Injection devices

A one-shot throwaway injection device has a barrel that houses a syringe initially in a retracted state held back by a trigger against a drive spring. Actuation of the trigger causes the syringe to be thrust forwards by the spring acting on its plunger until the needle is fully projecting, and then the dose is ejected by the final expansion of the spring. Release of the trigger allows a return spring to urge the syringe back and retract the needle. The barrel is a unitary plastics moulding of two longitudinally split halves hinged together with the trigger integrally formed with one of these halves. The other components and the syringe are positioned in one half which is then closed up and fastened to the other half to complete the barrel.

BACKGROUND OF THE INVENTION

This invention relates to injection devices.

It concerns devices which are fitted with a syringe having a capsule with a needle projecting from the forward end and a plunger from the rear end. A trigger and spring mechanism, when operated, shoots the syringe forwardly to project the needle, and then continues to act on the plunger to eject the dose. There is also a return spring arrangement to retract the needle after use, thereby making it safe.

Hitherto, these firing devices have been quite complicated and expensive, and it is necessary to load and unload the syringe before and after use and to keep the device itself for repeated use. It is too expensive simply to throw away. Also there have been problems with ensuring that the return spring works properly.

However, unloading particularly has its dangers with a sharp and possibly contaminated needle, and it is the aim of this invention to provide an injection device which is simple and cheap enough to be thrown away with the syringe safely retracted inside it.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided an injector device for containing and operating a syringe having a capsule with a needle projecting from the forward end and a plunger from the rear end, the device having a first spring initially in a compressed energised state at the rear end of the device held by a trigger, and a second spring initially not fully energised and surrounding the capsule, wherein operation of the trigger releases the first spring which first urges the syringe forwardly by acting on the plunger and thence through the dose within the syringe, and secondly, when the syringe reaches a needle projecting position, presses the plunger forwards relative to the capsule to eject the dose, and wherein the second spring, fully compressed by this action, then exerts itself to retract the syringe and its needle, characterised in that the device has an integrally moulded two-part body formed in an open state, the trigger also being part of the integral moulding, and in that the body is closed and secured around a dose filled syringe in the retracted position and the first and second coil springs.

Conveniently, the body is in two substantially semi-cylindrical halves, joined by at least one thin web along adjacent longitudinal edges.

Preferably the trigger is a portion separated from a respective half of the body by all but webs that form a transverse hinge at an intermediate position along the trigger. The rear end of the trigger may have an inward projection that initially maintains the first spring primed, release being by pressing inwardly on the forward end. This forward end may have a pawl to catch behind the capsule when the capsule reaches the needle projecting position, thereby to prevent retraction under the influence of the second spring as long as the forward end remains pressed inwardly or the trigger is operated positively to withdraw the pawl.

The trigger may be duplicated, with one on each half, these triggers being squeezed together to operate the device.

Generally, there will also be a separately moulded protective cap to fit over the forward end of the completed body. This cap is conveniently adapted to co-operate with the trigger to prevent that being operated while the cap is on. The cap can also have an internal formation that projects into the barrel to co-operate with a sheath initially provided over the needle of the capsule, removal of the cap causing the sheath to be pulled off the needle.

The cap may be refitted after use, to be thrown away with the injection device.

According to another aspect of the invention there is provided an injector device for containing and operating a syringe having a capsule with a needle projecting from the forward end and a plunger from the rear end, the device having a first spring initially in a compressed energised state at the rear end of the device held by a trigger, and a second spring initially not fully energised and surrounding the capsule, wherein operation of the trigger releases the first spring which first urges the syringe forwardly by acting on the plunger and thence through the dose within the syringe, and secondly, when the syringe reaches a needle projecting position, presses the plunger forwards relative to the capsule to eject the dose, and wherein the second spring, fully compressed by this action, then exerts itself to retract the syringe and its needle, characterised in that the trigger is adapted to provide an obstruction to the syringe to prevent the retraction thereof as long as the trigger is maintained in its operated state, the retraction requiring release or an alternative operation of the trigger.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The injection device is designed to contain and operate a syringe having a capsule1, a needle2at its forward end, and a plunger3at its rearward end which can actuate a piston4within the capsule to eject a dose through the needle2. The rear end of the capsule has an outwardly projecting rim5. This syringe is of known form.

The body of the injection device is formed by two generally semi-cylindrical halves6and7brought together and secured by adhesive or welding for example, or by snap-fitting lugs and sockets, to make a barrel with tapers at each end. The halves6and7are moulded in one piece in an opened-out condition, being joined by a single long web, or several shorter webs8. These extend along one pair of adjacent longitudinal edges of the halves6and7between the tapering ends, and serve as hinges when the halves are closed together.

Towards its forward end the body reduces internally at a shoulder9to a passage10which serves as a longitudinal guide for the capsule1. At about the mid-length, there are internal ribs11non-obstructive to the piston4and the member described below which drives it but which form an abutment for the rim5. A coil spring12, initially only partially compressed, surrounds the capsule to act between the shoulder9and the out-turned rim5. The forward end of the barrel is open for passage of the needle2.

At the rear end the barrel is closed and provides a seat for another coil spring13, initially compressed and nesting in the rearward facing cup of a slider14forming a drive member. The forward end of this slider bears against the rear end of the piston4and it has a finger15projecting forwardly to one side of that rear end and outside the cylindrical envelope of the spring13. The slider14is prevented from rotating by wings16which run in internal grooves17along the barrel, these grooves being formed by rebates inside the edges of the halves6and7coming together when the device is closed up.

The half6of the barrel is formed with a trigger18of generally rectangular form extending lengthwise of the barrel. It is separated from the half6around most of its periphery except for two short webs19at opposite sides in the region of the ribs11. These webs form a transverse hinge, the plastics material of which the barrel is moulded allowing a certain flexible resilience. The rear end of the trigger18has one part, such as inwardly projecting abutment20, against which the finger15initially bears. At the leading end of each trigger, as best seen inFIG. 6, there is a finger pad21proud of the barrel, forward of which are two undercut parallel wings22. Between these wings, and stepped down to the envelope of the barrel, there is a second part, such as pawl23with a tooth24projecting inwardly at its forward end. The second part can hinge about its rear end by virtue of the plastics construction. Another finger pad25is provided towards the rear of the trigger.

As supplied, this injection device has a cap26which fits closely over the forward portion of the barrel, as shown in outline in FIG.1. It has a rearward extension27to engage the undercuts below the wings22and over the back of the pawl23. It is illustrated approaching this position in FIG.6. At the forward end, the cap may have an internal formation which extends inside the barrel and which engages behind the base of a needle sheath (not shown) in known manner.

In theFIG. 1position, the injector is inoperative, the trigger18being held against actuation by the extension27of the cap26. The spring12is partially compressed and semi energised, and the spring13is fully compressed and therefore fully energised. When the device is to be used, the cap is pulled off, this simultaneously freeing the trigger and removing the sheath.

The device is then applied against the skin of the patient and the finger pad21is pressed in as shown in FIG.2. This hinges the trigger18so that the abutment20is moved outwardly, clear of the finger15, thus freeing the compressed spring13. This expands and, through the slider14and the plunger3, thrusts the syringe forwards.

The trigger action depresses the pawl23towards the syringe, where the tooth24might interfere with the spring11. However, because of its flexibility, the pawl bends outwards and snaps over the rearward turns of the spring12and the rim5. The spring12is slightly stiffer than the spring13over the intermediate and final parts of the latter's expansion, in order to ensure the return of the syringe, but the momentum of the forward thrust ensures that the spring12is fully compressed.

When that is achieved, the capsule1is arrested and the pawl23snaps back into alignment with the trigger for the tooth24to engage behind the rim5as shown inFIGS. 2 and 3. It may be long enough to remain engaged if the trigger18is released, or it may be short, requiring the finger pad21to be held down. In any event, the needle2is now fully projected, but the spring13, no longer opposed by the spring12, continues to expand and the plunger3presses the piston4forwards, ejecting the dose.

The device is then withdrawn from the patient and the finger pad21released if the device is a short tooth version. The trigger18springs back to its initial position, the pawl23releasing from the rim5. With a long tooth version, the user presses on the rear finger pad25to tilt the trigger back and release the pawl. The spring12can now exert itself and push the syringe back, retracting the needle2to the position of FIG.4. The cap26may then be refitted, and the device thrown away.

There is a risk that, when pulling off the cap26, the user will hold the barrel in a manner that will squeeze the finger pad21, thereby prematurely firing the device. To prevent this, the rim of the cap and the trigger may be so configured that pressure on the finger pad will prevent release of the cap. For example, the end of the extension27may be slightly out-turned and the undercuts of the wings22notched to receive the out-turned end. The user will, therefore, have to grip the barrel clear of the trigger, allowing the cap to snap free.

It will be understood that the barrel can have one or more windows, particularly in the forward part in order that the state and position of the syringe can be visually checked.