Breech loaded fixed needle syringe and automatic injection device having the same

1 . A fixed needle syringe comprising:

a medicine compartment;

a hypodermic needle in fluid communication with said medicine compartment, said hypodermic needle being permanently fixed to said medicine compartment;

a piston slideably disposed in said medicine compartment; and

a plunger secured to said piston, said plunger having a bore defined therethrough, said bore allowing access to said piston through said plunger and said piston being made of a self-sealing, pierceable material.

2 . The fixed needle syringe of claim 1 , further comprising an end cap at a breech end of said medicine compartment, said end cap preventing withdrawal of said piston from said medicine compartment.

3 . The fixed needle syringe of claim 1 , wherein said plunger is removably secured to said piston.

4 . The fixed needle syringe of claim 3 , wherein said plunger is removably secured to said piston by a threaded connection.

5 . The fixed needle syringe of claim 1 , further comprising one or more needle guiding surfaces defined in said bore of said plunger.

6 . (canceled)

7 . A fixed needle syringe comprising:

a medicine compartment;

a self sealing piston slideably disposed in said medicine compartment;

a hypodermic needle in fluid communication with and permanently fixed to said medicine compartment, said hypodermic needle having a slenderness ratio of between about 60 and 120; and

a plunger secured to said self sealing piston, said plunger having a bore therethrough, said bore allowing access to said self sealing piston through said plunger.

8 . The fixed needle syringe of claim 7 , wherein said slenderness ratio is about 85.

9 . The fixed needle syringe of claim 7 , wherein said hypodermic needle has a flow ratio of less than about 2.

10 . A fixed needle syringe comprising:

a medicine compartment;

a self sealing piston slideably disposed in said medicine compartment;

a hypodermic needle in fluid communication with and permanently fixed to said medicine compartment, said hypodermic needle having a flow ratio of less than about 2; and

a plunger secured to said self sealing piston, said plunger having a bore defined therethrough, said bore allowing access to said self sealing piston through said plunger.

11 . The fixed needle syringe of claim 10 , wherein said flow ratio is less than about 1.8.

12 . The fixed needle syringe of claim 10 , wherein said flow ratio is less than about 1.5.

13 . The fixed needle syringe of claim 10 , wherein said hypodermic needle has a slenderness ratio of between about 60 and 120.

14 . A method of injecting a medicine, comprising:

introducing a medicine supply needle into a medicine compartment of a permanently fixed needle syringe through a hollow plunger and a self-sealing, pierceable piston of said fixed needle syringe; and

urging medicine from said medicine supply needle into said medicine compartment.

15 . The method of claim 14 , further comprising:

removing said hollow plunger from said piston;

inserting said syringe in a first assembly so that a hypodermic needle of said fixed needle syringe is proximate a lower seal of said first assembly; and

securing a second assembly to said first assembly so that a rod of said second assembly is proximate said piston.

16 . The method of claim 15 , further comprising:

placing said lower seal on an injection site; and

releasing an injection spring in said second assembly to drive said rod in an injection direction, said rod moving said hypodermic needle through said lower seal into said injection site and moving said piston to expel said medicine from said medicine compartment through said hypodermic needle.

17 . The method of claim 16 , further comprising moving a retraction spring of said first assembly to a compressed state as said rod moves in said injection direction.

18 . The method of claim 17 , further comprising:

disconnecting said injection spring from said rod so that said retraction spring moves said hypodermic needle through said lower seal in a direction opposite said injection direction.

19 . An injection kit comprising:

a breech loadable fixed needle syringe having a hypodermic needle permanently fixed to a medicine compartment, a self-sealing, pierceable piston slideably disposed in said medicine compartment, and a hollow plunger removably secured to said piston so that said medicine compartment is fillable through said hollow plunger and said piston;

an injection assembly; and

a retraction assembly, said injection and retraction assemblies being configured to operatively secure said syringe therein.

20 . The injection kit of claim 19 , further comprising one or more injection site antiseptic swabs.

21 . The injection kit of claim 19 , further comprising a package containing said syringe, said injection assembly, and said retraction assembly.

22 . The injection kit of claim 21 , wherein said package is terminally sterilized.

23 . A method of injecting a medicine, comprising:

urging medicine into a medicine supply needle into a medicine compartment of a permanently fixed needle syringe through a hollow plunger and a self-sealing, pierceable piston in said fixed needle syringe;

withdrawing said medicine supply needle from said permanently fixed needle syringe;

turning said permanently fixed needle syringe so that air in said medicine compartment is proximate a hypodermic needle of said permanently fixed needle syringe; and

depressing said hollow plunger to expel said air through said hypodermic needle.

24 . The method of claim 23 , further comprising:

removing said hollow plunger from said self-sealing, pierceable piston;

inserting said fixed needle syringe in a first assembly so that said hypodermic needle is proximate a lower seal of said first assembly; and

securing a second assembly to said first assembly so that a rod of said second assembly is proximate said self-sealing, pierceable piston.

25 . The method of claim 24 , further comprising:

placing said lower seal on an injection site; and

releasing an injection spring in said second assembly to drive said rod in an injection direction, said rod moving said hypodermic needle through said lower seal Into said injection site and moving said self-sealing, pierceable piston to expel said medicine from said medicine compartment through said hypodermic needle.

26 . The method of claim 25 , further comprising:

moving a retraction spring of said first assembly to a compressed state as said rod moves in said injection direction; and

disconnecting said injection spring from said rod so that said retraction spring moves said hypodermic needle through said lower seal in a direction opposite said injection direction.