Automatic syringe

Details Automatic syringe Automatic syringe

2000-07-17

2004-12-14

Hayes, Michael J. (Department: 3763)

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

C604S145000, C604S198000

Reexamination Certificate

active

06830560

ABSTRACT:

This invention relates to automatic syringes, particularly for the delivery of drugs and other substances to human and animal subjects.
The problems associated with conventional syringes arise from the fact that they are unsuitable for use by untrained users. They are liable to cause injury and infection if not disposed of correctly, are available for re-use by drug addicts if not disposed of properly, and they are painful to the patient if not used correctly. Many patients are “needlephobic” and thus are extremely reluctant to use syringes regardless of the objective pain caused by a syringe even when used correctly.
In order to combat user compliance problems due to a fear of needles, a number of needleless syringe designs have been proposed. Such syringes deliver a drug to the subject by forcing the drug through the skin of the subject under air pressure.
The pressure required for such delivery is quite high—of the order of 6 atmospheres (approximately 600 kPa). This in itself gives rise to problems, since it leads to vials being broken occasionally under high pressure. It also means that the syringe must be primed before use, since a pre-filled ready-to-use syringe cannot be stored under such high pressure over a shelf life of months or years. Thus, the user or a physician or nurse is required to prepare the syringe before it can be used, which detracts from its attractiveness for self-administration.
A further problem which arises in needleless delivery is that the high pressure is primarily required to drive the drug through the stratum corneum layer of the skin. Underlying layers of the skin, and the subcutaneous tissue itself present relatively little resistance to the passage of the high-velocity powder. Because different patients have different skin types and thicknesses, and because the thickness and penetrability of the skin varies widely over a single patient's body, the level of the needleless syringe delivery pressure must be regulated to drive the drug correctly past the stratum corneum.
A failure to correctly regulate the level of the driving pressure may result in an incorrect level of delivery due to insufficient levels of drug passing the stratum corneum, or due to the drug being delivered past the target tissue to the wrong type of tissue. For example if the delivery pressure is too high the drug may be delivered to the bone surface underlying the delivery region.
A further problem with needleless syringes is that they are considerably more bulky than conventional syringes due to the complex delivery mechanism and the thickness of walls required to contain the pressurised gas.
Alternative drug delivery devices are known which correctly deliver the drug in an automatic fashion but have certain disadvantages when compared to syringes. For example, our own WO-A-97/21457 discloses a drug delivery device containing a reservoir in communication with a needle, and a gas generator adapted to drive a medicament from the reservoir to the subject via the needle.
The device of WO-A-97/21457 is adapted to be affixed to the skin by an adhesive coating (covered before use by a release liner). When attached to the skin and actuated, delivery is automatic. After completion of delivery, the device is pulled away from the skin, causing the needle to be concealed by means of a displaceable cover, before the device is disposed of.
The device disclosed in WO-A-97/21457 is bulkier than that of a syringe which would deliver the same volume of drug, due to the configuration of the housing and the displaceable cover, which must provide a surface of sufficient surface area to be attached to the skin.
Additionally, when compared with a syringe, more steps are involved in effecting a suitable injection with the device disclosed in WO-A-97/21457 (for example, the release liner must be peeled away before the device can be operated). This makes the device less attractive to patients in need of an immediate injection because of the longer time needed to administer individual injections.
The above-mentioned prior art device while simpler than a needleless injector, is still somewhat complex as regards the automatic actuation of the gas generator and the locking snap mechanism which ensures that the needle is properly concealed by the displaceable cover before and after use. Added complexity results in higher costs and a greater possibility of device malfunction.
The present invention aims to overcome these and other disadvantages of the prior art and provide a syringe which is preferable to conventional syringes as well as to needleless injectors or automatic infusion pumps.
The invention provides a syringe comprising:
a) a barrel having a liquid drug reservoir therein;
b) a delivery needle mounted on the first end of the barrel;
c) a gas generator located at the second end of the barrel, the gas generator in communication with the reservoir when the gas generator is activated, so as to drive a liquid from the reservoir through the needle;
d) gas generation activation means; and
e) a sleeve resiliently mounted on the first end of the barrel between a first position where the tip of the needle is concealed by the sleeve to a second position where the tip of the needle is revealed,
f) whereby when the sleeve is placed against an injection site and the barrel is moved toward the injection site, the sleeve is caused to move from the first position to the second position, and the needle is caused to penetrate the injection site, such that activation of the gas generator drives a liquid from the reservoir into the injection site through the needle.
The syringe according to the present invention addresses the problems associated with conventional syringes in a number of respects. Firstly, it causes the needle to be deployed automatically and the gas generator to be actuated automatically by pressing the sleeve against the skin and moving the barrel relative to the sleeve (e.g. as part of one movement in which the barrel is gripped and pressed, sleeve first, against the skin).
Because the penetration of the needle is controlled by the extent of movement of the components of the syringe, incorrect injection is less likely. Furthermore, because the gas generator itself causes the delivery of the drug, the speed and amount of delivery are predetermined and out of the control of the user. Automatic delivery also prevents needle injuries from occurring as a result of the user having to manipulate the syringe during the time when the needle is penetrating the skin.
Needle injuries are further prevented because the sleeve conceals the needle when in the first position. Not only does this prevent accidental injury, but it also addresses user compliance problems. It is the experience of many doctors and nurses that many patients are prepared to have injections administered but will close their eyes or turn their heads during injection. For such patients it is not the actual pain of injection, but rather the sight of the injection taking place or the sight of the needle itself, which causes distress.
In cases where a patient cannot watch an injection taking place, self-injection is not practical. The syringe according to the invention provides a solution, since not only does it allow the needle to remain invisible during delivery, but it allows the patient to self-inject without looking at the needle at all.
In contrast to needleless syringes, the syringe according to the present invention does not require a significant amount of pressure to deliver the drug as the needle pierces the outer layers of skin enabling the liquid drug to flow subcutaneously at relatively low pressure. As a result, the present invention does not require pre-pressurised chambers since a relatively simple gas generator creating a relatively low pressure can be employed. The syringe according to the present invention can be sold and safely stored for extended periods of time in a pre-filled condition which ensures sterility.
Because the present invention is automatically injected no priming is required on the part of the user,

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