Abstract:
A medication delivery pen having a repeat-dose feature that limits motion of the dose control mechanism using an adjustable repeat-dose stop on the dose knob. In addition, the medication delivery pen also provides the user a simple mechanism for setting and correcting the dose and a drive mechanism that makes the dispensing operation as easy as possible requiring as little force as necessary.

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 medication delivery pen that provides a mechanical advantage that uses less force to delivery the selected dose than would be needed to push directly on a plunger within a vial, a re-settable and/or repeatable dosing feature, and a self-priming feature all within the device using relatively few components. 
     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 The needle cannula may be withdrawn from the vial, and the medication may be injected into a patient by moving the plunger in a distal direction.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 pens require the user to continually set or reset the desired dose before each injection. As a result, users with impaired vision and fine motor skills have found it difficult to readily set the dose on such pens especially when using a medication delivery pen having a wide range of dosage settings available. Since it is particularly common among patients with diabetes to have complications of the disease causing impaired vision and fine motor skills even more of a need has been found to address this problem. Hence, it is necessary to provide a medication delivery pen having a simple mechanism for setting the desired dose, repeating the dose when necessary, and priming the medication delivery pen prior to use. It is also important to provide a medication delivery pen that makes the dispensing operation as easy as possible requiring as little force as necessary. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a medication delivery pen that addresses the aboveidentified problems. The medication delivery pen has a repeat-dose feature that limits motion of the dose control mechanism using an adjustable repeat-dose stop on the dose knob. In addition, the medication delivery pen also provides the user a simple mechanism for setting and correcting the dose and a drive mechanism that makes the dispensing operation as easy as possible requiring as little force as necessary. 
     Another feature of the present invention is that the medication delivery pen provides a simple means for retracting the plunger when reloading the medication delivery pen with a new vial. 
    
    
     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 medication delivery pen shown in FIG. 1 fully assembled and in a ready for use condition. 
     FIG. 3 is a cross-sectional view of the medication delivery pen shown in FIG. 2 in a set dose condition and ready for dispense of medication. 
     FIG. 4 is a cross-sectional view of the rod barrel tube shown in FIG.  1 . 
     FIG. 5 is a cross-sectional view of the medication delivery pen shown in FIG. 2 along line A—A. 
     FIG. 6 is a cross-sectional view of a portion of an alternative medication delivery pen that has a feature that it allows it to be reloadable. 
     FIG. 7 is a cross-sectional view of yet another medication delivery according to the present invention having means for setting a desired dose and repeating delivery of that desired dose in consecutive injections. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A multi-feature medication delivery pen  10  according to the present invention is shown in FIG.  1 . Medication delivery pen  10  includes a cap  11  removably attached to a body  40  so to cover a vial retainer  35  containing a vial  30 . As shown in FIG. 2 vial  30  includes a proximal end  31  and a distal end  32  having a vial cap  33  that securely holds a vial septum  34  on distal end  32 . Vial  30  also includes a vial piston  39  therein to form a sterile sliding seal within vial  30  to hold medication therein. As shown in FIG. 2 a pen-needle assembly  20  is releasably engaged to a distal end  36  of vial retainer  35 . Pen-needle assembly  20  includes a double-ended needle cannula  21  having a distal point  24  and a proximal point (not shown). Double-ended needle cannula  21  is mounted on a hub  23  including means for attaching hub  23  to distal end  36  of vial retainer  35 . A proximal end  37  of vial retainer  35  is snap-fit onto a distal end  42  of body  40  or can be mounted thereto by other means, e.g., threads. 
     As shown in FIGS. 1-3, medication delivery pen  10  includes a rod barrel tube  70 , a clicker  90 , a lens and ring assembly  60 , and a dose knob  50 . Rod barrel tube  70  includes a distal end  71  and a proximal end  72 , with an outer barrel  73  extending from distal end  71  and surround a rod barrel  74 . As shown in FIG. 1 outer barrel  73  may have a pair of openings  75  through its outer surface. Rod barrel  74  includes a set of external threads  76  that mate with a set of internal threads  53  within dose knob  50 , described below, and a set of internal threads  77  that mate with a threaded shaft  101  on a plunger  100  having a distal face  102  and a proximal end  105 . Plunger  100  also includes a pair of keyways  104  extending from distal face  102  to a keyway stop  103  near proximal end  105 . Rod barrel tube  70  also include a plurality of ratchet pawls  78  at distal end  71  that are received within body  40  and engage with ratchet  41  located within body  40  near its distal end  42 . Distal end  42  of body  40  also includes a pair of keys  43 , shown in FIG. 2, that extend into body  40  to engage with the pair of keyways  104  on plunger shaft  101  of plunger screw  100 . Rod barrel tube  70  also includes a window  79  located near its proximal end  72  through which a plurality of dosage numerals  51  printed on dose knob  50  are visible to a user for setting of the desired dose. Dose knob  50  also includes a dose knob cap  54  that is permanently attached to a proximal end  55  of dose knob  50 . Dose knob  50  also includes internal threads  53  that engage rod barrel outer diameter threads  76  on rod barrel  74  so that dose knob  50  is threaded out of rod barrel tube  70  as a dose is being set, as shown in FIG.  3 . During the dose setting operation rod barrel tube  70  is prevented from rotating within body  40  by interaction of ratchet pawl  78  on rod barrel tube  70  and ratchet  41  within body  40 . 
     Dose knob  50  also includes a plurality of key slots  52  arranged axially on the outer surface of dose knob  50  so to receive a matched plurality of keys  91  on the inside of clicker  90  as clicker  90  is mounted onto dose knob  50 . Clicker  90  also includes a plurality of clicker fingers  92  on its outer circumference that interacts with a plurality of slots  61  within lens and ring assembly  60 . Interaction between clicker fingers  92  and slots  61  occur during the dose setting operation to provide the user with audible and/or tactile feedback during this operation. Lens and ring assembly  60  provide a feature of magnifying the dosage numeral  51  on the outside surface of dose knob  50  to aide the user in setting the dose during the setting operation using lens  62  integrated thereto. 
     Dose knob  50  has an enlarged proximal end  55  onto which dose knob cap  54  has been attached and may have a textured surface and/or an indentation to provide easy operator manipulation of dose knob  50  during dose setting of medication delivery pen  10 . In addition, it should be appreciated that dose knob cap  54  could be integrally molded at proximal end  55  of dose knob  50 . 
     FIG. 5 is a cross-sectional view of medication delivery pen  10  shown in FIG. 2 along lines A—A and more clearly show the interaction between the ratchet  41  within body  40  and ratchet pawl  78  at distal end  71  of rod barrel tube  70 . FIG. 5 also shows that ratchet pawl  78  at ratchet surface  41  only prevent rotation in one direction so that after a dose has been set as shown in FIG.  3  and pressure is applied to dose knob cap  54  rod barrel tube  70  is free to rotate within body  40 . As rod barrel tube  70 , rotates interaction between rod barrel internal threads  77  and threaded shaft  101  of plunger screw  100  occurs to move plunger screw  100  in the distal direction a distance corresponding to the desired dose that was set. Plunger screw  100  moves in the distal direction because it is prevented from rotation by interaction of keys  43  in body  40  and keyways  104  on plunger screw  100 . 
     FIG. 6 is a cross-sectional view of a section of an alternative medication delivery pen that provides the pen with the ability to be reloaded when vial has been fully used and must be replaced. This embodiment is substantially similar to the earlier embodiment except that key  43  within body  40  has been replaced with a plunger screw key  200  that is free to rotate when vial retainer  235  is removed from body  240 , but when vial retainer  235  is fully threaded to pen body  240  plunger screw key  200  is prevented from rotating. Plunger screw key  200  includes a proximal face  201  having a plurality of teeth that engage with matching plurality of teeth  244  within body  240 . Plunger screw key  200  also includes a shoulder  202  around the circumference that is received in a circumferencial internal diameter clearance slot  245  within body  240  to retain plunger screw key  200  within body  240 . Plunger screw  200  also includes a pair of keys  203  that engage keyway  104  and plunger screw  100 , discussed above. Interaction between key  203  and keyway  104  prevent plunger screw  100  from rotating when plunger screw key  200  is prevented from rotating because of the interaction between key  204  on plunger screw key  200  and key  244  within body  240  when a proximal end  237  of vial retainer  235  applies sufficient pressure on shoulder  202 . 
     FIG. 7 is yet another embodiment of a medication delivery pen according to the present invention and, more particularly, shows a feature that allows the user to set a desired dose for repeated delivery. As shown in FIG. 7 this feature is provided by the incorporation into the first embodiment of a dose knob having a distal end  301  and a proximal end  302 , wherein proximal end  302  includes a well about its outer surface and a plurality of stop adjuster rotation detents  304  are located within proximal end  302  of dose knob  300 . A stop adjuster  310  includes a distal end  311  and a proximal end  312  with distal end  311  being inserted into circumferencial well  303  in dose knob  300 . Stop adjuster  310  also includes a set of external threads  313  and a plurality of stop adjuster rotational detents  314  within an inner surface that engage with corresponding stop adjuster rotational detents  304  on dose knob  300 . Stop adjuster rotation detents  304  and  314  provide the user with tactile feedback during the operation of setting the repeat dose. 
     A dose stop  320  includes a plurality of dose stop keys  321  extending radially from dose stop  320  and a set of internal threads  322  that engage with outer threads  313  on stop adjuster  310 . A dose knob cap  330  is attached to dose knob  300  after stop adjuster  310  has been mounted on dose knob  300  to retain stop adjuster  310  thereon. In addition, dose knob cap  330  can provide a textured surface and/or indentations for use during dose setting, as described above. 
     After a dose has been set by the user, the user would rotate stop adjuster  310  to move dose stop  320  in a proximal direction until a proximal face  323  of dose stop  320  comes into contact with a distal face  393  on a clicker  390 . Of course, clicker  390  provides the same features and functions as clicker  90  in the earlier embodiment. Rotation of stop adjuster  310  cause dose stop  320  to move because of interaction between internal threads  322  and stop adjuster outer diameter thread  313  and interaction between dose stop key  321  and a dose knob keyway  305  on dose knob  300 . When dose stop is in the position desired by the user further proximal movement of the dose knob is prevented beyond the set desired dose. Dose stop  320  remains in the position it has been set to until change at a later point by the user via stop adjuster  310 . 
     While the present invention has been described with respect to a preferred and a number of alternative embodiments, it is apparent that various changes can be made without departing from the scope of the invention as defined by the appended claims.