Safety syringe adapter for cartridge-needle unit

A safety syringe adapter (4) has a hollow body (26) sized to house a cartridge-needle unit (6) to which a carrier (24) is fixed. The cartridge-needle unit and carrier therewith are movable from a use position, with the needle tip (58) exposed, to a safe disposal position, with the needle tip within the body. A stem assembly (28) has an elongate stem (60) and a coaxial tubular stem extension (64) and is movable to a post-injection position, at which the stem extension becomes secured to the carrier. Pulling the stem assembly proximally causes the cartridge-needle unit to move to its safe-disposal position so the needle tip is within the body for safe disposal.

BACKGROUND OF THE INVENTION 
Various medications are often supplied using cartridge-needle units and a 
syringe adapter. The cartridge-needle units include a barrel having a 
piston at one end and a needle assembly at the other with the 
pharmaceutical to be injected housed within the syringe barrel between the 
piston and the needle assembly. The adapter typically includes a hollow 
body sized to hold the barrel of the cartridge-needle unit and a stem 
designed to engage the piston. The cartridge-needle unit is mounted within 
the adapter body and the injection is given. After use, the 
cartridge-needle unit is disposed of while the body and stem of the 
adapter can be reused. 
One of the problems with health care delivery is risk of infectious 
diseases being spread through accidents, especially needle sticks, with 
used syringes. There have been many attempts to create safety syringes in 
which the needle is either manually or automatically drawn into the barrel 
or other housing of the syringe after use. However, these designs have not 
fully addressed the problems associated with the safe disposal of 
conventional cartridge-needle units after use. 
SUMMARY OF THE INVENTION 
The present invention is directed to a safety syringe adapter for use with 
a conventional cartridge-needle unit which has few parts, is inexpensive 
to produce and is easy to use. 
The safety syringe adapter is designed for use with a cartridge-needle unit 
of the type having a barrel housing a piston and a needle assembly at the 
distal end of the barrel. The adapter includes a hollow body having open 
proximal and distal ends and is sized to house the cartridge-needle unit 
therein. A carrier is securable to the distal end of the cartridge-needle 
unit and is movable, together with the cartridge-needle unit, within the 
body from a distal position, with the tip of the needle exterior of the 
body, to a proximal position, with the needle tip positioned within the 
body. 
A stem assembly includes an elongate stem, which engages the piston, and a 
stem extension, which extends parallel to the stem. The stem assembly is 
movable in a distal direction from a pre-use position, prior to an 
injection, to a post-injection position, after an injection, at which 
point the stem extension becomes secured to the carrier. Pulling the stem 
assembly in a proximal direction causes the carrier and cartridge-needle 
unit therewith to move in a proximal direction as well until the stem 
assembly reaches a safe disposal position. At this point the tip of the 
needle is positioned within the body and the carrier becomes secured to 
the body at the proximal position. Further proximal movement of the stem 
extension can be prevented, such as by engagement of radially inwardly 
extending teeth carried by the body with a locking region on the stem 
extension. The used syringe can now be disposed of safely. 
One of the primary advantages of the invention is that it is adapted for 
use with conventional cartridge-needle units, such as that made by Wyeth 
Labs, Inc. of Philadelphia, Pa. No specially designed ampules or 
cartridge-needle units need be used. Also, the user needs to simply pull 
on the stem assembly after the injection has been given to pull the needle 
into the hollow body and lock the syringe into its safe disposal 
condition. No twisting or separate manipulation of buttons or latches 
needs to be accomplished. A further advantage of the invention is that it 
can be made using only three parts, in addition to the cartridge-needle 
unit. It can thus be relatively inexpensive to produce and suitable for 
use as a disposable adapter.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1-3 illustrate a safety syringe 2 including a safety syringe adapter 
4 and a cartridge-needle unit 6. Cartridge-needle unit 6 can be a 
commercially available cartridge-needle unit such as made by Wyeth Labs, 
Inc. of Philadelphia, Pa. Cartridge-needle unit 6 includes a barrel 8 
having a distal end 10, a proximal end 12, a needle assembly 14 at distal 
end 10 and a piston 16 housed within barrel 8 at proximal end 12. 
Cartridge-needle unit 6 is filled with a pharmaceutical or other liquid. 
In the preferred embodiment, needle assembly 14 has external threads 8 and 
a removable safety sheath 20 covering a needle cannula 2. 
Adapter 4 includes, in the preferred embodiment, three parts: a carrier 24, 
a hollow body 26 and a stem assembly 28. Carrier 24 is generally 
cylindrical in shape and has internal threads 30 sized to engage external 
threads 18 formed on needle assembly 14 to create a cartridge needle unit 
assembly. Carrier 24 also includes a radially outwardly extending boss 32 
which acts as a guide element within body 26 as discussed below. 
Body 26 has a generally cylindrical side wall 34 defining a hollow interior 
36 extending from an open distal end 38 to an open proximal end 40. The 
initial entry of carrier 24 into interior 36 of side wall 34 through end 
38 is accommodated by a tapering entrance ramp 41 along which boss 32 
slides. A pair of finger ledges 42 extend radially outwardly from body 26 
at proximal end 40. 
Side wall 34 has an axially extending slot 44 within which boss 32 slides. 
Slot 44 extends from a distal retaining region 46, which is defined in 
part by relatively small retaining shoulders 48, through a proximal 
locking region 50 and on to a slot extension 52. Proximal locking region 
50 is defined in part by relatively large locking shoulders 54 which are 
created by a narrowing slot portion 56 adjacent proximal locking region 
50. As will be discussed in more detail below, boss 32 fits within and is 
normally retained within distal retaining region 46 when syringe 2 is in 
its pre-use condition of FIGS. 1 and 3 by virtue of retaining shoulder 48. 
However, upon exertion of a moderate proximally directed force, boss 32 
can be moved proximally (that is towards finger ledges 42) within slot 44 
by expanding slot 44. Continued proximal movement causes boss 32 to engage 
within proximal locking region 50. However, since locking shoulders 54 are 
much larger than retaining shoulders 48, distal movement of carrier 24 is 
effectively not possible. The lateral deflection of side wall 34 as boss 
32 passes within narrowing slot portion 56 is accommodated by the 
provision of slot extension 52. The configuration of boss 32 and of slot 
44 effectively prevents distal movement of carrier 24 when boss 32 is in 
distal retaining region 46 and both distal and proximal movement of 
carrier 24 when boss 32 is within proximal locking region 50. 
As shown in FIG. 3, cartridge-needle unit 6 is secured to carrier 24 
through the engagement of threads 18, 30 so that cartridge-needle unit 6 
moves with carrier 24 as carried 24 moves from its distal position, with 
boss 32 engaged within region 46, see FIGS. 3 and 5, to its proximal 
position, with boss 32 engaged within region 50, see FIG. 7. As shown in 
FIGS. 1, 3 and 6, the tip 58 of needle 22 is external of body 26 when 
carrier 24 is in its distal position and cartridge-needle unit 6 is in its 
use position. Tip 58, see FIG. 7, is positioned within body 26 when boss 
32 is in its proximal position and cartridge-needle unit 6 is in its 
safe-disposal position. 
This movement of carrier 24 and cartridge-needle unit 6 is accomplished by 
movement of stem assembly 28. Stem assembly 28 includes a stem 60 
extending from a thumb pad 62 and a stem extension 64 also extending from 
thumb pad 62 coaxially with and surrounding stem 60. As shown in FIG. 3, 
the tip 66 of stem 60 is threaded to a threaded stud 68 extending from 
piston 16, as is conventional. 
Stem extension 64 is generally cylindrical and fits between barrel 8 and 
side wall 34 so as to stabilize both cartridge-needle unit 6 and stem 60. 
Stem assembly 28 is moved from its pre-use or as-shipped position of FIG. 
3 to its post-injection position of FIG. 6 by the user pressing on thumb 
pad 62 while grasping finger ledges 42, as is conventional. At the end of 
this movement, as shown in FIG. 6, an outer tapered surface 70 formed at 
the distal end of stem extension 64 frictionally engages a complementary 
inner tapered surface 72 of carrier 24. The frictional engagement between 
surfaces 70, 72 is sufficient so that when the user subsequently pulls on 
thumb pad 62 in a proximal direction, the frictional engagement overcomes 
the resistance of retaining shoulders 48, thus pulling carrier 24 and 
cartridge-needle unit 6 therewith in the proximal direction until boss 32 
engages proximal locking region 50. At this point carrier 24 and 
cartridge-needle unit 6 are effectively locked within body 26 with tip 58 
sheltered by side wall 34 of the body as shown in FIG. 7. 
To prevent the inadvertent or unauthorized removal of stem assembly 28 from 
body 26, body 26 has a pair of spring tabs 74 with radially inwardly 
directed teeth 76 at open proximal end 40 of body 26. Teeth 76 are 
positioned to engage a tapered locking region 78 formed in stem extension 
64. Region 78 is defined in part by a radially extending shoulder 80 which 
teeth 76 engage in the event of attempted complete removal of stem 
assembly 28 from body 26. 
In the preferred embodiment, the pre-use and safe-disposal positions of 
stem assembly 28 relative to body 26 are the same proximal position as 
shown in FIGS. 3 and 7. However, stem assembly 28 could assume different 
proximal positions relative to body 26 if desired. 
In use, syringe 2, in the pre-use condition in FIGS. 1 and 3, is selected 
and safety sheath 20 is removed. The injection is then given in a 
conventional manner by pressing on thumb pad 62 while grasping finger 
ledges 42. At the end of an injection, stem assembly 28 is in the post 
injection position of FIG. 6 so that surfaces 70, 72 frictionally engage. 
To prepare for disposal of syringe 2, thumb pad 62 is pulled in the 
proximal direction until stem assembly 28 is in its safe-disposal position 
and carrier 24 is in its proximal position, see FIG. 7, thus placing 
syringe 2 in its safe-disposal condition with needle tip 58 positioned 
within body 26. Used syringe 2 can then be safely disposed of. 
In the preferred embodiment, components of safety syringe adapter 4 are 
made of suitable plastics, such as polycarbonate. It is preferable that 
the user be able to see the contents of cartridge-needle unit 6 so that 
body 26 and stem assembly 64, at least, are preferably made of transparent 
or clear material. In the preferred embodiment, stem assembly 64 is 
generally cylindrical; however, other elongate stem extension structures, 
such as the axially extending rods tied together at their distal ends with 
a circular ring, could be used. The engagement between stem extension 64 
and carrier 24 can be other than a tapered friction fit. For example, 
detents, barbed elements, spring fingers or, threaded engagement elements 
could be used between stem extension 64 and carrier 24. Also, stem 
assembly 28 could be configured to become secured to proximal end 12 of 
barrel 8 when at its post-injection position rather than being secured to 
carrier 24. Locking carrier 24 in its proximal position could be 
accomplished using other catch elements; for example a one-way ratchet 
between carrier 24 and the inner surface of side wall 26, or an inwardly 
biased tooth extending into interior 36 from side wall 26 to catch on 
carrier 24, could be used. Carrier 24 could be secured to cartridge needle 
unit 6 other than by threads 18, 30; for example, carrier 24 could be 
configured to snap over and engage the shoulder of needle assembly 14 
adjacent distal end 10 of barrel 8. 
Other modifications and variations can be made to the disclosed embodiment 
without departing from the subject of the invention as defined in the 
following claims.