Abstract:
An air shot or priming mechanism for an injection pen. The injection pen comprises a cartridge-holder and a housing. The cartridge-holder interacts with a nut-member capable of driving the piston rod forward when relatively rotated. The cartridge-holder is rotational coupled to the housing such that rotation of the cartridge-holder relatively to the housing causes the nut-member and the piston rod to rotate relatively, thus the relative angular rotation between the cartridge-holder and the housing determines the size of the air shot so performed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of International Application Number PCT/DK2004/000818, filed Nov. 25, 2004, which claims priority to European Patent Application Number 03388085.7, filed Dec. 8, 2003, and U.S. Provisional Application Ser. No. 60/528,302, filed Dec. 10, 2003, the contents of each of which is incorporated herein in its entirety.  
       THE TECHNICAL FIELD OF THE INVENTION  
       [0002]     The invention relates to a medical delivery device by which medicine may be apportioned in preset doses from a cartridge. The invention especially relates to an air shot mechanism for such medical delivery device.  
       DESCRIPTION OF RELATED ART  
       [0003]     Some medication such as insulin is self-administered. The typical diabetes patient will require injections of insulin several times a day.  
         [0004]     Medication delivery device have been developed to facilitate the self-administration of medication. The typical medication delivery device includes a cartridge-holder into which a cartridge containing insulin or other medication is loaded.  
         [0005]     The medical delivery device can either be a durable delivery device having an exchangeable cartridge or it can be a prefilled delivery device having an encapsulated cartridge.  
         [0006]     The cartridge-holder is an elongated structure with proximal and distal ends. The distal end of the cartridge-holder includes means for engaging a double-ended needle assembly. The double-ended needle assembly pierces an elastomeric seal in the distal end of the cartridge such that an end of the needle assembly enters the cartridge.  
         [0007]     The proximal end of the cartridge is closed of by a slidable plunger such that the content of the cartridge can be pressed out through the needle assembly when the plunger is moved towards the distal end of the cartridge.  
         [0008]     When a user wants to self-administer a dose of medicament, a cartridge is loaded into the medical delivery device and a double-ended needle is mounted on the distal end of the device. The user then selects a dose and operates the medical delivery device to urge the plunger distally to deliver the selected dose.  
         [0009]     The double-ended needle mounted on the medical delivery device contains air in the interior lumen and if the user leaves the double-ended needle on the medical delivery device for a longer period of time air can be sucked into the cartridge e.g. due to temperature variations. It is therefore recommendable to ensure that both the double-ended needle assembly and the cartridge are emptied for air before a dose is set and injected.  
         [0010]     To get rid of possible air a small dose of medicine is set and an injection operation is made without insertion of the double-ended needle into the skin. By this so called air shot, air is driven out through the double-ended needle. At the point of the double-ended needle it can easily be seen if all air has been expelled. If a fine liquid jet is not seen at the end of the air shot a new small dose must be set and a new air shot be made until such a jet is seen.  
         [0011]     To avoid having to perform repetitive settings of a small dose and subsequent air shots, the user may feel an impulse to set a somewhat larger dose to make sure only one air shot has to be made. This has lead to the development of medical delivery devices having a separate air shot button by which a predetermined amount can be expelled.  
         [0012]     Such medical delivery devices are disclosed in WO 98/10814 and EP 937 477.  
         [0013]     The medical delivery devices so disclosed has a separate air shot button formed as a ring or collar surrounding the housing of the device. The ring interfaces with a nut member inside the housing. When rotating the ring, the nut member rotates with it and drives forward the piston rod.  
         [0014]     It is however rather cumbersome for people to rotate this relatively small ring. This is particular difficult for people having impaired sight or reduced motor skills which are often the case with people suffering from diabetes.  
         [0015]     It is also a drawback that the ring, as disclosed in WO 98/10814, is left unprotected when the cap is not mounted such that it can be accidentally operated if the medical delivery device is left unattended with the double-ended needle mounted on the medical delivery device e.g. if the medical delivery device is left laying on a table. The medical delivery device could e.g. roll by it self on a sloping surface and expel expensive medicine.  
       DESCRIPTION OF THE INVENTION  
       [0016]     In order to avoid these drawbacks, the cartridge-holder itself is according to the present invention used as a mean for performing an air shot.  
         [0017]     The cartridge-holder is due to its size easy gripable and is usually covered by a cap when the device is not used.  
         [0018]     When a user wants to perform an air-shot, the user rotates the cartridge-holder relatively to the housing. Since the cartridge-holder is operational coupled to the piston rod drive which comprises the piston rod guide and the nut-member, one of these parts are rotated relatively to the other when the cartridge-holder or the housing is rotated.  
         [0019]     The relative rotation between the piston rod guide and the nut-member will cause the piston rod to be moved forward.  
         [0020]     The relative rotational movement between the cartridge-holder and the housing is in a preferred embodiment defined by a limiter on the housing being movable relatively to an opening provided in the cartridge-holder.  
         [0021]     The location of the limiter and the opening is not in anyway bound, the limiter could be provided either on the housing or on the cartridge-holder and the opening vice versa. Which one is moved is indifferent, what counts is the relative movement between the opening and the limiter.  
         [0022]     The nut-member is provided with a distal part and a proximal part which parts carries a number of ratchet pawls. The distal ratchet pawls interface a ratchet on the interior of the cartridge-holder whereas the proximal pawls interface a ratchet on the interior of the housing.  
         [0023]     Now when rotating the cartridge-holder in a first direction the distal ratchet pawls slides over the ratchet on the interior of the cartridge-holder whereas the proximal pawls are locked by the ratchet on the interior of the housing thereby preventing the nut-member from rotating.  
         [0024]     When rotating back the cartridge-holder in an opposite rotational direction, the nut-member do follow the rotation and since the piston rod is rotational locked, it will be screwed forward by the rotation of the nut-member. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS:  
       [0025]     The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which:  
         [0026]      FIG. 1  Shows a cross-sectional view of the delivery device according to the invention.  
         [0027]      FIG. 2  Shows an exploded perspective view of the delivery device according to the invention.  
         [0028]      FIG. 3  Shows a detailed cross-sectional view of the dose setting mechanism according to an embodiment of the invention.  
         [0029]      FIG. 4  Shows a detailed cross-sectional view of the air shot mechanism according to an embodiment of the invention.  
         [0030]      FIG. 5  shows a perspective view of the housing according to an embodiment of the invention.  
         [0031]      FIG. 6  shows a cross-sectional view of the housing according to an embodiment of the invention.  
         [0032]      FIG. 7  shows a perspective view of the scale drum according to an embodiment of the invention.  
         [0033]      FIG. 8  shows a view of the lay-out of the tracks of the scale drum in  FIG. 7   
         [0034]      FIG. 9  shows a perspective view of the scale drum according to yet an embodiment. 
     
    
       [0035]     The figures are schematic and simplified for clarity, and they just show details, which are essential to the understanding of the invention, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts.  
       DETAILED DESCRIPTION OF EMBODIMENT:  
       [0036]     Initially it may be convenient to define that, the term “distal end” of the injection device  1  is meant to refer to the end carrying the injection needle, whereas the “proximal end” is meant to refer to the opposite end carrying the injection button  35 . When the term “distal end” are used for other parts of the injection device  1 , it is meant to refer to the end pointing towards the distal needle carrying end of the injection device  1 , whereas the term “proximal end” refer to the end pointing towards the proximal end of the injection device  1 .  
         [0037]      FIG. 1  and  2  discloses the injection device  1  according to the invention. Exterior the injection device  1  comprises a cartridge-holder  10  coupled to the distal end of a housing  20 . The housing  20  comprises the dose setting and injection mechanism.  
         [0038]     A scale drum  30  is in its outer wall provided with a helical track  31  which is engaged by a helical rib  21  along the inner wall of the housing  20 . At its proximal end the scale drum  30  has a diameter exceeding the inner diameter of the housing  20  to form a dose setting button  32  which on its cylindrical outer wall is knurled to ensure a good finger grip.  
         [0039]     A piston rod guide  40  having a flange  41  near the proximal end and having a number of longitudinal fins  42  provided at its inner sidewall fits into the scale drum  30 .  
         [0040]     The piston rod  50  has at its proximal end a knob  51  having an outer diameter larger than the diameter of the piston rod  50  which knob  51  fits into the piston rod guide  40 . The knob  51  has a number of longitudinal slots  52  into which slots  52  the fins  42  on the piston rod guide  40  fits such that the piston rod  50  and the piston rod guide  40  is coupled to each other so that rotation but not longitudinal displacement is transmitted between the two elements. The piston rod  50  is further provided with a non circular cross section and an outer thread  53   
         [0041]     The piston rod guide  40  is coupled to the scale drum  30  through a dish  45  having ratchet teeth both at its proximal side  46  and at its distal side  47 . One or more piston rod guide pawls  43  provided on the flange  41  of the piston rod guide  40  interfaces with the teeth of the dish  45  on the proximal side  46 . The teeth provided on the distal side  47  of the dish  45  interfaces a ratchet provided in the scale drum  30 .  
         [0042]     The scale drum  30  is at the most proximal end provided with an injection button  35 . The injection button  35  shown in details in  FIG. 3  is rotatable secured in the scale drum  30  by having a ring shaped projection  37  inserted into a ring shaped channel  33  on the inside surface of the scale drum  30 . A resilient part  36  urges the proximal surface of the flange  41  of the piston rod guide  40  towards the dish  45  and the not shown ratchet at the proximal end of the scale drum  30 .  
         [0043]     The scale drum  30  is further provided with a number of slits  34  such that the distal area of the scale drum  30  can be forced outward in a peripheral direction when the knob  51  of the piston rod  50  enters the distal end of the scale drum. The function of this will be explained later.  
         [0044]     In the distal end of the injection device  1  a needle holder  2  is secured to the cartridge-holder  10 . The needle holder  2  has a thread  3  or similar fastening mean onto which a not shown injection needle can be fastened. The needle holder  2  and the cartridge-holder  10  could alternatively be moulded as one unit.  
         [0045]     A cartridge  5  containing a fluid medicament is provided inside the cartridge-holder  10 . The cartridge  5  has an open proximal end which is sealed by a rubber piston  6 . By forcing the rubber piston  6  in the distal direction, the fluid medicament in the cartridge  5  can be pressed out through the not shown injection needle fastened to the distal end of the injection device  1 . The injection needles most commonly used are doubled pointed injection needles having a fore-needle for penetrating the skin of a user and a back-needle for penetrating a not shown rubber membrane at the distal end of the cartridge  5 .  
         [0046]     The cartridge  5  can be either replaceable or it can be permanently encapsulated in the injection device  1 .  
         [0047]     A nut member  60  is provided in the junction between the cartridge-holder  10  and the housing  20  which nut member  60  has an inner thread  63  corresponding to the outer thread  53  of the piston rod  50 . When the piston rod  50  is rotated relatively to the nut member  60 , the piston rod  50  is screwed forward further into the cartridge  5 .  
         [0048]     A pressure foot  55  is located between the piston rod  50  and the rubber piston  6 . The pressure foot  55  is preferably provided with a peripheral ring  56  on both sides such that the force from the forward movement of the piston rod  50  is transmitted to the rubber piston  6  at the periphery of the rubber piston  6 .  
         [0049]     Further a one-way coupling  70  is provided. This one-way coupling  70  has a hole  71  which mates the not circular cross section of the piston rod  50  to allow axially displacement but not rotation of the piston rod  50  in relation to the one-way coupling  70 . On the exterior the one-way coupling  70  is provided with pawls  72  which interfaces a first ratchet  22  on the inside surface of the housing  20 , such that the one-way coupling  70  can be rotated relatively to the housing  20  in one direction but not in the opposite direction. The allowed rotational direction being the one that screws the piston rod  50  forward in the tread  63  of the nut member  60  preventing backwards movement of the piston rod  50 . During injection, the one-way coupling  70  will henceforth be free to rotate in the ratchet  22  of the housing  20 .  
         [0050]     When a dose is set by rotating the dose setting button  32  in a clockwise direction, the scale drum  30  is screwed out of the housing  20  and the dose setting button  32  together with the injection button  35  is lifted away from the proximal end of the housing  20 . The piston rod guide  40  is kept non-rotational due to its coupling to the piston rod  50  which again is prevented from rotation by the one-way coupling  70  interfacing the housing  20 . If a dose is reduced by rotating the dose setting button  32  in an anticlockwise direction the pawl mechanism  72 ,  22  between the one-way coupling  80  and the housing  20  is sufficient reluctant to rotate in its not blocking direction to prevent the piston rod guide  40  from following this anti-clockwise rotation.  
         [0051]     As the scale drum  30  is screwed out of the housing  20 , the not shown pawl teeth of the scale drum  30  rides over the pawl teeth on the distal side  47  of the dish  45  thereby making a clicking sound e.g. indicating the number of doses being set.  
         [0052]     When injecting the set dose, the injection button  35  is pushed back in the distal direction towards the housing  20 . During this movement the scale drum  30  rotates in the anti clock wise direction. The pressure applied to the injection button  35  forces the piston rod guide pawls  43  on the flange  41  to engage the pawl teeth on the proximal side  46  of the dish  45 . Both this engagement and the engagement between the not shown pawl teeth provided on the interior of the proximal end of the scale drum  30  and the pawl teeth on the distal side  47  of the dish  45  is non rotational when the scale drum  30  is rotated in the anti clockwise direction. Due to this the piston rod guide  40  is rotated with the scale drum  30 . This rotation forces the piston rod  50  to rotate due to the coupling  42 ,  52  between the piston rod guide  40  and the piston rod  50 . As the piston rod  50  is rotated, it is screwed out of the inner thread  63  of the nut member  60  and further into cartridge  5  located in the cartridge holder  10 . This forward movement of the piston rod  50  moves the rubber piston  6  inside the cartridge  5  and expels the fluid medicament confined in the cartridge  5  out of the not shown injection needle mounted to the needle holder  2 .  
         [0053]     The one-way coupling  70  is coupled to the neighbouring nut member  60  through a click-on connection which is best seen in  FIG. 4 .  
         [0054]     The nut member  60  comprises two parts, a distal part  64  and a proximal part  66  which are connected through an intermediate part  65 . These three parts  64 ,  65 ,  66  are preferably moulded as one part—the nut member  60 .  
         [0055]     The distal part  64  of the nut member  60  has on its periphery a number of distal ratchet pawls  67  interacting with a cartridge holder ratchet  17  provided on the interior of the cartridge holder  10 .  
         [0056]     The proximal part  66  of the nut member  60  has on its periphery a number of proximal ratchet pawls  68  interacting with a second ratchet  28  provided on the interior of the housing  20 .  
         [0057]     The cartridge holder  10  is connected to the housing  20  in a way allowing rotation. The cartridge holder  10  is at its proximal end provided with a circular protrusion  13  located on the exterior surface. This circular protrusion  13  engages a circular groove  23  provided in the interior of the housings  20  distal end. The circular protrusion  13  is able to rotate within the groove  23 . A limiter  14  in the shape of a protrusion on the exterior of the cartridge holder  10  moves within an opening  24  in the housing  20  during rotation such that the angular size of the opening  24  defines the angle that the cartridge holder  10  can be moved relatively to the housing  20 .  
         [0058]     When the piston rod  50  has pushed the pressure foot  55  and the rubber piston  6  to the distal end of the cartridge  5  and the cartridge  5  is about to be empty, the knob  51  on the piston rod  50  enters the distal area of the scale drum  30 . When setting up a dose, the scale drum  30  will be moved in the proximal direction relatively to the knob  51  on the piston rod  50 . When the knob  51  is in the end of the distal area of the scale drum  30 , the peripheral area of the distal end of the scale drum will be pressed outward due to the diameter difference between the knob  51  and the inside diameter of the distal area of the scale drum  30 . The slits  34  facilitate this peripheral movement. The housing  20  is on the inside provided with a end-of-content ratchet  34  which will be engaged by the peripheral part of the distal area of the scale drum  30  during its outward movement thereby preventing further movement of the scale drum  30  in the proximal direction. This locking of the scale drum  30  is coordinated with the content of the cartridge  5  such that the mechanism prevents the user for dialling up a dose larger than the content remaining in the cartridge  5 . The distal end of piston rod guide  40  and/or the distal area of the scale drum  30  must be configured to enable the peripheral movement of the distal area of the scale drum  30 , e.g. by providing the scale drum  30  with inwardly pointing protrusions  341  which will force the distal area of the scale drum  30  in the peripheral direction when encountering the conical distal part of the knob  51  as best seen in  FIG. 4 .  
         [0059]     When performing an air shot the user rotates the cartridge holder  10  in the anti clockwise direction and the cartridge holder distal ratchet  17  on the cartridge holder  10  will ride over the distal pawls  67  on the nut member  60 . The proximal pawls  68  on the nut member  60  engages the second ratchet  28  of the housing  20  in a way preventing rotational movement between the housing  20  and the nut member  60 . After a certain angular rotation of the cartridge-holder  10 , the limiter  14  will engage the side of the opening  24  and thereby prevent further rotation.  
         [0060]     Following this, the user rotates the cartridge holder  10  back in the clockwise direction until the limiter  14  engages the opposite side of the opening  24 . During this rotation, the cartridge holder ratchet  17  will engage the distal ratchet pawls  67  on the nut member  60  and rotate the nut member  60  in the anti clock wise direction. Further, the proximal pawls  68  on the nut member  60  are free to rotate in the ratchet  28 . The pawls  72  on the one-way coupling  70  engages the ratchet  22  on the interior of the housing thereby preventing the one-way coupling  70  from rotating inside the housing  20   
         [0061]     Since the nut member is rotated relatively to the piston rod  50  which is rotational locked by the one-way coupling  70 , the piston rod  50  is moved towards the distal end of the cartridge holder  10  moving the rubber piston  6  inside the cartridge  5  forward in the distal direction if a cartridge  5  is inserted in the device  1   
         [0062]     Another air shot mechanism is disclosed on  FIG. 7  and  8 . The scale drum  130  is provide with a helical track  131  At the proximal end of the scale drum  130 , the helical track  131  is divided in to primary track  1311  and a secondary track  1312 .  
         [0063]     In usual operation when a dose is being set or expelled, the helical rib  121  of the housing  20  is guided in the helical track  131  and the primary track  1311 .  
         [0064]     When an air shot is set, the user pulls the knob  132  of the scale drum  130  in the proximal direction away from the housing  20 . This movement forces the helical rib  121  into the secondary track  1312  by sliding on the sidewall  1312  of the primary track  1311 . This new position is indicated by  121 A.  
         [0065]     The dose setting button  132  will now be in a position where it protrudes from the proximal end of the housing  20 . In order to release the predetermined air shot the user must push back the dose setting button  132  to its original position. Doing so, the thread  121 A will abut the end surface  1314  of the secondary track  1312  in stead of the end surface of the primary track. This movement will release a dose due to the supplementary rotation of the scale drum  130 . The predetermined dose of this air shot dose is decided by the difference in the angular position of the two end surfaces  1314 , 1315  of the primary track  1311  and the secondary track  1311 .  
         [0066]     Yet another embodiment is disclosed in  FIG. 9 . In this embodiment the zero point on the scale drum  230  will be located more towards the distal end of the scale drum  230  than normal. The result being that the proximal part of the scale drum  230  carrying the dose setting button will protrude from the proximal end of the housing when the number zero is present in the window in the housing. In order to ensure this position a spring urging the scale drum in the proximal direction can be present.  
         [0067]     When an air-shot is made, the scale drum  230  is simply screwed in the anti clockwise direction moving the scale drum  230  in the distal direction in the housing. As the proximal end of the scale drum  230  is provided with a number of ratchet teeth  2301  interfacing a number of opposite directed ratchet teeth  2411  provided on a flange  241  on the piston rod guide  240 , the piston rod guide  240  will be forced to follow the rotation of the scale drum  230 . When the scale drum is returned to the zero position after the air-shot, the ratchet teeth  2301  on the scale drum  230  will override the ratchet teeth on the flange  241  of the piston rod guide  240 . Once the scale drum  230  has returned to its zero position, the user can perform another airshot by rotating the scale drum in the anti clockwise direction or the user can set a desired dose by rotating the scale drum in the clockwise direction.  
         [0068]     Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject matter defined in the following claims.  
       LISTING OF PARTS  
       [0000]    
       
           1  Injection Device 
         2  Needle Holder      3  Thread      
           5  Cartridge 
         6  Rubber Piston      
           10  Cartridge Holder 
         13  Circular Protrusion      14  Limiter      17  Cartridge Holder Ratchet      
           20  Housing 
         21  Helical Rib      22  First Ratchet      23  Circular Groove      24  Opening      28  Second Ratchet      
           30  Scale Drum 
         31  Helical Track      32  Dose Setting Button      33  Ring Shaped Channel      34  end-of-content ratchet      341  inwardly pointing protrusion      
           35  Injection Button 
         36  Resilient Part      37  Ring Shaped Projection      
           40  Piston Rod Guide 
         41  Flange      42  Longitudinal Fins      43  Piston rod guide Pawls      
           45  Dish 
         46  Proximal Side      47  Distal Side      
           50  Piston Rod 
         51  Knob      52  Longitudinal slots      53  Outer Thread      
           55  Pressure Foot 
         56  Peripheral Ring      
           60  Nut Member 
         63  Inner Thread      64  Distal Part      65  Intermediate Part      66  Proximal Part      67  Distal Ratchet Pawls      68  Proximal Ratchet Pawls      
           70  One-way Coupling 
         71  Hole      72  Pawls      121  Helical Rib      121 A New Position of Helical Rib      
           130  Scale Drum 
         131  Helical Track      132  Dose Setting Button      1311  Primary Track      1312  Secondary Track      1313  Side Wall      1314  End Wall of Primary Track      1315  End Wall of Secondary Track      
           230  Scale Drum 
         2301  Scale drum ratchet teeth      240  Piston rod guide      241  Flange      2411  Flange ratchet teeth