Needleless injector drug capsule and filling method

Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...

Reexamination Certificate

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Details

C604S411000

Reexamination Certificate

active

06251091

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a disposable needleless injector and to a method for filling the same.
BACKGROUND OF THE INVENTION
Needleless injectors are used as an alternative to hypodermic syringes to inject drugs and medicaments through a patient's skin into the underlying tissue. A typical injector comprises a high pressure piston pump which dispenses the drug through a small hole with sufficient force to pierce the epidermis and diffuse into the tissues. The present invention is directed to the filling of capsules for use in such injectors.
Axiomatic to the storage of the drug in the capsule is that the filling procedure is compatible with the equipment and protocols established within the pharmaceutical industry, and a number of otherwise promising ideas have failed to become commercialised because this requirement was overlooked. None of the prior art capsules have all of the features necessary for optimum storage of the drug and compatibility with filling machines.
The stringent requirements for ensuring optimum sterility and quality control of drug packaging means that there is a trend towards pre-filling the drug capsule. However, a prefilled capsule must be able to withstand thermal expansion and contraction due to ambient temperature fluctuations. The possible results of the latter is that increased and unacceptable outgassing of the drug could occur, or the drug could expand and leak past the seals.
SUMMARY OF THE INVENTION
According to the present invention there is provided a needleless injector capsule in combination with an adaptor used in filling the capsule, the capsule defining a chamber which has injectate therein and is provided with an injection orifice, a piston being located for movement within the chamber, the adapter being removably connected to the capsule and having a bore which communicates with the capsule chamber via the injection orifice and is partly filled with excess injectate, the bore being closed to the exterior by a sealing means.
According to another aspect of the invention there is provided a method of filling a needleless injector capsule with injectate, the capsule defining a chamber which is for receiving injectate and is provided with an injection orifice, a piston being located for movement within the chamber, the adapter being removably connected to the capsule and having a bore which communicates with the capsule chamber via the injection orifice, the method comprising the steps of:
(a) introducing injectate into the capsule chamber through the injection orifice and excess injectate into bore of the adaptor; and
(b) closing the bore of the adaptor to the exterior by a sealing means, leaving the bore partly filled with excess injectate.
It is necessary that the pressure induced in the drug increases very rapidly at the start of the injection, so that the liquid effectively strikes the skin to pierce it. (Conversely, if the pressure rise is too slow, the skin moves away from the jet causing the jet to splash sideways without penetration). It follows therefore that the “hydraulic circuit”—i.e. the drug capsule, its method of attachment, and the piston should be relatively rigid, otherwise much of the input energy at the start of the injection will be wasted in distorting these components. Less obvious is that any trapped air in the liquid drug will be compressed during the injection and thus absorb energy. Of course, a small quantity of entrapped air is permissible and almost inevitable, because unless rigorous de-gassing of the drug is carried out before filling, very small bubbles of air will come out of solution and coalesce within the injectate.
In a preferred form of the above method air is evacuated through the injection orifice before injectate is introduced into the capsule chamber and adaptor bore.
The invention also provides a needleless injector capsule in combination with an adaptor for use in filling the capsule, the capsule defining a chamber which is for receiving injectate and is provided with an injection orifice, a piston being located for movement within the chamber, the adaptor being removably connected to the capsule and having a bore which communicates with the capsule chamber via the injection orifice, the adaptor bore having a first portion of smaller cross-section adjacent the injection orifice and a second portion of larger cross-section remote from the said orifice. Such a construction is particularly suitable for carrying out the above filling method including evacuation of air.
The capsule is preferably connected frangibly to the filling adaptor, which also serves as a reservoir to accommodate expansion and contraction of the injectate. Immediately prior to use the filling adaptor is broken off the capsule to expose the injection orifice.


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