This invention relates to an accessory for use in the needleless injection of a stream of injectate through the skin of a subject.

Needleless injectors are used as an alternative to needle-type hypodermic syringes for delivering liquid drugs and medicaments directly through the patient's skin and into the tissues without using a hollow needle. Such injectors consist of a piston pump driven by a spring or pressurised gas, which ejects the liquid drug or medicament through a small discharge orifice at a sufficient rate and pressure to pierce the skin and enter the tissues through the hole thus formed.

Such injectors have been known for over fifty years, and, until recently, multi- dose injectors were a common device for vaccinating large numbers of people economically. However, with the advent of AIDS, and the increase in other highly infectious diseases such as hepatitis B, it was found that such multi-dose injectors could pick up infectious body fluid from one patient and transfer it to the next. This occurred as the result of the nozzle and its surrounding structure touching the skin: either infectious fluid already on the skin or a slight reflux of infectious blood through the injection hole in the skin would be sufficient to contaminate the nozzle. Consequently, multi-dose injectors are now hardly used except in veterinary applications. Nevertheless, such injectors have the lowest cost per dose of any parenteral delivery system, and there have been attempts recently to provide injectors which have the drug delivered from a disposable capsule attached manually to the injector. However, when vaccinating large numbers of people, such methods can be inconvenient, and they certainly add to the cost.

According to the present invention there is provided a member for use in needleless injection of a stream of injectate through the skin of a subject, said member being suitable for placing in contact with the skin during injection and being piercable by the stream of injectate when delivered thereto at pressure such that after passage through the member it is at a pressure suitable for passage through the skin.

The member is preferably in the form of a self adhesive patch formed of a thin plastics material. Needleless injectors may be designed to have ample power to pierce such a patch without detriment to the injection efficiency. Preferably, the

patch material is substantially self-sealing immediately after the injection, i.e. the hole produced in the patch by the injection has a tendency to close up and prevent reflux of injectate and/or blood. Optionally, the patch material may be coated or impregnated with a disinfectant, anti-bacterial material, or other an ti- infection material.

The advantage of the injection patch is that each patient's skin is covered before contact with the injector nozzle, and there is thus no contamination of the nozzle. After the injection, the patch material closes the wound to prevent oozing of the fluid. If required, the patch may include an absorbent layer, or the patch material itself may be absorbent, so as to further reduce the chance of contaminating the injector nozzle. After the injection, the patch is left in place for a short time until the injectate has dispersed somewhat within the tissues. This has the added advantage that scratching of the infection site is prevented whilst the patch is in place. This is similar to the recommended practice of holding a sterile swab in place after any type of injection.

The patches may be applied by the patients or by an assistant, or automatically by a device attached to the injector. If the patches are applied some minutes prior to the injection, the outer surface is preferably protected from contamination by a tamper-evident film, which is removed immediately before the injection. The patches may be releasably pre-assembled onto a carrier strip, and protected by a further strip or individual cover, the whole being sterilised.

An alternative to using individual patches is to use a continuous strip of material which may be automatically indexed past the nozzle to protect it for each injection. This, however, does not have the advantage of continuing the protection of the injection site for a short time after the injection.

The invention will now be further described by way of example, with reference to the accompanying drawings in which:

Figure 1 is a perspective view showing a member in the form of a patch;

Figure 2 is a diagrammatic representation of a continuous strip of patches;

Figure 3 is a perspective view of a needleless injector fitted with a cartridge for feeding patches automatically;

Figure 4 is a cross-section through the cartridge of Figure 3, and showing also

part of the needleless injector of Figure 3 prior to firing; and

Figure 5 is a view corresponding to Figure 4 but showing the injector as it is fired.

Referring first to Figure 1, patch 1 comprises a flexible, skin-protecting film

2 preferably formed of a suitable plastics material such as polyethylene or a self- sealing material sold under the Trade Mark PARAFILM. The film 2 has a surface

3 which, in use, is contacted by the needleless injector, and this surface is covered prior to use by a peel-off protective film 4 which also acts as a tamper-evident layer. The surface of the skin-contacting film 2 which is on the other side of the film to the surface 3 is coated with a layer of adhesive 5, which in turn may be protected by a removable release film 6. The adhesive 5 is selected to be suitable to be adhered to the patient's skin. Often there is a small reverse flow of medicament after an injection, and to allow for this the skin-contacting film 2 may be absorbent and anti¬ bacterial (or anti-infection in some other way), or may have a layer of material thereon which is absorbent and anti-infection.

Preferably, the colour of the protective film 4 is different to that of the skin- contacting film 2, or it is visually distinguishable in some other way, for example by giving it a pattern, e.g. of stripes, to enable immediate recognition that the film has been removed and the sterile surface is exposed.

The patch is used by removing the release film and sticking the patch to the patient's injection site. Immediately before the injection is given, the protective film

4 is removed. The injector nozzle is pressed against the skin-contacting film 3 and the injectate is fired through that film and through the adhesive layer 5. Preferably the film 3 and the adhesive layer 5 are integrated with one another to a sufficient extent to ensure that there is no possibility of small pieces of film 3 or adhesive 5 being torn away and injected into the patient.

Figure 3 shows a multi dose injector 7 with a cartridge 8 removably attached to the injection end thereof, so as to enable a plurality of injections to be given successively, each through a respective patch applied automatically to the skin of the patient. The injector 7 has an injection nozzle 7a (see Figures 4 and 5). The cartridge 8 is shown in more detail in Figure 4.

As can be seerr in Figure 4, the cartridge 8 comprises a housing 9 within

which a carrier strip 10 having a plurality of patches 1 thereon is wound up on a reel 11. The cartridge 8 has a yoke 12 by means of which it is removably attached to the front end of the injector 7. To this end, the barrel 13 of the injector is fixedly mounted in a passageway 14 formed in the yoke 12. A compression spring 15 surrounds the barrel 13 and bears against the yoke 12 at one end and, at the other end, against an abutment 16 fixedly mounted with the casing 9. The yoke 12 is free to slide within a collar 17 which forms an extension from the main body of the casing 9.

As already mentioned, the carrier strip 10, with the patches 1 carried thereon, is wound on a spool 11. The free end of the strip is threaded over support rollers 18 which are positioned either side of an opening 19 in the front of the casing. After passing over the rollers 19 the strip passes over a drive wheel 20 and through a nip formed between the drive wheel 20 and a pinch roller 21. The latter keeps the strip in fric onal contact with the surface of the drive wheel, so that when the drive wheel rotates in the direction of the arrow R, by the means described below, the carrier strip is pulled from the spool. After leaving the nip between the drive roller 20 and pinch roller 17 the strip exits the cartridge through an opening 22.

The drive wheel 15 has a toothed wheel 23 mounted coaxially thereon for rotation therewith. A pawl 24 is urged into engagement with the toothed wheel 23 by a compression spring 25, and a rack 26, pivotally mounted on the yoke 12, is also urged into contact with the toothed wheel 23, this time by means of a tension spring 27 acting between the rack and the yoke. The manner of operation of these components will become apparent from the ensuing description of the operation of the device.

When the device is to be used the front of the cartridge 8 is placed on the patient's skin 28, with the opening 19 opposite the intended injection site. Assuming that a patch 1 is already located opposite the opening 19, as shown in Figures 4 and 5, the injector 7 is pushed towards the patient's skin 28 in the direction of the arrow F, which causes the yoke 12 to move in the same direction, from the position shown in Figure 4 to that shown in Figure 5. This compresses the spring 15. The nozzle 7a of the injector 7 presses against the patch located opposite the opening 19, which is thereby pressed onto'the skin 28, and the injector is operated at this point and the

injectate is fired through the patch and into the patient's tissues. During this part of the procedure, the pawl 24 prevents movement of the drive wheel 20. It is greatly preferred that the injector should operate automatically on reaching the optimum skin contact force, and an injector which operates in this manner is described in PCT published application WO 93/03779, to which attention is directed for further details.

The patch becomes detached from the carrier strip 10 as a result of the above- described operation, and remains adhered to the patient's skin after removal of the injector nozzle 7a, thus providing short-term protection for the wound, and containing any reflux of injectate. After the injector is removed, spring 15 returns the cartridge 8 to the position shown in Figure 4, and the rack 26 indexes the drive wheel 20 in the direction of arrow R to move the next patch into position for application.

Figure 2 is a diagram showing the structure of an embodiment of carrier strip 10, with patches 1 , for use in the device described above. It will be seen that the carrier strip comprises a film 30, with a release film 31 on one face thereof, to prevent the patch adhesive 5 (see below) from sticking to the film 30 when the strip is rolled up, and adhesive 32 on the opposite face. The patches are secured to the strip by means of the adhesive 32. Each patch 1 comprises a skin-contacting film 2 and adhesive 5, as in the case of the patches shown in Figure 1 , and on the face adjacent the carrier strip 10 each patch has a release film 33 to enable it to detach itself readily from the carrier strip after injection.