WO2011073176A1

WO2011073176A1 - Syringe

Info

Publication number: WO2011073176A1
Application number: PCT/EP2010/069597
Authority: WO
Inventors: Tony Bedford; Duncan Bishop; Andrew Gow; Dave Harris; Nick Hawson; Dominic Lloyd-Lucas; Martin Murphy; Christophe Royer
Original assignee: Novartis Ag
Priority date: 2009-12-15
Filing date: 2010-12-14
Publication date: 2011-06-23

Abstract

A syringe (2) including a barrel (4) with discharge end (5) defining a discharge passage, plunger (12) being adapted to move axially within the barrel and capable of displacing fluid from the chamber through the discharge end; the plunger includes a control arm (22, 24) including a first releasable stop element and a second non-releasable stop element, the first and second stops are both axially spaced from the rear end of the plunger, the control arm has a first configuration in which the first stop element is axially aligned with a stop surface (32) defined by a part of the barrel (4), the first stop element is adapted to limit the axial movement of the plunger; and a second configuration in which the first stop element is disposed out of alignment with the stop surface and the second stop element is axially aligned with the stop surface, the second stop element is adapted to limit the plunger movement from the first stop element to the second stop element.

Description

Syringe

The present invention relates to a syringe and, in particular, to a syringe adapted to permit priming, followed by dosing of a pre-determined dose.

It is often desirable to deliver a relatively small volume of fluid from a syringe in a method that is both accurate and reproducible. Typically, syringes containing fluids are first primed, to ensure that no air or other gas is present in the syringe and then a second, delivery (dosage) step is performed to deliver the required volume of fluid. However, it is difficult to deliver accurately a relatively small volume of fluid during the delivery step using a conventional syringe.

WO01/62319, US3,934,586 and WO03/004080 all describe dual stage syringes, but none of them addresses the issue of delivering accurately and reproducibly a relatively small volume of a fluid.

According to a first aspect of the present invention, there is provided a syringe for dispensing a fluid, the syringe including a barrel including a discharge end defining a discharge passage, and a plunger disposed within the barrel, the plunger being adapted to move axially within the barrel such that the plunger and discharge end define a variable volume chamber within the barrel and the plunger is capable of displacing fluid from the chamber through the discharge end; wherein the plunger includes a control arm which includes a first releasable stop element and a second non-releasable stop element, wherein the first and second stops are both axially spaced from the rear end of the plunger and wherein the control arm has a first configuration in which the first stop element is axially aligned with a stop surface defined by a part of the barrel, whereby the first stop element is adapted to limit the axial movement of the plunger, and a second configuration in which the first stop element is disposed out of alignment with the stop surface and the second stop element is axially aligned with the stop surface, whereby the second stop element is adapted to limit the plunger movement from the first stop element to the second stop element.

By having a first, releasable stop, a priming stroke can be defined in which the plunger is moved from a start position to the first stop. The first stop can then be removed or by-passed by moving the control arm from the first configuration to the second configuration. When the first stop is removed, by disposing it out of alignment with the stop surface, the syringe may l be used to deliver a dose of fluid contained therein by further movement of the plunger from the first to the second stop. The spacing between the first and second stops corresponds to a fixed dose for a given internal diameter of the barrel. Thus, the second stop element is disposed rearwardly from the first stop element and the spacing between the first and second stop elements defines the dosing stroke of the plunger.

Locating the first and second stops on a control arm and spacing both of the stops from the end of the plunger means that it is possible to achieve accurate and reproducible dosing of relatively small doses of the fluid by controlling the spacing between the stops. This is because the second stop is well defined. In the art, the second stop is often defined by a plunger button engaging or contacting the barrel body. However, this opens up the possibility that the user does not fully displace the plunger, resulting in an underdose being delivered. Additionally or alternatively, there is the possibility of foreign material becoming lodged at the rear of the barrel, which would prevent complete displacement of the plunger to the second stop. This would also result in an underdose being delivered. For doses having relatively small volumes, it is important that the dosing stroke is well defined.

In an embodiment of the invention as defined anywhere herein, the control arm is resiliency deformable, wherein the first configuration represents a rest or non-deflected position, and the second configuration represents a deflected position. In such an arrangement, the control arm must be urged from the first configuration to the second configuration in order to remove or release the first stop.

The plunger may include a retaining element to retain the control arm in the second configuration. For example, this might include an axially slidable collar or sleeve carried by the plunger or a two-part clip, wherein one part of the clip is carried by the control arm and the other part of the clip is carried by the plunger. In this arrangement, the syringe may be used one-handed, as the control arm does not need to be manually retained in the second configuration and the retaining element prevents the accidental return of the control arm to the first configuration from the second configuration and the consequent re-engagement of the first stop.

In a further embodiment of the invention as defined anywhere herein, the plunger includes a shaft connected at one end to a piston disposed in use within the barrel and connected at the other end to a push button, and the control arm is hingedly coupled to the shaft. This arrangement provides a control arm which is relatively straightforward to engineer and is intuitive for a user to operate.

The barrel may include a collar comprising a collar body which defines therethrough a shaft guide channel, wherein the shaft of the plunger is slidably retained within the guide channel. The collar body may further define the stop surface.

The guide channel may be adapted to receive therein the first stop element when the control arm is in the second configuration.

In order to maintain the first stop element aligned with the stop surface, for example during the priming step, the shaft of the plunger may include an orientation controlling element which is adapted to maintain the axial orientation of the plunger shaft relative to the guide channel. This ensures that the plunger remains in the desired axial orientation until the priming step is complete and the first stop element of the plunger has engaged the stop surface.

In an embodiment of the invention as defined anywhere herein, the orientation controlling element includes a spline (a longitudinally extending rib) carried by the plunger shaft which is located in use within a spline channel defined through the collar.

The interaction of the spline carried by the plunger shaft with the spline channel prevents unwanted movement, e.g. rotation, of the plunger relative to the barrel.

The skilled person will appreciate that the plunger may include more than one spline, wherein the splines are circumferentially offset from each other.

In such an embodiment, the barrel and/or collar typically includes corresponding spline channels for each spline.

A common arrangement for plungers is to include a cruciform-shaped shaft. Thus, in an embodiment of the invention as defined anywhere herein, the plunger shaft has a cruciform cross sectional configuration. In such an embodiment, the collar body may define a guide channel having complimentary cruciform shape. In embodiments where the spline channel is adapted to receive therein the first stop element when the control arm is in the second configuration, one or more of the splines may include a longitudinal notch which is capable of receiving therein at least a part of the control arm. Thus, the first stop element of the control arm may have a cross-section which is smaller than or congruent with the cross section of the notch formed within the respective spline, wherein the first stop element extends laterally outwards from the spline in the first configuration of the control arm and is axially aligned with the spline in the second configuration of the control arm. In other words, the first stop element may be contained within the notch in the second configuration of the control arm.

Of course, the first stop element may extend beyond the notch defined by the spline in embodiments where the spline channel is adapted to receive therein the first stop element, i.e. in addition to the spline itself. The first stop element may be a forward facing end wall of the control arm.

The second stop element may extend outwardly from the first stop element. In such embodiments, the second stop element may be carried by the control arm and is spaced rearwardly from the first stop element to define a dosing stroke which is the spacing between the first and second stop elements.

The second stop element may be defined by an edge portion of a control button which defines a substantially planar button surface. In such an embodiment, it is clear to a user how to operate the syringe: the syringe is primed by urging the plunger forwards until the first stop engages or contacts the stop surface. The control button is then pressed, which moves the control arm from the first to the second configuration, whereupon the first stop element is disengaged from (moved out of alignment with) the stop surface. The plunger is then again urged forwards until the second, non-releasable, stop element engages or contacts the stop surface, at which point the dose stroke is complete.

In an embodiment of the invention as defined anywhere herein, the plunger includes a pair of opposed control arms. By having two or more control arms, the possibility of the first stop element accidentally and/or unintentionally being disposed out of axial alignment with the stop surface is significantly reduced. According to a second aspect of the invention, there is provided a plunger assembly for use with a syringe barrel, the assembly including a collar adapted to engage one end of the barrel; and a plunger including a piston adapted to be located within the barrel, an elongate shaft extending from the piston and a push button at the end of the shaft opposite to the piston, wherein the elongate shaft is slidably retained within the collar, and wherein the plunger shaft includes a control arm which includes a first releasable stop element and a second non-releasable stop element, wherein the first and second stops are both axially spaced from the push button and wherein the control arm has a first configuration in which the first stop element is axially aligned with a stop surface defined by the collar, whereby the first stop element is adapted to limit the axial movement of the plunger, and a second configuration in which the first stop element is disposed out of alignment with the stop surface and the second stop element is axially aligned with the stop surface, whereby the second stop element is adapted to limit the plunger movement from the first stop element to the second stop element.

The additional features described and defined herein in connection with the first aspect of the invention may apply equally to the second aspect of the invention. Thus, the second aspect of the invention may include any, some or all of the additional features described

hereinabove.

According to a third aspect of the invention, there is provided a syringe kit including a syringe barrel and a plunger assembly according to the second aspect of the invention.

According to a fourth aspect of the invention, there is provided a pre-filled syringe for dispensing a fluid, the syringe including a barrel including a discharge end defining a discharge passage, the barrel containing therein a medicament in fluid form; and a plunger disposed within the barrel, the plunger being adapted to move axially within the barrel such that the plunger and discharge end define a variable volume chamber within the barrel and the plunger is capable of displacing fluid from the chamber through the discharge end;

wherein the plunger includes a control arm which includes a first releasable stop element and a second non-releasable stop element, wherein the first and second stops are both axially spaced from the rear end of the plunger and wherein the control arm has a first configuration in which the first stop element is axially aligned with a stop surface defined by a part of the barrel, whereby the first stop element is adapted to limit the axial movement of the plunger, and a second configuration in which the first stop element is disposed out of alignment with the stop surface and the second stop element is axially aligned with the stop surface, whereby the second stop element is adapted to limit the plunger movement from the first stop element to the second stop element. The additional features described and defined herein in connection with the first aspect of the invention may apply equally to the fourth aspect of the invention. Thus, the fourth aspect of the invention may include any, some or all of the additional features described hereinabove.

As used herein, the term "forward" means towards the discharge end of the syringe and the term "rearward" means away from the discharge end of the syringe.

The skilled person will appreciate that the features specified above in connection with embodiments of the invention may be combined with each other and any of the aspects of the invention as defined. Thus, the present invention includes within its scope an aspect of the invention combined with two or more of the features described anywhere herein as optional features. All such combinations of features described herein are considered to be made available to the skilled person.

Embodiments of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a syringe according to a first embodiment of the invention; Figure 2 is side elevational view of the syringe shown in Figure 1 ;

Figure 3 is a plan view from above of the plunger assembly of the syringe shown in Figure 1 ; Figure 4 is a perspective view of a syringe according to a second embodiment of the invention; and

Figure 5 is a side elevational view of the syringe shown in Figure 4.

For the avoidance of doubt, the skilled person will appreciate that in this specification, the terms "up", "down", "front", "rear", "upper", "lower", "width", etc. refer to the orientation of the components as found in the syringe when installed for normal use as shown in the Figures.

A syringe 2 according to a first embodiment of the invention is shown in Figures 1 , 2 and 3. The syringe 2 includes a barrel 4 defining a cylinder therein. Located at the rear of the barrel 4 is a collar 6 and at the opposite end, i.e. the front, of the barrel 4 is a discharge end 5 which defines therein a discharge passage. Secured to the discharge end 5 is a connecting collar 8 of a hypodermic needle 10.

The skilled person will appreciate that the hypodermic needle connecting collar 8 may be a simple friction fit with the discharge end 5 of the barrel 4 or it may be a locking collar, such as a Luer-Lok collar. The connection of hypodermic needles to syringe barrels is well known in the art and will not be described in detail herein.

The syringe 2 further includes a plunger assembly 12. The plunger assembly 12 consists of a plunger shaft 14 which terminates at its rearward end in a push button 16 and terminates at its forward end in a piston (not shown) located within the cylinder defined by the barrel 4. The plunger shaft 14 is slidably retained within the collar 6.

The push button 16 defines a rearward facing push button surface 16a which is substantially planar.

The plunger shaft 14 is cruciform in cross-section and defines a pair of opposed vertical splines 18 and a pair of opposed horizontal splines 20. Included in the plunger assembly 12 is a pair of opposed control arms 22, 24 hingedly connected to the plunger shaft 14 adjacent to the push button 16. Figure 2 shows the control arms 22, 24 in a first configuration in which the distal ends of the control arms 22, 24 are laterally spaced from the plunger shaft 14. The forward facing end surfaces of the control arms 22, 24 define the first stop elements.

The width of each of the control arms 22, 24 is slightly greater than the width of the corresponding vertical spline 18, and the height of each of the control arms 22, 24 is slightly less than the corresponding vertical spline 18. The collar 6 includes a body which defines therein a plunger shaft guide channel in the form of a cruciform aperture 30 substantially about the longitudinal axis of the barrel 4. Each of the four arms of the cruciform-shaped aperture 30 has a height which is slightly greater than the height of the corresponding spline 18, 20. The width of the horizontal arms is similarly slightly greater than the width of the corresponding horizontal splines 20. However, the width of the vertical arms of the cruciform aperture 30 is such that they are slightly wider than the width of the corresponding control arms 22, 24.

The body of the collar 6 about the cruciform aperture 30 defines a stop surface.

The vertical splines 18 each define a notch 40 which is sized to accommodate the corresponding control arm 22, 24 in their second configuration in which the control arms 22, 24 are arranged axially within the corresponding vertical spline 18. Thus, each notch 40 is substantially equal in length to the corresponding control arm 22, 24 and the depth of each notch 40 is substantially identical to the height of the corresponding control arm 22, 24.

The front facing wall of each of the control arms 22, 24 includes a recess (not shown) which is configured to receive therein a corresponding protrusion (not shown) which extends outwards from the rear facing wall of each of the vertical splines 18.

Extending outwardly from the control arms 22, 24 are respective control buttons 26, 28 in the form of short cylindrical bodies. The forward facing side wall portion of each control button 26, 28 defines a respective second stop element. In use, the barrel 4 includes a medicament in fluid form and the plunger is disposed in a start position in which the first stop elements defined by the forward facing walls of the control arms 22, 24 are spaced from the stop surface defined by the body of the collar 6. The control arms 22, 24 are in their rest position, as shown in Figure 2. A user initiates a priming step to remove any gas or dead volume from within the barrel by urging the plunger forward via the rearward facing push button surface 16a. This causes the piston within the barrel 4 to move forward, expelling the unwanted gas and priming the syringe. The priming stroke is continued until the forward facing end walls of the control arms 22, 24 engage the stop surface defined by the body of the collar 6.

Once the priming step is complete, the user exerts a force on each of the two control buttons 26, 28 which urges them towards each other. This causes the control arms 22, 24 to be located within the corresponding notch 40 of the respective vertical spline 18 and for the forward facing end walls of the control arms 22, 24 to become axially aligned with the vertical arms of the cruciform aperture 30. Thus, in this second configuration of the control arms 22, 24, the forward facing end walls of the control arms 22, 24 are no longer axially aligned with the stop surface defined by the body of the collar 6 and are capable of being received into the vertical arms of the cruciform aperture 30. When the control arms 22, 24 are fully located within the corresponding notch 40, the protrusions extending from the rearward facing end wall portions of the vertical splines 18 engage with the respective recesses formed in the forward facing end walls of the control arms 22, 24 such that the control arms 22, 24 are releasably retained in the second configuration.

Once the control arms 22, 24 are in their second configuration, the hypodermic needle 10 is inserted into or through the skin of a patient and the dose stroke is commenced. The dose stroke is defined by the short distance between the forward facing end walls of the control arms 22, 24 and the forward facing side walls of the cylindrical-shaped control buttons 26, 28. At the end of the dose stroke, the forward facing side walls of the cylindrical-shaped control buttons 26, 28 engage the stop surface defined by the body of the collar 6.

The skilled person will appreciate that the actual dose delivered by the syringe during the dose stroke is a function of the internal diameter of the barrel 4 and the spacing between the first stop elements (the forward facing end walls of the control arms 22, 24) and the second stops (the forward facing side walls of the cylindrical-shaped control buttons 26, 28). The delivery dose can be varied by varying one or both of these physical properties.

A second embodiment of the invention is shown in Figures 4 and 5.

A syringe 102 according to the second embodiment of the invention includes a barrel 104 defining a cylinder therein. Located at the rear of the barrel 104 is a collar 106 and at the opposite end, i.e. the front, of the barrel 104 is a discharge end 105 which defines therein a discharge passage. Secured to the discharge end 105 is a connecting collar 108 of a hypodermic needle 1 10.

The syringe 102 further includes a plunger assembly 1 12. The plunger assembly 1 12 consists of a plunger shaft 1 14 which terminates at its forward end in a piston (not shown) located within the cylinder defined by the barrel 4. The plunger shaft 1 14 is slidably retained within the collar 106. A push button 1 16 is slidably coupled to a rear end portion of the plunger shaft 1 14 and defines a rearward facing push button surface 1 16a which is substantially planar. A cylindrical sleeve 150 extends forward from the push button 1 16 and overlies a portion of the plunger shaft 1 14. The push button 1 16 and associated sleeve 150 can move axially relative to the plunger shaft 1 14 within fixed limits.

The plunger shaft 1 14 is cruciform in cross-section and defines a pair of opposed vertical splines 1 18 and a pair of opposed horizontal splines 120.

Included in the plunger assembly 1 12 is a pair of opposed control arms 122, 124 hingedly connected to the plunger shaft 1 14 adjacent to the push button 1 16. A proximal portion of the control arms 122, 124 adjacent to the push button 1 16 is disposed within the sleeve 150. Figure 5 shows the control arms 122, 124 in a first configuration in which the distal ends of the control arms 122, 124 are spaced from the plunger shaft 1 14. The hinged arrangement of the control arms 122, 124 is such that they are biased towards this first configuration and they provide a resistive force against movement towards each other. The forward facing end surfaces of the control arms 122, 124 define the first stop elements.

The width of each of the control arms 122, 124 is substantially the same as the width of the corresponding vertical spline 1 18, and the height of each of the control arms 122, 124 is slightly less than the corresponding vertical spline 1 18.

The collar 106 includes a body which defines therein a plunger shaft guide channel in the form of a cruciform aperture 130 substantially about the longitudinal axis of the barrel 104. Each of the four arms of the cruciform-shaped aperture 130 has a height which is slightly greater than the height of the corresponding spline 1 18, 120 and a width which is similarly slightly greater than the width of the corresponding splines 1 18, 120.

The body of the collar 106 about the cruciform aperture 130 defines a stop surface.

The vertical splines 1 18 each define a notch 140 which is sized to accommodate the corresponding control arm 122, 124 in their second configuration in which the control arms 122, 124 are arranged axially within the corresponding vertical spline 1 18. Thus, each notch 140 is substantially equal in length to the corresponding control arm 122, 124 and the depth of each notch 140 is substantially identical to the height of the corresponding control arm 122, 124.

Extending outwardly from the control arms 122, 124 are respective lugs 126, 128 in the form of triangular-shaped wedges. The forward facing wall of each of the lugs 126, 128 defines a respective second stop element. In use, the barrel 4 includes a medicament in fluid form and the plunger is disposed in a start position in which the first stop elements defined by the forward facing walls of the control arms 22, 24 are spaced from the stop surface defined by the body of the collar 6. The control arms 22, 24 are in their rest position, as shown in Figure 2. A user initiates a priming step to remove any gas or dead volume from within the barrel by urging the plunger forward via the rearward facing push button surface 1 16a. As the frictional forces between the piston and the cylinder defined within the barrel 104 and between the plunger shaft 1 14 and the cruciform aperture 130 are less than the resistive forces exerted by the control arms 122, 124, the force exerted by the user on the push button 1 16 causes the piston within the barrel 104 to move forward, expelling the unwanted gas and priming the syringe 102. The priming stroke is continued until the forward facing end walls of the control arms 122, 124 engage the stop surface defined by the body of the collar 106.

When the forward facing end walls of the control arms 122, 124 engage the stop surface defined by the body of the collar 106, further movement of the plunger shaft forward is prevented.

At this point, the hypodermic needle 1 10 is inserted into or through the skin of a patient and the dose stroke initiated.

To initiate the dose stroke, the user continues to apply force to rearward facing surface 1 16a of the push button 1 16. As the plunger shaft 1 14 is prevented from moving forward by the forward facing end walls of the control arms 122, 124 contacting the stop surface, the force is directed through the sleeve 150 to the control arms 122, 124. This force overcomes the resistive force of the control arms 122, 124 and urges them towards each other until they become axially aligned with the vertical splines 1 18 and contained within the respective notches 140. At this point the forward facing end walls of the control arms 122, 124 no longer contact the stop surface defined by the body of the collar 106 and the control arms 122, 124 are capable of entering the respective arms of the cruciform aperture 130.

When the forward facing end walls of the control arms 122, 124 disengage from the stop surface, the plunger shaft and the attached piston can continue to move forward for the dose stroke until the outwardly extending lugs 126, 128 contact the stop surface, at which point the dose step is complete.

Example 1

Tests of the first embodiment syringe described above were carried out as follows: Test Apparatus

The syringe plunger and collar were assembled to a sample 1 ml syringe barrel. A needle was fitted to the discharge end of the syringe barrel.

Preparation and Measurement

The syringe was filled with a nominal volume of RO/DI water, held vertically and tapped to release air bubbles, and primed to the first stop. A clean Eppendorf Tube was tared on an analytical balance. The control buttons were urged towards each other to release the first stops and to permit dosing, and the plunger depressed to the second stop, discharging the dose into the vial.

The vial was then closed and weighed.

The test was repeated, re-using the syringe, but taking a clean vial each time. Calculation

Dose mass was calculated from the difference in weight of the vial.

Dose volume was calculated from the mass by dividing by density.

Density = 998.022kg/m³ at lab conditions of 21°C and 42%RH Apparatus

Sartorius ME235S-OCE analytical balance (5 decimal places / 1 g)

300 μΙ Eppendorf Tubes

Syringe Device as described above

Results

Table 1

The results from N = 10 measurements

The dose delivered by the prototype in the tests is in the range 53.02 ± 5.5μΙ i.e. 47.52 to 58.52μΙ.

The syringe delivered a well controlled dose, within a tolerance of ± 5.5μΙ, which is within tolerance of ± 7.5μΙ associated with the acceptance limits.

Claims

1 . A syringe for dispensing a fluid, the syringe including a barrel including a discharge end defining a discharge passage, and a plunger disposed within the barrel, the plunger being adapted to move axially within the barrel such that the plunger and discharge end define a variable volume chamber within the barrel and the plunger is capable of displacing fluid from the chamber through the discharge end; wherein the plunger includes a control arm including a first releasable stop element and a second non-releasable stop element, wherein the first and second stops are both axially spaced from the rear end of the plunger and wherein the control arm has a first configuration in which the first stop element is axially aligned with a stop surface defined by a part of the barrel, whereby the first stop element is adapted to limit the axial movement of the plunger; and a second configuration in which the first stop element is disposed out of alignment with the stop surface and the second stop element is axially aligned with the stop surface, whereby the second stop element is adapted to limit the plunger movement from the first stop element to the second stop element, the control arm is resiliency deformable and the first configuration represents a rest or non-deflected position, and the second configuration represents a deflected position.

2. A syringe according to Claim 1 , wherein the plunger includes a retaining element to retain the control arm in the second configuration.

3. A syringe according to Claim 2, wherein the retaining element is selected from an axially slidable sleeve and a two-part clip, wherein one part of the clip is carried by the control arm and the other part of the clip is carried by the plunger.

4. A syringe according to any preceding claim, wherein the plunger includes a shaft connected at one end to a piston disposed in use within the barrel and connected at the other end to a push button, and the control arm is hingedly coupled to the shaft.

5. A syringe according to Claim 4, wherein the barrel includes a collar comprising a collar body which defines therethrough a shaft guide channel, wherein the shaft of the plunger is slidably retained within the guide channel, and wherein the collar body defines the stop surface.

6. A syringe according to Claim 5, wherein the guide channel is adapted to receive therein the first stop element when the control arm is in the second configuration.

7. A syringe according to Claim 5 or 6, wherein the shaft of the plunger includes an orientation controlling element which is adapted to maintain substantially fixed the axial orientation of the plunger shaft relative to the guide channel.

8. A syringe according to Claim 7, wherein the plunger shaft has a cruciform cross- sectional configuration and the collar body defines a guide channel having a complimentary cruciform shape.

9. A syringe according to any preceding claim, wherein the first stop element includes a forward facing end wall of the control arm.

10. A syringe according to any preceding claim, where the second stop element is a projection from the control arm which extends outwardly from the first stop element and is spaced rearwardly from the first stop element.

1 1 . A syringe according to Claim 10, wherein the second stop element is defined by a forward facing wall portion of a cylindrical control button carried by the control arm.

12. A syringe according to any preceding claim, which includes a pair of opposed control arms.

13. A plunger assembly for use with a syringe barrel, the assembly including a collar adapted to engage one end of the barrel; and a plunger including a piston adapted to be located within the barrel, an elongate shaft extending from the piston and a push button at the end of the shaft opposite to the piston, wherein the elongate shaft is slidably retained within the collar, and wherein the plunger shaft includes a control arm including a first releasable stop element and a second non-releasable stop element, wherein the first and second stops are both axially spaced from the push button and wherein the control arm has a first configuration in which the first stop element is axially aligned with a stop surface defined by the collar, whereby the first stop element is adapted to limit the axial movement of the plunger, and a second configuration in which the first stop element is disposed out of alignment with the stop surface and the second stop element is axially aligned with the stop surface, whereby the second stop element is adapted to limit the plunger movement from the first stop element to the second stop element.

14. A pre-filled syringe for dispensing a fluid, the syringe including a barrel including a discharge end defining a discharge passage, the barrel containing therein a medicament in fluid form; and a plunger disposed within the barrel, the plunger being adapted to move axially within the barrel such that the plunger and discharge end define a variable volume chamber within the barrel and the plunger is capable of displacing fluid from the chamber through the discharge end; wherein the plunger includes a control arm including a first releasable stop element and a second non- releasable stop element, wherein the first and second stops are both axially spaced from the rear end of the plunger and wherein the control arm has a first configuration in which the first stop element is axially aligned with a stop surface defined by a part of the barrel, whereby the first stop element is adapted to limit the axial movement of the plunger, and a second configuration in which the first stop element is disposed out of alignment with the stop surface and the second stop element is axially aligned with the stop surface, whereby the second stop element is adapted to limit the plunger movement from the first stop element to the second stop element.