Injection device

[0001] The present application claims priority under 35 U.S.C. §119 to United Kingdom Patent Application Nos. GB0601309.8 filed Jan. 23, 2006, GB0602411.1 filed Feb. 7, 2006, and GB ______ filed Mar. 21, 2006. The entire disclosures of the above-referenced patent applications are incorporated herein by reference in their entirety.

[0002] This invention relates to the field of injection devices for the administration of liquid medication, for example, interferon.

[0003] One typical known device is described in WO00/09186 (Medi-Ject Corporation) for “Needle assisted jet injector” and this document gives a useful summary of other prior art devices.

[0004] The device of WO 00/09186 includes a needle which is, in one embodiment, retractably located within an injector nozzle assembly. Upon activation of a force-generating source, a portion of the needle extends past the nozzle assembly and penetrates the outer layer of skin to deliver medicament via jet injection to a deeper region. After activation, the needle retracts back into the nozzle assembly. The retractable needle is housed within the nozzle and is pushed forward so that it emerges in order to deliver an injection by the liquid medicament itself, when the medicament is itself pushed forward by the plunger.

[0005] Another injection device is described in our co-pending international patent application, published under number WO 2005/070481. Some of the reference numerals in the present application correspond with the equivalent components in the device described in WO 2005/070481. This device requires that the needle is moved axially so that it can appear beyond the end of the nozzle for the duration of the injection, after which the needle retracts automatically, so that it is never in sight of the user. The device also requires that the plunger is moved axially so that medicament is ejected. The overall complexity of the injection device is significantly reduced by both of these requirements being effected by one component, namely an inner housing and the device has the significant advantage that it can be built around a conventional or standard syringe presentation.

[0006] The injection device of WO 2005/070481 is designed to be used in conjunction with a standard drug presentation e.g. a syringe comprising a needle, barrel preloaded with medicament and a plunger. There is a significant commercial advantage in being able to use a standard syringe, which will have been subjected to numerous clinical trials, drug stability studies and regulatory approval. Any modification to the standard syringe may require further trials and approval, adding delay and expense. The present invention is relevant to any injection device for use in conjunction with a syringe (whether preloaded or not and whether single-use or reusable), not only the device described in WO 2005/070481.

[0007] The barrel of a syringe is usually glass, since glass has the most favourable storage properties for many drugs. However, glass is notoriously fragile and there is a risk of damage or breakage of the syringe during injection if the forces to which the syringe is subjected by the injection device are not properly controlled. This is particularly so where the liquid medicament is relatively viscous, requiring greater force to expel it from the syringe via the needle. Barrels made of materials other than glass, for example polyethylene or cyclic olefin polymers are less brittle when subjected to normal forces during injection, but still would benefit from the invention described below.

[0008] In the known device described in our co-pending patent application no WO 2005/070481 and illustrated in FIGS. 1-3 of the present application, the syringe is supported within the injection device by a barrel or syringe holder 9. The syringe holder 9 comprises an elongate housing which closely surrounds the glass barrel of the syringe. The annular flange 90 at the rear of the syringe barrel rests on a barrel seat 91 at the rear of the syringe holder 9. The annular flange 90 at the rear of the syringe barrel is often referred to as a “finger flange” because, during a conventional (manual) injection using a syringe, the user's index and middle fingers rest naturally in front of the “finger flange” in order to provide the necessary resistance to allow depression of the plunger by the thumb to deliver the medicament.

[0009] The barrel seat, for example in the form of an annular flange, preferably prevents forward axial movement of the syringe with respect to the syringe holder so that, in use, the syringe barrel and the syringe holder move axially together as one unit.

[0010] In use, as described in WO 2005/070481, there are three stages of delivering an injection. Before delivering an injection (referring to FIG. 1 of the present application), the end cap 15 is pulled off, taking the rigid needle cover 17 (if present) and rubber needle sheath 16 with it. In the first stage of delivering an injection, as shown in FIG. 2 of the present application, the tags 7B at the forward end of the inner housing 7 are in contact with the syringe barrel 90, which is pushed axially forward (taking the syringe holder 9 with it), so that the needle 10, which is fixed to the front end of the barrel, moves in the direction indicated by the arrow so that eventually it protrudes beyond the nozzle 11 at the front of the device. Forward travel of the barrel and syringe holder is limited when a surface 9A of the syringe holder reaches an endstop 11A inside the nozzle or front housing 11.

[0011] Referring now to FIG. 3, the second stage of the injection is the delivery of the medicament wherein the tags 7A at the rear of the inner housing 7 depress the plunger 8 into the barrel of the syringe. During this stage, the barrel of the syringe is held axially stationary, by abutment of the annular “finger” flange 90 against the barrel seat 91, which results in the barrel being placed in tension as the plunger pushes the non-compressible liquid medicament towards the forward end of the barrel. This tension is undesirable in a glass barrel, which may become damaged or broken, especially if the medicament comprises a particularly viscous liquid which requires greater force to expel it from the syringe via the needle. Viscous medicaments are desirable in certain applications, where the use of a sustained-release viscous medicament reduces the frequency that an injection is required.

[0012] It is desirable to minimise the diameter of the needle so far as is possible, because the smaller the diameter of the needle, the less painful is the resulting injection. However, for a given length of needle, the smaller the needle diameter, the greater the force required to eject the medicament from the syringe.

[0013] It is also desirable to minimise the duration of the injection, i.e. to maximise the speed at which the medicament is delivered from the syringe. Particularly when the needle diameter is small, minimising the duration of the injection also means an increase in the force used to eject the medicament from the syringe.

[0014] An increase in the forces on the syringe consequently increases the likelihood of the syringe breaking during the injection. The risk of the syringe breaking during injection is significant, and is not only inconvenient and costly but is also potentially dangerous. If breakage occurs, it is possible :that glass fragments and/or the needle may become detached and exit the front of the device causing injury. Furthermore, there is the risk that the remaining medicament will leak or be ejected from the device in an uncontrolled manner, potentially delivering the wrong dose into the patient, or causing injury e.g. if the medicament contacts the patient's skin or eyes. These problems are amplified when the medicament is viscous as a more powerful energy source is needed in such applications so that the forces involved are greater. It is known that a typical breakage of the syringe during injection would occur at the finger flange, whereby the finger flange 90 on the syringe barrel breaks as a result of its abutment against the barrel seat 91. It is therefore highly desirable to minimise the likelihood of breakage of the syringe. In the third stage of the injection (not illustrated in the present application but shown in WO 2005/070481), once the medicament has been delivered and the inner housing 7 is no longer in contact with the barrel or plunger of the syringe, the secondary spring 12 pushes the syringe holder (and hence the syringe contained therein) axially rearwardly so as to retract the syringe back into the housing so that the used needle is concealed from view.

[0015] According to a first aspect of the present invention, there is provided an injection device comprising a housing in which can be mounted a syringe comprising

• • [0016] a barrel for holding a volume of medicament,
  • [0017] a needle at one end of the barrel and
  • [0018] a plunger axially-moveable in the barrel to a forwardmost position, the injection device further comprising a syringe support means for supporting the barrel at an axial location at or forward of the forwardmost position of the plunger and having a reaction surface for the syringe, whereby in use said reaction surface provides an axial compressive force on said barrel when a forward axial force is applied to the plunger.

[0019] According to a second aspect of the invention there is provided a method of assembling an injection device comprising the steps of:

• • [0020] providing a first part-assembly comprising a front housing and a closely fitting end cap;
  • [0021] providing a second part-assembly comprising a rear part of the injection device;
  • [0022] providing a syringe comprising a barrel for holding a volume of medicament, a needle at one end of the barrel and a plunger axially-moveable in the barrel;
  • [0023] providing a syringe support means;
  • [0024] inserting the syringe axially into the rear end of the syringe support means until said syringe support means supports the syringe at a predetermined axial location;
  • [0025] inserting the front end of said syringe and syringe support means into said first part-assembly;
  • [0026] assembling said first part-assembly and second part-assembly together.

[0027] According to a third aspect of the invention there is provided a method of assembling an injection device comprising the steps of:

• • [0028] providing a first part-assembly comprising a syringe support means, a front housing and a closely fitting end cap;
  • [0029] providing a second part-assembly comprising a rear part of the injection device;
  • [0030] providing a syringe comprising a barrel for holding a volume of medicament, a needle at one end of the barrel and a plunger axially-moveable in the barrel;
  • [0031] inserting the syringe axially into the rear end of the first part-assembly until said syringe support means supports the syringe at a predetermined axial location;
  • [0032] assembling said first part-assembly and second part-assembly together.

[0033] Further features of the invention are defined in the appended claims.

[0034] Preferred embodiments of the present invention will now be more particularly described, by way of example only, with reference to the accompanying drawings in which:

[0035] FIG. 1 (PRIOR ART) is a perspective view of a known injection device;

[0036] FIG. 2 (PRIOR ART) is a plan view, partly in section of the FIG. 1 device, with the cap and needle cover removed, ready for actuation;

[0037] FIG. 3 (PRIOR ART) is a plan view, partly in section of the FIG. 1 device, with the needle exposed, ready for the plunger to be depressed in order to deliver the medicament;

[0038] FIG. 4 is a perspective view of an injection device embodying one aspect of the present invention;

[0039] FIG. 5 is a plan view, partly in section of the FIG. 4 device, with the cap and needle cover removed, ready for actuation;

[0040] FIG. 6 is a plan view, partly in section of the FIG. 4 device, with the needle exposed, ready for the plunger to be depressed in order to deliver the medicament;

[0041] FIG. 7 is a perspective view of the syringe holder;

[0042] FIG. 8 is a cross-sectional view of the syringe holder of FIG. 7;

[0043] FIG. 9 is a cross-section view of the syringe holder of FIG. 7, showing a syringe in place;

[0044] FIG. 10 is a cross-section view of the syringe holder of FIG. 7, showing a syringe and rigid needle cover in place;

[0045] FIG. 11 shows detail, drawn to a larger scale, of the interface between the front of the glass syringe barrel and the syringe holder illustrated in FIG. 10;

[0046] FIG. 12, drawn to a larger scale, is a cross-sectional view of the modified front housing;

[0047] FIG. 13, drawn to a larger scale, is a perspective cross-sectional view of the front housing;

[0048] FIG. 14 is a cross-sectional view of the front housing, cap and syringe holder assembled together;

[0049] FIG. 15 is a perspective view of the front housing, cap and syringe holder assembled together;

[0050] FIG. 16 is a cross-sectional view of the front housing, cap, syringe holder and syringe assembled together;

[0051] FIG. 17 is a cross-sectional view of an alternative embodiment of the syringe holder;

[0052] FIG. 18 is a part-assembly view showing the syringe holder of FIG. 17 together with its spring retainer, a syringe therein and the end cap and front housing;

[0053] FIG. 19 shows the part-assembly of FIG. 18 with the rigid needle cover removed;

[0054] FIG. 20 is a perspective view of the syringe holder of FIG. 17 together with its spring retainer;

[0055] FIG. 21 is a perspective view of a syringe holder, end cap and front housing, showing an alternative means of retaining the gripping means against the syringe barrel;

[0056] FIG. 22 is a perspective view of the syringe holder of WO 2005/070481, modified in accordance with an alternative embodiment of the invention; and

[0057] FIG. 23 is a perspective view of another embodiment of the syringe holder together with a needle cover.

[0058] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other components, integers or steps.

[0059] Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0060] Throughout the following description, reference to a “forward” direction means the direction which is towards the patient when the injection device is in use. The “forward” end of the injection device is the end nearest the patient's skin when the device is in use. Similarly, reference to a “rearward” direction means the direction which is away from the patient and the “rearward” end of the device is the end furthest from the patient's skin when the injection device is in use.

[0061] Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

[0062] As described above, a disadvantage of the known prior art is that the barrel of the syringe is placed in tension as the plunger pushes the non-compressible liquid medicament towards the forward end of the barrel for delivery. This tension is undesirable in a glass barrel, which may become damaged or broken, especially if the medicament comprises a particularly viscous liquid which requires greater force to expel it from the syringe. There is a possibility that the glass syringe might break in the region of its finger flanges, as a result of the forces to which it is subjected during delivery of an injection. One way to mitigate this problem is to reduce the effect of those forces in the region of the finger flanges. For example, the syringe holder of WO 2005/070481 can be modified as illustrated in FIG. 22. The syringe holder 9 has a helical slit 92 which, in use, provides resilience to the region of the barrel seat 91 on which is located the finger flange of the syringe (not. illustrated). The resilient flexing absorbs shock and reduces the risk of breakage of the syringe in the region of the finger flanges.

[0063] Other means for reducing the effect of forces in the region of the finger flanges can be envisaged, for example, providing a cushion in the form of an O-ring or moulding a relatively soft or elastomeric material into a harder substrate in the region of the barrel seat 91.

[0064] It is known that a typical breakage of the syringe during injection would occur at the finger flange, whereby the finger flange 90 on the syringe barrel breaks as a result of its abutment against the barrel seat 91. However, the applicant has recognised that it is also possible that the syringe could break at the forward end of the barrel. This is potentially more serious as larger straight glass fragments may be ejected from the front of the device, as well as the unsecured needle, and any remaining medicament will leak out in an uncontrolled manner.

[0065] The risk of breakage or damage to the glass syringe may be reduced by ensuring that the barrel is held in compression during delivery of the medicament (stage two of the injection process described in WO 2005/070481), rather than being in tension. This can be achieved by supporting the forward end of the barrel and having a reaction surface at which an axial compressive force can be applied to the barrel when a forward axial force is applied to the plunger during delivery of the medicament.

[0066] In the injection device of the present invention, the conventional syringe holder 9 is replaced with a more complex syringe holder which is capable of supporting the syringe at the front end of its barrel instead of at its rear flange 90 during delivery of the medicament. In the embodiment described below, the syringe holder supports the syringe at the front shoulder of its barrel and provides a reaction surface there for the front shoulder of the barrel. By “front shoulder” is meant the region at which the largest diameter of the barrel reduces to a smaller diameter at the nozzle. The front shoulder 92 is indicated in FIG. 9. Alternatively, the syringe could be supported and the reaction surface provided at the front end of the syringe barrel, or at the narrowed “cone” where the needle is attached thereto and these embodiments are described in more detail below. The syringe can, in fact, be supported at any place on the barrel which, in use, is forward of the forwardmost position of the fully-depressed syringe plunger and where a reaction surface for the syringe can be provided (so that the barrel is held in compression throughout the delivery of the medicament).

[0067] However, the desired supporting or holding of the barrel by the syringe holder at its front end presents an assembly difficulty for a product where it is desired to keep manufacturing and assembly costs to a minimum. In the prior art device, the syringe can simply be dropped into the rear end of the syringe holder until its flange 90 rests on the barrel seat 91. This determines the axial position of the syringe with respect to the syringe holder. In practice, the prior art syringe holder is supplied ready-assembled with the front part of the device, so that the pre-filled syringe can simply be dropped into the syringe holder and then the front part of the device (including the syringe) can be attached to the ready-assembled rear part of the device in a simple two-stage assembly operation.

[0068] In the present invention, it is not possible to use the finger flange 90 and barrel seat to determine the axial position of the syringe with respect to the syringe holder. This is because the syringe holder needs to actively support the syringe at its front end (preferably at the front shoulder 92 of the glass barrel). In the preferred embodiment there are inwardly-directed gripping means to retain the front shoulder of the glass barrel at a specific axial location with respect to the syringe holder. The standard syringe is usually supplied with a rigid needle cover 17 which has a diameter almost the same as the largest diameter of the glass barrel (see FIG. 10). If the syringe is inserted into the syringe holder needle-first (or rather needle-cover first), any inwardly-directed gripping means would foul on the rigid needle cover as it attempts to pass. There is also the risk of the needle being damaged during assembly, for example if it is pushed into any inwardly-directed gripping means. Such damage to the needle is highly undesirable, in particular because it often cannot be readily detected (if the needle is concealed within a rigid needle cover and/or a rubber needle sheath. The damage to the needle only becomes apparent during delivery of the medicament.

[0069] This problem is solved by the use of a syringe holder 100 as illustrated in FIGS. 7 and 8. The syringe holder 100 comprises an elongate rear portion 102 in which there are viewing windows 103 so that the medicament chamber in the barrel of a syringe held therein would be visible. There is a barrel seat 101 (equivalent to barrel seat 91 in the prior art device) at the rear end of the rear portion 102, but in practice this is not intended to abut the flange 90 of the syringe barrel (unlike in the prior art device).

[0070] The syringe holder also has an intermediate portion 105 of comparable diameter to the rear portion, and a front portion 106 of narrower diameter. The intermediate portion 105 is provided with a discontinuous annular flange 104. Together, the intermediate and front portions 105, 106 include radially-spaced slots 107 which define a plurality of radially flexible fingers 108. In the illustrated embodiment, there are three flexible fingers 108, but four or some other number of fingers may be provided. FIG. 23 shows an embodiment in which four flexible fingers 108 are provided on the syringe holder 100. The four fingers necessarily each are thinner than those in the three-finger embodiment. A typical needle cover 17 is shown in FIG. 23 (illustrated without the rest of the syringe for simplicity). The needle cover has a slot 17A therein. If the syringe holder 100 is appropriately aligned with the needle cover of a syringe held therein, there is a possibility that one of the relatively thin flexible fingers 108 may undesirably snag or drop into slot 17A, possibly causing damage to the underlying needle that would not become apparent until an injection is delivered. This disadvantage can be overcome by ensuring that each of the flexible fingers 108 is preferably wider than the needle cover slot 17A, as illustrated by the three-finger embodiment of FIG. 7.

[0071] As shown in FIG. 8, gripping means 109 preferably in the form of a discontinuous annular inwardly-directed protrusion, are provided on the interior of the flexible fingers 108 in the intermediate section 105. Referring to FIG. 9, when a syringe is located within the syringe holder 100, the gripping means 109 abuts the front shoulder 92 of the barrel in order to define the axial position of the barrel with respect to the syringe holder.

[0072] The term “gripping means” is not limited to means which grip radially-inwardly onto the barrel, although in some embodiments they may do so. More important is the fact that the gripping means 109 (or equivalent) supports the syringe in a desired axial location and provides a reaction surface for the syringe so that the barrel will be held in compression during delivery of the medicament.

[0073] As can be seen from FIGS. 10 and 11, the rigid needle cover 17 has a greater diameter than the diameter normally available at the gripping means 109. In other words, the internal diameter between the gripping means 109 is smaller than the exterior diameter of the needle cover 17. However, as will be explained in more detail below, when the syringe is inserted into the syringe holder, as the rigid needle cover 17 passes the gripping means 109, the flexible fingers 108 flex radially-outwardly to create sufficient diameter for the needle cover to pass the inwardly-protruding gripping means, without exerting excessive force on the needle therein, thus minimising the risk of damage to the needle. Once the needle cover has passed, the flexible fingers 108 spring back into their normal position (having smaller internal diameter than the exterior diameter of the needle cover) and the gripping means 109 locate at the front shoulder 92 of the barrel. In this position, the gripping means 109 are axially located between the needle cover and the front shoulder of the barrel.

[0074] The front portion 106 of the syringe support 100 is provided with a plurality (preferably two) equispaced tags 110, whose purpose will be described later below.

[0075] The most straightforward way to,assemble the syringe and injection device is in a three stage procedure, namely:

• • [0076] 1. inserting the syringe into the syringe holder, until the gripping means 109 locate at the front shoulder 92 of the barrel;
  • [0077] 2. inserting the syringe and syringe holder into the front part of the injection device;
  • [0078] 3. assembling the front part to the rear part of the injection device.

[0079] Compared with the two-stage assembly procedure of the prior art device, the extra assembly stage is disadvantageous but initially seems necessary as it is not obvious how stages 1 and 2 could be readily combined so that the syringe holder can be supplied ready-assembled with the front part of the device. This is because, once assembled into the front part of;the device, the flexible fingers 108 would be prevented from flexing radially outwardly by their necessarily close abutment with the front housing, thus preventing insertion of the syringe and rigid needle cover.

[0080] Therefore, in a further embodiment of the invention, a modified front housing for the injection device is provided which enables a two-stage assembly procedure to be used.

[0081] The modified front housing 200 (analogous to nozzle 11 in the prior art) is illustrated in FIG. 12. The front housing 200 has a bore 201, of sufficient diameter to allow passage therethrough of the needle 10, needle cover 17 and the front and intermediate portions 105,106 of the syringe holder (but not the flange 104).

[0082] The interior surface of the bore 201 is provided with two (or more) equispaced longitudinal slots 202, each having a rear section 203 with a tapered surface providing a varying depth and a forward section 204 of substantially constant depth. The boundary between the forward and rear sections of each slot 202 is defined by a step 205.

[0083] The slots 202 are positioned so that they can be aligned with the tags 110 at the front portion of the syringe holder.

[0084] The slots 202 enable the syringe holder 100 to be assembled into the front housing 200 at a specific axial position (relative to the front housing) so that the flexible fingers 108 stand clear of the front housing instead of being surrounded therein.

[0085] The slots 202 also provide radial location for the syringe holder 100 as it is inserted therein.

[0086] FIG. 14 shows a modified end cap 300 (analogous to end cap 15 in the prior art) designed for use with the modified front housing 200 and how the syringe holder 100 is inserted into the front housing 200. The front housing 200 is inserted into the end cap 300 so that its leading surface 206 abuts the interior of the end cap, so that no further forward movement of the front housing within the end cap is possible.

[0087] The close abutment of the end cap 300, front housing 200 and syringe holder 100 means that, if present, the rigid needle cover 17 is retained securely in position such that the risk of the needle cover accidentally becoming loose or detached is minimised, thereby minimizing possible loss of integrity of the seal between the rubber needle sheath and the needle, which would otherwise compromise the sterility of the medicament contained within the syringe.

[0088] The end cap has an upstanding annulus 301 which protrudes into and is a close fit in the bore 201 of the front housing 200. The upstanding annulus 301 has two equispaced protrusions on the exterior surface thereof which locate in longitudinal slots 202 when the end cap and front housing are assembled together. Once assembled together, the upstanding annulus of the end cap and the step 205 together define a space 302 into which tags 110 on the syringe holder 100 can locate.

[0089] In order to insert the syringe holder 100 into the front housing 200, the tags 110 are aligned with and pushed into the slots 202 until the tags 110 “click” over the step 205 and locate in the space 302. This is the position illustrated in FIGS. 14 and 15. Now the syringe holder 100 is suitably axially located such that the gripping means 109 and flexible fingers 108 are not constrained within the front housing 200 and end cap 300.

[0090] The front housing, end cap and syringe holder are supplied in this ready-assembled condition, together with the ready-assembled rear part of the injection device, for final assembly with a pre-filled syringe.

[0091] It is therefore a straightforward two-stage procedure to finally assemble the syringe into the device, namely:

• • [0092] 1. inserting the syringe into the ready-assembled front housing, end cap and syringe holder until the gripping means 109 locate at the front shoulder 92 of the barrel (as shown in FIG. 16);
  • [0093] 2. assembling the front part to the ready-assembled rear part of the injection device (not illustrated).

[0094] FIGS. 4-6 show the fully assembled injection device including syringe holder 100. With reference to FIG. 5, it can be seen that (unlike in the prior art device) the flange 90 of the barrel does not contact the barrel seat 101 of the syringe holder 100, there being a gap G therebetween. This is a result of the relative axial positions of the syringe holder and syringe being determined at the front end, by gripping means 109 and front shoulder 92 and means that undesirable tension is not applied to the glass barrel during delivery of the medicament.

[0095] An alternative embodiment of the syringe holder is illustrated in FIGS. 17-20. Where possible, the same reference numerals as were used in relation to FIGS. 8-9 are used to identify like components of the alternative embodiment. Note that FIGS. 17-20 show the front end of the device at the left side of the Figures, whereas FIGS. 8-9 show the front end of the device at the right side of the Figures.

[0096] In the FIG. 17 embodiment of the syringe holder 100′, the radially-flexible fingers 108′ have their free ends extending in the forward direction (compare with the radially-flexible fingers 108 in FIG. 8 which have their free ends extending in the rearward direction). The gripping means comprise inwardly-directed enlarged heads 109′ at the end of the flexible fingers 108. As is best seen in FIG. 19, the enlarged heads 109′ are capable of gripping the cone 93 at the front of the syringe barrel. The cone 93 is the region where the needle 10 is attached to the syringe barrel.

[0097] As shown in FIG. 18, when a syringe is assembled with the syringe holder 100′, the rigid needle cover 17 (which is of comparable diameter to the syringe barrel) causes the flexible fingers 108′ to flex radially-outwardly so that the enlarged heads 109′ rest on the exterior of the needle cover 17.

[0098] When the end cap 300 and rigid needle cover 17 are removed axially in the direction of the arrow in FIG. 18, the enlarged heads 109′ should move radially-inwardly into contact with the cone 93 of the syringe so as to grip the front end of the barrel to provide the compressive force during injection. However, if the flexible fingers 108′ are made from plastic and if the device is stored in the FIG. 18 configuration for many months before use (both of which are likely), it is possible that the fingers 108′ will no longer automatically flex properly inwardly upon removal of the needle cover 17.

[0099] Therefore, a spring retainer 111 is provided. The spring retainer 111 is made from steel, other metal or other material which does not significantly lose its resilience over time. The spring retainer has elongate fingers which cooperate with the flexible fingers 108′ so as to urge them radially-inwardly. Once the needle cover 17 has been removed, the spring retainer 111 urges the enlarged heads 109′ into firm contact with the cone 93 of the syringe, even if the flexible fingers 108′ are no longer capable of doing so. This position is illustrated in FIGS. 19 and 20.

[0100] As illustrated in FIG. 21, the gripping means (109 or 109′) could alternatively be provided in the form of a clip 112, inserted axially into a slot 113 in the syringe holder so as to clip onto the front of the barrel.

[0101] Other means of providing a reaction surface for the front of the barrel so as to provide a compressive force during injection can be envisaged, for example a tapered elastomeric bush which could be snapped into place once the needle cover has passed during assembly. It may be possible to grip the frontmost part of the cone, where the needle enters the cone, rather than gripping the exterior thereof. Alternatively, other means for gripping the front shoulder of the barrel, or the exterior of the cone may be envisaged.

[0102] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0103] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0104] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0105] The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including:any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.