Automatically operable safety shield system for syringes

Description [0001] The present invention concerns automatically operable safety shield systems for use with a syringe, as well as automatically operable safety shield systems comprising a syringe, protecting against needle stick injuries.

[0002] Needle stick injuries pose a substantial threat to health since they can frequently result in the transmission of disease from one person to another. Once a needle stick injury occurs then it is typically necessary to screen the injured person for a substantial period for e.g. HIV or hepatitis infection, and it may also be necessary to restrict the type of work they do, or the people they work with. The whole experience, even if the injured person has not been infected, is highly traumatic and extremely costly for healthcare providers. Infection is quite unacceptable if the stick injury could have been prevented in the first place. Needle stick injuries are of particular concern to healthcare professionals who are most frequently exposed to possible contamination and are in most frequent contact with infected patients. The recognition of the dangers posed by needle stick injuries has resulted in a general desire to prevent their occurrence, and various types of safety system are available which either retract the needle or shield it after use in order to minimise the possibility of needle stick injuries. The use of such safety systems is being encouraged and enforced by various pieces of "sharps" legislation in the USA, as well as by healthcare insurers and providers.

[0003] Examplesofpriorartsafetysystemsinclude EP 0966983 which discloses a shield system for prefilled syringes, comprising an outer syringe holder and an inner shield. In use, a prefilled syringe comprising a barrel having a proximal flange, a distal needle, and containing a plunger, is inserted within the enclosure defined by the outer holder and inner shield and is held by the outer enclosure. When sufficient pressure is exerted on the holder by the syringe barrel (for example by pressure exerted on the plunger when the contents of the syringe barrel have been completely injected) the shield is released and is urged in a distal direction by a spring located between the barrel and shield, putting the shield in an extended position and covering the needle.

[0004] However, the prior art devices, including EP 0966983, have a numberof disadvantages and potential problems in their design and construction. For example, the devices of EP 0966983 are prone to accidental triggering of the shield mechanism since sufficientforce (e.g. caused by accidental dropping) exerted on the syringe barrel will in turn exert sufficient force on the outer holder to trigger the shield mechanism. Also, it would appear that the insertion of a syringe into the outer holder/inner shield arrangement with sufficient force to cause it to be retained by the holder may cause triggering of the shield mechanism. Alternatively, this possibility may be avoided by placing the syringe in the enclosure defined by the holder before engaging the shield with the holder. However, such a method of manufacture of the device is somewhat complicated and cumbersome, and would prevent the sale and distribution of the holder/shield arrangement independent of any syringe to be used with it. In addition, the actual triggering of the shield mechanism requires the discrete step of exerting a greater force on the plunger rod than that applied during injection, and is done subsequent to removal of the needle from the patient (numbered paragraph 27). This means that a potentially unacceptable period exists during which needle sticks may occur, and requires an additional step in the use of the syringe. Another disadvantage encountered is that the spring extends to cover the syringe barrel. This can be particularly problematic when injecting a patient since the contents of the syringe barrel are no longer fully visible when the spring is extended, despite the fact that it may be necessary to see them in order to ensure that a proper dosage of medicament has been administered to a patient. Similarly the extended spring makes it difficult to view any label on the syringe barrel, which may be necessary to confirm that the correct medicament was administered to a patient.

[0005] The fact that the shield mechanism, including the shield, spring, trigger mechanism and holder must all be grouped together (see for example Figure 5 of EP 0966983) means that the safety shield arrangement can be undesirably large.

[0006] It is frequently necessary when using syringes to insert the needle at a specific acute angle (for example it may be that a long solid medicament formulation must be inserted subcutaneously within a narrow depth range) in order that "coring" is avoided whereby a core of tissue is cut by the needle, in turn causing tissue bruising and trauma and possibly affecting the efficacy of the injected medicament. Bulky safety shields cannot have a finger grip (flange), or at least one of useful dimensions, around the whole of their perimeter whilst still allowing for a sufficiently acute (i.e. shallow) angle to be achieved between the needle and the patient’s skin, and so instead are typically provided with laterally-extending flanges radially opposite one another. They are typically manipulated such that when the needle enters the skin the flanges are positioned such that they do not contact the skin (i.e. they are parallel to the plane of the surface of the skin). However depressing the plunger (which may require a relatively large amount of force to be exerted in a careful and controlled manner when injecting e.g. a solid medicament formulation) can then prove to be difficult since the flanges are in an inconvenient position. Users sometimes overcome this and gain a good grip on the flanges by rotating the syringe by 90 degrees after the needle has entered the skin (i.e. so that the flanges are perpendicular to the plane of the surface ofthe skin). However, the large bore and sharp edges of the needle tip may cause the rotation to cut a "core" of tissue from the patient, in the same fashion as a groundsman cuts a hole on a green on a golf course. This is, naturally, problematic and it is desirable to avoid it.

[0007] US 5163918 discloses a disposable safety syringe having an extendable safety shield. However, its construction is significa ntly different to that of the present invention and hasa number ofsignificantdisadvantages which are overcome by the present invention. In partic-ular, these disadvantages result from the syringe barrel forming part of the safety shield mechanism, from the use and location of an exposed spring, from the limited movement which can be achieved with the syringe plung-er, and from the safety clips employed with the syringe. [0008] The spring is also exposed when the protective sleeve is not in the retracted position. When moving to the extended position, movement could easily be hindered by the spring catching on e.g. the hand of a user or by snagging on clothing etc. The spring in the device of various embodiments of the present invention is always enclosed and so cannot be interfered with.

[0009] The protective sleeve of US 5163918 is also provided with finger grips which are held by a user. Their use means that the protective sleeve cannot extend over the needle until after the user has released their grip on eitherthesleeveortheplunger. Doingthiswiththeneedle in the patient could lead to sudden movement of the needle and tissue damage. Therefore the needle can only safely be covered after it has been removed from the patient, and is not done so until the user consciously lets go of the protective sleeve or plunger, which can result in the needle being unnecessarily exposed. The present invention provides an automatically operable shield system (i.e. which is operated as a result of the of the plunger rod being fully depressed and without any additional intervention from the user) which covers the needle as it is withdrawn from the patient, ensuring that it is not exposed. The automatically operable system of the present invention allows in a single fluid movement (depression of a plungerrod) both the administration of a medicament to a patient and the operation of the safety shield system. [0010] Specifically, the spring used to extend the protective sleeve over the needle extends over the syringe barrel. As discussed above, this is a disadvantage since it may damage the barrel, and can hinder viewing of the contents of the syringe barrel, and therefore it may be difficuIt or impossible to provide exact metered doses of medicaments. In the case of solid depots to be administered to patients, medical requirements typically require that the presence (or absence) of the depot in the syringe barrel can be easily determined by eye, both before and after injection. The spring ocduding the syringe barrel would substantially hinder this.

[0011] In order to prevent unwanted triggering of the release mechanism, the plunger of US 5163918 is provided with removable safety means comprising either a tearable strip or removable cap through which it is free to move but the release mechanism trigger is not. This can result in an injection being given to a patient, only for the clinician to find that the safety means has not been removed, at which point the plunger must be retracted to allow the removal of the safety means. This may cause discomfort and trauma to the patient. Embodiments of the present invention provide alternate safety means which must be removed prior to movement of the plunger, therefore avoiding the above problem.

[0012] Furthermore, the locking mechanism of the present invention makes use (see below) of the outer shield stop member which locked it in place in the retracted position both to prevent its further extension, as well as its retraction. US 5163918 instead requires additional tabs to achieve a similar aim, which clearly adds unnecessary complexity to the device. Although not required in the present invention, in certain embodiments additional engagement means are also provided to prevent the unwanted further extension of the outer shield, thus making the present invention more mechanically resilient.

[0013] In addition, the design of the syringes of US 5163918 inevitably makes them larger (more lengthy) than those of the present invention. When the protective sleeve of US 5163918 is moved to its extended position, it is left covering a substantial portion of the syringe barrel. This means that in orderto covera large needle, a lengthy protective sleeve and therefore a lengthy syringe barrel is necessary. This can make the overall syringe somewhat unnecessarily large and unwieldy, and its size can cause concern to patients. In contrast, when in its extended position the outer shield of the present invention is left covering a relatively insubstantial portion of the syringe barrel. This means that the devices of the present invention can be smaller and more convenient.

[0014] In manufacturing terms, the syringes of US 5163918 must be manufactured and sold as complete items. The present invention allows for the manufacture of the syringe, optionally containing a medicament, separately from the manufacture of the safety shield arrange-ment, the two being subsequently combined. This means that a stock of safety shields can be prepared without needing to incurthe costs of maniifacturing complete devices. Similarly, a wide range of syringes pre-filled with medicaments can be kept, and combined with safety shields as and when necessary. Overall this can allow for smaller stocks of components to be kept (thereby saving money forthe manufacturer) and forthe manufacturing process to respond rapidly to demand for any particular product.

[0015] The present invention also provides the advantage over US 5163918 when a syringe is to be filled by a dinician and then used with it - the prior art device only allows for the partial movement of the plunger, meaning that when filling the syringe it will inevitably end up containing air which must subsequently be removed. This removal of air can be extremely difficu It, if not impossible, and injecting air into a patient typically causes tissue damage. The present invention allows full movement of the plunger in the syringe barrel, and so air can be expelled priorto drawing medicament into the syringe. The filled syringe can then be combined with a safety shield arrangement and the medicament administered to the patient.

[0016] Other safety shield arrangements include those of US 5201720, US 5271744, US 5855839, US 4850968 and those referenced by EP 0966983. Amongst these, US 5201720 discloses an arrangement comprising an inner holder with two stop members and an outer shield comprising openings engageable by the stop members in the extended and retracted positions, said stop members and openings in the retracted position being disen-geable via push rods and a spring which faci litates movement of the outer shield from the retracted to the extended configuration.

[0017] Thus, the present invention overcomes the prior art disadvantages and provides an alternative and improved safety shield system for syringes. Particular advantages of the present invention are that it is less bulky than prior art devices, that the safety shield mechanism is substantially less proneto being accidentallytriggered and isresilientto attemptstoforceapartholderandshield for example by exerting force on the syringe barrel, that the safety shield mechanism is activated by the movement of the plunger rod rather than by pressure exerted on the syringe barrel, and can be achieved as an integral part of the injection process ratherthan as an additional discrete step, and that in various embodiments its spring does not extend substantially over the syrínge barrel, [0018] According to the present invention there is provided an automatically operable safety shield system for use with a syringe, said safety shield system comprising:

an inner holder having proximal and distal portions and defining an enclosure into which said syringe may be inserted;

an outer shield having proximal and distal portions, mounted outwards from said inner holder and being axially movable relative to said inner holder between retracted and extended positions;

a spring positioned between a first detent on said inner holder and a second detent on said outer shield, and urging said outer shield to its extended position, said spring preferably positioned between a first distal detent on said inner holder and a second distal detent on said outer shield;

said inner holder having at least one first opening and said outer shield having at least one first stop member, said first stop member being engageable with said first opening when said outer shield is in said retracted position;

said inner holder having distal to said first opening at least one first indentation, said first stop member being engageable with said first indentation when said outer shield is in said extended position; and a trigger positioned within said inner holder and axially movable relative to said inner holder such that it can contact said first stop member when it is engaged with said first opening and disengage said first stop member from said first opening, allowing said spring to move said outer shield to said extended position.

[0019] Syringes are ordinarily comprised of a generally cylindrical portion, known as a barrel, a needle or other piercing or connecting element secured to one end of the barrel, and a piston or stopper slidably positioned within the barrel. A plunger rod is typically engaged with the piston such that movement of the plunger rod causes movement of the piston. The needle may be removably secured to the barrel, or it may be permanently secured to the barrel. The plunger rod may be slidable from a drawn-back extended (proximal-most) position in which it can contain medicament to a distal most (forwardmost) position in which any medicament is expelled.

[0020] The automatically operable safety shield system may additionally comprise a syringe comprising a barrel, a needle, a piston and a plunger rod movable within said barrel, said plunger rod having a protrusion, said syringe being operationally coupled to said trigger such that movement of said plunger rod protrusion to contact said trigger causes disengagement of said first stop memberfrom said first opening, allowing said spring to move said outer shield to said extended position.

[0021] The first and second detents may be positioned as desired on the inner holder and outer shield, for example at their distal or proximal ends. However, the positioning of the first and second detents at the distal portions of the inner holder and outershield is most preferred since this allows the spring to be kept covered by the outer shield at all times, and for the spring not to extend over the syringe barrel even when the outer shield is in its extended position.

[0022] Springs used in the systems of the present invention are typically (but not necessarily) coil springs, and a person skilled in the art will be aware of alternative springs which may be used in The invention. The skilled person will also be aware of variants of coiled springs, such as tapered coil springs and coi I springs with variable coiling along their length, which are equally useful in the present invention.

[0023] Also provided according to the present invention is an automatically operable safety shield system, comprising:

a syringe comprising a barrel, a needle, a piston and a plunger rod movable within said barrel, said plunger rod having a protrusion;

an inner holder having proximal and distal portions and defining an enclosure into which said syringe may be inserted;

an outer shield having proximal and distal portions, mounted outwards from said inner holder and being axially movable relative to said inner holder between retracted and extended positions;

a spring positioned between a first distal detent on said inner holder and a second distal detent on said outer shield, and urging said outer shield to said extended position;

said inner holder having at least one first opening and said outer shield having at least one first stop member, said first stop member being engageable with said first opening when said outer shield is in said retracted position;

said inner holder having distal to said first opening at least one first indentation, said first stop member being engageable with said first indentation when said outer shield is in said extended position; and said syringe being operationally coupled to said inner holder and outer shield such that axial movement of said plunger rod protrusion relative to said inner holder causes said plunger rod protrusion to contact said first stop member when it is engaged with said first opening and disengage said first stop memberfrom said first opening, allowing said spring to move said outer shield to said extended positíon.

[0024] In order to prevent unwanted movement of the syringe plunger rod, the syringe may be provided with a safety clip removably secured to the portion of said plunger rod exposed from said barrel such that movement of said plunger rod is prevented when said safety clip is secured to said plunger rod.

[0025] Said outer shield and inner holder may have, respectively, proximal and distal abutment surfaces in opposing relationship to one another, which can engage one another to prevent movement of said outer shield beyond its extended position.

[0026] Theinnerholderandoutershield maybeofany desired shape. For example, they may be of a generally cylindrical shape. An example of a cylinders is one having a circular cross-section (commonly referred to as a right circular cylinder). Alternatively, a cylinder may have an elliptical cross-section. This may be particularly useful in ensuring that the inner holder and outer shield cannot be put together in an incorrect arrangement, or rotated relative to one another during use. Cylinders include those that are slightly tapered, for example by at least 0.5 degrees.

[0027] The inner holder and outer shield may also be constructed so as to avoid their relative rotation by providing guide means for their axial movement. Guide means may take the form of grooves in the inner holder and/or outer shield. For example, the first stop members may slide along a groove on the inner holder. Similarly, the outer shield proximal abutment surface may be guided towards the inner holder distal abutment surface by a groove on the outer shield.

[0028] The inner holder an/or outer shield may each be formed as a single piece, or may be constructed from more that one piece. Such construction will be readily apparent to a person skilled in the art.

[0029] Allembodimentofthepresentinvention provide the distinct advantage over the prior art of it being the movement of the plunger rod, rather than of e.g. the syringe barrel, which enables the spring to move the shield to the extended position. This is typically the position where the plunger rod is fully depressed and the contents of the syringe have been expelled and e.g. injected into a patient. The disengagement of the first stop member from the first opening may be achieved either by direct contact of a plunger rod protrusion with the first stop member, or by an indirect communication of the plunger rod protrusion with the first stop member.

[0030] Direct contact may be achieved by e.g. providing the plunger rod with a thumb stop which has an axial extension which, when the plunger rod is depressed, contacts the first stop member. Alternatively, the plunger rod may for example be provided with a thumb stop and an additional protrusion which, when the plunger rod is de-pressed, contacts the first stop member.

[0031] Indirect contact may be achieved by any arrangement which can communicate movement caused by the plunger rod (or plunger rod protrusion) to the first stop member. The exact nature of the arrangement will depend on the construction of the plunger rod. For example a plunger rod may have a thumb stop which, when the plunger rod is depressed, contacts a member (such as said trigger) located within the inner holder which in turn contacts the first stop member and causes its disengagement from the first opening.

[0032] The first stop member may be lockably engageable with the first indentation. It may engage the first indentation such that axial movement, both.distal and prox-imal, of the outer shield relative to the inner holder is prevented. The inner holder first indentation may be replaced by any other arrangement or means, for example a protruding member such as an escarpment of frusto-conical portion which inhibits the relative movement of the inner holder and outer shield, although the prevention of any axial movement is preferred.

[0033] The first distal detent may protrude outwardly from the inner holder, and the second distal detent may protrude inwardly from the outer shield.

[0034] The syringe may be retained within the inner holder by any appropriate means. For example, in order to ensure the correct positioning of the syringe relative to the inner holder the syringe may abut an inner holder detent, for example an upper surface of an inner holder first distal flange. It may also be advantageous to provide the inner holder with syringe engagement means for engaging and retaining the syringe. For example, the inner holder and syringe barrel may be designed so that they make an interference fit, the syringe once inserted into theinnerholderonly being removablewiththeapplication of substantial force, for example of at least 50N, more particularly at least 70-80N or 100N.

[0035] Thus the syringe may be axially immovable relative to the inner holder.

[0036] The use of an interference fit (also referred to as a friction fit) obviates the need for other retaining mechanisms for the syringe, for example frustoconical portions formed in the inner holder to retain the syringe within a certain area. This in turn means that the syringe need not have any flanges as are typically provided in the form of finger grips, allowing for the syringe to be of smaller dimensions than those used in prior art devices and therefore for the safety shield arrangement to be smaller. It may of course be desirable to retain at least a small flange simply to aid in the manipulation of the syringe barrel during the manufacture of the syringe, particularly in the case of prefilled syringes.

[0037] The skilled person will be familiar with a number of materialssuitablefortheconstruction ofthe innerhold-er and the outer shield of the device. Preferably the material is sufficiently clearto allow the contents or label of a syringe inserted into the inner holderto be viewed. Suitable materials include: polystyrene, modified polystyrenes and polystyrene copolymers, polycarbonates, pol-yethersulphones, polypropylenes, cyclic olefine copolymer resins, copolyesters such as Eastar (RTM) copolyester DN003 [copolyester made from terephthalic acid (or dimethyl terephthalate), ethylene glycol and 1,4 cy-clohaxanedimethanol], and acrylonitrile butadiene styrene copolymer (ABS). A particularly preferred material is Eastar (RTM) copolyester DN003 (Eastman Chemical Company). Also useful are MABS (methyl methacrylate / acry Ιο n itrile / butadiene / styrene copolymer, grade Terlux 2812 TR (RTM)). Polycarbonates include Lexan (RTM)GR 1210and Lexan 124R-112. Cyclicolefine resin copolymers include Topas (RTM) 6013 X5.

[0038] For some applications, devices of the present invention may be required to be supplied in a sterile state. The skilled person will be familiar with the sterilisation of pharmaceutical devices and the methods for the sterilisation of such devices, for example using heat, gaseous techniquesorgamma irradiation. The physical properties of materials used in the construction of devices of the present invention for sterilisation is required to be not substantially affected by the sterilisation. For example, in some materials the sterilisation process may introduce stress fractures or change the material from being clear to being opaque. A preferred method for sterilisation of devices of the present invention is gamma-irradiation. However, gamma-irradiation can induce changes in the colour of plastic materials and can also cause stressfractures in plastic materials. We have found that gammairradiation of Eastar (RTM) copolyester DN003 produces substantially no colour changes and does not substantially affectthe physical properties of the material. Thus, a preferred material for devices of the present invention suitable for sterilisation by gamma-irradiation is Eastar (RTM) copolyester DN003.

[0039] The syringe barrel may be constructed from polypropylene. Alternatively, the syringe barrel may be divided into a number of sections. For example it may comprise upper and lower portions made of high density polythene engaging and retaining a transparent section, for example comprising glass or polystyrene. The lower portion may engage the inner holder. The transparent section may be lensed to provide a magnified view of the contents of the syringe barrel.

[0040] In the case of syringe barrels having no flanges or reduced size flanges, the inner holder may be arranged such that the inserted syringe barrel acts to minimise the possibility of accidental disengagement of the first stop member and first opening by e.g. fingers or other small objects being inserted into the inner holder, and the syringe plunger rod may have a flange with a protrusion, for example an axially protruding collarwhich, when the plunger rod is depressed, passes around the outside of the syringe barrel and contacts, either directly or indirect-ly, the first stop memberto cause its disengagement. [0041] The reduced dimensionsofthe innerholderand outer shield (relative to prior art shield and holder arrangements) allowforthe provision of at least one radially extending protrusion usable as a finger grip, forexample a flange of usable dimensions, for example extending at least 2mm, 3mm, 4mm or 5mm, around the whole of the circumference of the proximal end of the inner holder. This still allows even large bore needles to be inserted into a patient at an angle which does not cause coring. Thisis particularlyusefulsince itenablestheusertoread-ily hold the inner holder at a variety of positions and allows hand positions to be changed without losing the grip required for a satisfactory injection, or without necessitating rotation of the syringe and the possible coring which might result.

[0042] The outer shield (rather than the inner holder) may be free (i.e. it may not have) at its proximal end of radially extending protrusions, such as tabs or a flange, useable as a finger grip.

[0043] The syringes used with the present invention may be used with liquids, suspensions such as microparticle formulations or solid medicament formulations (also referred to as depots) to be injected subcutaneously. Such injections of depots require that the syringe piston extends through the bore of the syringe needle to ensure that the solid medicament formulation has been wholly expelled from the syringe. The protruding piston can act to lessen the chance of needle sticks if the needle is exposed for any reason, and thus retaining the piston in its extended position by for example ensuring that the depressed plunger rod cannot be pulled back can therefore provide a useful additional safety feature. Examples of microparticle formulations which may be used with the invention include the leuprolide microparticle formulation Lupron (RTM). Examples of solid medicaments which may be used with the present invention include the gos-erelin depot formulation Zoladex (RTM).

[0044] The inner body may additionally comprise plunger rod retaining means, which prevents backwards movement of said plunger rod when it is at least almost at its forwardmost position. As mentioned above, the plunger rod is slidable between an extended position and a forwardmost position. At its forwardmost position the plunger rod causes the disengagement of the first stop member from the first indentation, and it is typically this forwardmost position at which it is desirable to retain the plunger rod, although it may also be desirable to retain the plunger rod at a position almost at the forwardmost position. For example the plunger rod retaining means may comprise a deflectable memberor members, forex-ample a frustoconical arrangement or an escarpment or so-called slip back prevention teeth, in the inner holder which allows the plunger rod to be depressed past an upper (i.e. proximal) inclined surface (typically, by elas-ticallydeforming it)butwhich providesa lower(i.e.distal) abutmentsurface which prevents removal ofthe plunger rod.

[0045] This also provides a number of additional advantages to The invention. Firstly, in varíous embodiments of The invention, particularly those which use e.g. a trigger to communicate movement of the plunger rod to the first stop member, the plunger rod retaining member can make it more difficult to accidentally (or inten-tionally)forcethedisengagementofthefirststopmember from the first indentation by e.g. jamming fingers into the gap formed between the plunger rod and the inner body to move the trigger, simply by reducing the size of the gap. Secondly, if, somehow, after the apparatus of the invention have been used and the outer shield is in the extended position, sufficient mechanical damage is caused to the apparatus that the outer shield is able to move back towards its retracted position, the first stop member will not be able to re-engage the first indentation and therefore the outer shield will always be urged by the spring back towards its extended position.

[0046] The arrangement of the spring with the first and second distal detents of the inner holder and outer shield means that when extended the spring covers an area from the inner holder first distal detent to the outer shield second distal detent, i.e. the spring does not expand to coverthe syringe barrel. Therefore, when the inner holder is made of a transparent material, it is possible even after extension of the outer shield to view the contents of the inner holder, meaning that in the case of medicament formulations the complete expulsion of the contents of the syringe may be readily confirmed at any time.

[0047] The fact that the spring does not extend to cover the syringe barrel also provides the useful advantage that the spring cannot damage the syringe barrel, such damage being a recognised problem in the prior art which frequently necessitates the use of an additional protecting member when e.g. using a syringe having a glass barrel (see for example EP 0966983 column 7 lines 19-21).

[0048] In order to ensure that the squeezing of the shield system by a user does not prevent it from working, the inner holder may be provided with a finger grip area comprising a flange and a rigid section of the inner holder. Squeezing of this will not cause the inner dimensions of the inner holder to be reduced and therefore the safety shield system will function correctly.

[0049] The first stop member may engage an abutment surface of the first opening. The first stop member may be provided in the form of an arced flexible member extending from the outer shield, i.e. extending outwardly and then inwardly. Such an arrangement may allow for the first stop member when engaged with the abutment surface of the first opening to have the centre of its pivotal axis inwards of the point of engagement. This means that if an attempt is made, either accidentally or intentionaIly, to disengage the first stop member and first opening by pulling them apart, they wilI in fact engage one another more strongly than before and thereby resist being pulled apart. This is a feature lacking in other prior art devices which forexample have flexible stop members which disengage upon the exertion of sufficient force.

[0050] The invention will be further apparent from the following description together with the drawings of the accompanying Figures which show, by way of example only, one form of safety shield and syringe arrangement. Of the Figures:

Figure 1 shows a side view of a safety shield and syringe arrangement of The invention, having an outer shield in its retracted position;

Figure 2 shows a section on line M-M of Figure 1;

Figure 3 showsasideviewofthearrangementofFig-ure 1, having been axially rotated through 90 degrees;

Figure 4 shows a section on line N-N of Figure 3; Figure 5 shows a side view of an inner holder;

Figure 6 shows a section on line C-C of Figure 5;

Figure 7 shows a section on line D-D of Figure 5;

Figure 8 shows a section on line E-E of Figure 5;

Figure 9 shows a cut-away view along line A-A of

Figure 5;

Figure 10 shows a side view of the inner holder of Figure 5, having been axially rotated through 90 degrees;

Figure I I shows a section on line B-B of Figure 10;

Figure 12 shows a side view of an outer shield;

Figure 13 shows a section on line K-K of Figure 12;

Figure 14 shows a cut-away view along line H-H of

Figure 12;

Figure 15 shows a side view of the outer shield of Figure 5, having been axially rotated through 90 degrees;

Figure 15a shows an enlarged view of circled area L of Figure 15;

Figure 16 shows a cut-away view along line G-G of Figure 15;

Figure 17 shows a side view of a trigger;

Figure 18 shows a section on line F-F of Figure 17;

Figure 19 shows a top view of the trigger of Figure 17;

Figure 20 shows a perspective view of a safety shield and syringe arrangement, shown in more detail in Figures 21,30 and 31;

Figure21 shows a partially cut away perspective view of a safety shield and syringe arrangement of the present invention, the outer shield being in its extended position;

Figure 22 shows a front view of the arrangement of face 232 of inner holder 20. Releasing the grip on inner holder 20 allows spring 40 to expand slightly, urging apart inner holder 20 and outer shield 30, and opposing abutment surfaces 150,330 engage one another and prevent further relative movement of inner holder 20 and outer shield 30. The outer shield is now engaged in a retracted position.

[0058] The arrangement of arms 310 and heads 320 of stop mem bers 300 is such that the centre of the pivotal axis of arms 310 is radially inwards of the area of contact of abutment surfaces 150,330. In contrast with prior art devices whose holder and shield parts may be disengaged by exerting sufficient force, this means that attempting to pull apart (i.e. disengage) inner holder 20 and outer shield 30 causes stop members 300 to engage inner holder20 more substantially.

[0059] Trigger 50 is then slid into mouth 11 of inner holder 20 such that neck 400 contacts heads 320.

[0060] Syringe 60 is then inserted, needle 430 first, into mouth 11 of inner holder 20 and slid towards end 110 suchthatneedle430and needlecover431 protrudefrom end 110. Insertion is halted when barrel 410 contacts upper abutment surface 231 of distal flange 230. Proximal and distal ends of barrel 410 of syringe 60 are constructed from high density polythene and an interference fit is formed with collar 220 such that it cannot be readily removed from innerholder20 withoutthe exertionofsub-stantial force. Flange 420 prevents trigger 50 from being removed from mouth 111, but does not exert any force upon trigger 50 and does not cause and movement of trigger 50 which may result in the disengagement of inner holder 20 and outer shield 30.

[0061] In use, safety clip 470 is removed from plunger rod 450, and needle cover 431 is also removed. Needle 430 is inserted into a patient (not shown) and thumb push 460 depressed to slide piston 440 through barrel 410 and expel solid medicament formulation (not shown) from needle 430 and to cause piston 440 to extend from needle 430. Simultaneously (i.e. not as part of a separate step), thumb push 460 enters mouth 111 and contacts trigger 50, causing it to move axially. This axial movement of trigger 50 is hindered by heads 320, but curved neck400 deflects heads 320 outwardly as trigger 50 moves axially. Sufficient axial movement of trigger 50 and thus outwards movement of heads 320 causes opposing abutment surfaces 150,330 to become disengaged, allowing axial movement of outer shield 30. Spring 40 urges apart inner holder 20 and outer shield 30 and as needle 430 is removed from patient 480 outer shield 30 is caused to slide over inner holder 20, covering needle 430 and preventing any possible needle sticks. During the sliding step, rotation of inner holder 20 and outer shield 30 relative to one another is prevented by grooves 145,185 guiding heads 320 of stop members 300 and second frustoconical portions 190 respectively. As needle 430 is fully removed from patient 480 heads 320 pass over inclined tongues 180 and lockably snap into first indentations 170, preventing further axial movement of inner holder 20 and outer shield 30. Simultaneously, abutment surfaces 280 and side walls 290 slide over second frustoconical portions 190 with a tight fit, abutment surfaces 280 contacting upper abutment surfaces 200, and preventing any further extension as an additional safety feature. The outer shield is now locked in an extended position. The entire operation of the safety shield and syringe arrangement 10 of the present invention can be readily achieved by a person using a single hand.

Example 2 [0062] A second embodiment is as Example 1 except that syringe barrel 410 does not have flange 420, and trigger 50 is not held in mouth 111, instead being replaced by axial extension 600 of thumb push 460. This configuration minimises the possibility of accidentally causing disengagementofopposing abutment surfaces 150,330 whilst placing syringe 60 in inner holder 20, or of otherwise accidentally causing disengagement of opposing abutment surfaces 150,330. Absent flange 420, it is also possibletoreducethediameterofmouth 111 andthere-fore either reduce the overall dimensions of inner holder 20 or to extend flange 120 to allow for further improved gripping by a user.

Example 3 [0063] A third embodiment is identical to Example I except that mouth 111 is provided with deflectable frus-toconical portions 500 (not shown) having upper (proximal) inclined surfaces 501 (not shown) and lower (distal) abutment surfaces 502 (not shown) substantially perpendicular to the axis of the inner holder. In use, as thumb push 460 enters mouth 111 (and the solid medicament formulation is expelled from needle 430 and piston 440 extends from needle 430) it deflects frustoconical portions 500 and passes beyond them, at which point they return to their original shape and present abutment surfaces 502 which oppose thumb push 460, preventing its removal from mouth 111. This means that piston 440 is locked in position extending from needle 430 such that even if outer shield 30 is removed or damaged such that needle 430 is exposed, needle sticks are substantially prevented.

Example 4 [0064] An alternative embodiment having altered (generally narrower than those shown in other Figures) dimensions is shown in Figures 30, 31, 20 and 21. In par-ticular, inner holder 20 has a length of about 68 mm and a diameter of about 10 mm in the proximal portion which is covered by outer shield 30, and having a narrowed flange 120. Notably, outer shield 30 is of a two-part construction.

[0065] T rigger 50 is also provided with first and second curved protrusions 630, 610extending radially outwards around the whole of its circumference, trigger 50 (and/or mouth 111) being sufficiently elasticaIly deformable to allow them to be forced past corresponding third curved protrusion 620 which extends radially inwards around the whole of the circumference of mouth 111. When the apparatus of the present invention is constructed, trigger 50 is inserted into mouth 111 of inner holder 20 and first curved protrusion 630 abuts third curved protrusion 620. Sufficient downwards force can readily be applied to trigger 50 to cause it to elastically deform to allow first curved protrusion 630 to pass over third curved protrusion 620. As trigger 50 is pushed further downwards, second curved protrusion 610 abutsthird curved protrusion 620. Sufficient downwards force is then applied to trigger 50 to cause it to elastically deform to allow second curved protrusion 610 to pass over third curved protrusion 620. Trigger 50 is thus fully inserted as shown in Figures 30 and 31. Although downwardsforce can be readily applied to trigger 50 to insert it into mouth 111, once in place it is extremely difficult for a person to apply sufficient upwards force to trigger 50 to remove it from mouth 50, and may be considered to be permanently located within mouth 111.

[0066] With this two-stage insertion of trigger 50, devices of the present invention are stored and shipped with inner holder 20, outer shield 30 and spring 40 engaged with one another and trigger 50 inserted into mouth 111 of inner holder 20 such that third curved protrusion 620 is located between first and second curved protrusions 630 and 610. Syringe 60 can be inserted into mouth 111 and engage inner holder 20 without contacting trigger 50. Even if trigger 50 is accidentally contacted whilst syringe 60 is being inserted, second curved protrusion 610 hinders it from moving beyond third curved protrusion 620 and therefore prevents it from disengaging stop members 300 from first openings 130. When syringe 60 has been fully inserted then sufficient force can be applied to trigger 50 to push second curved protrusion 610 past third curved protrusion 620. Syringe arrangement 10 is now ready for use.

[0067] Depending on the construction and deformability of mouth 111 and thumb push 460, as well as the dimensions of thumb push 460, it is possible for a protrusion extending radially inwards around the whole of the circumference of mouth 111 to be used to prevent the removal of thumb push 460 from mouth 111.