WO2009023913A1

WO2009023913A1 - Safety syringe with plunger locking means

Info

Publication number: WO2009023913A1
Application number: PCT/AU2008/001210
Authority: WO
Inventors: Graeme Francis Walton; Allan Walsh; Chris Dolan
Original assignee: Global Medisafe Holdings Limited
Priority date: 2007-08-20
Filing date: 2008-08-20
Publication date: 2009-02-26
Also published as: CN101932351A; KR101557398B1; EA201000318A1; MX2010001974A; BRPI0814925A2; CN101932351B; AP2010005197A0; EP2187997A1; CA2696951A1; JP2010536441A; KR20100087076A; AU2008288687A1

Abstract

Λ safety syringe (11) is disclosed. The safety syringe has a retractable needle facility (14/15) incorporated therein, the syringe comprising a barrel (12) and plunger (13) and needle assembly. The needle is caused to retract into the barrel of the syringe upon completion of injection once it has been used, by means of engagement between the needle assembly and the end of the plunger. Locking means (28) preferably in the form of a locking bush is provided in the body of the syringe to engage the plunger once it is retracted after use, so that the syringe is rendered incapable of being used further.

Description

SAFETY SYRINGE WITH PLUNGER LOCKING MEANS Technical Field

This invention relates to a safety syringe having a retractable needle for use in the medical or dental profession or in personal drug administration so that the physician, surgeon or other needle operator might be protected from injury by the needle after its use. In particular it relates to locking means for retaining the plunger to which the needle is attached, and hence the needle, in the retracted position.

Background

The danger of injury and possible infection from the HlV or hepatitis B virus to medical practitioners using needles in the normal course of their business is well documented.

Further, persons who are in the habit of administering drugs to themselves run a severe risk of contacting either of the specified viruses, or indeed contacting other viruses if a needle, once used, is reused in an unstcriJised form.

There have been many proposals aimed at reducing the number of so-called needle-stick injuries and various attempts have been made to provide a safe system for disposal of such needles once used, but such prior proposals have had deficiencies.

Many solutions to the foregoing problems provide for retractable needles. One of the major disadvantages in many previous proposals is that the syringe although rendered initially safe by having the needle retracted, does not usually provide means for preventing further access to the needle. In other words, lhe plunger may be depressed again causing the needle to re-emerge from the barrel of the syringe, or in some other instances may be withdrawn altogether form the barrel of the syringe thereby gaining , access to the needle.

Object of the Invention It is an object of the present invention to provide a syringe which to some extent solves or at least ameliorates some or all of the foregoing disadvantages by employing a retractable surgical needle, and for permanently storing that surgical needle, once used, in a substantially safe manner. In particular, the present invention provides for a positive locking facility to prevent the plunger, to which the withdrawn needle is attached, from being reactivated or withdrawn altogether, once the syringe is rendered safe by having the needle retracted. At the very least the invention provides an alternate means for accommodating the needle of a used syringe to protect against accidental injury arising from unwanted contact with the exposed needle once the syringe has been used.

Although the following description generally refers to a syringe of conventional size, no such limitation is intended thereby, and reference to a syringe is meant to encompass any other needle/syringe combination or needle alone including slimline syringes, where, by suitable adaptation, the invention may also be usefully applied. Disclosure of the Invention

According to the present invention there is provided a safety syringe having a retractable needle facility incorporated therein, the syringe comprising a barrel and plunger and needle assembly, wherein the needle is caused to retract into the barrel of the syringe upon completion of injection once it has been used, by means of engagement between the needle assembly and the end of the plunger, and wherein locking means is provided in the rear of the body of the syringe in the form of a ring to engage the plunger once it is retracted after use, so that the syringe is rendered incapable of being used further in that the plunger can neither be pushed down again to reactive the needle, nor can it be removed altogether from the barrel of the syringe to gain access to the needle; and wherein fitment of the ring to the plunger is facilitated by a plunger comprising two portions which are joined after the ring is fitted thereto.

Preferably a region of weakness is provided in toe plunger, located on the shaft of the plunger in the vicinity of where it extends from the end of the syringe body when fully withdrawn, so that after the needle is retracted into the body of the syringe, and the plunger is engaged with the locking means, the plunger is broken off so that it cannot be depressed again, or readily removed by gripping it and exerting force, thereby further assisting in rendering the syringe incapable of being used again.

Tt will be understood that whilst the invention is arguably improved by the ability to break off the plunger as well, it should be appreciated that this is an extra step and one that some users might ignore. Therefore the present invention provides for the locking means to be of sufficient resistance to prevent the plunger from being depressed or removed so that it does not matter that the plunger is broken off. In other words, even before the plunger is broken off, the present invention envisages that the syringe will be rendered ineffective against ether deliberate or even accidental re-use as might occur if the syringe were knocked as it was being placed on a table for example.

Fitment of the bush or ring to the plunger is achieved by having a two part plunger, the two parts of which are fitted after the ring is fitted about the shank of the plunger. Various means by which this may be achieved include having the shank of the phinger in two portions so that they can be fitted together after the ring is located on one part, or having the end portion of the plunger which is the thumb tab separate until the ring or bush is fitted.

The bush or ring may utilise any one of a variety of methods to engage the plunger once it has engaged the needle and caused it to be withdrawn into the barrel of the syringe, including, but not necessarily limited to twisting or pulling the plunger through or into the bush as the case may be. In those bushes where a twisting motion is required, the bush may be a twist-lock bush or a threaded bush or may be a luer-lock type bush. Alternatively in embodiments where a pull motion is required, the bush may be a pull- lock bush or snap-lock bush. Examples of these bushes are illustrated in the accompanying drawings and discussed below in relation to the description of the respective drawings.

Thus in the foregoing embodiments, the bush is pressed into the barrel when/after the plunger is inserted during manufacture. A variety of locking options are also available to retain the bush in the barrel, once it thus inserted. Any combination of locking mechanism to retain the plunger in the locking bush may be coupled with any one of the such means by which the bush itself is retained in the barrel of the syringe.

It will be appreciated that there are many different means available by which the bush can be used to lock the plunger and these are contemplated as being within the scope of the invention. It is also preferred that a vertical or longitudinal protrusion within the end of the barrel where the bush is inserted, is provided whereby the bush may be prevented from turning, particularly in those cases where a split bush is utilised or where a twisting action is required to lock the plunger in the bush. The plunger itself is provided with a flange about its distal end to prevent it from being pulled right through the locking means, in this way the syringe will not only be rendered ineffective against the plunger being depressed again, but also rendered safe in that the plunger with the needle attached cannot be removed altogether. Thus, once the plunger locks into the bush, neither the plunger nor the bush itself may be withdrawn to otherwise gain access to the needle located within the barrel after it has been withdrawn into the barrel.

Thus, locking of the plunger in the bush is preferably provided by a flange located on the plunger, preferably located just above the piston region of the plunger, allowing the plunger to be thus locked against die bottom of the bush, and preventing the plunger from being entirely withdrawn.

By providing a break point in the plunger, as discussed above, it will also prevent or at least ininimise the possibility of further tampering, especially preventing access to the plunger in a way which allow it to be forced back into the barrel or gripped for removal by excessive force. Thus for example one preferred embodiment utilises a twist lock feature including corresponding threaded regions in the barrel of the syringe and on the plunger, so that after an injection the plunger is withdrawn and locked in position by twisting the plunger to engage the corresponding threaded portions.

Alternatively the locking means is provided by a twist lock feature including a twist lock bush having helix grooves therein located in the barrel of the syringe and corresponding lugs located on the plunger for engagement in the helix grooves, so that after an injection, the plunger with the needle attached is withdrawn and locked in position by twisting the plunger to engage the lugs in the corresponding helix grooves. Again, as an alternative, the locking means may be provided by a twist lock feature including a twist lock bush having helix grooves therein located in the barrel of the syringe and lugs located on the plunger for engagement in the helix grooves, so that after an injection the plunger is withdrawn and locked in position by twisting the plunger to cause the lugs to move through the corresponding helix grooves and pass completely through the bush.

In this embodiment, a permanent lock facility is provided in the form of a ramp or other protrusion to prevent the lugs from returning through the grooves of the bush and hence preventing the plunger from passing back through the bush into the barrel of the syringe. More preferably however, it has been found that a locking bush with a simple flange arrangement is both easy to produce and effective. In this arrangement a flange around the internal perimeter of the bush allows a corresponding flange on the plunger to pass in one direction, but by virtue of the shape of the flanges prevents its return. In combination with an additional flange on the plunger as described above, the plunger is prevented from being drawn right through the bush providing an effective lock against movement in either direction.

Instead of a flange around the entire internal perimeter of the bush, it has been found that a pair of fingers function just as efficiently. Movement of the fingers to allow the first flange of the plunger to pass can be achieved by shaping the internal region of the barrel to allow the fingers to bend back as the flange of the plunger passes, snapping back by virtue of the resilience once the first flange has passed.

Although much of the following description refers to a particular safety syringe having a retractable needle with certain features, it will be understood that the twist locking mechanism may be utilised with any syringe having any form of retractable needle facility.

The invention finds application for example in one broad embodiment which provides a syringe having a retractable needle facility incorporated therein, so that in a first storage position prior to use, the needle is safely enclosed within the body of the syringe and in a second in use position, the needle is caused to extend from the body of the syringe so as to function as a useful needle and syringe combination in known fashion, and wherein the needle is then caused to retract again into the body of the syringe, once it has been used, so as to return it to the first storage position; the syringe comprising a body and plunger, wherein the plunger has means associated with the end thereof contained within the body of the syringe to releasably engage a boss of the needle located in the syringe body so as to retain the needle within the syringe body in the first storage position, and wherein the body of the syringe has means located at the end thereof opposite to where the plunger extends from the body tor releasably retaining the needle boss in the second in use position so that the needle extends from the syringe body, the plunger being used to bring the needle boss into engagement with the end of the syringe body; the plunger then being able to be disengaged from the needle boss so as to enable the plunger to be withdrawn and thereby take in fluid into the syringe and then to be used to inject same into a patient in known fashion; and when upon completion of injection, and the needle having been withdrawn from the patient, the plunger is once again brought into engagement with the needle boss and withdrawn so as to cause the needle boss to be released from the end of the syringe body so that the needle is once again retracted into the body of the syringe, the needle remaining attached to the end of the plunger; and wherein locking means is provided in the body of the syringe in the form of a ring to engage the plunger once it is retracted after use, so that the syringe is rendered incapable of being used further in that the plunger can neither be pushed down again to reactive the needle, nor can it be removed altogether from the barrel of the syringe to gain access to the needle; and wherein fitment of the ring to the plunger is facilitated by a plunger comprising two portions which are joined after the ring is fitted thereto. Alternatively, the invention finds application for example in another broad embodiment which provides a single use safety retractable syringe having a retractable needle, the syringe including a hollow barrel, a plunger which slideably fits in the barrel, a piston which fits on the forepart of the plunger, and an actuator mechanism, which is located in the forepart of the barrel and which is able to be fitted therein through the open end of that forepart of the hollow barrel, the actuator mechanism having a stem for supporting a needle hub, and means located on the end of the plunger to engage the actuator and cause it to retract with the needle upon completion of the injection, wherein the stem of the actuator is hollow and provided with at least one flexible finger member and wherein at the point where the actuator is located in the barrel, there is provided an inner flange on the barrel and a corresponding flange on the actuator mechanism, the respective flanges being so shaped, having bevel surfaces on one side and right angled surfaces on the other, so that when the plunger is depressed, the flange of the actuator mechanism locks against the corresponding inner flange of the barrel, by virtue of the opposing right angled surfaces coming into contact, so that in normal use the actuator will not be dislodged from the barrel when the piston is depressed during an injection under normal use conditions, and wherein only a minimal force is required to have the stem of the plunger engage with the actuator, thereby reducing discomfort in use; and wherein locking means is provided in the body of the syringe in the form of a ring or bush to engage the plunger once it is retracted after use, so that the syringe is rendered incapable of being used further in that the plunger can neither be pushed down again to reactive the needle, nor can it be removed altogether from the barrel of the syringe to gain access to the needle; and wherein fitment of the ring to the plunger is facilitated by a plunger comprising two portions which are joined after the ring is fitted thereto. Again, the plunger is thus caused to engage with the locking bush and preferably snapped off at the break point to render the syringe safe and ineffective against further use.

The invention is thus of particular benefit in that the needle is not only safely retracted after use, but is locked in that position by means oCLhe locking bush. Snapping off the plunger also renders the syringe both ineffective for subsequent use as well as providing additional safety in that there is no means by which the needle can be caused to re-emerge or caused to extend from the syringe body, whether accidentally or through deliberate tampering and also takes up less space in a "sharps" container. Brief Description of the Drawings

The invention may be better understood from the following non-limiting description of preferred embodiments, in which:

Figures 1 is a cross sectional view of one embodiment of the invention utilising a 5 locking bush according to one aspect of the invention in which a snap lock bush is utilised to retain the plunger after use;

Figure 2 is a cross sectional view of the plunger utilised in the embodiment of Figure 1, showing a thumb tab fitted to the shank of the plunger in the form of a cap,

Figure 3 is a cross sectional view of the shank of the plunger and the thumb tab io separated,

Figure 4 is a cross sectional view of the end of the barrel of Figure 3 to which a locking bush is to be fitted,

Figure 5 is a cross sectional view of a preferred embodiment of a locking bush for use with the syringe and its components as illustrated in Figures 1 to 4,

15 Figure 6 is a plan view of the locking bush of Figure 5,

Figures 7 and 8 show from two perspectives the bush of Fig 5,

Figure 9 is a cross sectional view of the end of the plunger and the bush of the previous figures, after engagement has taken place,

Detailed Description of the Drawings

20 Referring generally to the Figures, there is shown a syringe according to one aspect of the invention generally referenced 11 , which comprises a syringe body or barrel 12, a plunger 13 slideable therein and a needle 14. The needle 14 is provided with a hub 15. The plunger 13 is shown separately in Figures 2 and 3 for greater clarity, where it comprises a stem 44 and thumb tab 43 in the form of a cap located on the stem portion

25 44.

The needle hub 15 is located by interference fit in an actuator 16, fitted inside the end of the barrel 12. The needle 14 is protected by a cover 21 prior to use.

Clip means 22 are located within the needle hub 15 to engage with the end of the plunger 13, when the plunger 13 is brought into contact with the needle hub 15 at the end of the injection.

5 Plunger 13 is also provided with a piston region 26 about its lower periphery which seals against the inside of the syringe body 12, when inserted therein. Plunger 13 has a thumb tab 24.which is fitted on to the plunger stem like a cap as shown in Fig 2 and Fig 3.

A break groove or weaker region 27 is provided at a suitable location on the plunger 13, o so that it may be broken off after it has retracted the needle 14 into the barrel of the syringe 12, that is to say, after use as described below.

A locking bush or ring 28 is located in the rear or upper region of the barrel 12. The bush is first fitted over the shaft or stem 44 of the plunger 13 during assembly and the thumb tab 24 is snapped onto the shaft 44 and held in place by suitable means, using fors example mechanical means such as snap lock facility as illustrated in Fig 2 to 3 or adhesive or welding means.

Details of the locking bush 28 and relevant portions of the syringe 11 pertaining to its use are illustrated in detail in Figures 4 to 9.

Referring to Fig 5 to 8, locking bush 28 has a flange 30 located about its periphery and a0 pair of fingers 31 depend from the bush 28 formating with a corresponding circumferential groove region 32 located between circumferential flanges 33 and 34 located near the end region of the plunger 13. The flange 33 and fingers 31 are suitably ramped on one side to provide ease of passing, but have faces on the other side which are effectively parallel with each other, so as to prevent return. s Turning to Fig 4, the profile of the inner region 35 of the end of the barrel 12 similarly allows for ease of fitment and retention of the bush 28 therein specifically by providing a groove 36 into which flange 30 locates for mating engagement with appropriate ramping where required to assist in fitment. In particular a recess 37 is provided behind the fingers 31 of the bush 28 when it is in place (as shown in Figure 1 ), so that the fingers 31 can deform as the end of the plunger 13 engages therewith.

A flange 38 is also located about the periphery of the bush to strengthen it and assist in alignment of lhe bush 28 when being fitted to the barrel 12. Essentially flange 38 stops 5 the bush from twisting and popping out when the plunger is retracted fully into the bush or ring and force exerted thereon.

Specifically, the first flange 33 is able to pass the fingers 31 by pushing them into the recess 37 as that region ofthe plunger 13 passes the fingers 31 of the bush 28. The second flange 34 is provided with a greater diameter than that of flange 33 so as to be 10 prevented from passing the fingers 31, thereby locking the plunger 13 when the fingers 31 thus engage in the groove 36. The plunger 13 can the be neither pulled further through the bush 28 by virtue of flange 34_» nor can it be depressed again by virtue of flange 33.

Thus in use, after an injection has been completed, the plunger 13 is pushed home to 15 engage with the needle hub 15. The plunger 13 with needle 14 engaged is then retracted, the needle 14 being thus withdrawn into barrel 12, the plunger 13 being then drawn fully back so as to engage with the locking bush 28 by means of flanges 33 and 34 preventing the plunger from moving in either direction once the fingers 31 have engaged in the groove 36 located therebetween.

20 The plunger 13 is then snapped off at break point 27. With the plunger 13 disabled and the needle 14 retracted inside the body 12 ofthe syringe 11, it is rendered totally useless and may then be disposed of safely.

Illustrated in Figs 10 to 12 are three alternate embodiments ofthe two part plunger arrangement. In Fig 10, the stem ofthe plunger 13 is split into two components 41 and 25 42, whereas in Fig 11 and Fig 12 the thumb tab 43 is separate from the stem 44 prior to assembly, ie prior to assembly so as to allow in either case, the bush or ring to be fitted over the stem portion ofthe plunger, the portions being joined after the ring or bush is fitted. Subsequently, the plunger is the fitted into the barrel and the bush or ring locked into position. Alternatively, the portion 41 or 44 as the case may be, is fitted into the barrel during assembly and the ring or bush fitted thereto, and then portion 42 or 43 respectively fitted to portion 41 or 44. it will be appreciated by those skilled in the art that many modifications and variations may be made to the embodiments described herein without departing from the spirit or scope of the invention.

Throughout the specification the word "comprise" and its derivatives are intended to have an inclusive rather than exclusive meaning unless the context requires otherwise.

The invention disclosed herein has utility in that provides an alternate means for a safety syringe having a retractable needle facility which can be rendered useless after an injection by locking the plunger and breaking it off

Claims

1. A safety syringe having a retractable needle facility incorporated therein, the syringe comprising a barrel and plunger and needle assembly, wherein the needle is caused to retract into the barrel of the syringe upon completion of injection once it has been used, by means of engagement between the needle assembly and the end of the plunger, and wherein locking means is provided in the rear of the body of the syringe in the form of a ring or bush to engage the plunger once it is retracted after use, so that the needle/syringe is rendered incapable of being used further in that the plunger can neither be pushed down again to reactive the needle, nor can it be removed altogether from the barrel of the syringe to gain access to the needle; and wherein fitment of the ring to the plunger is facilitated by a plunger comprising two portions which are joined after the ring is fitted thereto.

2. Λ safety syringe according to claim 1 wherein a region of weakness is provided in the plunger, located on the shaft of the plunger in the vicinity ol^" where it extends from the end of the syringe body when fully withdrawn, so that after the needle is retracted into the body of the syringe, and the plunger is engaged with the locking means, the plunger may be broken otTso to render the syringe incapable of being used again.

3. A safety syringe according to any one of the preceding claims in which the bush is pressed into the barrel after the plunger is inserted.

4. A safety syringe according to any one of the preceding claims, in which any suitable locking mechanism to retain the plunger in the locking bush is coupled with any suitable means by which the bush itself is retained in the barrel of the syringe.

5. A safety syringe according to any one of the preceding claims in which a vertical or longitudinal protrusion within the end of the barrel where the bush is inserted, is provided whereby the bush is prevented from turning.

6. A safety syringe according to any one of the preceding claims in which the plunger is provided with a flange about its distal end to prevent it from being pulled right through the locking means.

7. A safety syringe according to claim 6 in which the plunger is able to be locked against the bottom of the bush, preventing the plunger from being entirely withdrawn.

8. A safety syringe according to any one of the preceding claims in which the bush 5 utilises twisting or pulling of the plunger through or into the bush.

9. A safety syringe according to claim S in which the bush is a twist-lock bush and the twisting is provided by a threaded bush or a lucr-lock bush.

10. A safety syringe according to either claim 8 or claim 9 in which the syringe utilises a twist lock feature including corresponding threaded regions in the barrel of the io syringe and on the plunger, so that after an injection the plunger is withdrawn and locked in position by twisting the plunger to engage the corresponding threaded portions.

1 1. A safety syringe according to either claim 8 or claim 9 in which the syringe utilises locking means in the form of a twist lock feature including a twist lock bush having is helix grooves therein located in the barrel of the syringe and corresponding lugs located on the plunger for engagement in the helix grooves, so that after an injection, the plunger is withdrawn and locked in position by twisting the plunger to engage the lugs, in the corresponding helix grooves.

12. A safely syringe according to either claim 8 or claim 9 in which the locking means ₂0 is provided by a twist lock feature including a twist lock bush having helix grooves therein located in the barrel of the syringe and lugs located on the plunger for engagement in the helix grooves, so that after an injection the plunger is withdrawn and locked in position by twisting the plunger to cause the lugs to move through the corresponding helix grooves and pass completely through the bush.

₂5 13. A safety syringe according to either claim 8 or claim 9 in whiςh the locking means is provided by a bush having two spiral grooves, which mate with two lugs on the plunger which engage the spiral grooves when the plunger is retracted locking the plunger 13 as it is twisted.

14. A safety syringe according to either claim 8 or claim 9 in which the locking means is in the form of a bush having a thread, and wherein as the plunger is retracted and the thread is engaged with a corresponding thread on the plunger, rotation will stop when the shoulder in the bush is reached, whilst at the same time the flange above the piston locks onto the bottom of the threaded bush.

15. A safety syringe according to any one of claims 1 to 7 in which the bush is a pull- lock bush or snap-lock bush.

16. A safety syringe according to claim 15 in which the locking means has a ramp or other protrusion to prevent the lugs from returning through the grooves of the bush and hence preventing the plunger from passing back through the bush into the barrel of the syringe.

17. A safety syringe according to claim 16 in which a flange is located arotmd the internal perimeter of the bush allows a corresponding flange on the plunge* Wp^UftT in one direction, but by virtue of the shape of the flanges prevents its return and wherein in combination with an additional flange on the plunger as described above, the plunger is prevented from being drawn right through the bush providing an effective lock against movement in either direction.

18. A safety syringe according to claim 16 in which a pair of fingers cooperates with the first flange of the plunger allowing it to pass by virtue of the shaping of the flanges in ramped arrangement and by the shaping of the internal region of the barrel to allow the fingers to bend back as the flange of the plunger passes, snapping back by virtue of the resilience once the first flange has passed

19. A safety syringe according to claim 16 in which the locking bush is a snap-lock bush in which the inside has a locking taper and a step, so that as the plunger is retracted through the snap lock tapered flange, it engages the tapered locking fingers by spreading them to allow the plunger through, and wherein the tapered fingers snap back around the plunger taper and the two steps, one on the plunger Λtϊd the other at the top of the fingers inside the bush, lock thereby making it impossible for the plunger to be pushed down or pulled either way.

20. A safety syringe according to claim 1 having a retractable needle facility incorporated therein, so that in a first storage position prior to use, the needle is safely enclosed within the body of the syringe and in a second in use position, the needle is caused to extend from the body of the syringe so as to function as a useful needle and syringe combination in known fashion, and wherein the needle is then caused to retract again into the body of the syringe₄ once it has been used, so as to return it to the first storage position; the syringe comprising a body and plunger, wherein the plunger has means associated with the end thereof contained within the body of the syringe to releasably engage a boss of the needle located in the syringe body so as to retain the needle within the syringe body in the first storage position, and wherein the body of the syringe has means located at the end thereof opposite to where the plunger extends from the body for releasably retaining the needle boife in the second in use position so that the needle extends from the syringe body, the plunger being used to bring the needle boss into engagement with the end of the syringe body; the plunger then being able to be disengaged from the needle boss so as to enable the plunger to be withdrawn and thereby take in fluid into the syringe and then to be used to inject same into a patient in known tashion; and when upon completion of injection^ and the needle having been withdrawn from the patient, the plunger is once again brought into engagement with the needle boss and withdrawn so' aβ-to cause the needle boss to be released from the end of the syringe body so that theτ>eedie is oace again retracted into the body of the syringe, the needle remaining attached to the end of the plunger, and wherein locking means is provided in. the_. body of the syringe in the form of a ring^{^} to engage the plunger once it is retracted after use, so that the syringe is rendered incapable of being used further in that the plunger can neither be pushed down again to reactive the needle, nor can it be removed altogether from the barrel of the syringe to gain access to the needk; and wherein fitment of the ring or bush over the plunger is facilitated by a plunger comprising two portions which are joined after the ring is fitted thereto.

21. A safety syringe according to claim 20 wherein the two portions of the plunger comprise a stem portion and a separate thumb tab portion.

22. A single use safety retractable syringe having a retractable needle, the syringe including a hollow barrel, a pluager which slideably fits in the barrel, a piston which fits on the forepart of the jftunger, and an actuator mechanism, which is located in the forepart of the barrel and which is able to be fitted therein through the open end of that forepart of the hollow barrel, the actuator mechanism having a stem for supporting a needle hub, and means located on the end of the plunger to engage the actuator and cause it to retract with the needle upon completion of the injection, wherein the stem of the actuator is hollow and provided with at least one flexible finger member and wherein at the point where the actuator is located in the barrel, there is provided an inner flange on the barrel and a corresponding flange on the actuator mechanism, the respective flanges being so shaped, having bevel surfaces on one side and right angled surfaces on the other, so that when the plunger is depressed, the flange of the actuator mechanism locks against the corresponding inner flange of the barrel, by virtue of the opposing right angled surfaces coming into contact, so that in normal use the actuator will not be dislodged from the barrel when the piston is depressed during an injection under normal use conditions, and wherein only a minimal force is required to have the stem of the plunger engage with the . actuator, thereby reducing discomfort in use; and wherein locking means is provided in the body of the syringe in the form of a ring or bush to engage the plunger once it is retracted after use, so that the syringe is rendered incapable of being used further in that the plunger can neither be pushed down again to reactive the needle, nor can it be removed altogether from the barrel of the syringe to gain access to the needle; and wherein fitment of the ring to the plunger is facilitated by a plunger comprising two portions which are joined after the ring is fitted thereto

23. A safety syringe according to any one of claims 20 to 22, wherein after the plunger has been caused to engage with the locking bush it is then snapped off at the break point to render the syringe safe and ineffective against further use.

4. A safety syringe having locking means for locking the plunger thereof after use to preventing further use of the syringe substantially as disclosed herein in conjunction with the drawings.