Abstract:
A medication delivery pen includes a housing having an actuator disposed in the proximal end of the housing for setting and administering a dosage of medication, a medication-containing cartridge assembly having a cartridge with a pierceably sealed distal end, an open proximal end removably attachable to the distal end of the housing, and a piston in sliding, fluid tight engagement within the cartridge. A drive mechanism is coupled between the actuator and the cartridge to exert an axial force on the piston to inject the set dosage of medication. The actuator triggers the drive mechanism to administer the injection of medication held in the cartridge and a processor is coupled to the actuator to determine a value equal to the dosage set by the actuator. The drive mechanism includes a pair of half nuts in rotational engagement with the actuator, a non-rotatable lead screw having a distal end for exerting the axial force on the piston to inject the set dosage of medication, a proximal end, and threads extending between the proximal and distal ends. The nuts open and close radially to selectively engage with the threads of the lead screw for axially advancing along the lead screw upon rotation of the actuator.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention relates to a diagnostic and medication delivery system having a medication delivery pen, blood monitoring device and a lancer removably mounted in a common housing. 
     2. Description of Related Art 
     Home diabetes therapy requires the patient to carry out a prescribed regimen that involves self-testing blood glucose levels and administering an appropriate dose of insulin. Insulin has traditionally been injected by a hypodermic syringe, which suffers from numerous drawbacks. For example, syringes are not preloaded with medication, requiring the user to carry a separate medical vial. Syringes also require a degree of dexterity and sufficient visual acuity on the part of the patient to line up the needle of the syringe with the rubber septum on the medical vial and to ensure that the syringe is loaded with the proper dosage. As a result, unintentional needle pricks commonly occur. 
     To overcome the drawbacks of syringes, medication delivery pens have been developed, which facilitate the self-administration of medication such as insulin. Such delivery pens use prepackaged insulin and may be used repeatedly until the medication is exhausted. Mechanical and electronic pens are available. Electronic pens incorporate electronic circuitry that sets and/or indicates the appropriate dosage of insulin and stores data for subsequent downloading such as the time, date, amount of medication injected, etc. 
     In additional to downloading data, the electronic capabilities of such pens can also be used to mechanically simplify the pen and enhance the pen&#39;s ease of use. For example, some known pens employ an interlock mechanism to prevent actuation of the injection button when the medication cartridge is not properly connected to the pen so that an overdose does not occur. The interlock mechanism is relatively complex from both a mechanical perspective and a patient perspective. The electronic detection of the presence or absence of a properly connected cartridge can eliminate the need for such an interlock. 
     Additional mechanical improvements to medication delivery pens are also desirable to increase reliability and ensure that the proper dosage of medication is delivered. For example, known pens must undergo a priming process every time they are loaded with a cartridge. Priming ensures that the drive mechanism is in contact with the piston inside the cartridge so that the full axial travel of the drive mechanism is used to inject medication rather than being used in part to approach and contact the piston. If priming is not properly performed by the user, the actual dosage of medication that is delivered will not equal the desired dosage. Accordingly, there is a need to eliminate or reduce the amount of priming that the user must perform. 
     SUMMARY OF THE INVENTION 
     The subject invention relates to an electronic medication delivery pen which has mechanical features that reduce the amount of priming that must be performed, eliminates the need for an interlock mechanism to prevent overdosing, increases the reliability of the drive mechanism, and ensures that the full dosage of medication is delivered upon injection. 
     In accordance with the present invention, a medication delivery pen includes a housing having opposing proximal and distal ends. An actuator is disposed in the proximal end of the housing for setting and administering a dosage of medication. A medication-containing cartridge assembly includes a cartridge having a pierceably sealed distal end, an open proximal end removably attachable to the distal end of the housing, and a piston in sliding, fluid tight engagement within the cartridge. A drive mechanism is coupled between the actuator and the cartridge to exert an axial force on the piston to inject the set dosage of medication. The actuator triggers the drive mechanism to administer the injection of medication held in the cartridge. A processor is coupled to the actuator to determine a value equal to the dosage set by the actuator and a memory device is coupled to the processor to store the dosage value determined by the processor. The drive mechanism includes a pair of half nuts in rotational engagement with the actuator, a non-rotatable lead screw having a distal end for exerting the axial force on the piston to inject the set dosage of medication, a proximal end, and threads extending between the proximal and distal ends. The nuts open and close radially to selectively engage with the threads of the lead screw for axially advancing along the lead screw upon rotation of the actuator. 
     Because the half nuts advance along the lead screw, thus eliminating the need for a rotatable lead screw, the inventive medication delivery pen advantageously reduces the likelihood that components will improperly engage with one another due to their misalignment during operation. 
     In accordance with another aspect of the invention, a first spring is provided in the housing to bias the lead screw in the distal direction so that the lead screw remains in contact with the cartridge piston when the cartridge assembly is attached to the housing. This feature advantageously reduces the amount of priming that must be performed upon installation of a new cartridge. 
     In accordance with yet another aspect of the invention, a release nut is provided to engage with the lead screw at a location distally of the half nuts. The release nut is located at a first axial position when the cartridge is attached to the housing and a second axial position when the cartridge is removed from the housing. The release nut activates the processor so that the processor is in an operational state when the release nut is in the first axial position and is in a disabled state when the release nut is in the second axial position. Accordingly, since the pen will be automatically disabled when the cartridge is not properly inserted, the present invention advantageously avoids the need for a separate interlock mechanism. 
     In accordance with yet another aspect of the invention, at least one dial stop element couples the distal ends of the half nuts to the release nut so that the axial travel of the half nuts is limited to a minimum value, thereby limiting the injectable dosage of medication to a minimum value. Likewise, the dial stop element may also limit the axial travel of the half nuts to a maximum value, thereby limiting the injectable dosage of medication to a maximum value. 
     In accordance with another aspect of the invention, the actuator includes a rotatable knob and a plunger in rotational engagement with the rotatable knob. The plunger has a plurality of axial splines located on its distal end that define slots therebetween. The housing has at least one radially extending boss that aligns with the slots in select rotational states of the plunger to allow axial motion of the plunger and misaligns with the slots in other rotational states of the plunger to prevent axial motion of the plunger. The select rotational states of the plunger aligning with the boss correspond to an integer number of dosage units. This feature of the invention advantageously ensures that the user can only inject a whole number of units of medication. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS.  1 ( a ) and  1 ( b ) show perspective views of a medication delivery pen of the subject invention; 
     FIGS.  2 ( a ) and  2 ( b ) are exploded perspective views of the pen shown in FIG. 1 showing the details of the proximal and distal ends, respectively; 
     FIG.  3 ( a ) shows the drive mechanism situated in the bottom case of the pen housing and FIG.  3 ( b ) shows the bottom case without the drive mechanism to illustrate the various bearings surfaces that operatively interact with the drive mechanism; 
     FIG. 4 shows a perspective view of the drive mechanism in which the half nuts and dial stops are positioned for maximum dosage (FIG. 4 a ) and minimum dosage (FIG. 4 b ); 
     FIG. 5 shows a perspective view of the plunger situated in the pen housing when in a rotational orientation corresponding to an injectable state (FIG. 5 a ) and a noninjectable state (FIG. 5 b ) and the mechanism for biasing the plunger into an injectable state (FIG. 5 c ); 
     FIG.  6 ( a ) shows the clutch arrangement employed in the drive mechanism of the pen and FIGS.  6 ( b ) and  6 ( c ) show the portions of the clutch arrangement formed on the plunger and the dose knob insert, respectively; and 
     FIG.  7 ( a ) shows a schematic diagram of the piezoelectric sensor arrangement that is used to determine the dosage that is set by rotation of the dose knob and FIGS.  7 ( b ) and  7 ( c ) show the deformation of the sensor arrangement when the plunger rotates clockwise and counter-clockwise, respectively. 
    
    
     DETAILED DESCRIPTION 
     As shown in FIGS. 1 and 2, the medication delivery device includes a rotatable dose knob  34 , housing  100 , cartridge retainer  6 , and needle assembly  4 . A display  14  is visible through a window  18  in the housing  100 . The overall operation of the medication delivery pen is as follows. First, a cartridge  8  is loaded within cartridge retainer  6 , and cartridge retainer  6  is removably attached to housing  100 . When the cartridge retainer  6  is removed from the housing  100 , a lead screw  50  is forward biased by lead screw spring  44  to ensure that the distal end of the lead screw is always in contact with the cartridge piston  7  located in cartridge  8 . As a result, the amount of priming that must be performed by the user upon inserting a new cartridge  8  is minimized. The needle assembly  4  is affixed to the end of cartridge  8 . Fluid communication is accordingly established between the injection portion of needle assembly  4 , and the interior of cartridge  8 . Eject button  40  is pressed to release dose knob  34 . Once the appropriate dosage is set by rotation of dose knob  34 , dose knob  34  is depressed, exerting a force upon piston  7 , which is movably positioned within cartridge  8 . Piston  7  displaces fluid within cartridge  8 , causing its injection into body tissue through needle assembly  4 . 
     Referring to FIGS. 2 and 3, a dosing mechanism includes dose knob  34 , clutch spring  32 , dose knob insert  38 , plunger  26 , half nuts  12 , lead screw  50 , and keyed release nut  52 , which are collectively used to set the dosage of medication that is to be injected. The housing  100  includes bottom case  46 , middle case  24 , and top case  16 . The dosing mechanism is situated between the bottom and middle cases  46  and  24 . As detailed below, the interior surface of middle and bottom cases  24  and  46  provide working surfaces along which the various components of the dosing mechanism are operable. The dose knob insert  38  is attached to the dose knob  34 . As detailed below, clutch spring  32  exerts an axial load to ensure a positive rotational engagement between the dosing knob  34  and plunger  26 . As a result, the plunger  26  is driven rotationally when the user dials the dosing knob  34 . The plunger  26  includes a hollow, generally cylindrical body having a series of axial slots  72  extending from its distal end. Axial slots  72  define a series of axial splines  78  between adjacent ones of the slots  72 . Two of the slots, 180° apart, are through-slots  54 . The intermediate surface portion  80  of plunger  26  has an outer diameter that is larger than the diameter of the plunger  26  along splines  78 . A plurality of splines  74  project radially from surface  80  of plunger  26 . 
     A pair of half nuts  12  each have a semi-cylindrical body having a flange  62  on its distal end and a radially projecting boss  70  on its proximal end. Bosses  70  are disposed in the axial slots  54  of plunger  26  so that half nuts  12  and plunger  26  are in rotational engagement with one another. Accordingly, as the plunger  26  rotates upon rotation of dosing knob  34  by the user, half nuts  12  axially advance along lead screw  50  until the desired dosage is reached. A keyed release nut  52  located on lead screw  50  has tabs  152  that fit inside slots  150  on the lead screw  50  so that release nut  52  guides the lead screw  50  axially and prevents it from rotating. (See FIGS. 4 a  and  4   b ) 
     Bottom and middle cases  46  and  24  provide bearing surfaces  64  and  65  for the half nuts  12 , bearing surfaces  56  and  57  for the keyed release nut  52 , bearing surfaces  110  and  111  for the dial stop insert  10 , bearing surfaces  227  and  228  for the plunger  26 , bearing surfaces  240  and  241  for the eject button  40  and eject button spring  28 , and bearing surfaces  234  and  235  for dose knob  34 . The middle case  24  also provides anchoring posts  23  for the PC board assembly  22  and access ports  25  so that the electronics located on PC board assembly  22  can communicate with sensors co-located with the mechanical components. 
     Keyed release nut  52  has a pair of recesses  60  (see FIG. 4 b ) on its proximal face in which dial stop inserts  10  are situated. Dial stop inserts  10  and keyed release nut  52  travel in unison as the cartridge retainer  6  is inserted and removed from the body of the delivery device. The axial motion of the dial stop inserts is limited by bosses  59 . As explained below, dial stop inserts  10  provide mechanical stops for minimum, i.e. zero, and maximum dosages. Upon removal of the cartridge retainer  6 , keyed release nut  52  moves distally, allowing the half nuts  12  to also move distally under the action of half nut spring  42 . As a result, the radially extending bosses  70  of half nuts  12  contact raised circumferentially extending surface  68  of bottom and middle cases  46  and  24  so that the half nuts  12  are prevented from further traveling in the axial direction and are forced to open radially to release the lead screw  50 , thus allowing the system to be reset. Conversely, upon insertion of cartridge retainer  6 , keyed release nut  52  moves in the proximal direction, forcing the half nuts  12  to advance along surface  66  of bottom and middle cases  46  and  24  so that the half nuts  12  close in the radial direction and engage with the lead screw  50 . 
     The axial travel of keyed release nut  52  in either direction is limited by two pins  92  that engage with slots  58  formed in the bottom and middle cases  46  and  24 . Slot  58  in body middle  24  is a through-hole slot while slot  58  in body bottom  46  is a recessed slot rather than a through-hole. Slots  58  also prevent rotational movement of the key nut  12 . Half nut bearing surfaces  64  and  65  provide a bearing surface for the half nuts  12  when they are engaged with the lead screw  50  (which only occurs when the cartridge retainer  6  is attached to the housing  100 ). The axial travel of the half nuts  12  is limited by dial stop  10 , as described below. As shown in FIG.  4 ( a ) and  4 ( b ), half nuts  12  each have a distal flange  62  that have a plurality of teeth. The teeth have a radial length, an axial thickness and are circumferentially located along the outer perimeter of flanges  62 . The teeth are located on both the distal surface  61  and proximal surface  63  of the flange  62 . As seen in FIG.  4 ( a ), the teeth  161  on the distal surface  61  engaging the lower stop surface  9  of the dial stop insert  10  provides a stop so that the user cannot dial below zero. Similarly, as seen in FIG.  4 ( b ), the teeth  163  on the proximal surface  63  engaging the upper stop surface  9  of the dial stop insert  10  provides a stop so that the user cannot dial above the maximum dose of the pen. 
     As shown in FIGS.  5 ( a )-( c ), plunger  26  has a plurality of recessed slots  72  and  54  located on its distal end which define splines  78  between adjacent slots  72  and  54 . Slots  72  and  54  are open on their distal end. A plurality of radially extending bosses  76  are located on bottom and middle cases  46  and  24 . For an injection to occur, slots  72  and  54  must be radially aligned with bosses  76  (FIG. 5 a ). When the dosage is not set to an integer number of units (FIG. 5 b ) splines  78  are prevented from moving axially by bosses  76 , thus preventing injection of fractional units. In described, slots  72  and  54  both perform the same function. Plunger  26  also has a plurality of angled radial slots  126  proximal to the splines  74 . The number of angled radial slots  126  is equal to the number of slots  72  and  54 . Tabs  124  are provided on the bottom case  46 , middle case  24  and on the face  222  of bearing surface  228 . When the plunger  26  is in the dosing mode, the half hut spring  42  biases the plunger  26  towards the bearing surface  228 . The interaction of the angled radial slots  126  and the tabs  124  rotationally align the plunger  26  so that the plunger  26  is biased in a rotational state that aligns slots  72  and  54  with bosses  76 . 
     As shown in FIGS.  6 ( a ) and  6 ( b ), plunger  26  has a circumferential groove  82  located on its proximal end. Groove  82  has a distal wall  84  that serves as a bearing surface with the distal surface  37  of the dose knob insert  38  during injection. Groove  82  also has a proximal wall  83  that acts as a bearing surface with the angled surface  39  of the dose knob insert  38  when a dose is dialed. The plunger  26  has  4  radial slots  326  at its proximal end. The radial slots  326  have angled faces  328 . A stepped clutch seat  30  has  4  radial splines  130 . The stepped clutch disk also has two slots  132  that rotationally engage with two splines  138  located on the dose knob insert  38 , which is in turn rotationally coupled to the dose knob  34 . A clutch pumping spring  32  exerts an axial load on the stepped clutch seat  30  and the dose knob, assuring a positive rotational engagement between the dosing knob assembly, which includes the dose knob  34 , dose knob insert  38 , and the plunger  26 . When the rotational movement of the half nuts  12  is restrained by the dial stop inserts  10 , the splines  130  located on the stepped clutch disk  30  advance along the angled faces  328  of plunger  26 , compressing the clutch pumping spring  32 . As a result, the plunger  26  will not rotate, preventing damage to the mechanism that could be caused by excessive torque. 
     The dosage that is dialed by dose knob  34  is measured by a piezoelectric sensor, discussed below, that determines the number of rotations that the plunger  26  undergoes as the dose knob is rotated. Specifically, the piezoelectric sensor is activated by splines  74  located on an intermediate surface portion  80  of the plunger  26 . The intermediate surface portion  80  of plunger  26  has an outer diameter that is larger than the diameter of boss  70  on half nuts  12  so that the bosses  70  do not interfere with the piezoelectric sensor. 
     An eject button  40  is accessible to the user via a hole in the bottom case  46 . Eject button  40  locks dose knob  34  in its depressed state after completion of the injection so that the clutch spring can finish delivering the dose of medication, as described below. This is accomplished as follows. The eject button  40  is biased toward the bottom case  46  by eject button spring  28 , which is housed in middle case  24 . Eject button  40  is proximally biased by the eject button spring  28  and limited by the bearing wall  240 . Dose knob  34  includes a distal end  88  that has a larger diameter than its proximal end  90 . While the dose knob  34  is in its extended position, the eject button  40  is riding on the larger diameter distal end  88  of the dose knob  34 . Dose knob  34  is proximally biased by the half nut spring  42 . Accordingly, when the dose knob  34  is depressed, the eject button  40  snaps onto the smaller diameter proximal end  90  of the dose knob  34  so that the dose knob  34  is locked axially. A lead screw sleeve  36  is provided to prevent interaction between lead screw spring  44  and clutch pumping spring  32 , which are coaxially located within dose knob  34 . 
     Once the eject button  40  locks dose knob  34  in its depressed state, clutch spring  32  serves to complete the distal movement of the plunger  26  and half nuts  12 . This guarantees that the full dosage is delivered. The full dosage is delivered when the distal face  61  of flange  62  contacts the lower stop surface  9  of the dial stop insert  10  (FIG. 4 a ). At this time, the distal surface  37  of the dose knob insert  38  is no longer in contact with the distal surface  84  of groove  82 , which is located on plunger  26 . This configuration improves upon prior art medication delivery pens, which sometimes required the user to repeatedly depress dose knob  34  to ensure full delivery of the medication. 
     As previously mentioned, keyed release nut  52  has a pin  92  that extends in through-hole slot  58  of body middle  24 . Pin  92  activates a cartridge removal switch on the PC board  22  so that the display indicates that the cartridge has been removed. Specifically, when pin  92  is situated towards the proximal end of slot  58 , the switch is in its open state and the display is in its normal operational state. When pin  92  is situated against the distal end of slot  58 , the switch is in its closed state and the display indicates that the cartridge has been removed. 
     The dosage, which is set by rotation of dose knob  34 , is measured by a piezoelectric sensor arrangement that interacts with the splines  74  on plunger  26 . As shown in FIG.  7 ( a ), the piezoelectric sensor  300  arrangement includes a flexible base  302  such as a spring. Disposed on one side of the base are two piezoelectric films  304  and  306  that are coplanar with the flexible base  302 . A pawl  308  extends orthogonal from the side of the flexible base  302  opposite to the piezoelectric films  304  and  306 . The pawl  308  is positioned along the flexible base  302  so that a plane through the pawl  308  and the flexible base  302  extends between the two films  304  and  306 . The sensor arrangement is positioned with respect to the plunger  26  so that as the plunger  26  rotates the splines  74  engage with the pawl  308 , which in turn causes deformation of the flexible base  302  (see FIGS. 7 b  and  7   c ). The deformation of the flexible base  302  causes a corresponding deformation of the piezoelectric films  304  and  306 . The films  304  and  306  generate a pair of electrical signals each time the pawl  308  is released by one of the splines  74 , based on direction of rotation and deformation of films  304  and  306 . The curvatures of the deformed films are opposite to one another and depend on the direction in which the plunger  26  is rotating. For example, in FIG.  7 ( b ) the plunger  26  is rotating in the clockwise direction and in FIG.  7 ( c ) the plunger is rotating in the counter-clockwise direction. As shown, the curvatures of each film are opposite to one another in FIGS.  7 ( b ) and  7 ( c ). Since the curvatures of the films are always opposite to one another, they will generate electrical signals of opposite phase. In FIG.  7 ( b ), for instance, film  304  may generate a positive signal while film  306  may generate a negative signal. In FIG.  7 ( c ), however, the films will produce signals opposite in sign: film  304  will generate a negative signal and film  306  will generate a positive signal. Accordingly, the signs of the signals generated by the two piezoelectric films  304  and  306  can be used to distinguish between clockwise and counter-clockwise rotation. In addition, the absence of either signal identifies the failure of one of the films  304  and  306  and is used to identify and display a malfunction in the medication delivery pen. 
     The piezoelectric sensor will send the pair of electrical signals to the processor located on the PC board  22  each time the pawl  308  is released by one of the splines  74 . Each pair of signals that is generated denotes a rotation of the dose knob  34  by a predetermined amount, and thus corresponds to a predetermined incremental increase or decrease in dosage. Since rotation of the dose knob  34  in one direction increases the dosage and rotation of the dose knob  34  in the other direction decreases the dosage, the processor can determine whether the dosage is being increased or decreased. By summing the number of pairs of signals that are detected by the sensor (adding increasing dosages and subtracting decreasing dosages), the processor can calculate the final dosage that has been dialed by the user. 
     The dosage that is set by rotation of the dose knob  32  is displayed on display  14  in the following manner. Prior to injecting a dosage of medication, the eject button  40  is depressed so that the dose knob  34  is released in preparation for the injection. When eject button  40  is depressed it activates a start button  140  on PC board assembly  22 . Eject button  40  serves as a normally open switch. When eject button  40  is depressed to release the dose knob  34 , the eject button  40  closes the switch (which remains closed the entire time the dose knob  34  is extended), sending an interrupt signal to a processor so that it enters a mode in which the dosage is displayed on display  14 . After the dose knob  34  has been completely depressed, eject button  40  is released under the action of the eject button spring  28  and in turn opens the switch. The action of opening the switch indicates to the processor that the user has fully depressed the dose knob  34 . The clutch spring  32  takes approximately 5 seconds to complete delivering the medication. The display will continue to show the dosage for a predetermined period of time after the delivery of the medication. 
     A memory button  95  is provided on the PC board  22  and available to the user through window  18  so that the user can review information concerning a predetermined number, e.g., five, of previous injections. Memory button  95  is a normally open switch. When the user depresses memory button  95  to close the switch, the processor causes the display  14  to enter a memory review mode, which displays the size of the previous dose and an indication of when the last dose was taken. Each time the memory button  95  is depressed the display provides the dose size and elapsed time for a previous injection. That is, if memory button is depressed four times in succession, the display will show the size of and elapsed time since the fourth previous injection. While the display may be relatively limited in the number of prior injections it can display, a data port accessible through upper body  16  can be used to download information concerning a much greater number of injections. 
     The memory button  95  can also be used to prevent a priming dose from being recorded. If memory button  95  is depressed while dose knob  34  is being depressed, the dose delivered will not be recorded because the processor assumes it is a priming dose. However, if the dose delivered while the memory button  95  is depressed is greater than or equal to a prescribed number of units, e.g., 4, the dose will be recorded.