Abstract:
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. The pen also includes 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. A processor is coupled to the actuator to determine a value equal to the dosage set by the actuator. A memory device is coupled to the processor to store at least the dosage value determined by the processor. A display is located on the housing and coupled to the processor for displaying information provided by the processor. In a first state the actuator engages with the drive mechanism to deliver the medication and in a second state is disengaged from the drive mechanism. In its second state, the actuator serves as a user adjustable input for changing and setting mode parameters of at least one preselected mode of the pen.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention relates to an improved electronic medication delivery pen. 
     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. 
     While electronic pens that mechanically simplify the device have been proposed, it has been found that there remains a need for additional features and improvements that further utilize the electronic capabilities of the pen. For example, it would be desirable to automatically determine the amount of insulin that remains in a cartridge from which one or more dosages of medication have been delivered. Likewise, it would be desirable to automatically determine the size of the cartridge that is installed in the pen as well as the type of medication contained in the cartridge, thus allowing many different types of cartridges to be used in a single pen while reducing the likelihood of user error resulting from misidentifying the cartridge or manually entering incorrect information into the pen. 
     SUMMARY OF THE INVENTION 
     The subject invention relates to an electronic medication delivery pen in which the value of different modes such as time and date modes are changed by the actuator when the actuator is disengaged from the drive mechanism of the pen. 
     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. The pen also includes 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. A processor is coupled to the actuator to determine a value equal to the dosage set by the actuator. A memory device is coupled to the processor to store at least the dosage value determined by the processor. A display is located on the housing and coupled to the processor for displaying information provided by the processor. In a first state the actuator engages with the drive mechanism to deliver the medication and in a second state is disengaged from the drive mechanism. In its second state, the actuator serves as a user adjustable input for changing and setting mode parameters of at least one preselected mode of the pen. 
     In some embodiments of the invention the actuator includes a rotatable knob for setting the dosage of medication. The rotatable knob also serves as the user adjustable input when the actuator is in the second state. The rotatable knob may be rotated when in the second state for changing and setting the mode parameters. Other user-inputs that may be provided include a user-activatable mode button located on the housing for selecting the preselected mode of the pen from among multiple modes such as a time and date mode, and an eject button for selectively alternating between the first and second states of the actuator. 
     In accordance with one aspect of the invention, the medication delivery pen also includes a sensor coupled to the processor for detecting status information pertaining to the drive mechanism to determine a quantity of medication remaining in the cartridge. Such status information may include, for example, the linear position of a leadscrew that forms part of the drive mechanism. 
     In accordance with another aspect of the invention, the cartridge has an encoded portion which identifies at least one characteristic of the cartridge. A sensor is coupled to the processor for detecting the encoded portion of the cartridge so that the processor can determine the corresponding characteristic of the cartridge. The characteristic of the cartridge that is determined from the encoded portion may be the type of medication in the cartridge or the size of the cartridge, for example. The encoded portion of the cartridge may be a color code. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a medication delivery pen of the subject invention; 
     FIG. 2 is a an exploded perspective view of one embodiment of a drive mechanism that may be used in the pen shown in FIG. 1; 
     FIG. 3 is a perspective view of the medication delivery pen shown in FIG. I with the cartridge retainer removed; 
     FIG. 4 is an exploded perspective view of the medication delivery pen shown in FIG. 1 with the cartridge retainer removed; 
     FIG. 5 is another perspective view of the medication delivery pen shown in FIG. 1 with the cartridge retainer attached and locked onto the upper body; 
     FIG. 6 is a simplified block diagram of the medication delivery pen shown in FIG. 1 showing the electrical communication paths between components; and 
     FIG. 7 shows a simplified diagram of a medication cartridge located in the cartridge retainer in which the cartridge includes a color code that is detected by a sensor via a light pipe or light guide situated in the cartridge retainer. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a medication delivery pen in accordance with the present invention. The medication delivery pen includes a rotatable adjusting knob  12 , a push button  24 , an eject button  23 , an upper body  14 , a center body  16 , and a medication cartridge retainer  18 . Rotatable adjusting knob  12 , eject button  23 , and push button  24  are operatively coupled to a drive mechanism (see FIG. 2) located in upper and center bodies  14  and  16 . Cartridge retainer  18  is adapted for receiving a medication cartridge of the type described below. The cartridge retainer  18  is coupled to an end of center body  16  so that the drive mechanism is operatively coupled to the medication cartridge. 
     As shown in FIG. 2, cartridge retainer  18  is adapted for receiving a cartridge  46  of the type including an internal piston  46   b  and a pierceable seal  46   a  at one end thereof. An end cap  19  is inserted through cartridge retainer  18  to extend from a distal end of cartridge retainer  18 . A needle assembly  50  is detachably coupled to end cap  19  by threads  19   a , friction, or the like. Needle assembly is disposable so that the medication delivery pen can be used multiple times. In some cases only the needle  50   b  itself may be disposable. 
     When in the inject mode, the drive mechanism serves to translate the rotational displacement of adjusting knob  12  into a corresponding displacement of lead screw  26  via rotation of plunger  22  and half nuts  28 . Push button  24  is then depressed a fixed distance so that the lead screw  26  contacts the piston  46   b , displacing the piston  46   b  by a distance equal to the displacement of lead screw  26  so that fluid within cartridge  46  is forced through needle assembly  50 . It should be noted that while FIG. 2 shows the details of one embodiment of a drive mechanism that may be employed in the present invention, this drive mechanism is shown for illustrative purposes only. More generally, the inventive medication delivery pen may employ many different types of drive mechanisms. 
     Referring again to FIGS. 2, and  3 - 5  a plunger  22  is at least partially positioned within the portion of housing  20  defined by adjusting knob  12 , upper body  14  and center body  16 . Plunger  22  includes a hollow, substantially cylindrical body  22   a  including a band of radially projecting splines  22   b  extending outwardly therefrom. A pair of opposing projections  22   c  extend radially inwardly from the distal end of the cylindrical body  22   a . As shown in FIG. 5, the proximal end of plunger  22  is secured to a rotatable push button  24 . Push button  24  fits within adjusting knob  12  when plunger  22  is fully inserted within housing  20 . 
     A lead screw  26  is positioned within and coaxially with plunger  22  and includes an enlarged distal end  26   a  and a tapered proximal end  26   b , connected by an elongate threaded body  26   c . A pair of longitudinal grooves  26   d  are formed within threaded body  26   c  and receive the radially inwardly extending projections  22   c  of plunger  22 . Lead screw  26  is accordingly rotatable with plunger  22  and capable of sliding axially with respect to plunger  22 . 
     A pair of half-nuts  28  are positioned within center body  16 , with each half-nut  28  including a semi-cylindrical body portion  28   a  and a radially enlarged end portion  28   b . The distal end of each half-nut  28  includes threads  28   c  that are used to threadably engage with lead screw  26  and the proximal end of each half-nut  28  includes a pivot shaft  28   d  that receives a metal pin  28   e  to provide an axis about which each half-nut  28  can pivot. Metal pins  28   e  inserted in each pivot shaft  28   d  also provide more definite control over the dose setting operation, described below, and prevent skewing of half nuts  28  on threaded lead screw  26 . Body portions  28   a  of half-nuts  28  are positioned at least partially within a locking ring  30  having a hollow, generally cylindrical body portion  30   a  defining a generally elliptical passage  30   e  for receiving half-nuts  28 . A distal end  30   b  of locking ring  30  is radially enlarged and includes a pair of angular projections  30   c  that extend axially from the distal end of locking ring  30  and the side of locking ring  30  includes a pair of pins  30   d . The proximal end  18   b  of cartridge retainer  18  includes a pair of angular projections  18   c  that are spaced to receive angular projections  30   c  when cartridge retainer  18  is mounted on housing  20 , which is described further below. 
     A helical coil spring  32  is positioned over locking ring  30  and half-nuts  28  and through locking sleeve  31 , with one end of coil spring  32  bearing against the radially enlarged portions  28   b  of half-nuts  28  while the opposite end of coil spring  32  bears against the radially enlarged distal end  30   b  of locking ring  30 . Distal end  30 b of locking ring  30  mounts within center body  16  which also receives finishing ring  29 . The proximal end portion  28   b  of half-nuts  28  abut splines  22   b  of plunger  22 . 
     Locking ring  30  is slidably mounted within locking sleeve  31  such that the pair of pins  30   d  on locking ring  30  are mounted and travel within slot  31   a  at a distal end of locking sleeve  31 . With this structure locking ring  30  is axially movable within locking sleeve  31  but rotates with locking sleeve  31 . Locking sleeve  31  also includes a pair of L-shaped grooves  31   b  that slidably receive each of the shafts  28   d  on half-nuts  28 . Each pivot shaft  28   d  in conjunction with its respective L-shaped groove  31   b  on locking sleeve  31  and a long groove  16   c  within center body  16  provides a mechanism that prevents the removal of cartridge retainer  18  and cartridge  46  from housing  20 , unless injector button  24  is in a down or loading position. This feature is more clearly shown in FIGS. 4 and 5. In FIG. 4 injector button  24  is in the down or loading position and device  10  is in the proper position for receiving cartridge retainer  18  and, in particular, lugs  18   a  can enter slot  16   a  of center body  16 . As shown in FIG. 4, locking ring  30  is oriented so that tabs  30   c  do not block access to slot  16   a  and in this orientation pivot shafts  28   d  of half-nuts  28  are located in notches  31   e  at the end of each lower leg  31   d  of L-shaped groove  31   b . After a cartridge  46  has been loaded into cartridge retainer  18 , cartridge retainer  18  is mated with center housing  16  such that lugs  18   a  enter slot  16   a . Then, as shown in FIG. 5, cartridge retainer  18  is rotated in a clockwise direction such that lugs  18   a  drive tabs  30   c  in a clockwise direction which moves locking sleeve  31  and causes pivot shaft  28   d  to slide out of each notch  3   e  and into each leg  31   d  of each L-shaped groove  31   b . At this point, spring  32  drives half-nuts  28  in the proximal direction to extend injector button  24  from the proximal end of assembly  10 , if the eject button  23  is depressed. 
     Referring to FIG. 6, a microprocessor  32  is located in upper body  14 . The microprocessor  32  determines the dosage of medication to be injected based upon the number of rotations of adjusting knob  12  as determined by a dosage sensor  160 . Dosage sensor  160  may be any appropriate mechanism for determining the number of rotations, whether complete or incremental, that adjusting knob  12  undergoes in setting the dosage. Dosage sensor  160  may employ optical, magnetic, piezoelectric, or other means. For example, dosage sensor  160  may be an optical encoder in which an encoder disk is splined to the plunger  22  so that the plunger  22  is rotationally splined but axially free to travel within the disk. As the adjusting knob  12  is rotated, the plunger  22  rotates, which in turn rotates the encoder disk, whose rotational motion is detected by an optical receiver. The number of rotations of the encoder disk is translated into a dosage amount by the microprocessor  32 . The microprocessor  32  provides the dosage information to a display  34  such as an LCD display for indicating the amount of medication that will be injected. The display  34  may also indicate other information such as the time and date. This information may be input to microprocessor  32  via mode buttons accessible on housing  20 . 
     The operation of the medication delivery pen is as follows. Cartridge  46  is loaded within cartridge retainer  18  and cartridge retainer  18  is attached to housing  20 . The needle assembly  50  is then affixed to the end of cartridge  18 . Fluid communication is accordingly established between the injection portion of needle assembly  50  and the interior of cartridge  46 . In order to set the dosage, eject button  23  is depressed so that push button  24  is ejected into its extended position in preparation to inject the medication. Once the appropriate dosage is set via rotation of adjusting knob  12 , push button  24  is depressed, causing the drive mechanism to exert a force upon piston  46   b , which is movably positioned within cartridge  46 . Piston  46   b  displaces fluid within cartridge  46 , causing its injection into body tissue through needle assembly  50 . Assuming the device is loaded and push button  24  is in the depressed position, three steps are followed in the injection procedure: press eject button  23 , set the dose via adjusting knob  12 , and make the injection. 
     More specifically, the injection procedure begins by first pressing eject button  23 , which causes the display to be reset to zero and causes ejection of push button  24  so that the pen enters its injection mode. Adjusting knob  12  is then rotated away from the zero setting to set the desired dosage. The drive mechanism travels along the length of housing  20  a distance that is proportional to the dosage displayed on display  34 . Once the desired dose has been set, push button  24  is pushed fully in, which pushes the drive mechanism forward so that the drive mechanism performs the function of a piston rod so that the correct amount of medication in cartridge  46  is discharged through needle assembly  50 . 
     FIG. 6 shows a simplified block diagram of the medication delivery pen shown in FIGS. 1-3. which illustrates the communication paths between the various elements of the pen. As previously mentioned, adjusting knob  12  is rotated to set the dosage and dosage sensor  160  measures the number of rotations (including partial rotations) of adjusting knob  12 . Dosage sensor  160  is coupled to microprocessor  32 , which keeps track of the accumulated rotations of actuator knob  12 . Microprocessor  32  converts the accumulated number of rotations into a dosage value that is to be administered. Microprocessor  32  is coupled to memory storage components such as ROM  142  and RAM  144 . The ROM  142  electronically stores the programs employed by microprocessor  32  to determine the dosage based on the accumulated number of rotations of adjusting knob  12 . ROM  142  can also store additional programs that relate to other functions performed by microprocessor  32  such as the selection from among various display formats for displaying data on display  34 . The RAM  144  stores information about the injection such as the dosage, time, and date so that these parameters may be subsequently recalled for display by the user or a medical practitioner. In some embodiments of the invention the information stored by RAM  144  may also be downloaded to an external device such as a computer through a data port  146 . RAM  144  communicates with data port  146  via microprocessor  32 . Data port  146  may be a bidirectional port for transferring data in both directions so that data such as revised programs, for example, can be uploaded to microprocessor  32 . One or more mode buttons  148  located housing  20  allow the user to input information such as the time, date, and alarm settings and to select the desired display mode. A battery  150  such as a lithium battery, for example, supplies power to the previously mentioned electronic components. 
     Push button  24  and eject button  23  are each coupled to microprocessor  32  so that microprocessor  32  is activated when either of buttons  23  and  24  are depressed. When eject button  23  is depressed and push button  24  is in its ejected state, the pen enters its injection mode in preparation for the delivery of medication. When eject button  23  is in its ejected state and push button  24  is in its depressed state, the pen enters its non-injection mode. Since push button  24  is in its ejected state only when eject button  23  is in its depressed state, microprocessor  32  will cause an error message to be displayed on display  34  if it detects that both push button  24  and eject button  23  are in their depressed states. As previously discussed, in the non-injection mode push button  24  is disengaged from the drive mechanism. That is, when the pen is in its non-injection mode (e.g., when push button  24  is in its depressed state), rotation of adjusting knob  12  does not cause any displacement of the lead screw such as lead screw  26  shown in FIG.  2 . Accordingly, the rotational state of adjusting knob  12  is now available to perform other functions. Upon detecting that the pen is in its non-injection mode, microprocessor  32  is available to perform other functions in accordance with the current operational mode of the pen. Similarly, upon detecting that the pen is in its inject mode, microprocessor  32  operates to determine the dosage that is set by adjusting knob  12 . 
     In accordance with the present invention, the rotational state of adjusting knob  12  when push button  24  is disengaged from the drive mechanism is employed to set and adjust the value of the current operational mode of the medication delivery pen. The operational mode of the pen is selected by the mode button or buttons  148 . Specifically, repeated activation of mode button  148  directs microprocessor  32  to enter different modes such as a time, date and alarm mode. The given mode that is selected via mode button  148  is reflected by display  34 . For example, in the time mode, the current time appears on display  34 . Once in a given mode, adjusting knob  12  is rotated to change the setting of that mode. For example, in the time mode, adjusting knob  12  changes the time setting while in the alarm mode adjusting knob  12  changes the setting of the alarm or alarms. 
     As further indicated in FIG. 6, a displacement sensor  180  provides information about the status of the injection mechanism to microprocessor  32 . For example, the displacement sensor  180  can be used to determine the linear displacement of the drive mechanism, which is related to the amount of insulin that has been delivered. Displacement sensor  180  may be located in the grooves  26  of lead screw  26 . In the particular embodiment of the invention shown in FIG. 2, sensor  180  determines the linear displacement of lead screw  26 . As previously mentioned, the linear displacement of lead screw  26  is equal to the linear displacement of piston  46   b  in cartridge  46 . The displacement of lead screw  26  may be measured on an incremental basis or on an absolute scale. An absolute scale is preferred because the displacement is directly proportional to the amount of insulin that remains in the pen. Accordingly, by detecting the position of lead screw  26  and providing this information to microprocessor  32 , the amount of deliverable medication that remains in cartridge  46  can be displayed on display  34 . 
     Displacement sensor  180  may be any appropriate mechanism that can determine the linear position of lead screw  26  at any given time. For example, similar to dosage sensor  160 , displacement sensor  180  may employ optical, magnetic, or other means. 
     As further indicated in FIG. 6, a cartridge sensor  190  coupled to microprocessor  32  is employed to identify the type of cartridge  46  that is inserted into the cartridge retainer  18 . The cartridge  46  may be identified by a color code that is provided on the cartridge  46 . For example, if the pen is to be employed to deliver insulin, different insulin cartridges may be coded in accordance with the standard proposed by the International Diabetes Federation. This proposed standard assigns a unique color code to each different preparation of insulin, regardless of manufacturer. By providing the pen with the capability to detect the type of insulin or other medication that is installed in the cartridge retainer  18 , the operation of the device is simplified from the user&#39;s perspective. Additionally, the likelihood of user error arising from inadvertently inputting incorrect information into the pen is substantially reduced. 
     Cartridge sensor  190  may be located in cartridge retainer  18  so that it receives light directly from the color code on cartridge  46 . Alternatively, cartridge sensor  190 , which may be a photodetector, for example, may be provided on the same pc-board as the microprocessor  32  and other electronic components. In this case, as indicated in FIG. 7, the cartridge sensor  190  is connected to a light pipe or light guide  192  that is located in cartridge retainer  18 . The light pipe or light guide terminates at a position to receive light reflected from the color code  49  on the cartridge  46 . The light pipe or light guide  192  may be molded directly into cartridge retainer  18 , and in the case of a light pipe, may comprise a series of exposed facets of cartridge retainer  18  itself, which are oriented to transfer the light reflected from the color code  49  to the cartridge sensor  190 . The light reflected from the cartridge  46  and directed to cartridge sensor  190  may be ambient light or light that is provided by cartridge sensor  190  via the light pipe or light guide  192 . The use of ambient light is preferable, however, to minimize power consumption. 
     In some embodiments of the invention the color code may be provided at a plurality of locations on cartridge  46 . In this case a corresponding number of cartridge sensors may be employed to detect the plurality of codes. This arrangement advantageously reduces the likelihood of decoding errors since the processor will only identify the cartridge if a majority (or all) of the sensors are in agreement. If the sensors are not in agreement, an error condition will be indicated on display  34 . The sensors may be configured so that their maximum sensitivity is located at a common wavelength, or alternatively, at different wavelengths. 
     Medication cartridges are often available in different sizes. For example, insulin cartridges are currently available in 1.5 and 3.0 ml sizes. Conventional medication delivery pens can only accept a single cartridge size, however. One problem in providing a pen that accommodates multiple cartridge sizes is that the ratio between the number of units of medication delivered and the linear displacement of the piston in the cartridge is different for each size cartridge. The present invention overcomes this problem by providing, in some embodiments, a second cartridge sensor  195  may be located in cartridge retainer  18  to identify the size of the cartridge  46  that is inserted into the cartridge retainer  18 . Sensor  195  may be similar in type to sensor  190  and may be positioned to detect, for example, the outer edge of the cartridge. Alternatively, sensor  195  may be a mechanical sensor or the like. Once the size of the cartridge has been determined, the microprocessor  32  can adjust the calibration accordingly so that the proper relationship between the total rotational displacement of the adjusting knob  12  and the linear displacement of the piston in the cartridge  46  is used in determining the actual dosage of medication that is delivered.