in one embodiment of the invention, be an annular web. Preferably such spigot(s) is/are shaped so as to assist their deflection when an ampoule is inserted in the syringe body but to abut the adjacent end of the ampoule once it has been inserted. For example the axially outer face thereof may be inclined while the inner face may be flat in a radial direction.

0010The invention will now be further described with reference to the accompanying drawings, wherein:- <ul id="ul0001" list-style="none"><li>Fig. 1 is an axial sectional view of one preferred embodiment of the single-use syringe according to the present invention, with an ampoule inserted therein, in a condition of use; and</li><li>Fig. 2 is a view corresponding to Fig. 1, showing the syringe in a condition for disposal.</li></ul>

0011The illustrated syringe comprises a generally cylindrical barrel 10, closed at one end thereof. The barrel 10 is moulded in a synthetic polymeric material and has, formed integral therewith and projecting from its closed end, an axial extension 11. A double-ended hypodermic needle 12 extends axially through the extension 11. A hollow sheath 13 is a sliding push-fit upon the extension 11 and has an aperture 13<u style="single">a</u> in its closed end, through which the needle 12 is able to project when the sheath is in its inward position illustrated in Fig. 1. The sheath 13 has a pair of lateral projections 14 to assist movement of the sheath over the length of the extension 11.

0012At its open end, the syringe barrel 10 is formed with a pair of resilient, inwardly-projecting spigots 15, which reduce the effective minimum diameter of the open end to slightly less than that of a conventional ampoule 16. The spigots 15 have an inclined outer face and a flat inner face and are readily deflected when the ampoule 16 is being inserted in the barrel 10, but when the spigots return to their natural position they project inwardly beyond the open end of the ampoule such that their flat inner faces prevent its withdrawal from the barrel 10. The inward end of the ampoule 16 is closed by a cap 17 which is readily pierced by the adjacent end of the needle 12 when the ampoule is first inserted in the barrel 10.

0013In use, the ampoule 16 is loaded into the barrel until the cap 17 is pierced and the spigots 15 have resumed the illustrated position. The bung 18, which as usual in such ampoules is slidable within the ampoule 16, may then be pushed further into the ampoule by means of a plunger rod 19, which is inserted in the open end of the barrel 10 and abuts the bung 18. In this way, the liquid within the ampoule is expressed through the needle and an injection may be carried out in the usual manner.

0014When the injection has been completed, the plunger rod 19 is removed and the bung 18 remains in the position shown in Fig. 2, the ampoule being retained within the syringe barrel by the spigots 15. The sheath 13 is now slid along the extension 11 until its inward end nests in an annular slot 20 in the extension. The slot 20 retains the sheath against retraction and in this position, as illustrated in Fig. 2, the sheath completely encloses the previously-exposed end of the needle 12. The syringe assembly as illustrated may now be safely discarded, without any serious risk of its illicit re-use.