Abstract:
A medication delivery pen is provided having a lead screw with an enlarged portion at a first end thereof and an end longitudinally opposite the first end in contacting engagement with a plunger of a medication cartridge. The lead screw is selectively axially displaceable by a user when selectively administering a predetermined dosage amount of medication for injection into a patient. The medication delivery pen also includes a driver coaxially disposed about the lead screw; and, a reset ring non-rotatably disposed on the driver and axially slidable thereon and therealong. The reset ring is axially movable with respect to the driver when a dosage amount is set by a user of the medication delivery pen. The reset ring engages the enlarged portion of the lead screw upon a predetermined extent of relative axial movement between the reset ring and the lead screw. With this arrangement, the reset ring advantageously prevents setting a dose on a medication delivery pen that is greater than the medication which is available.

Description:
CROSS-REFERENCE TO PRIOR APPLICATIONS 
   This application claims priority of U.S. Provisional Patent Application No. 60/415,198, filed Oct. 1, 2002. 

   FIELD OF THE INVENTION 
   The present invention relates to fixed and adjustable dose medication delivery pens. 
   BACKGROUND OF THE INVENTION 
   Hypodermic syringes are used to deliver selected doses of medication to patients. The prior art hypodermic syringe typically includes a syringe barrel having opposed proximal and distal ends; the proximal end being generally defined as the end located away from a patient, and the distal end being generally defined as the end located near the patient during use. A cylindrical chamber wall extends between the proximal and distal ends and defines a fluid containing chamber. The proximal end of the prior art syringe barrel is substantially open and receives a plunger in sliding fluid tight engagement with an interior surface of the chamber wall. 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 direction toward the proximal end (a proximal direction) draws fluid through the lumen of the needle cannula and into the chamber. Movement of the plunger in a direction toward the distal end (a 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 after the needle has been caused to pierce the patient&#39;s skin or by injection into an intravenous tube or other similar device or structure. 
   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 selecting a dose of medication to be delivered by the pen and a driving apparatus for urging the plunger of the vial in a distal direction for a distance corresponding to the selected dose. 
   The user of the prior art pen mounts a 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 a zero setting 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, and removes and discards the empty vial. 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, prior art medication delivery pens have their shortcomings. For example, prior art medication delivery pens do not prevent the patient from dialing a dose that is greater than the amount of medication remaining in the vial. For example, a patient may thus dial a dose of 0.45 ml, when only 0.30 ml of medication remains in the vial. The patient would only discover that fact after the medication was delivered, and the dose set knob was prevented from complete displacement by the set screw abutting the bottom of the vial. The patient would then have to determine the unadministered amount and use another vial to complete delivery of the desired dose. Such a situation would require two injections be made for administration of a single dose. That obvious inconvenience and additional discomfort from a second injection, in addition to the replacement of the spent vial, render such prior art self-administration devices unsatisfactory. 
   There is thus a need in the art for a medication delivery pen that overcomes the above-described shortcomings of the prior art. 
   SUMMARY OF THE INVENTION 
   To overcome the shortcomings of the prior art, a medication delivery pen is provided having a lead screw with an enlarged portion at a first end thereof and an end longitudinally opposite the first end in contacting engagement with a plunger of a medication cartridge. The lead screw is selectively axially displaceable by a user when selectively administering a predetermined dosage amount of medication for injection into a patient. The medication delivery pen also includes a driver coaxially disposed about the lead screw; and, a reset ring non-rotatably disposed on the driver and axially slidable thereon and therealong. The reset ring is axially movable with respect to the driver when a dosage amount is set by a user of the medication delivery pen. The reset ring engages the enlarged portion of the lead screw upon a predetermined extent of relative axial movement between the reset ring and the lead screw. With this arrangement, the reset ring advantageously prevents setting a dose on a medication delivery pen that is greater than the medication which is available. 
   These and other features of the invention will be better understood through a study of the following detailed description and accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view of a medication delivery pen constructed in accordance with the subject invention; 
       FIG. 2  is a cross-sectional view of a body of a medication delivery pen constructed in accordance with the subject invention; 
       FIGS. 3 and 4  are plan and cross-sectional views, respectively, of a driver of a medication delivery pen constructed in accordance with the subject invention; 
       FIG. 5  is a cross-sectional view taken along line  5 — 5  of  FIG. 2 ; 
       FIG. 6  is a perspective view of the proximal end of the driver of  FIG. 3 ; 
       FIG. 7  is a perspective view of a reset ring of a medication delivery pen constructed in accordance with the subject invention; 
       FIGS. 8 and 9  are plan and cross-sectional views, respectively, of a dose knob of a medication delivery pen constructed in accordance with the subject invention; 
       FIG. 10  is a perspective view of a lead screw of a medication delivery pen constructed in accordance with the subject invention; 
       FIG. 11  is a cross-sectional view of an assembled medication delivery pen constructed in accordance with the subject invention; 
       FIGS. 12 and 13  schematically depict the manner in which protrusions formed on the reset ring limit movement relative to the lead screw; and 
       FIG. 14  schematically depicts a resettable configuration of the reset ring of the subject invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to the Figures, particularly  FIG. 1 , a medication delivery pen is shown and generally designated with the reference numeral  10 . The medication delivery pen  10  may be used for the administration of various medications, including insulin; unless specified otherwise, the medication does not comprise a part of the present invention. In addition, the term “medication” is used in an illustrative and non-limiting manner to refer to any substance that may be injected into a patient for any purpose. The medication delivery pen  10  of the present invention may also be reusable or disposable. 
   The subject invention relates to limiting dose-setting at near-completion or completion of a drug cartridge as described below. As will be recognized by those skilled in the art and from the disclosure provided herein, various medication pen delivery designs can be used consistent with the teachings herein. To illustrate the subject invention, a representative, preferred embodiment of a medication delivery pen is described. Other embodiments and designs are within the scope and spirit of the subject invention. 
   With reference to  FIG. 1 , the medication delivery pen  10  generally includes a cap  12 , a cartridge holder  14 , a spinner  16 , a body  18 , a reset ring  20 , a dose knob  22 , a driver  24 , a lead screw  26 , and a thumb button  28 . With reference to  FIG. 11 , the cartridge holder  14  is formed to accommodate a drug cartridge  30 , which may be of any conventional design. By way of non-limiting example, the drug cartridge  30  may include an elastomeric septum  32  at a proximal end thereof and an open distal end  34  which exposes a slidable plunger  36 . Drug medication is contained within the drug cartridge  30  between the septum  32  and the plunger  36 . As will be described in more detail below, the spinner  16  is configured to engage the plunger  36  and force forward movement thereof in expelling drug from the drug cartridge  30 . A needle (not shown) is required to administer drug from the medication delivery pen  10 . The needle may be a double-ended cannula which is threadedly mounted onto threads  38  of the cartridge holder  14 . One end of the cannula is exposed for insertion into a patient, while the second end of the cannula is disposed to pierce the septum  32  of the drug cartridge  30 . After administration of the dose, the needle is removed, with the septum  32  self-sealing. The cap  12  is formed to releasably mount onto the cartridge holder  14 , such as with a snap fit, to limit contamination of the septum  32  and the surrounding portions of the cartridge holder  14 . A resilient holding arm  40  may extend from the cap  12  to provide holding force for the pen  10  in a patient&#39;s pocket. One or more windows (not shown) may also be provided in the cartridge holder  14  to give a visual indication of the drug level in the drug cartridge  30 . 
   With reference to  FIG. 2 , the body  18  is generally cylindrical, and may have threads or detents  42  which releasably engage (for a reusable embodiment) the cartridge holder  14 . A bulkhead  44  extends across the interior of the body  18  through which an aperture  46  is formed. The aperture  46  is defined to allow the non-rotational passage of the lead screw  26  therethrough. The body  18  also includes an interiorly-supported cylindrical wall  48  which defines a channel  50  therethrough. A transverse recess  52  is defined between the aperture  46  and the channel  50  which is at least partially bounded by wall  54 , that may be continuous or discontinuous. In addition, a dose setting thread  56  is formed on the interior of the body  18 , along with a window  58  for dosage selection. A pointer  60  may be defined on the body  18  that extends into the window  58  to clearly point out a selected dosage level. 
   With reference to  FIGS. 3 ,  4  and  6 , the driver  24  includes proximal and distal ends  62  and  64 , respectively, with a snap ring  66  being formed at the proximal end  62 . The snap ring  66  is formed to pass through the channel  50  of the body  18  and lock onto the wall  48  in the recess  52  ( FIG. 11 ). With the snap ring connection, the driver  24  is fixed axially relative to the body  18 , yet is able to rotate relative thereto. Internal threads  68  are also provided to threadedly engage threads  70  of the lead screw  26  ( FIG. 10 ). Additionally, as best shown in  FIGS. 3 and 4 , an annular stop  72  is preferably provided midway along the length of the driver  24 . 
   One or more longitudinal keyways  74  are defined on the driver  24  that extend completely through the wall thereof. One or more limited-depth channels  76  may also be formed on the driver  24 , and limited-depth slots  78  preferably extend longitudinally from the keyways  74  towards the distal end  64 . The limited-depth channels  76  and the limited-depth slots  78  do not extend fully through the wall of the driver  24 . Preferably, two of the keyways  74  are provided and located diametrically apart. It is also preferred that the limited-depth channels  76  and the limited-depth slots  78  generally terminate at the annular stop  72 . 
   In a preferred construction of the body  18 , as shown in  FIG. 5 , a plurality of ratchet teeth  80  extend from the cylindrical wall  48 . In addition, and as best shown in  FIG. 6 , one or more ratchet fingers  82  are formed on the proximal end  62  of the driver  24  and are located in proximity to the snap ring  66 . The ratchet fingers  82  are positioned within the channel  50  when the driver  24  is locked in the recess  52  ( FIG. 11 ). Preferably, the ratchet teeth  80  and the ratchet fingers  82  are formed to cooperate to allow the driver  24  to rotate in only one direction relative to the body  18 . Consequently, the ratchet teeth  80  and the ratchet fingers  82  provide a measure of protection against unwanted rearward movement of the lead screw  26  resulting from the driver  24  inadvertently rotating in a reverse direction. 
   With reference to  FIG. 7 , the reset ring  20  is tubular with, preferably, one or more inwardly extending splines  84  which are formed and located to be disposed in the limited-depth channels  76  and, if provided, the limited-depth slots  78  of the driver  24 . With the splines  84  extending into the limited-depth channels  76  and the limited-depth slots  78 , the reset ring  20  cannot be rotated relative to the driver  24 . However, the splines  84  are formed such to allow the reset ring  20  to axially move along the length of the limited-depth channels  76  and the limited-depth slots  78 . Also, as shown in  FIG. 7 , one or more protrusions  86  extend inwardly in the reset ring  20  which are formed and positioned to extend through the keyways  74  with the reset ring  20  being disposed on the driver  24 . The protrusions  86  must have sufficient length to engage an enlarged portion  88  formed on the lead screw  26  ( FIG. 10 ). It is preferred that more than one of the protrusions  86  be provided and at spaced-apart locations so that the enlarged portion  88  may be firmly engaged. In a preferred arrangement, the protrusions  86  extend from and are formed unitarily with the splines  84 . Alternatively, as will be recognized by those skilled in the art, the protrusions  86  may be formed separately from the splines  84 . Also, the splines  84  need not be provided; here, the protrusions  86  and the keyways  74  together can act to prevent relative rotation between the reset ring  20  and the driver  24 , yet allow for the reset ring  20  to axially slide along the driver  24 . Also, with this arrangement, the limited-depth channels  76  and the limited-depth slots  78  need not be provided. 
   In addition, grooves  90  are formed about the periphery of the reset ring  20 , preferably at equal intervals, and an annular rim  92  preferably extends radially beyond the grooves  90  at one end of the reset ring  20 . 
   As shown in  FIGS. 8 and 9 , the dose knob  22  is generally tubular having open proximal and distal ends  94  and  96 , respectively. A textured handle  98  is formed in proximity to the distal end  96  which is engagable by a user to rotate the dose knob  22  in setting a desired dosage amount on the pen  10 . The dose knob  22  includes one or more thread portions  100  externally formed to threadedly engage the dose setting thread  56  of the body  18 . Accordingly, the dose knob  22  may be rotated within the body  18  resulting in translation of that rotation to axial displacement of the dose knob  22  relative to the body  18  in setting a desired dose. Dosage indicia  102  may also be disposed externally of the dose knob  22 . 
   The dose knob  22  preferably includes one or more ratchet arms  104  formed to be biased inwardly. With reference to  FIG. 11 , in a fully-assembled state of the pen  10 , the dose knob  22  is coaxially disposed about the reset ring  20  with the ratchet arms  104  being aligned with the grooves  90  of the reset ring  20  so that rotation of the dose knob  22  relative to the reset ring  20  results in the ratchet arms  104  acting against the reset ring  20  in a ratcheting manner giving a user an audible signal of such rotation. Preferably, each of the ratchet arms  104  is formed with an inwardly extending detent  106  at an end thereof. It is preferred that the grooves  90  and the detents  106  coact to only permit rotation of the dose knob  22  relative to the reset ring  20  in one rotational direction. An inwardly extending lip  108  may optionally be provided in longitudinally aligning the reset ring  20  relative to the ratchet arms  104 . 
   With reference to  FIG. 10 , the lead screw  26  may be of any conventional type and is formed with a connecting end  110  onto which the spinner  16  is mountable using any known technique. With reference once again to  FIG. 1 , the thumb button  28  is also of any known conventional design and, as will be appreciated by those skilled in the art, may be mounted to the distal end  96  of the dose knob  22  using any technique. 
   With reference to  FIG. 11 , the completed assembly of the pen  10  is shown in cross-section. In operation, the dose knob  22  is dialed to a desired dose as indicated by the dosage indicia  102  which is viewable through the window  58  of the body  18 . As the dose knob  22  is rotated, the ratchet arms  104  rotate about the reset ring  90  and engage the grooves  90 . The ratchet arms  104  also engage the annular rim  92  of the reset ring  20  and urge the reset ring  20  axially and distally, without the reset ring  20  rotating, in concert with the distal movement of the dose knob  22 . Once set at a desired dose, the ratchet arms  104  are urged to engage the next encountered grooves  90 . The resiliency of the ratchet arms  104  provide a holding force that maintains the dose knob  22  in a fixed longitudinal position relative to other components of the pen  10 . Thereafter, the thumb button  28  is engaged and forced proximally resulting in rearward rotation of the dose knob  22  relative to the body  18  with the reset ring  20  and the dose knob  22  being driven in a proximal direction. Because of the fixed interengagement between the ratchet arms  104  and the grooves  90 , and the thread portions  100  of the dose knob  22  rotating within the dose setting thread  56  of the body  18 , the reset ring  20  rotates together with the dose knob  22 . In turn, the driver  24  is forced to rotate with the reset ring  20  due to the non-rotatable connection therebetween. The internal threads  68  of the driver  24  thus rotate about the lead screw  26 , and because the lead screw  26  cannot rotate within the aperture  46 , the lead screw  26  is caused to be translated proximally without rotation. As the lead screw  26  moves proximally, the spinner  16  engages the slidable plunger  36  and forces proximal movement thereof resulting in the expulsion of a desired dosage. Once the dose has been administered, this process can be repeated. 
   With the subject invention, the protrusions  86  advantageously prevent the dose knob  22  from being set to a dose greater than which is available for administration. With reference to  FIG. 12 , the enlarged portion  88  of the lead screw  26  is spaced from the protrusions  86  during normal operation and any desired dosage can be achieved. As shown in  FIG. 13 , with the drug cartridge  30  nearing completion, the setting of the dose knob  22  to a greater setting than available medication will result in the protrusions  86  engaging the enlarged portion  88  of the lead screw and not allowing the reset ring  20  to be axially moved therebeyond in a distal direction. As a result, the protrusions  86  establish the maximum amount that may be administered at that time, which may be less than a desired amount. As is readily apparent to those skilled in the art, the keyways  74 , the protrusions  86 , the enlarged portion  88  and other components are appropriately formed and positioned to preferably coincide the engagement of the protrusions  86  with the enlarged portion  88  to the amount of available medication for dosing. 
   As will be appreciated by those skilled in the art, the subject invention may be used with resettable and non-resettable designs. For example, as shown in  FIG. 14 , the annular rim  92  of the reset ring  20  may be formed with a proximally-facing ramped surface  112 . Thus, with the reset ring  20  being urged fully distally and into engagement with the annular stop  72  on the driver  24 , further dialing of the dose knob  22  causes the ramped surface  112  to go under the ratchet arms  104  thereby disengaging the reset ring  20  from the dose knob  22 . The reset ring  20  can be reengaged by the dose knob  22  at its most proximal position relative to the driver  24  coinciding with a zero dosage amount. With the annular rim  92  being formed flat instead of ramped, such resettability can be generally avoided. 
   In addition, the pen  10  may be a fixed dose design or a variable dose design as described above. With a fixed dose design, the annular stop  72  can be positioned so that the dose knob  22  is dialed to a predetermined amount with the reset ring  20  engaging the annular stop  72 . For variable dose designs, the annular stop  72  can be positioned to define a maximum dose amount allowing a user a wide dosage range. With the pen  10  being resettable and variable-dosing, a mistake in dosage setting can be corrected by fully dialing out the dose knob  22  and causing the pen  10  to be reset to zero. 
   The pen  10  may be formed as a disposable single use pen where the drug cartridge  30  cannot be replaced once spent. Here, the cartridge holder  14  is preferably permanently (i.e., non-removably) coupled to the body  18 . Alternatively, the pen  10  can be of the multiple use variety with the drug cartridge  30  being replaceable; preferably, with this arrangement, the cartridge holder  14  is removably mountable to the body  18 . 
   While the invention has been described in relation to the preferred embodiments with several examples, it will be understood by those skilled in the art that various changes may be made without deviating from the spirit and scope of the invention as defined in the appended claims.