CA2244170C - Medication delivery pen having an improved clutch assembly - Google Patents

Abstract

An improved medication delivery pen is provided for injecting fluids such as insulin within body tissue. The medication delivery pen includes a mechanism that prevents the removal of a cartridge unless an injector button on the medication pen is in a predefined position, a bayonet attachment and an improved clutch assembly in a dose setting mechanism that provides improved control over the torque necessary to rotate units counter ring in the medication delivery pen using a dose setting knob.

Description

.~ . CA 02244170 1998-07-29 5OF: Antonio Bendek, John Burbank, Charlie Bush, Jonathan Gabel, Lucio Gi~mh~ttict~, Roger Hoeck and Malcom Taylor FOR: MEI)ICATION DELI~ERY PEN IIAVING AN IMPROVED CLUI CII
ASSEMBLY

BACKGROI~D OF TIIE INVEN~ON

1. Field of the Invention 5The subject invention relates to an improved medication delivery pen.

2. Description of Related Art Hypodermic syringes are used to deliver selected doses of me~ tion to 20 p~tiP.nt~. The prior art hypodermic syringe includes a syringe barrel having opposed lal and distal ends. A cylindrical chamber wall extends between the ends and defines a fluid receiving chamber. The plv~lllal end of the prior art syringe barrel is subst~nti~lly open and receives a plunger in sliding fluid tight engagement. The distal end of the prior art syringe barrel includes a passage communic~ting with the chamber.
2s A needle c~nn~ may be mounted to the distal end of the prior art syringe barrel, such that the lumen of the needle c~nn~ communicates with the passage and the chamber of the syringe barrel. Movement of the plunger in a proximal direction draws fluid through the lumen of the needle cannula and into the chamber. Movement of the plunger in a plu~ al-to-distal direction urges fluid from the chamber and through the lumen of the needle c~nn~
s M~lic~tion to be injected with the prior art hypodermic syringe often is stored in a vial having a pierceable elastomeric seal. Medication in the prior art vial is ~ces~d by piercing the elastomeric seal with the needle r~nnlll~ A selected dose of the medication may be drawn into the chamber of the syringe barrel by moving theplunger a selected distance in a proximal direction. The needle c~nnul~ may be withdrawn from the vial, and the medication may be injected into a patient by moving the plunger in a distal direction.

Some medication, such as insulin is self-~mini~tered. The typical diabetes 15 patient will require injections of insulin several times during the course of a week or ~-. day. The required dose of insulin will vary from patient to patient-, and for each patient may vary during the course of the day and from day to day. Each diabetes patient will establish a regimen that is a~)pl~liale for his or her own medir~l condition and for his or her lifestyle. The legilllell typically incllldes some combh~lioll of a slow or ...?A;~
20 acting insulin and a faster acting insulin. Each of these re~imrn~ may require the diabetes patient to periodically self-~mini.~ter insulin in public locations, such as places of employment or ~l~u~ . The required m~nir~ tion of the standard prior art hypodermic syringe and vial can be inconvenient and e.l..b~ in~ in these public environme.nt.~, 2s Medication delivery pens have been developed to facilitate the self-~mini~tration of medication. One prior art medication delivery pen described in U.S.
Patent No. 5,279,585 includes a vial holder into which a vial of insulin or other medication may be received. The vial holder is an elongate generally tubular structure with proximal and distal ends. The distal end of the prior art vial holder includes s mounting means for eng~ging a double-ended needle c~nn~ The proximal end also includes mounting means for en~ing a driver and dose setting a~pdldlus as explained further below. A disposable vial for use with the prior art vial holder includes a distal end having a pierceable elastomeric seal that can be pierced by one end of a double-ended needle c~nn~ The ~J~u~ihllal end of this prior art vial includes a plunger10 slidably disposed in fluid tight engagement with the cylindrical wall of the vial. This prior art medication delivery pen is used by inserting the vial of medication into the vial holder. A prior art pen body then is connected to the proximal end of the vial holder. The pen body inchldes a dose setting appa~dlus for dç~ign~ting a dose ofmedication to be delivered by the pen and a driving appd dlus for urging the plunger of 15 the vial distally for a distance corresponding to the selected dose.

The user of the pen mounts a prior art double-ended needle c~nnlll~ to the distal end of the vial holder such that the proximal point c~nnl-l~ of the needle c~nnlll~
pierces the elastomeric seal on the vial. The user then selects a dose and ope,dles the 20 pen to urge the plunger distally to deliver the se~octe~ dose. The user then removes and discards the needle c~nnnl~ and keeps the prior art medication delivery pen in a convenient location for the next required me~ic~tion ~lmini~t~tion. The m~i~tion in the vial will become exh~lJstçd after several such ~lu~ l .d~ions of me li~tion. The user then sel)~dles the vial holder from the pen body. The empty vial may then be 2s removed and discarded. A new vial can be inserted into the vial holder, and the vial holder and pen body can be re~cse.mbled and used again as e~ldilled above.

The above described reusable medication delivery pen is effective and much more convenient for self-~clmini~tration of medication than the typical hypodermic syringe and separate medication vial. However, it has been found that there is the need s for additional features and improvements for such a medication delivery pen. For example, there is the need to prevent removal of the vial unless the injector button of the me~lic~tion delivery pen is in a selecte i position, to provide improved control over the torques available or nece.ss~ry to rotate a unit in~lic~tor using a dose setting appalalus, and to generally ~ n~ en or otherwise improve the dose setting app~al~ls 10 in the mediation delivery pen.

SUMMARY OF THE INVENTION

The present invention is directed to providing a medication delivery pen having 5 the features and improvements set forth above.

One object of the present invention is to provide a me~h~nism in the medication delivery pen that prevents the removal of a vial or cartridge unless the injector button of the meAic~tion pen is in a selecteA position. The feature is provided by using a pair 20 of bayon~ connections on the cartridge retainer to activate a locking mech~ni~m in the pen when the cartridge r~iller is rotated. In particular, when the injector button is in the up position, the pivot shafts on the half-nuts in the pen prevent rotation of a locking sleeve which prevents removal of the cartridge l~lailler and cartridge. However, when the injector button is in the down position the pivot shafts on the half nuts in the pen do 2s not prevent rotation of the locking sleeve, which then allows the cartridge retainer to rotate and the bayonet connections to be separated from the pen's housing to remove the cartridge.

Another object of the present invention is to improve the clutch assembly in themedication delivery pen to provide more contro1 over the torques necessary to rotate s the unit indicator in the pen using the rotation of a dosing knob in the dose setting a~pal~lus.

A third object of the present invention is to improve the dose dis~nsing apparatus to provide more definite control over the dose dispensing operation by0 preventing skewing of the drive mech~ni~m.

These and other aspects, f~lur~s and advantages of the present invention will become a~;,ll from the following detailed description taken in conjunction with the accolllp~lying drawings.

DESCRImON OF THE DRAWINGS

Fig. 1 is a perspective view of a medication delivery pen of the subject 20 invention;

Fig. 2 is a perspective view of the medication delivery pen shown in Fig. 1 withthe plunger extended;

2s Fig. 3 is a perspective view of the medication delivery pen shown in Fig. 1 with the plunger moving axially during an injection;

Fig. 4 is a perspective view of the medication delivery pen shown in Fig. 1 withthe cartridge retainer removed;
s Figs. Sa and Sb are exploded perspective views of the pen shown in Fig. 1 further including a needle assembly;

Fig. 6 is an enlarged perspective of the clutch assembly;

Fig. 7 is an exploded perspective view of the meli~tion delivery pen shown in Fig. 1 with the cartridge retainer removed;

Fig. 8 is another perspective view of the medication delivery pen shown in Fig.
5 1 with the cartridge retainer ~ che~1 and locked onto the upper body;

.
Fig. 9 is a cross sectional view taken along lines 9-9 as shown in Fig. l;

Fig. 10 is a cross sectional view taken along lines 10-10 as shown in Fig. 2;
Fig. 11 is a cross sectional view taken along lines 11-11 as shown in Fig. 4;

Fig. 12 is an enlarged cross sectional view of the ms~lic~tion delivery pen shown in Figs. 2 and 10 to more clearly show the clutch assembly;

Fig. 13 is an enlarged cross sectional view of the zero detection clip shown in Fig. Sb; and Fig. 14 is a cross sectional view taken along lines 14-14 as shown in Fig. 13.

s DETAILED DESCRIPIION

An improved injection device 10 for injecting insulin or other me~ tion is provided by the present invention. As shown in Pigs. 1-3, the device inrhl~les an adjusting knob 12, an upper body 14, a center body 16, and a cartridge l~i~. 18 All o of these element~ have a generally cylindrical configuration and are arranged coaxially to define a generally cylindrical housing 20 which can easily be handled by a patient or medical ~tten-l~nt Referring to Figs. 4, Sa and 7-12, a plunger 22 is at least paItially positionedS within the portion of housing 20 defined by adjusting knob 12, upper body 14 and center body 16. Plunger 22~in~1u~,es a hollow5~subst~ y cylin-1ri~1 body ~a in-hl(ling a band of radially ~luje~i,~g splines 22b e~t~n-1ing oul~a,dly th~lc;rlolll. A
pair of opposing projections 22c extend radially inwardly from the front end of the ~;ylin.1.;~l body 22a. As shown in Figs. Sa and 5b, the rear end of plunger 22 is 20 secured to a hub 25 having a rotatable push button 24 snapped therein. Push button 24 fits partially within adjusling knob 12 when plunger 22 is fully inserted within housing 20.

A lead screw 26 is positioned within and coaxially with plunger 22 and includes 2s an enlarged front end 26a and a tapered rear end 26b, conn~ted by an elongatethreaded body 26c. A pair of longitll~in~l grooves 26d are formed within threaded body 26c and receive the radially inwardly e~tenrling projections 22c of plunger 22.
Lead screw 26 is accordingly rotatable with plunger 22 and capable of sliding axially with respect to plunger 22.

s A pair of half-nuts 28 are positioned within center body 16, with each half-nut 28 in~h~ding a semi-cylin-lri~l body portion 28a and a radially enlarged end portion 28b. The front end of each half-nut 28 includes threads 28c that are used to threadably engage with lead screw 26 and the rear end of each half-nut 28 includes a pivot shaft 28d that receives a metal pin 28e to provide an axis about which each half-nut 28 can o pivot. Metal pins 28e inserted in each pivot shaft 28d also provide more definite control over the dose setting operation, described below, and prevent skewing of half nuts 28 on threaded lead screw 26. Body portions 28a of half-nuts 28 are positioned at least partially within a locking ring 30 having a hollow, generally cylindrical body portion 30a defining a generally elliptical passage 30e for receiving half-nuts 28. A
front end 30b of locking ring 30 is radially enlarged and inl llldes a pair of angular plojeclions 30c that extend axially from the r~.~ of lockin~ ring 30 a~d the side of locking ring 30 includes a pair of pins 30d. The pro~l,al end 18b of cartridge ~ er 18 includes a pair of angular projections 18c that are spaced to receive angularpn~ lions 30c when cartridge l~iner 18 is mounted on holl~ing 20, which is desc- ibffl further below.

A helical coil spring 32 is positioned over locking ring 30 and half-nuts 28 andthrough locking sleeve 31, with one end of coil spring 32 bearing against the radially enlarged portions 28b of half-nuts 28 while the opposite end of coil spring 32 bears 2s against the radially enlarged front end 30b of locking ring 30. Front end 30b of locking ring 30 mounts within center body 16 which also receives fini~hing ring 29.

The rear end portion 28b of half-nuts 28 abut splines 22b of plunger 22, as shown in Fig. 9.

T.ocl~ing ring 30 is slidably mounted within locking sleeve 31 such that the pair s of pins 30d on locking ring 30 are mounted and travel within slot 31a at a distal end of locking sleeve 31. With this structure locking ring 30 is axially movable withinlocking sleeve 31 but rotates with locking sleeve 31. Locking sleeve 31 also in~ludes a pair of L-shaped grooves 31b that slidably receive each of the shafts 28d on half-nuts 28. Each pivot shaft 28d in conjunction with its respective L-shaped groove 31b on o locking sleeve 31 and a long groove 16c within center body 16 provides a mech~ni~m that prevents the removal of cartridge rt;~inel 18 and cartridge 46 from housing 20, unless injector button 24 is in a down or loading position. This feature is more clearly shown in Figs. 7 and 8. In Fig. 7 injector button 24 is in the down or loading position and device 10 is in the proper position for receiving cartridge retainer 18 and, in particular, lugs 18a can enter slot 16a of center body 16. As shown in Fig. 7, locking ring 30 is o.;e.ll~d so that tabs 30c do-~not block access to slot 16a and in this o.;...~ ;on pivot shafts 28d of half-nuts 28 are located in notches 31e at the end of each lower leg 31d of L-shaped groove 31b. After a cartridge 46 has been loaded into cartridge .~hler 18, cartridge l~in~r 18 is mated with center hou~ing 16 such that 20 lugs 18a enter slot 16a. Then, as shown in Fig. 8, cartridge ~inel 18 is rotated in a clockwise direction such that lugs 18a drive tabs 30c in a clockwise dir~ which moves locking sleeve 31 and causes pivot shaft 28d to slide out of each notch 31e and into each leg 31d of each L-shaped groove 31b. At this point, spring 32 drives half-nuts 28 in the p~xilllal direction to extend injector button 24 from the plo~llal end of 25 assembly 10, if dose settings rings 36 and 38 are set to zero.

As shown in Fig. 5b, upper body 14 includes an opening 14a in which a transparent window 34 is mounted. A units counter ring 36 and a tens counter ring 38 are positioned in adjoining relation beneath window 34, with both counter rings 36 and 38 including outer surfaces having numerals thereon visible through window 34.
s An O-ring 40 made from an elastomeric material is mounted in units counter ring 36 to hold a tr~ncmic.cion key 44 in position. Tr~ncmicsion key 44 is provided for en~ging and fli~.n~ging the units and tens counter rings 36, 38, and is located within a ch~nn.ol formed in units cou,lt~,r ring 36, as shown in Fig. 12. A zero detection clip o 42, more clearly shown in Figs. 13 and 14, is positioned between the inner surfaces of counter rings 36 and 38 and the outer surface of plunger 22. Zero detection clip 42, as shown in Figs. Sb, 13 and 14, includes a generally cylindrical body 42a having a radially enlarged front end 42b. A lower spring member 42c extends axially within a slot formed within clip body 42a and includes a ridge 42d that is engageable with S groove 38a formed within the inner surface of tens counter ring 38, as best shown in Fig. 14. Zero detection clip 4~1so incllldes an axially el~tPn~ing upper spring member 42e, the position of which is controlled by the rotational positions of the units and tens coullter rings 36, 38. Upper spring m.omber 42e in~ des a distal surface 42f that is engageable with splines ~b of plunger 22 when pushed into its active position by units 20 coullt~,l ring 36 or by tens coul,~r ring 38. The inner surface of units counter ring 36 functions as a cam and controls the radial position of upper spring member 42e of the zero det~ctic)n clip 42.

The inner surface of units counter ring 36 is splined, with the spline surface 2s being engageable with small splines 22d of plunger 22. Engagement between ring 36 and plunger 22 occurs when spring 32 is in the el~tended position shown in Fig. 10.

Units counter ring 36 is then driven by adjusting knob 12 through a specially clesigned clutch detent spring lS, more clearly shown in Fig. 6. Clutch detent spring lS includes a ring lSa having four internal tabs lSb that mount ring lSa onto units counter ring 36 and four legs lSc that are driven by rotation of adjusting knob 12. The present s invention provides a clutch detent spring lS that is made of a flexible metal that can be manufactured to provide a predetermined slip torque action between adjusting knob 12 and units counter ring 36.

Fig. 6 is an enlarged perspective view of clutch detent spring lS and shows its lO comle~ion with adjusting knob 12, clutch nut 13 and units counter ring 36. Clutch detent spring lS includes ring lSa having four outer legs lSc extentling in the distal direction with each leg lSc having a protrusion lSd thereon e~cten-1ing away from rotational axis lSr of clutch detent spring lS. Internal tabs lSb co~ polld to notches 36a on units counter ring 36 that receive a respective internal tab lSb and hold clutch S detent spring lS onto units counter ring 36 together with the clutch nut 13 that is threaded onto units counter ring 36. When units counter ring 36 with clutch detent spring lS mounted thereon is assembled into adjuslhlg knob 12, ~l~llusions 15d on clutch detent spring lS mate with inner surface 12a of adjuslhlg knob 12 and travel in detents 12b on inner surface 12a until a ~l~1e~e...-in~1 torque is en(~.n~ d by units 20 counter ring 36 which then causes clutch detent spring 15 to rotate with respect to ~ J~il;ng knob 12. The hll~l~l feature of the present invention is that when theclutch detent spring lS is m~mlfa~lred with angle ~ of each outer leg lSc with respect to rotational axis lSr, the clutch detent spring lS is preset to provide release from adjusting knob 12 at a predele~ led torque.
2s As shown in Fig. Sa, cartridge retainer 18 is adapted for receiving a cartridge 46 of the type including an internal piston 46b and a pierceable seal 46a at one end thereof. A threaded end cap 19 is inserted through cartridge retainer 18 to extend from a distal end 18d of cartridge retainer 18 and is provided with threads 19a for securing a double ended needle assembly 50. The proximal end of cartridge ~il~er 18 includes S the pair of bayonet lugs 18a on angular projections 18c that engage with the pair of slots 16a at the distal end of center body 16.

Needle assembly 50 includes a c~nn~ 50a having a sharp distal end 50b for yie~ g the skin of a patient or user and a sharp ~ al end 50c for piercing 10 pierceable seal 46a of cartridge 46 with a lumen (not shown) therethrough. Needle assembly 50 includes a cup-shaped hub 50d holding c~nn~ 50a so that sharp y~lal end 50c projects outwardly from the interior of cup-shaped hub 50d. Cup-shaped hub 50d includes an internal thread that is colnyatil)le with thread l9a on end cap 19, so that needle assembly 50 may be removably attached to end cap 19 with its sharp 5 p~ lal end 50c piercing pie~l)le seal 46a to establish fluid co,,,,,,~ tion with the interior of c~tridge 46.

The operation of the injection device 10 shall now be descrihe~l with l~,f.,re.lce to the ~ lp~l~ying figures. Generally ~e~king, cartridge 46 is loaded within the20 device, and a double ended needle assembly 50 is affixed to the end of c~tridge ldt~er 18. Fluid c~llllllunication is accol.lingly established between the injection portion of double ended needle assembly 50 and the interior of cartridge 46. Once the apy~yl;ale dosage is set, push button 24 is urged fol~ lly, causing lead screw 26 to exert force upon piston 46b movably positioned within cartridge 46. Piston 46b 2s displaces fluid within cartridge 46, causing its injection into body tissue through double ended needle assembly 50. The specific functions which are performed using the injection device are described separately herein. l~sllming the device is loaded and push button 24 is in the down position, three steps are followed in the injection procedure: set to zero, set the dose, and make the injection.

s First, adjusting knob 12 is rotated back to the zero setting on both counter rings 36 and 38. As will be described in more detail he~ below, adjusting knob 12 turns clutch detent spring 15 which then turns units counter ring 36. R~llse the splines on units counter ring 36 and plunger 22 are ~ eng~ged plunger 22 and the lead screw 26 do not turn. When rings 36 and 38 reach zero, their slots align and release upper o spring member 42e of zero detection clip 42. This in turn releases plunger 22 and push button 24 which move under pressure from spring 32 via the two half nuts 28 until the p~ al ends of large splines 22b of plunger 22 are stopped by an inner surface ofunits counter ring 36. This movement also carries lead screw 26. Small splines 22d on the plunger 22 engage with the splined units counter ring 36 and are ready for setting a 1S dose.

,, Adjusting knob 12 is then rotated away from the zero (O) setting. Adjusting knob 12 turns clutch detent spring 15, which turns units counter ring 36, which turns pl~lng~r 22. Plunger 22 is engaged with longit~1in~1 grooves 26d in lead screw 26 which turns and screws fOlwald in the nut formed by the two half nuts 28. The lead screw's travel is plvpo,lional to the number of units displayed by the counter rings 36, 38.

When the desired dose has been set, push button 24 is pushed fully in which 2s pushes plunger 22, two half nuts 28, and lead screw 26 fol~al.ls. Plunger and lead screw 26, as coupled by half nuts 28, accordingly ~,Çollll the function of a piston rod. The total travel is determined by push buKon 24 that slides into and is stopped by adjusting knob 12. The first part of the travel brings the end of lead screw 26 into contact with piston 46b of cartridge 46; the second part of the travel moves piston 46b of cartridge 46 forward and delivers the measured amount of me ii--Ation. While seKing s the dose, lead screw 26 is moved forward in proportion to the dosage set; this ~lict~nce d~ nules the proportion of the pre-injection and injection travel. Plunger 22 and push buKon 24 are locked in position by upper spring member 42e of the zero detection clip 42 following an injection.

o When a dose is set, units counter ring 36 pushes upper spring member 42e of zero detection clip 42 into its active position. Zero detection clip 42 includes a clicker 42g that generates a click for each unit as it passes over larger splines 22b on plunger 22. Units counter ring 36 drives the tens counter ring 38 through 36 degrees of rotation every time units counter ring 36 passes zero via trAn~mi~ion key 44. Lower spring member 42e of zero detection clip 42 has a ridge 42d which engages with the 5~ ~r grooves 38a inside the tens counter ring 38 and creates a-click every ~ime the tens counter ring 38 turns.

If the dose is set at the maximum dialable dose (he~iu~arler "TMDDn), tens 20 counter ring 38 reaches a stop, and trAnsmi.~.~ion key 44 engages in the last location in the tens counter ring 38. If adjusting knob 12 is turned further, rings 36 and 38 are unable to turn and adjusting knob 12 slips without further effect. Clutch detent spring 15 is designed to limit the torque which will be IIA~ (ed to the counler rings and prevents u~ ..lional damage.

The travel of lead screw 26 is limited to the safe travel of piston 46b in the cartridge 46. If lead screw 26 reaches the end of its travel, projections 22c inside plunger 22 reach the end of grooves 26d in lead screw 26 and prevent it from further movement. Lead screw 26 prevents plunger 22 and counter rings 36 and 38 from turning. Adjusting knob 12 will then cause clutch detent spring lS to slip without 5 further effect. The counter rings will indicate the travel of the lead screw to this point, and th~crolc, the quantity of insulin rem~ining in the cartridge.

~ When adjusting knob 12 is rotated away from the zero (0) setting, and there are more than TMDD units ~~ ing in cartridge 46, the counter rings will stop at TMDDunits as described above. If there are less than TMDD units rem~ining, the counter rings will stop as described above and display the rem~ining capacity of cartridge 46.
In either case, the user can then turn adjusting knob 12 back until the counter rings display the dose to be ~clmini~tered.

After a complete injection has been made, push button 24 can be left in the loading position. As d~scribed above, when device 10 is in the loading position cartridge retainer 18 can be removed from center body 16 of housing 20 and cartridge 46 can be removed. When cartridge retainer 18 is removed from housing 20, the ~.llirti~'~l shape defined by the inner wall of locking ring 30 allows two half nuts 28 to open under prcs~ulc from spring 32 and to free lead screw 26, as shown in Fig. 11.

A new cartridge 46 can then be inserted into cartridge .c~i"el 18 which is then locked back onto center body 16 using the bayonet or lugs 18a on cartridge lclail~er 18.
As cartridge retainer 18 moves towards center body 16, piston 46b of cartridge 46 will 2s push lead screw 26 into the device. Cartridge Ic~il~er 18 has two angular projections 18c that engage with angular projections 30c ex~ç~ g from locking ring 30. When cartridge retainer 18 is then rotated the projections 18c and 30c cause locking ring 30 to turn the same arnount. In addition, after cartridge retainer 18 has rotated and each lug 18a on cartridge retainer 18 has entered its respective recess 16b in slot 16a inside center body 16, cartridge ,~iner 18 is prevented from turning further. The elliptical s inner wall of locking ring 30 moves two half nuts 28 into engagement with lead screw 26. The position of lead screw 26 is then determined by the position of the piston 46b in cartridge 46.

Upper body 14 houses the four parts which comprise the counter me~h~nism.
o Window 34 in upper body 14 shows the numbers printed on the outside of the twocounter rings 36 and 38, and indicates the number of units to be injected from 0 to TMDD. Units counter ring 36 is turned by adjusting knob 12 through clutch detentspring 15. When units counter ring 36 has turned to numbered position "8", tr~n~mi~ion key 44 meets the cam molded inside upper body 14. The tr~n~mis~ion key lS 44 is then forced to slide up the face of the cam, and reaches the top in position "9".
The elastic ring 40 is fle~d by this movement and ...~ in~ the ~ ...i.csion key 44 in contact with the cam. This movement also brings the opposite end of tr~n~mi~ion key 44 into engagement with one of the slots 38b inside the tens coun~el ring 38, shown in Fig. 5b. When units counter ring 36 is turned further, tr~n~mi~ion key 44 ll~l~
20 the movement to tens counter ring 38, and the two rings turn together. At position "10" the window 34 now displays "10" and ~ ion k¢y 44 has rotated 36 degrees to the end of the raised face of the cam inside the upper body 14.

If units counter ring 36 is turned further, tr~nsmi.~ion key 44 is free to slide2s down the face of the cam inside upper body 14 under pleS~ from elastic ring 40.
This movement ~ en~ges the two counter rings, and the counter will now read " 11 " .

This movement is repeated each time the units counter ring 36 moves from position "8", through positions "9" and "0" to position "1". The reverse procedure is identical.

The tens counter ring 38 has stops in the "0" and TMDD positions to prevent s the counter mech~ni~m from going beyond a maximum reading of TMDD or a mh~l-ul,l reading of 0 units. In both of these positions the ll ~ )n key 44 is in its active, engaged position. It should be noted that if the stops for the tens counter ring 38 were moved, the reading could continue up to 99 units.

o The slot in units counter ring 36 has an angled face which works as a cam, forcing the upper spring member 42e down into its active position as soon as the units counter ring 36 leaves the "0" position. The units counter ring 36 holds the zero detection clip 42 in its active position up to position "9". In position "10" the tens cou~ r ring 38 has moved, and now holds the zero detection clip 42 in its activeposition. From position "10" to position TMDD zero detection clip 42 is held in its active position by tens counter ring 38. When an injection is-made, plunger 22 slide~-through the zero detection clip 42 until the end of its travel. At this point the end of upper spring member 42e drops behind the end of spline 22b and prevents plunger 22 from moving out under ~ ;iUIt; from spring 32. The collll)ol~ents can be dP~ign~l so 20 that this movement will make a cli~ing sound, co.-riii-g that a complete injection has been made.

When the counter is set to "0" as shown in Fig. 10, the slots inside the two counter rings 36 and 38 align with upper spring member 42e of zero detection clip 42 and allow it to spring up into its rest position. This movement frees plunger 22 and allows a new dose to be set.

Cartridge 46 is easily loaded and substantially fully visible to the user. Two way dosage adjustment is possible, which allows corrections to be made quickly and easily. The dosage to be ~(1mini~tered is clearly displayed and will remain displayed s subsequent to the injection procedure. In order to insure that a complete injection has been made, the device produces a click and locks in the closed position only when the plunger is fully inserted.

While the invention has been described with respect to a ~lcÇerlcd embodiment lo illustrated in Figs. 1-14, it should be understood that variations from this preferred embodiment may be provided, and are considered to be within the scope of the subject mvention.

Claims (7)

1. A medication delivery pen comprising:
a housing having a distal end and a proximal end;
a cartridge retainer for receiving a cartridge containing medication, said cartridge retainer being removably mountable on the distal end of said housing;
means in said housing for setting a desired dose of medication to be dispensed from the cartridge having a rotatable dose setting knob and a dosing ring that displays the amount of the desired dose being set;
means in said housing for dispensing the desired dose of medication from the cartridge; and means in said dose setting means for controlling torque applied by said rotatable dose setting knob to said dosing ring during rotation of said dosing knob including a clutch having a clutch detent spring attached to said dosing ring and rotatably mounted to said dose setting knob to rotate within said dose setting knob when a predetermined torque is applied to said dose setting knob.

2. A medication delivery pen according to claim 1, wherein said clutch detent spring includes a plurality of outer legs and a plurality of internal tabs, wherein said internal tabs attach to said dosing ring and said outer legs are in sliding contact with said dose setting knob.

3. A medication delivery pen according to claim 2, wherein said dose setting knob includes a plurality of detents on an inner surface and each of said plurality of outer legs on said clutch detent spring includes protrusion that rides in a respective one of said plurality of detents until said predetermined torque is applied to said dose setting knob, which then causes each of said plurality of protrusions to slip out of each of said plurality of detents.

4. A medication delivery pen according to claim 3, wherein each of said outer legs are positioned at a predetermined angle .theta. such that said predetermined torque can be applied to said dosing ring by said dose setting knob.

5. A medication delivery pen according to claim 1, further comprising attachment means between said cartridge retainer and said housing for attaching and unattaching said cartridge retainer to said housing.

6. A medication delivery pen according to claim 5, wherein said attachment means is a bayonet.

7. A medication delivery pen according to claim 6, wherein said bayonet includes a pair of projections on the proximal end of said cartridge retainer and a pair of slots in the distal end of said housing.