Abstract:
A medication delivery pen having very few parts allowing it to be manufactured at a very low-cost. The medication delivery pen also includes an automatic release mechanism to allow the user to easily reset the dose on the medication delivery pen and a mechanism for allowing the lead screw to easily retract back into the body of the medication delivery pen when the vial retainer has been removed to receive a new vial.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a medication delivery pen having a variety of features and, more particularly, a low-cost medication delivery pen having very few parts. 
     2. Description of Related Art 
     Hypodermic syringes are used to deliver selected doses of medication to patients. The prior art hypodermic syringe includes a syringe barrel having opposed proximal and distal ends. A cylindrical chamber wall extends between the ends and defines a fluid receiving chamber. The proximal end of the prior art syringe barrel is substantially open and receives a plunger in sliding fluid tight engagement. The distal end of the prior art syringe barrel includes a passage communicating with the chamber. A needle cannula may be mounted to the distal end of the prior art syringe barrel, such that the lumen of the needle cannula 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 proximal-to-distal direction urges fluid from the chamber and through the lumen of the needle cannula. 
     Medication 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 accessed by piercing the elastomeric seal with the needle cannula. A selected dose of the medication may be drawn into the chamber of the syringe barrel by moving the plunger a selected distance in a proximal direction. The needle cannula may be withdrawn from the vial, and the medication may be injected into a patient by moving the plunger in a distal direction.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-administered. The typical diabetes patient will require injections of insulin several times during the course of the 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 appropriate for his or her own medical condition and for his or her lifestyle. The regimen typically includes some combination of a slow or medium acting insulin and a faster acting insulin. Each of these regimens may require the diabetes patient to periodically self-administer insulin in public locations, such as places of employment or restaurants. The required manipulation of the standard prior art hypodermic syringe and vial can be inconvenient and embarrassing in these public environments. 
     Medication delivery pens have been developed to facilitate the self-administration of medication. One prior art medication delivery pen 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 mounting means for engaging a double-ended needle cannula. The proximal end also includes mounting means for engaging a driver and dose setting apparatus 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 cannula. The proximal end of this prior art vial includes a plunger 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 includes a dose setting apparatus for designating a dose of medication to be delivered by the pen and a driving apparatus for urging the plunger of the vial distally for a distance corresponding to the selected dose. 
     The user of the pen mounts a prior art double-ended needle cannula to the distal end of the vial holder such that the proximal point of the needle cannula pierces the elastomeric seal on the vial. The patient then selects a dose and operates the pen to urge the plunger distally to deliver the selected dose. The dose selecting apparatus returns to zero upon injection of the selected dose with this prior art medication delivery pen. The patient then removes and discards the needle cannula, and keeps the prior art medication delivery pen in a convenient location for the next required medication administration. The medication in the vial will become exhausted after several such administrations of medication. The patient then separates the vial holder from the pen body. The empty vial may then be removed and discarded. A new vial can be inserted into the vial holder, and the vial holder and pen body can be reassembled and used as explained above. 
     The above described medication delivery pen is effective and much more convenient for self-administration of medication than the hypodermic syringes that use separate medication vials. However, the above-described medication delivery pen requires a number of parts which make the manufacture of these pens very expensive. Hence, it is necessary to provide a medication delivery pen having a simple mechanism for setting the desired dose that uses as few parts as necessary without losing functionality or standard features. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a medication delivery pen that addresses the aboveidentified problems. The medication delivery pen uses only tens parts and still provides numerous features that have become expected by medical delivery pen users. 
     The medication delivery pen according to the present invention includes a mechanism that automatically disengages the drive mechanism from the dose control mechanism to permit the user to reset the dose on the medication delivery pen. 
     Another feature of the present invention is an automatic mechanism that allows the user to easily load a new vial and reposition the lead screw when the vial retainer has been removed from the body of the medication delivery pen. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a medication delivery pen according to the present invention. 
     FIG. 2 is a cross-sectional view of the driver in the medication delivery pen shown in FIG.  1 . 
     FIG. 3 is a partial perspective view of the distal end of the driver shown in FIG.  2 . 
     FIG. 4 is a perspective view of the retract nut shown in FIG.  1 . 
     FIG. 5 is a perspective view of the reset ring shown in FIG.  1 . 
     FIG. 6 is a cross-sectional view of the body of the medication delivery pen shown in FIG.  1 . 
     FIG. 7 is a distal end view of the body shown in FIG.  6 . 
     FIG. 8 is a perspective view of the dose set knob of the medication delivery pen shown in FIG.  1 . 
     FIG. 9 is a cross-sectional view of the medication delivery pen shown in FIG. 1 fully assembled and in a dose setting condition. 
     FIG. 10 is a cross-sectional view of the medication delivery pen shown in FIG. 9 in a reset dose condition. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A medication delivery pen  10  according to the present invention is shown in FIG.  1 . Medication delivery pen  10  includes a cap  1  removably attached to a vial retainer  2  so to cover vial retainer  2  between uses of medication delivery pen  10 . Vial retainer  2  receives a vial (not shown) that is commonly used in such medication delivery pens to provide medication and/or insulin for an injection. Medication delivery pen  10  includes a body  5  having a distal end  51  and a proximal end  52 , with vial retainer  2  being attached to distal end  51  of body  5 . Medication delivery pen  10  also includes a dose set knob  7 , a driver  8 , a lead screw  9 , a lead screw spinner  3 , a retract nut  4 , a reset ring  6 , and a thumb button  71 . Each of these elements are more clearly shown in FIGS. 2-8 and are more fully described below. 
     FIG. 2 is a cross-sectional view of driver  8  having a distal end  81  and a proximal end  82 , wherein distal end  81  includes a snap ring  83  used to attach retract nut  4  onto distal end  81  of driver  8 . In addition, driver  8  includes a plurality of ratchet fingers  84  at distal end  81 , as more clearly shown in FIG.  3 . These ratchet fingers  84  engage a ratchet  53 , shown in FIG. 6, within body  5  to allow driver  8  to rotate only in one direction with respect to body  5 . Driver  8  also includes a set of threads  85  that interface with a matching set of threads  93  on lead screw  9 , shown in FIG.  1 . 
     FIG. 4 is a perspective view of retract nut  4  that more clearly shows an attachment ring  41  that mates with snap ring  83  on distal end  81  of driver  8  to rotatably attach retract nut  4  onto driver  8 . Retract nut  4  also includes an opening  42  therethrough having a pair of flat sides  43  that mate with set of flat sides  94  on lead screw  9 , shown in FIG. 1, to prevent lead screw  9  from rotating with respect to retract nut  4 . Retract nut  4  also has a distal surface  45  and a proximal end  46 , proximal end  46  having a set of radial splines  44  that mates with a set of radial splines  54  within body  5  to prevent retract nut  4  and lead screw  9  from rotating when these splines  44  and  54  are engaged. As more clearly shown in FIG. 9, these splines  44  and  54  are fully engaged when vial retainer  2  is mounted onto body  5  and accordingly prevent retract nut  4  and lead screw  9  from rotating with respect to body  5 . However, when vial retainer  2  is not mounted into body  5 , retract nut  4  and lead screw  9  are free to rotate which permits lead screw  9  to be free to backdrive into body  5  as the user pushes a new vial into place. A lead screw spinner  3  is attached to a distal end  91  of lead screw  9  and is allowed to spin freely on lead screw  9 , shown in FIG. 1, in relation to a rubber plunger (not shown) within the vial as lead screw  9  is backdriven into body  5 . 
     When vial retainer  2  locks retract nut  4  into mating radial splines  54  within body  5 , lead screw  9  is locked against rotation which then enables threads  85  within driver  8  to drive lead screw  9  in the distal direction towards and against the rubber plunger within the vial during a dispensing operation. Snap ring  83  on driver  8  also allows retract nut  4  to float captive thereon thus trapping it from spinning down lead screw  9 , when exchanging vials should a user invert medication delivery pen  10  when changing vials. 
     FIG. 5 is a perspective view of reset ring  6  having a plurality of keys  63  therein that travel within a respective set of keyways  86  on driver  8 , shown in FIG.  1 . Reset ring  6  also includes a distal end  61  and a proximal end  62 , proximal end  62  having a flange  65  and a plurality of ratchets  64  extending from flange  65  to distal end  61 . Ratchets  64  engage with a plurality of ratchet fingers  73  on a distal end  71  of dose set knob  7 , shown in FIG.  8  and discussed further below. 
     FIG. 6 is a cross-sectional view of body  5  more clearly showing distal end  51  and proximal end  52  having a set of dose setting threads  58  therein together with a dose viewing window  55 . Another set of threads  56  located within distal end  51  are used to attach vial retainer  2  in this embodiment. Of course, other means for attaching vial retainer  2  to body  5  could also be used and fall within the scope of the present invention as long as sufficient force is applied to retract nut  4  to prevent rotation of retract nut  4  and lead screw  9  within body  5  when vial retainer  2  is attached to body  5 . FIG. 7 is a distal end view of body  5  more clearly showing radial splines  54 . 
     FIG. 8 is a perspective view of dose set knob  7  having a distal end  71  and a proximal end  72 , with a textured section  76  near proximal end  72  to aide the user in turning dose set knob  7  to set a desired dose when using medication delivery pen  10 . Distal end  71  includes the plurality of ratchet fingers  73  that engage ratchet  64  on reset ring  6  when setting a dose, as shown in FIG. 9, until medication delivery pen  10  is in a reset condition, as shown in FIG.  10 . When medication delivery pen  10  is in the reset condition, reset ring  6  has disengaged from dose set knob  7  as clearly seen in FIG.  10 . Alternatively, as shown in FIG. 9 during a dose setting condition, reset ring  6  is within dose set knob  7  such that ratchet  64  are engaged with ratchet fingers  73 . When a user is turning dose set knob  7  and thereby turning reset ring  6  because of the engagement of ratchet  64  and ratchet fingers  73 , keys  63  within reset ring  6  interact with keyways  86  on driver  8  to cause driver  8  to rotate about lead screw  9  and move driver  8  in a proximal direction along lead screw  9 . After a desired dose has been set by the user using dose set knob  7  and the desired dose is to be dispensed, movement of dose set knob  7  in a distal direction will cause driver  8  to push lead screw  9  in the distal direction and thereby dispense medication from the vial. 
     The user sets a desired dose by rotating dose set knob  7  in a counter clockwise direction until the desired dose is displayed in dose display window  55  in body  5 . Dose set knob  7  includes a plurality of dosage numerals  74  that show through window  55  and an “R”  75  that identifies a “reset condition” for medication delivery pen  10 . When the desired dose is reached, the user depresses a thumb button  71  attached to proximal end  72  of dose set knob  7  until dose set knob  7  has fully returned within body  5 . 
     A significant function of the drive mechanism within medication delivery pen  10  is that if the user overshoots the desired dose, medication delivery pen  10  can be reset so that the user may redial for the desired dose. This is accomplished by rotating dose set knob  7  completely past the maximum value (30 or 60) until an “R” on dose set knob  7  is displayed in window  55  within body  5 . This disengages ratchet fingers  73  within dose set knob  7  from ratchet  64  on reset ring  6  by forcing them apart and releasing reset ring  6  from within dose set knob  7 . This action is caused by keys  63  engaging with a set of stops  87 , shown in FIG. 1, at a proximal end of each keyway  86  on driver  8 . Dose set knob  7  is then free to rotate back to an initial dose position (“0”) upon which ratchet fingers  73  are forced to reengage with ratchet  64  on reset ring  6 . Disengaging and re-engaging ratchet  64  and ratchet fingers  73  requires significant tactile manipulation and results in an audible click which alerts the user that the resetting function has been performed. 
     While the present invention has been described with respect to a preferred embodiment, it is apparent that various changes can be made without departing from the scope of the invention as defined by the appended claims.