WO1993002726A1

WO1993002726A1 - Improvements in or relating to syringes

Info

Publication number: WO1993002726A1
Application number: PCT/GB1992/001444
Authority: WO
Inventors: John Lawson Stanford
Original assignee: University College London
Priority date: 1991-08-01
Filing date: 1992-08-03
Publication date: 1993-02-18
Also published as: GB9116595D0

Abstract

An intradermal hypodermic syringe is formed in two parts, namely a dosing unit which incorporates the needle (9) and piston (7) and a piston pushrod and holder sub-assembly (20) to which the dosing unit is temporarily fitted for use. In use, the piston pushrod is placed in simple abutting relationship to the piston (18) but is not connected to it whereby the piston cannot subsequently be withdrawn after use, a separate, single use, retraction element (15) being provided to enable the dosing unit to be filled. The syringe comprises a guard (27) which extends from the dosing unit body lengthwise of the syringe past the tip of the needle (9) to prevent accidental contact with the needle tip.

Description

IMPROVEMENTS IN OR RELATING TO SYRINGES

The present invention relates to syringes, particularly, but not exclusively, to syringes of the hypodermic intradermal type.

One of the problems of using syringes particularly in medical applications is the possibility of pricking oneself with the needle. Clearly this can be dangerous particularly if it has just been used to inject a person suffering from a disease such as AIDS.

Another problem is trying to ensure that needles are not reused, as may occur where their use is not supervised by qualified medical personnel, eg, possibly in Third World countries or illicitly as by drug addicts. According to a first aspect of the present invention there is provided for use in a hypodermic syringe having a discharge piston pushrod, a dosing unit comprising a body having an internal volume, a hypodermic needle attached to the body and forming an integral part of the dosing unit and a piston within the internal volume of the body for discharging material from the internal volume through the needle, the piston being unattached to any pushrod operative to cause a discharge stroke thereof.

According to a second aspect of the invention there is provided a holder for use with a dosing unit having a hypodermic needle and piston as a hypodermic syringe, the holder comprising a generally cylindrical hollow barrel having a piston pushrod therein for operating the piston, a seat defined at the other end of the barrel for receiving the dosing unit with its needle extending longitudinally away from the barrel and a safety guard extending longitudinally away from the barrel so as to be in side-by- side relation to the needle when the dosing unit is installed to restrict access to the tip of the needle. As will become apparent from the following description, both aspects of the invention may be embodied in the same hypodermic syringe. The first aspect of the invention addresses the problem of preventing re-use and overcomes it effectively preventing the dosing unit of the syringe from being refilled. In a conventional syringe, the pushrod is connected to the piston to enable it to be retracted during a filling operation. Having the two unconnected, as in the first aspect of the invention, requires an alternative filling method which can be adapted to hamper re-use of the needle, for example, by providing a single-use piston retraction element which is detached from the dosing unit after a filling operation and which cannot thereafter easily be re-attached.

As to the second aspect of the invention, the guard is intended to reduce the risk of accidental contact with the needle tip while administering an injection. Preferably the guard is rigid. Alternatively it can be resilient and shaped so as to cover the tip and be deflected out of the way during an intentional injection. Preferably the needle extends right up to the internal volume of the piston cylinder and the closed end of the cylinder is of a surface shape complementary to that of the facing surface of the piston so that the only dead space when the piston is in its fully discharge position is, for practical purposes, the interior volume of the needle. This low dead space volume reduces wastage of the liquid which is injected.

The dosing unit can be releasably attached to the holder by providing a mounting on the holder in the form of a cradle into which the dosing unit is releasably insertable and in which it is held captive during use. Once the dosing unit is firmly fixed to the holder/pushrod sub-assembly, the pushrod is able to make contact with the outer face of the piston but not to connect to it. A further preferred feature of the invention is the attachment of a cap to the dosing unit, whether or not it is integral with the holder, in order to seal hermetically the latter. The cap may be attached by means of complementary circumferential formations on the inner periphery of the cap and the outer periphery of the dosing unit.

The invention will be further described by way of non-limitative example with reference to the accompanying drawings in which:-

Figures la and lb are longitudinal sectional view through the holder and dosing unit in one form of syringe embodying both aspects of the present invention;

Figure 2a shows the dosing unit of fig lb prior to filling; and

Figure 2b shows part of a variant of the dosing unit of figure 2a.

Referring first to figure 2a, this illustrates the dosing unit 1 of the syringe prior to filling. The dosing unit comprises a cylindrical body 3 having an internal volume 5 in which is located a cylindrical piston 7 of any suitable material. The movement of the piston 7 is limited in one direction by the end 3a of the dosing unit body and, at the outer end by a radially inwardly directed rib 3b which retains the piston 7 captive within the body 3.

A hypodermic needle 9 extends forwardly of the body 3 and is permanently attached to it. A removable cylindrical cap 11 protects the needles prior to filling and use. It will be noted that the surface of the end 3a of the body 3 is of complementary shape, in this case simply plain, to that of the facing surface of the piston 7 so that when the piston 7 is in its fully discharged position, there is no dead space within the internal volume 5 and the only dead space within the dosing unit as a whole is the internal volume of the needle 9.

In order to facilitate filling, a retraction element 13 comprising a finger grip 15 is attached to the piston 7. The finger grip 15 is connected to the piston 7 via a flexible link 17 which has an enlarged end accommodated in a recess in the outer end face of the piston 7.

The dosing unit is filled by removing the cap 11, inserting the needle 9 into the required liquid and then pulling the finger grip 15 away from the body 3 of the dosing unit. The connection of the retraction element 13 to the piston 7 and the ribbed end wall 3b of the body 3 are designed such that the force required to detach the retraction element from the piston 7 is greater than that required to extract the piston 7 from the internal volume 5 by pulling. The link 17 could, if desired, be provided with a weakened portion near the piston 7 which would be broken off at the end of the filling operation and thereby prevent refilling. The flexibility of the link 17 is intended to ensure that pushing the finger grip 15 towards the dosing unit 3 causes the link to flex rather than to push the piston 7 towards its discharge position. Thus the element 13 is intended as a single-use filling only attachment. Once the dosing unit is filled and the retraction element 13 detached, the dosing unit is temporarily fitted, for the purpose of administering an injection, to the holder 20 shown in figure la. This comprises a generally cylindrical hollow barrel 21 having a slidable pushrod 23 mounted therein. A part 21a of the barrel 21 is cut away so as to provide, in conjunction with an inwardly directed annular ridge 25 a seat for accommodating the dosing unit 1 in a secure fashion. The ridge 25 provides a reaction surface to resist leftwards movement of the dosing unit 1 as the pushrod 23 is pushed towards it. It will be noted that the pushrod 23 has a reduced diameter end portion 23a which can extend into the interior of the dosing unit body 3 and abut the outer end face of the piston 7. Extending forwardly (ie, leftwardly in figure la) of the barrel 21 is a safety guard 27. This is defined by an extension of 27a of the diametral cutaway which forms the seat 21a and an obliquely cut portion 27b so that the guard overall resembles the shape of a trocar. It will be noted that the end of the guard 27 extends longitudinally away from the barrel somewhat beyond the tip of the needle. This means that while the needle can be inserted into the patient's skin obliquely as in an intradermal injection it restricts access to the tip longitudinally of the syringe and therefore will serve to restrict inadvertent contact with the tip. Further, since the radially inner surface of the guard 27 is part cylindrical, it serves as a guide to assist in repositioning the closure cap 11 on the dosing unit while the latter is still installed in the holder while reducing inadvertent contact with the needle tip during that operation.

It will be noted that the external surfaces of the unit 3 are plain, in particular devoid of any finger grip or flange which would assist a user in gripping the unit in an attempt to operate it in the absence of the holder 20. Figure 2b shows part of a variant of the dosing unit of figure 2a in which the body 3 is provided with a circumferential groove 30 complementary to the cross- sectional shape of the rib 25 to ensure more secure engagement of the unit with the holder 20. This would enable the cap 11 to be fitted more firmly to the body 3 during insertion of the dosing unit in the holder and its subsequent removal.

Claims

1. For use in a hypodermic syringe having a discharge piston pushrod, a dosing unit comprising a body (3) having an internal volume (5) , a hypodermic needle (9) attached to the body and forming an integral part of the dosing unit and a piston (7) within the internal volume of the body for discharging material from the internal volume through the needle, the piston being unattached to any pushrod operative to cause a discharge stroke thereof.

2. A dosing unit according to claim 1 and comprising a single-use retraction element (13) detachably or frangibly connected to the piston (7) for enabling the piston to be retracted during a filling operation, the element being ineffective to cause a discharge stroke of the piston.

3. A dosing unit according to claim 2 wherein the retraction element comprising a finger grip (15) attached to the piton by a flexible link (17) whereby pulling on the finger grip causes the piston (7) to be retracted while pushing on the finger grip causes the link to flex.

4. A dosing unit according to claim 1, 2 or 3 wherein means (3b) are provided to retain the piston captive within the internal volume.

5. A dosing unit according to claim 4 and claim 2 or 3, wherein the force required to free the piston (7) from its captive position by pulling exceeds that required to disconnect the retraction element from the piston.

6. A dosing unit according to any one of the preceding claims, wherein the internal volume is filled with a pre-measured dose of sterile reagent.

7. A dosing unit according to any one of the preceding claims, wherein the internal volume of the body is cylindrical, the end of the internal volume nearest the needle having a surface shape complementary to that of the facing surface of the piston and the needle extends from its tip to that end face of the internal volume of the body whereby substantially the only dead space within the dosing unit is the interior volume of the needle.

8. In combination, a dosing unit according to any one of the preceding claims and a holder (20) therefor in which it can be detachably installed for use, the holder having a mounting (21a, 25) for receiving and holding the unit and a piston pushrod (23) slidable relative to the mounting for operating the piston of the unit, the pushrod being unconnected to the piston, so that once the dosing unit is discharged by a discharge stroke of the pushrod acting on the piston, retraction of the pushrod does not retract the piston.

9. A combination according to claim 8, wherein the holder comprises a generally cylindrical hollow barrel having the pushrod slidable therein and a portion of the barrel wall at one end thereof cut away to provide a seat for the dosing unit.

10. A combination according to claim 8 or 9 and including a safety guard (27) extending longitudinally away from the barrel in side-by-side relation with the needle to restrict access to the tip of the needle.

11. A combination according to claim 10 wherein the guard is attached to the barrel.

12. A holder for use with a dosing unit having a hypodermic needle (9) and piston (7) as a hypodermic syringe, the holder (20) comprising a generally cylindrical hollow barrel (21) having a piston pushrod (23) therein for operating the piston, a seat (21a, 25) defined at the other end of the barrel for receiving the dosing unit with its needle extending longitudinally away from the barrel and a safety guard extending longitudinally away from the barrel so as to be in side-by-side relation to the needle when the dosing unit is installed to restrict access to the tip of the needle.

13. A holder according to claim 12 wherein the guard is trocar-shaped.

14. A combination according to any one of claims 8 to 11, wherein the holder is in accordance with claim 12 or 13.