Filling device for a needleless injector cartridge

#The present invention relates generally to hypodermic injection devices, and is for use with needleless injectors in particular.

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

#In WO 95/03844, a needleless injector is disclosed which uses efficient energy storage and release means to provide a very compact and easy-to-use device, and the present invention is intended primarily for use with that device, although of course it could be adapted for use with alternative injectors. Ideally, a needleless injector would be provided to the end user pre-filled with the drug, self-powered, and ready for immediate use. The pre-filling of the injector would preferably be done by the drug manufacturer, thereby ensuring sterility, correct dose, and conformity to the approved specification.

#A preferred embodiment will be described with reference to the accompanying drawings, in which:

#FIG. 1 shows a cross-section through a needleless injector containing a lyophilised drug and hypodermic syringe assembled to the injector;

#FIGS. 2a and 2b show a resilient seal, in plan view and longitudinal section, respectively;

#For the sake of simplicity, like parts are given the same numbers.

#Referring to FIG. 1, a needleless injector body 1 contains a drug cartridge 2 retained by a sleeve 3 having a threaded flange 18. The cartridge 2 contains a lyophilised drug 5, preferably preformed to fit closely to the internal container of the drug cartridge, and held firmly in place by a piston 4, adjacent to a discharge orifice 23. A syringe guide 22 is frangibly attached by a frangible connection 10 to the retaining sleeve 3. The syringe guide 22 is preferably tubular, open at one end to receive a syringe 8, and having a partial end wall 24. Inserted in a concentric hole in the end wall 24 is a resilient seal 6 (see also FIGS. 2a and 2b) which is biased to form an hydraulic seal around the discharge orifice 23 of the cartridge 2. Referring to FIG. 2, the resilient seal 6 has a hole 11 to sealingly receive the hypodermic needle 7 (FIG. 1) of the syringe 8, and may have circumferential ribs 12 to improve the sealing efficiency on the cartridge 2. A conical entry hole 14 helps to guide the needle into the hole 11. Preferably, the conical hole 14 is sealed with a frangible diaphragm 15, which may be made from a laminate of aluminium foil and plastics, or other material which is impervious to water vapour and capable of withstanding a pressure differential of up to 900 mbar. Retaining lip 25 serves to hold the seal 6 in the end wall 24 of the syringe guide 22 (FIG. 1).

#Referring to FIGS. 1 and 2, the filled syringe 8 is loaded into the open end of the syringe guide 22; the guide is long enough to align the syringe body so that the needle 7 is approximately concentric with the conical hole 14 in the seal 6. By pushing on the syringe body, the needle 7 ruptures the frangible diaphragm 15, and is guided by the conical hole 14 to enter the hole 11. The syringe body comes to rest on a rim 19, which extends axially from the end wall 24 of the syringe guide 22. The rim 19 may also locate the seal 6, so that the end of the needle 7 just touches the orifice 23 in cartridge 2. The bore of the needle 7 is now in hydraulic contact with the inside of the drug cartridge 2 via the orifice 23, and by acting on the plunger of the syringe 8, solvent 9 will be transferred into the drug cartridge 2. The hydraulic pressure created within the syringe 8 causes the piston 4 to move in the cartridge 2 until it stops at position 4a against an abutment 16 formed on the injector body. During this time, the turbulence of the inflowing solvent 9 will agitate the lyophilised drug 5, helping it to dissolve. An agitator (not shown) may be previously loaded together with the drug 5, so that by shaking the needleless injector after filling, rapid dissolution of the drug 5 will result.