Patent Description:
The invention relates to a multiple use pen-type injection device with improved functionality, including improved dial back of a set dose, and improved last dose control to prevent a dose from being set that is larger than the amount of drug remaining in a medication cartridge.

Various medication injection pen devices are known in the prior art. These prior art devices sometimes include features for enabling a user to correct a dose that has been set too large, which may be referred to as "dial back". Another feature that may be provided by some of the prior art devices is the ability to control a last dose of a medication cartridge such that a user cannot set a dose greater than the remaining amount of medication in the cartridge. This feature is referred to as last dose control or last dose management. Both of these features are desired by users of such pen devices; however, the prior art devices do not satisfactorily meet these needs. Many prior art devices may provide one of these features, but not both. Further, many of the prior art devices require additional steps for performing dial back, which are cumbersome and not intuitive to the user. Thus, there is a need in the art to provide improved functionality of dial back and last dose control mechanisms together in a medication injection pen. A medication injection pen having the features described in the preamble of claim <NUM> is described in <CIT>.

A medication injection pen according to the invention is defined by the features of claim <NUM>. Preferred embodiments are described within the dependent claims.

Exemplary embodiments of the present invention address at least the above problems and/or disadvantages and provide at least the advantages described below.

In accordance with an exemplary embodiment of the present invention, a medication injection pen includes a housing and a dose set knob having at least one internal tooth. A brake member has a plurality of axially extending splines. A driver includes at least one external tooth engaging the at least one internal tooth of the dose set knob and at least one ratchet arm engaging the plurality of axially extending splines. The driver is prevented from rotating with respect to the dose set knob while moving axially with the dose set knob during dose setting and dose correcting, and the driver rotates with the dose set knob during an injection.

In accordance with another exemplary embodiment of the present invention, a medication injection pen includes a housing and a dose set knob for setting and correcting a dose. A brake member is axially and rotationally fixed to the housing. A driver moves axially with the dose set knob when setting and correcting the dose, and moves rotationally with the dose set knob when injecting the set dose. A hollow piston rod moves axially when injecting the set dose. A brake core member is disposed within the hollow piston rod to substantially prevent rotational movement of the hollow piston rod.

Additional objects, advantages and salient features of exemplary embodiments of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with annexed drawings, discloses exemplary embodiments of the invention.

The above and other exemplary features and advantages of certain exemplary embodiments of the present invention will become more apparent from the following description of certain exemplary embodiments thereof when taken in conjunction with the accompanying drawings in which:.

Throughout the drawings, like reference numerals will be understood to refer to like elements, features and structures.

The matters exemplified in this description are provided to assist in a comprehensive understanding of exemplary embodiments of the invention with reference to the accompanying drawing figures. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the exemplary embodiments described herein can be made without departing from the scope and spirit of the claimed invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

<FIG> depicts a view of an injection pen <NUM> according to a first exemplary embodiment of the present invention. As shown, the injection pen <NUM> includes an pen upper body or housing <NUM>, which houses a plurality of dose setting and injection components. The pen upper body <NUM> is connected to a cartridge housing <NUM>, which houses a medication cartridge <NUM>, as shown in <FIG> and <FIG>. The injection pen <NUM> may also include a lower pen cap <NUM> to cover the cartridge <NUM> and cartridge housing <NUM> when the injection pen is not in use. As shown, the injection pen <NUM> includes a dose set knob <NUM> that includes a knob-like portion that is rotated by a user to set a desired dose. The dose set knob <NUM> also includes a plurality of numerals, as shown in <FIG>, corresponding to a number of dosage units that is visible through a window <NUM> provided on the pen upper body <NUM>. A user rotates the dose set knob <NUM> until the desired dose is visible in the window <NUM>. The pen upper body <NUM> may include an arrow or other indicator <NUM> to precisely indicate the set dose. Once the desired dose is set, a user presses the button <NUM> until the set dosage amount is completely injected. An outer shield <NUM> (<FIG>) can cover a needle <NUM> to prevent accidental needle sticks upon removal of the lower pen cap <NUM>.

Optionally, the pen upper body <NUM> can also include a second window <NUM> for indicating when the set dose is complete, as shown in <FIG>, <FIG> and <FIG>. An indicator or marker <NUM>, as shown in <FIG>, can be provided on the outer surface of the dose set knob <NUM> that is visible through the second window <NUM> only when the dose set knob <NUM> has returned to its initial position, thus indicating that the injection process is complete. <FIG> depicts a scenario when the dose set knob <NUM> has almost returned to its initial position. As shown, the indicator <NUM> is not visible through the window <NUM>, thus the user is notified that the injection is not complete. Once the marker <NUM> is visible in window <NUM>, as shown in <FIG>, the user is assured that the set dose was fully injected.

<FIG> depicts a cross-section of an injection pen <NUM> in accordance with the first exemplary embodiment of the present invention. Reference to the individual components may be better understood in view of the exploded assembly view shown in <FIG>. As shown, a push button <NUM> is provided at a proximal end, closest to a user and farthest from a needle <NUM>, of the pen upper body <NUM>. The push button <NUM> preferably comprises an annular bead or rim <NUM> that engages with a corresponding annular groove <NUM> provided on the internal surface of the dose set knob <NUM>. The annular rim and groove connection is preferably a friction fit that maintains the push button <NUM> in a biased position on the dose set knob <NUM> under the force of a button spring <NUM>, but allows the push button <NUM> to be pushed into the dose set knob <NUM> for injecting a set dose. The interior of the push button <NUM> accommodates a setback bearing insert <NUM> that rests on an internal surface at a proximal end of a setback member or driver <NUM>. The push button <NUM> is designed to rotate freely on the setback bearing insert <NUM>.

The setback member or driver <NUM> is a cylindrical member, as shown in <FIG>, coaxial with and surrounded by the dose set knob <NUM>. The setback member <NUM> is provided co-axially around a brake tower <NUM>, as shown in <FIG>, that is axially and rotatably fixed to the pen upper body <NUM>. The brake tower <NUM> co-axially surrounds a piston rod <NUM>, as shown in <FIG>. The piston rod <NUM> includes a set of keys <NUM> that engage a slot internal to the brake tower <NUM> to rotatably lock the piston rod <NUM> to the brake tower <NUM>. The piston rod <NUM> preferably includes a plurality of threads <NUM> provided on the interior surface thereof, as shown in <FIG>. The piston rod <NUM> co-axially surrounds a lead screw <NUM> that includes a series of threads <NUM> at least at its distal end, as shown in <FIG>. The lead screw threads <NUM> are in threaded engagement with the internal threads <NUM> provided on the piston rod <NUM>. As discussed further below, due to its threaded engagement with the lead screw <NUM>, the piston rod <NUM> is moved into the cartridge <NUM> during injection to press on a stopper <NUM> provided inside the cartridge <NUM> to expel a dose of medication. A wave clip or spring <NUM>, as shown in <FIG> and <FIG>, is provided between a distal end of the brake tower <NUM> and the cartridge <NUM> to bias the cartridge <NUM> in a distal direction to prevent any movement of the cartridge <NUM> during injection, and thus ensuring that an accurate dose is injected.

To set a dose using the injection pen <NUM> of the first exemplary embodiment, a user rotates the knob portion of the dose set knob <NUM> relative to the pen upper body <NUM>. An outer surface <NUM> of the dose set knob <NUM> includes a thread <NUM>, as best shown in <FIG>, that is in threaded engagement with a plurality of threads <NUM> (<FIG>) provided on the internal surface of the pen upper body <NUM>, as shown in <FIG>. Accordingly, as the dose set knob <NUM> is rotated relative to the pen upper body <NUM>, the dose set knob <NUM> screws or advances a distance out of the pen upper body <NUM>, as shown in <FIG>. The dose set knob <NUM> includes an annular shoulder or rim <NUM> on the interior surface thereof near the proximal end, as shown in <FIG> and <FIG>. This annular shoulder <NUM> engages with an enlarged portion or head <NUM> of the setback member <NUM>, as shown in <FIG> and <FIG>. The annular shoulder <NUM> of the dose set knob <NUM> preferably comprises a series of teeth or ridges <NUM> that engage with a plurality of similarly shaped teeth or ridges <NUM> provided on the enlarged head <NUM> of the setback member <NUM>. Preferably, the dose set knob teeth <NUM> and the setback member teeth <NUM> extend in opposite axial directions. During dose setting, the dose set knob <NUM> is free to rotate with respect to the setback member <NUM> in both clockwise and counter-clockwise directions. As this occurs, the plurality of teeth or ridges <NUM> on the dose set knob <NUM> slip past the teeth <NUM> provided on the head portion <NUM> of the setback member <NUM>, thus providing a tactile signal or clicking noise to indicate the setting of a dosage amount. As further described below, the dose set knob <NUM> is enabled to rotate relative to the setback member <NUM> during setting due to a one-way ratchet that prevents the setback member <NUM> from rotating together with the dose set knob <NUM> in the setting direction.

To correct a set dose that may have been set too high, the user simply rotates back the dose set knob <NUM> in the opposite direction. Rotation of the dose set knob <NUM> in this direction is not transferred to the setback member <NUM> due to the one-way ratchet between the setback member <NUM> and the brake tower <NUM>, as shown in <FIG>. The setback member <NUM> near its distal end includes a pair of ratchet arms <NUM>, as shown in <FIG> and <FIG>. The pair of ratchet arms <NUM> engages a plurality of splines or teeth <NUM> provided on the external surface of the brake tower <NUM>, as shown in <FIG> and <FIG>. The ratchet arms <NUM> and splines or teeth <NUM> are configured to allow relative rotation in only one direction, namely, the direction that enables injection of a set dose. The friction provided between the ratchet arms <NUM> and the teeth <NUM> on the brake tower <NUM> is greater than the friction between the corresponding teeth <NUM> and <NUM> on the setback member <NUM> and the dose set knob <NUM>, respectively. Thus, the dose set knob <NUM> can be rotated back to correct a set dose without causing rotation of the setback member <NUM> in this direction. Accordingly, the teeth <NUM> and <NUM> provided on the setback member <NUM> and dose set knob <NUM>, respectively, slip past each other to provide a clicking noise during dialing back of the dose, just as during normal dose setting, thereby indicating correction of the set dose.

As the dose set knob <NUM> screws or advances axially out of the upper body <NUM> during the setting of a dose, the setback member <NUM> is also caused to move axially out of the body by a corresponding distance. This axial movement is caused by the engagement between the annular shoulder <NUM> on the dose set knob <NUM> pushing against the enlarged head portion <NUM> of the setback member <NUM> during its movement out of the body. Once a desired dose is set, the user pushes the push button <NUM> which is coupled to the setback bearing insert <NUM> that is axially connected to the setback member <NUM>. Under the force applied by the user pressing the push button <NUM>, the setback member <NUM> is moved into a locking or meshing engagement with the dose set knob <NUM> via a meshing of the respective teeth or ridges <NUM> and <NUM> provided on the dose set knob <NUM> and the setback member <NUM>, respectively. As the user continues to press the push button <NUM>, the dose set knob <NUM> is caused to rotate and screw back down into the pen upper body <NUM> via the thread engagement between the thread <NUM> on the dose set knob <NUM> and the thread <NUM> in the pen upper body <NUM>. Rotation of the dose set knob <NUM> is then transferred to the setback member <NUM> due to their locking or meshed engagement. The force of the user pressing the button <NUM> is enough to overcome the friction between the ratchet arms <NUM> on the setback member <NUM> and the teeth or splines <NUM> on the brake tower <NUM>. As a result, the setback member <NUM> is enabled to rotate in this direction. As the setback member <NUM> rotates relative to the brake tower <NUM> during injection, the ratchet arms <NUM> produce a tactile signal or clicking noise as they ratchet past the teeth <NUM> on the brake tower <NUM>. This indicates to the user that injection of the set dose is taking place.

Rotation of the setback member <NUM>, as allowed during injection, is then transferred to the lead screw <NUM>, which is rotatably fixed to the setback member <NUM> via a key groove connection provided between the lead screw <NUM> and the setback member <NUM>. As shown in <FIG>, an internal surface <NUM> of the setback member <NUM> includes a groove or slot <NUM> that is engaged with a key <NUM> provided at the proximal end of the lead screw <NUM>, as shown in <FIG>. The setback member <NUM> preferably includes two oppositely disposed slots <NUM> for engaging two oppositely disposed keys <NUM> provided on the lead screw <NUM>. The setback member <NUM> moves axially relative to the lead screw <NUM> during dose setting and dose correcting, via the key <NUM> and slot <NUM> interconnection as shown in <FIG> and <FIG>. In one embodiment, the length of the slot <NUM> in the setback member <NUM> may be configured to correspond to a maximum dose to be injected in a single injection. The lead screw <NUM> is axially fixed with respect to the pen upper body <NUM> via a snap engagement with the brake tower <NUM> which is axially and rotatably fixed to the pen upper body <NUM> as discussed further below. As shown in <FIG> and <FIG>, the lead screw <NUM> includes a disk like portion <NUM> with an angled surface <NUM> that enables the lead screw <NUM> to snap in behind a rim or set of protrusions <NUM> provided on the interior of the brake tower <NUM>, as shown, thus axially locking the lead screw <NUM> with respect to the pen upper body <NUM>.

As described above, the lead screw <NUM> includes a plurality of threads <NUM> at its distal end that are in threaded engagement with a plurality of threads <NUM> preferably provided along the entire length of a hollow piston rod <NUM> as shown in <FIG>. The piston rod <NUM> is held non-rotatable with respect to the pen upper body <NUM> due to a non-rotatable coupling with the brake tower <NUM>, which is held axially and rotatably fixed with respect to the pen upper body <NUM>. The piston rod <NUM> includes a key or set of keys <NUM> at its distal end that engage with a slot <NUM> (<FIG>) provided on the internal surface of the brake tower <NUM> to prevent relative rotation therebetween while permitting the piston rod <NUM> to move axially with respect thereto. The threads <NUM> of the lead screw <NUM> have a flat portion <NUM> corresponding to a flat portion <NUM> of the piston rod <NUM> (<FIG>) such that axial movement of the lead screw during dose setting and dose correcting does not result in axial movement of the piston rod <NUM>. Accordingly, rotation of the lead screw <NUM> during injection of a dose causes the threads <NUM> of the lead screw <NUM> to engage the threads <NUM> of the piston rod <NUM>, thereby axially moving the piston rod <NUM>.

During assembly, the brake tower <NUM> is inserted into the pen upper body <NUM> from the distal end. As shown in <FIG>, the pen upper body <NUM> includes a transverse wall <NUM> that limits the movement of the brake tower <NUM> into the body <NUM> by blocking an enlarged distal portion <NUM> of the brake tower <NUM>, as shown. Further, an inwardly protruding key <NUM> is also provided distally from the transverse wall <NUM> on the internal surface of the pen upper body <NUM>, as shown in <FIG>. The key <NUM> engages with a slot <NUM> provided on the enlarged distal portion <NUM> of the brake tower <NUM>, as shown in <FIG>, to rotationally fix the brake tower <NUM> with respect to the pen upper body <NUM>. Preferably, a plurality of axially extending keys <NUM> are disposed on the inner surface of the pen upper body <NUM>, as shown in <FIG>, to engage a plurality of slots <NUM> on the enlarged distal portion <NUM> of the brake tower <NUM>.

Because the piston rod <NUM> is non-rotatable with respect to the body <NUM>, as the lead screw <NUM> is caused to rotate during injection, as described above due to its rotational coupling with setback member <NUM>, the piston rod <NUM> through its threaded engagement with lead screw <NUM> is caused to move in the distal direction to press against the stopper <NUM> provided in the medicament cartridge <NUM>, thus expelling a liquid medication therefrom. A mechanical advantage is preferably provided such that the dose set knob <NUM> moves further in the axial direction than the piston rod <NUM> during the injection, reducing the injection force that must be applied by the user. This is preferably accomplished by providing different pitches for the threaded connection between the dose set knob <NUM> and the pen upper body <NUM> and the threaded connection between the lead screw <NUM> and the piston rod <NUM>. The ratio between the thread pitches can vary depending on the liquid medication and the expected dose volumes. For example, the pitch ratio can be <NUM>: <NUM> or <NUM>: <NUM>, but is not limited thereto. The piston rod <NUM> is prevented from moving in the proximal direction because the lead screw <NUM> is rotatable in only a single direction (that which results in distal movement of the piston rod <NUM>) due to the one-way ratchet between the setback member <NUM> and the brake tower <NUM>. Thus, accurate dosing can be ensured because the piston rod <NUM> maintains its engagement with the stopper <NUM> between injections.

A dose stop member <NUM>, as shown in <FIG> and <FIG>, is provided for last dose management, to prevent the setting of a dose that is larger than the remaining amount of medication in the cartridge <NUM>. The dose stop member <NUM> is axially slidable but rotationally fixed with respect to the setback member <NUM> by being positioned between a pair of splines <NUM> provided on the outer surface of the setback member <NUM>. The dose stop member <NUM> is a half-nut like element, as shown, that is threaded on its outer surface with a plurality of threads <NUM>. These threads <NUM> are configured to engage with corresponding threads <NUM> provided on the interior of the dose set knob <NUM>, as shown in <FIG>. <FIG> depicts the dose stop member <NUM> in its initial position. As shown, the dose stop member <NUM> is threadedly engaged with one or two of the proximal-most threads of threads <NUM> provided on the dose set knob <NUM>. During dose setting, as the dose set knob <NUM> rotates relative to the setback member <NUM> and therefore also relative to the dose stop member <NUM>, the dose stop member <NUM> is caused to slide in the distal direction by a distance corresponding to the set dose due to its engagement with the threads <NUM> in the dose set knob <NUM>.

During injection, because the setback member <NUM> and the dose set knob <NUM> are rotationally coupled as discussed above, the dose stop member <NUM> will maintain its position relative to the threads <NUM> of the dose set knob <NUM>. The dose stop member <NUM> will move in the distal direction during dose setting until a distal edge <NUM> of the dose stop member <NUM> abuts an inwardly directed key <NUM> provided on the internal surface of the dose set knob <NUM>, as shown in <FIG> and <FIG>. In this position, the dose stop member <NUM> is prevented from further movement in the distal direction which also prevents further rotation of the dose set knob <NUM> to set an additional dose. In its final position, as shown in <FIG>, the dose stop member <NUM> is threadedly engaged with approximately two of the distal-most threads of threads <NUM> provided in the dose set knob <NUM>. As shown with respect to <FIG>, the total distance traveled by the dose stop member <NUM> from its initial position to its final position when it abuts key <NUM> provided on the dose set knob <NUM>, is greater than the length of either of the thread portions <NUM> and <NUM> provided on the dose stop member <NUM> and the dose set knob <NUM>, respectively.

<FIG> and <FIG> illustrate another embodiment with similar functionality as that described above, as apparent by the commonly assigned reference numerals to the various components in the form of "1xx". <FIG> and <FIG> illustrate an alternate embodiment of the dose stop member <NUM>', as shown. The dose stop member <NUM> is still a half-nut like element but is elongated with a greater number of threads <NUM>. The dose stop member <NUM> is also now threadedly engaged with only a single ¾ length thread <NUM> provided on the interior of the dose set knob <NUM>. The dose stop member still slides in the distal direction relative to the setback member <NUM> in the same manner as above until it abuts the key <NUM> on the interior of the dose set knob <NUM>. Alternatively, the dose stop members <NUM> and <NUM> can be configured to similarly slide in the proximal direction during setting of a dose until the dose stop members <NUM> and <NUM> abut the enlarged portions <NUM> and <NUM> near the proximal end of the setback members <NUM> and <NUM>, respectively, thus preventing further setting of a dose that would exceed the amount of medication remaining in the cartridges <NUM> and <NUM>.

<FIG> illustrate a third exemplary embodiment of an injection pen <NUM> with similar functionality to the above exemplary embodiments. Like reference numerals have been included where the depicted components are substantially the same in the form "2xx". Each of the components of the injection pen <NUM> shown in <FIG> and its respective functionality is substantially the same as the above exemplary embodiments unless described otherwise.

The exemplary embodiment depicted in <FIG> includes an additional element referred to as the brake tower core <NUM>. The brake tower core <NUM> is surrounded by the brake tower <NUM> and is provided axially and rotationally fixed to the brake tower <NUM>. As shown in <FIG>, the brake tower core <NUM> includes a plurality of teeth <NUM> provided on an enlarged surface <NUM> near the proximal end thereof. The plurality of teeth <NUM> preferably extend axially toward a distal end. The plurality of teeth <NUM> are configured to engage corresponding teeth <NUM> provided at a proximal end of the brake tower <NUM>. The corresponding tooth engagement prevents relative rotation between the brake tower core <NUM> and the brake tower <NUM>. The brake tower <NUM> is both axially and rotationally fixed to the pen upper body <NUM> in the same manner described above. As shown, the brake tower core <NUM> is a substantially cylindrical element with an open side <NUM> extending along an axial length of the brake tower core <NUM>, as shown in <FIG>. The open side <NUM> includes approximately one-fifth to one-quarter of the circumference of a cross section of the brake tower core <NUM>. The open side <NUM> forms two longitudinally extending edges <NUM> and <NUM> at each end of the open side <NUM>.

The brake tower core <NUM> functions to prevent rotation of the piston rod <NUM> relative to the brake tower <NUM> and thus the pen upper body <NUM>. As shown in <FIG>, the brake tower core <NUM> is surrounded by a hollow piston rod <NUM>. The hollow piston rod <NUM> includes a plurality of thread segments <NUM> provided along substantially the entire length of the hollow piston rod <NUM>. Each of the thread segments <NUM> has a length substantially the same as the portion of the circumference of the open side <NUM> of the brake tower core <NUM>. The thread segments <NUM> extend inwardly into the inner cavity of the hollow piston rod <NUM>. An outer surface of the piston rod <NUM> includes a plurality of window segments <NUM> that are "punched through" the surface of the piston rod <NUM> to protrude into the interior thereof. The window segments <NUM> are provided to aid in the manufacture of the hollow piston rod <NUM> to help form the inner thread segments <NUM>. The piston rod <NUM> is positioned with respect to the brake tower core <NUM> such that the thread segments <NUM> align with and protrude into the open surface <NUM> of the brake tower core, as shown in <FIG> and <FIG>. In this position, the pair of longitudinally extending edges <NUM> and <NUM> abut the respective edges of the protruding thread segments <NUM>, such that the piston rod <NUM> is prevented from rotating relative to the brake tower core <NUM>.

Similar to the above exemplary embodiments, a lead screw <NUM> is provided in the interior of the hollow piston rod <NUM>. A threaded portion <NUM> is provided at the distal end of the lead screw <NUM>. Threaded portion <NUM> is configured to engage the thread segments <NUM> provided on the interior of the piston rod <NUM>. Similar to the above exemplary embodiments, the lead screw <NUM> is rotationally fixed to a setback member <NUM> such that rotation of the setback member <NUM> during an injection is transferred to the lead screw <NUM>. Axial movement of the lead screw <NUM> relative to the brake tower core <NUM> is prevented in the proximal direction by the lead screw threads <NUM> being larger than the diameter of the opening at a distal end <NUM> of the brake tower core <NUM>, as shown in <FIG> and <FIG>. Axial movement of the lead screw <NUM> relative to the brake tower core <NUM> is prevented in the distal direction by a flange <NUM> of the lead screw <NUM> engaging the enlarged portion <NUM> of the brake tower core <NUM>. As such, due to the thread engagement between the threaded portion <NUM> of the lead screw <NUM> and thread segments <NUM> on the hollow piston rod <NUM>, relative rotation of the lead screw <NUM> with respect to the piston rod <NUM> (which is rotationally fixed to the brake tower <NUM>) drives the piston rod <NUM> axially in the distal direction inside the cartridge <NUM> to expel medication contained therein.

<FIG> illustrate a fourth exemplary embodiment of an injection pen <NUM> with similar functionality to the above exemplary embodiments. Like reference numerals have been included where the depicted components are substantially the same in the form "3xx". Each of the components of the injection pen <NUM> shown in <FIG> and its respective functionality is substantially the same as the above exemplary embodiments unless described otherwise.

The exemplary embodiment depicted in <FIG> includes a modified brake tower core <NUM>. The brake tower core <NUM> is surrounded by the brake tower <NUM> and is provided axially and rotationally fixed to the brake tower <NUM>. As shown in <FIG>, the brake tower core <NUM> has a pair of oppositely extending arms <NUM> and <NUM> extending from a proximal end <NUM> thereof. Tabs <NUM> and <NUM> extend upwardly from ends of each of the arms <NUM> and <NUM>. The arms <NUM> and <NUM> are received by V-shaped notches <NUM> at a proximal end <NUM> of the brake tower <NUM>. The arms <NUM> and <NUM> receive the disc-shaped portion <NUM> (<FIG>) of the lead screw <NUM> such that the tabs <NUM> and <NUM> abut the disc-shaped portion <NUM>. Accordingly, the lead screw <NUM> is allowed to rotate with respect to the brake tower core <NUM> during an injection. The brake tower <NUM> is both axially and rotationally fixed to the pen upper body <NUM> in substantially the same manner described above.

As shown, the brake tower core <NUM> is a substantially cylindrical element with an open side <NUM> extending along an axial length of the brake tower core <NUM>, as shown in <FIG>. The open side <NUM> includes approximately one-fifth to one-quarter of the circumference of a cross section of the brake tower core <NUM>. The open side <NUM> forms two longitudinally extending edges <NUM> and <NUM> at each end of the open side <NUM>.

The brake tower core <NUM> functions to prevent rotation of the piston rod <NUM> relative to the brake tower <NUM> and thus the pen upper body <NUM>. As shown in <FIG>, the brake tower core <NUM> is surrounded by a hollow piston rod <NUM>. The hollow piston rod <NUM> has threads <NUM> that preferably extend substantially continuously along an entirety of an inner surface <NUM> of the piston rod <NUM>, as shown in <FIG> and <FIG>. A tab or key <NUM> extends radially inwardly at a proximal end <NUM> of the piston rod <NUM>, as shown in <FIG>. A flange <NUM> for engaging the stopper <NUM> extends outwardly from a distal end of the piston rod <NUM>. The piston rod <NUM> is positioned with respect to the brake tower core <NUM> such that the tab <NUM> is received in the open surface <NUM> of the brake tower core, as shown in <FIG>. In this position, the pair of longitudinally extending edges <NUM> and <NUM> abut the respective edges <NUM> and <NUM> of the tab <NUM>, such that the piston rod <NUM> is prevented from rotating relative to the brake tower core <NUM>, thereby controlling angular orientation of the piston rod <NUM>. The tab or key <NUM> is at a proximal end of the piston rod <NUM> to that it can remain in the slot-like opening <NUM> of the brake tower core <NUM> as the piston rod <NUM> moves distally.

Similar to the above exemplary embodiments, a lead screw <NUM> is provided in the interior of the hollow piston rod <NUM>, as shown in <FIG>. A threaded portion <NUM> is provided at the distal end of the lead screw <NUM>, as shown in <FIG>. The threaded portion <NUM> is configured to engage the thread segments <NUM> provided on the interior of the piston rod <NUM>. Similar to the above exemplary embodiments, the lead screw <NUM> is rotationally fixed to a setback member <NUM> such that rotation of the setback member <NUM> during an injection is transferred to the lead screw <NUM>. Axial movement of the lead screw <NUM> relative to the brake tower core <NUM> is prevented in the proximal direction by the lead screw threads <NUM> being larger than the diameter of the opening at a distal end <NUM> of the brake tower core <NUM>, as shown in <FIG>. Axial movement of the lead screw <NUM> relative to the brake tower core <NUM> is prevented in the distal direction by inwardly extends tabs <NUM> of the brake tower <NUM> engaging a groove <NUM> of the lead screw <NUM> disposed between the enlarged portion <NUM> and the disc-shaped portion <NUM>. As such, due to the thread engagement between the threaded portion <NUM> of the lead screw <NUM> and the threads <NUM> of the hollow piston rod <NUM>, relative rotation of the lead screw <NUM> with respect to the piston rod <NUM> (which is rotationally fixed to the brake tower <NUM>) drives the piston rod <NUM> axially in the distal direction inside the cartridge <NUM> to expel medication contained therein.

<FIG> illustrate a fifth exemplary embodiment of an injection pen <NUM> with similar functionality to the above exemplary embodiments. Like reference numerals have been included where the depicted components are substantially the same in the form "4xx". Each of the components of the injection pen <NUM> shown in <FIG> and its respective functionality is substantially the same as the above exemplary embodiments unless described otherwise.

The exemplary embodiment depicted in <FIG> includes a further modified brake tower core <NUM>. The brake tower core <NUM> is surrounded by the brake tower <NUM> and is provided axially and rotationally fixed to the brake tower <NUM>. The brake tower core <NUM>, as shown in <FIG> and <FIG>, has a plurality of teeth <NUM> provided on an enlarged surface <NUM> near a proximal end thereof. The plurality of teeth <NUM> preferably extend axially toward a distal end. The brake tower <NUM> is substantially similar to the brake tower <NUM> shown in <FIG> and has a plurality of corresponding teeth <NUM> provided at a proximal end <NUM> of the brake tower <NUM> (<FIG>). The engagement between the brake tower teeth <NUM> (<FIG>) and the brake tower core teeth <NUM> prevents relative rotation between the brake tower core <NUM> and the brake tower <NUM>. The brake tower <NUM> is both axially and rotationally fixed to the pen upper body <NUM> in the same manner described above.

As shown in <FIG>, the brake tower core <NUM> has substantially planar opposing walls <NUM> and <NUM> extending from the enlarged portion <NUM>. An open side <NUM> is formed between the opposing walls <NUM> and <NUM> that extends along an axial length of the brake tower core <NUM>. The open side <NUM> includes approximately one-fifth to one-quarter of the circumference of a cross section of the brake tower core <NUM>. The open side <NUM> forms two longitudinally extending edges <NUM> and <NUM> at each end of the open side <NUM>.

The brake tower core <NUM> functions to prevent rotation of the piston rod <NUM> relative to the brake tower <NUM> and thus the pen upper body <NUM>. As shown in <FIG> and <FIG>, the brake tower core <NUM> is surrounded by a hollow piston rod <NUM>. The hollow piston rod <NUM> has threads <NUM> that extend along an entirety of an inner surface thereof. A bore <NUM> extends from a proximal end <NUM> to a distal end <NUM> of the piston rod <NUM>. Opposite sides <NUM> and <NUM> of an opening <NUM> for accessing the bore <NUM> are substantially flat, as shown in <FIG>.

The piston rod <NUM> is positioned with respect to the brake tower core <NUM> such that the planar walls <NUM> and <NUM> of the brake tower core <NUM> are received by the flat portions <NUM> and <NUM> of the bore opening <NUM> of the piston rod <NUM>. The lead screw <NUM> is inserted through the brake tower core <NUM> such that the lead screw threads <NUM> engage the piston rod threads <NUM> beyond a distal end <NUM> of the brake tower core <NUM>. Rotation of the lead screw <NUM> during an injection results in axial movement of the piston rod <NUM> due to the thread engagement therebetween. The engagement between the planar walls <NUM> and <NUM> of the brake tower core <NUM> and the flat portions <NUM> and <NUM> of the piston rod <NUM> prevent rotation of the piston rod <NUM> relative to the brake tower core <NUM> during injections.

Similar to the above exemplary embodiments, the lead screw <NUM> is rotationally fixed to a setback member <NUM> such that rotation of the setback member <NUM> during an injection is transferred to the lead screw <NUM>. Axial movement of the lead screw <NUM> relative to the brake tower core <NUM> is prevented in the proximal direction by the lead screw threads <NUM> being larger than the diameter of the opening at a distal end <NUM> of the brake tower core <NUM>, as shown in <FIG>. Axial movement of the lead screw <NUM> relative to the brake tower core <NUM> is prevented in the distal direction by a flange <NUM> of the lead screw <NUM> engaging the enlarged portion <NUM> of the brake tower core <NUM>. As such, due to the thread engagement between the threaded portion <NUM> of the lead screw <NUM> and the threads <NUM> of the hollow piston rod <NUM>, relative rotation of the lead screw <NUM> with respect to the piston rod <NUM> (which is rotationally fixed to the brake tower <NUM>) drives the piston rod <NUM> axially in the distal direction inside the cartridge <NUM> to expel medication contained therein.

<FIG> illustrate a sixth exemplary embodiment of an injection pen <NUM> with similar functionality to the above exemplary embodiments. Like reference numerals have been included where the depicted components are substantially the same in the form "5xx". Each of the components of the injection pen <NUM> shown in <FIG> and its respective functionality is substantially the same as the above exemplary embodiments unless described otherwise.

As shown in <FIG>, the lead screw <NUM> snaps into an interrupted ring forming a plurality of protrusions <NUM> on an inner surface of the brake tower <NUM>. In the sixth exemplary embodiment, a lead screw <NUM> has a continuous ring <NUM> into which a brake tower <NUM> snaps as shown in <FIG>. The continuous ring <NUM> is a flexible member facilitating assembly, as well as resisting disassembly forces due to the continuity of the ring <NUM>.

The lead screw <NUM> has an external thread <NUM> formed at a distal end <NUM> to engage threads of a piston rod <NUM>, as shown in <FIG> and <FIG>. The continuous ring <NUM> is disposed at a proximal end <NUM> of the lead screw <NUM>. The continuous ring <NUM> has an inner surface <NUM> and an outer surface <NUM>. A circumferential rim <NUM> extends from the inner surface <NUM> of the ring <NUM>. The circumferential rim <NUM> has an angled surface <NUM>, as shown in <FIG>, to facilitate insertion of the brake tower <NUM>.

A tower core <NUM> is disposed on the lead screw <NUM>, as shown in <FIG>. The tower core <NUM> has an open surface to receive the lead screw <NUM>. The lead screw <NUM> and brake tower core <NUM> are then inserted through an opening <NUM> at a proximal end <NUM> of the brake tower <NUM>, as shown in <FIG>. The opening <NUM> at the proximal end <NUM> of the brake tower <NUM> then flexes outwardly to receive the enlarged portion <NUM> of the brake tower core <NUM>, as shown in <FIG> and <FIG>. The lead screw <NUM> has not yet been connected to the brake tower <NUM> to allow the opening <NUM> at the proximal end <NUM> of the brake tower <NUM> to decompress, thereby reducing stress thereon. The enlarged portion <NUM> of the brake tower core <NUM> is received within an internal cavity of the brake tower <NUM>.

As shown in <FIG>, the lead screw <NUM> is snap-connected to the brake tower <NUM>. Pushing the lead screw <NUM> in the distal direction causes the angled surface <NUM> of the rim <NUM> of the ring <NUM> to flex outwardly along an angled surface <NUM> at the proximal end <NUM> of the brake tower <NUM>. The circumferential rim <NUM> snaps into a recess <NUM> formed in an outer surface <NUM> of the brake tower <NUM> adjacent the proximal end <NUM> thereof. The brake tower core <NUM> has not yet been rotationally locked to the brake tower <NUM> such that the brake tower core <NUM> is free to rotate.

As shown in <FIG>, the piston rod <NUM> is inserted in the internal cavity of the brake tower <NUM> from a distal end thereof. The internal threads <NUM> of the piston rod <NUM> are threaded onto the threads <NUM> (<FIG>) of the lead screw <NUM> such that the piston rod <NUM> is threaded in the proximal direction into the brake tower <NUM>. The piston rod <NUM> is threaded until a proximal end <NUM> of the piston rod <NUM> abuts the enlarged portion <NUM> of the brake tower core <NUM>. The brake tower core <NUM> is then pushed distally into the brake tower <NUM>, thereby locking the brake tower core <NUM> to the brake tower <NUM>. A pin (not shown) is inserted through a break <NUM> in the lead screw threads <NUM> to facilitate locking the brake tower core <NUM> to the brake tower <NUM>.

<FIG> illustrate a seventh exemplary embodiment of an injection pen <NUM> with similar functionality to the above exemplary embodiments. Like reference numerals have been included where the depicted components are substantially the same in the form "6xx". Each of the components of the injection pen <NUM> shown in <FIG> and its respective functionality is substantially the same as the above exemplary embodiments unless described otherwise.

The exemplary embodiment depicted in <FIG> includes an additional element referred to as a clicker body <NUM>, as shown in <FIG> and <FIG>. The clicker body <NUM> is surrounded by the dose set knob <NUM>, as shown in <FIG>. An upper surface <NUM> of an upper ring <NUM> is engaged by a push button <NUM>. A lower surface <NUM> of the upper ring <NUM> is engaged by a distal end <NUM> of a setback member <NUM>. A pair of flexible arms <NUM> are connected to the upper ring <NUM>, as shown in <FIG> and <FIG>. A lower ring <NUM> is connected to the upper ring <NUM>, as shown in <FIG>. The lower ring <NUM> has a pair of flexible arms <NUM> connected thereto, as shown in <FIG>. Hooks <NUM> are disposed at free ends of the upper ring flexible arms <NUM>, and hooks <NUM> are disposed at free ends of the lower ring flexible arms <NUM>. Preferably, the sloped surfaces of the upper ring hooks <NUM> and the lower ring hooks <NUM> form an angle of approximately <NUM> degrees. An opening <NUM> is formed in the clicker body <NUM> to receive the push button <NUM>. The upper ring flexible arm hooks <NUM> engage teeth <NUM> of the dose set knob <NUM>, as shown in <FIG>. The lower ring flexible arm hooks <NUM> engage teeth <NUM> of the setback member <NUM>.

The brake tower core <NUM> is surrounded by the brake tower <NUM> and is provided axially and rotationally fixed to the brake tower <NUM>. As shown in <FIG> and <FIG>, the brake tower core <NUM> has a key <NUM> extending axially at a proximal end. The key <NUM> is received by a V-shaped notch <NUM> disposed at a proximal end of the brake tower <NUM>. The key <NUM> has inwardly tapering sides, as shown in <FIG>, to facilitate engagement with the V-shaped notch <NUM> of the brake tower <NUM>, thereby rotationally locking the brake tower core <NUM> to the brake tower <NUM>. The brake tower <NUM> is both axially and rotationally fixed to the pen upper body <NUM> in the same manner described above. As shown in <FIG>, the brake tower core <NUM> is a substantially cylindrical element with an open side <NUM> extending along an axial length of the brake tower core <NUM>. The open side <NUM> includes approximately one-fifth to one-quarter of the circumference of a cross section of the brake tower core <NUM>. The open side <NUM> forms two longitudinally extending edges <NUM> and <NUM> at each end of the open side <NUM>.

The brake tower core <NUM> functions to prevent rotation of the piston rod <NUM> relative to the brake tower <NUM> and thus the pen upper body <NUM>. As shown in <FIG>, the brake tower core <NUM> is surrounded by a hollow piston rod <NUM>. The hollow piston rod <NUM> includes internal threads <NUM> extending along substantially an entire length of the hollow piston rod <NUM>, as shown in <FIG> and <FIG>. The piston rod <NUM> is positioned with respect to the brake tower core <NUM> such that an internally extending key <NUM> engages the longitudinally extending edges <NUM> and <NUM>, such that the piston rod <NUM> is prevented from rotating relative to the brake tower core <NUM>, as shown in <FIG>.

Similar to the above exemplary embodiments, a lead screw <NUM> (<FIG>) is provided in the interior of the hollow piston rod <NUM>. A threaded portion <NUM> is provided at the distal end of the lead screw <NUM>. The threaded portion <NUM> is configured to engage the internal threads <NUM> of the piston rod <NUM>. Similar to the above exemplary embodiments, the lead screw <NUM> is rotationally fixed to the setback member <NUM> such that rotation of the setback member <NUM> during an injection is transferred to the lead screw <NUM>. The lead screw <NUM> is snapped into the brake tower core <NUM>, which is snapped into the brake tower <NUM>, as shown in <FIG> and <FIG>. A flange <NUM> of the lead screw <NUM> is received by a groove <NUM> (<FIG>) of the brake tower core <NUM> such that a proximal end of the brake tower core <NUM> is received by an annular groove <NUM> of the lead screw <NUM> disposed between the proximal flange <NUM> and the flange <NUM> spaced inwardly therefrom. A flange <NUM> of the brake tower core <NUM> is received by an inwardly extending lip <NUM> of the brake tower <NUM>. Axial movement of the lead screw <NUM> relative to the brake tower <NUM> is prevented in the proximal direction by the flange <NUM> of the brake tower core <NUM> abutting the inwardly extending lip <NUM> of the brake tower <NUM>. Preventing proximal axial movement of the brake tower core <NUM> prevents proximal axial movement of the lead screw <NUM>, which is connected by a snap-fit to the brake tower core <NUM>. Axial movement of the lead screw <NUM> relative to the brake tower <NUM> is prevented in the distal direction by a flange <NUM> of the lead screw <NUM> abutting a distal end of the brake tower <NUM>. As such, due to the thread engagement between the threaded portion <NUM> of the lead screw <NUM> and the internal threads <NUM> on the hollow piston rod <NUM>, relative rotation of the lead screw <NUM> with respect to the piston rod <NUM> (which is rotationally fixed to the brake tower core <NUM>) drives the piston rod <NUM> axially in the distal direction inside the cartridge <NUM> to move the stopper <NUM> to expel medication contained therein.

To set a dose using the injection pen <NUM> of the seventh exemplary embodiment, the user rotates the knob portion of the dose set knob <NUM> relative to the pen upper body <NUM>. An outer surface <NUM> of the dose set knob <NUM> includes a thread <NUM>, as shown in <FIG>, that is in threaded engagement with a plurality of threads <NUM> provided on the internal surface of the pen upper body <NUM>, as shown in <FIG> and <FIG>. Accordingly, as the dose set knob <NUM> is rotated relative to the pen upper body <NUM>, the dose set knob <NUM> screws or advances a distance out of the pen upper body <NUM> (<FIG>). The dose set knob <NUM> includes an annular shoulder or rim <NUM> on the interior surface thereof near the proximal end, as shown in <FIG>. The annular shoulder <NUM> engages with an enlarged portion or head <NUM> (<FIG>) of the setback member <NUM>, as shown in <FIG>. The annular shoulder <NUM> of the dose set knob <NUM> preferably comprises a series of teeth or ridges <NUM> that engage with a plurality of similarly shaped teeth or ridges <NUM> provided on the enlarged head <NUM> of the setback member <NUM>. Preferably, the dose set knob teeth <NUM> and the setback member teeth <NUM> extend in opposite axial directions. During dose setting, the dose set knob <NUM> is free to rotate with respect to the setback member <NUM> in both clockwise and counter-clockwise directions. As this occurs, the plurality of teeth or ridges <NUM> on the dose set knob <NUM> slip past the teeth <NUM> provided on the head portion <NUM> of the setback member <NUM>, thus providing a tactile signal or clicking noise to indicate the setting of a dosage amount. As further described below, the dose set knob <NUM> is enabled to rotate relative to the setback member <NUM> during setting due to a one-way ratchet that prevents the setback member <NUM> from rotating together with the dose set knob <NUM> in the setting direction.

The clicker body <NUM> facilitates generating a tactile signal or clicking noise during dose setting. The upper ring hooks <NUM> of the clicker body <NUM> are locked to the teeth <NUM> (<FIG>) of the dose set knob <NUM> such that the clicker body rotates with the dose set knob <NUM> as the dose set knob <NUM> advances out of the pen upper body <NUM>. The lower ring hooks <NUM> slide over the teeth <NUM> (<FIG>) of the setback member <NUM>. Accordingly, a tactile signal or clicking noise is generated to indicate to the user that a dose is being set.

To correct a set dose that may have been set too high, the user simply rotates back the dose set knob <NUM> in the opposite direction. Rotation of the dose set knob <NUM> in this direction is not transferred to the setback member <NUM> due to the one-way ratchet between the setback member <NUM> and the brake tower <NUM>. The setback member <NUM> has a pair of ratchet arms <NUM>, as shown in <FIG>. The pair of ratchet arms <NUM> engages a plurality of splines or teeth <NUM> provided on the external surface of the brake tower <NUM>, as shown in <FIG> and <FIG>. The ratchet arms <NUM> and splines or teeth <NUM> are configured to allow relative rotation in only one direction, namely, the direction that enables injection of a set dose. The friction provided between the ratchet arms <NUM> and the teeth <NUM> on the brake tower <NUM> is greater than the friction between the corresponding teeth <NUM> and <NUM> on the setback member <NUM> and the dose set knob <NUM>, respectively. Thus, the dose set knob <NUM> can be rotated back to correct a set dose without causing rotation of the setback member <NUM> in this direction. Accordingly, the teeth <NUM> and <NUM> provided on the setback member <NUM> and dose set knob <NUM>, respectively, slip past each other to provide a clicking noise during dialing back of the dose, just as during normal dose setting, thereby indicating correction of the set dose.

The clicker body <NUM> also facilitates generating a tactile signal or clicking noise during dose correcting. The lower ring hooks <NUM> of the clicker body <NUM> are locked to the teeth <NUM> (<FIG>) of the setback member <NUM> such that the clicker body <NUM> is rotatably locked to the setback member <NUM>. Rotation of the dose set knob <NUM> as the dose set knob <NUM> is advanced back into pen upper body <NUM> to correct the dose causes the teeth <NUM> (<FIG>) of the dose set knob <NUM> to slide over the lower ring hooks <NUM> of the clicker body <NUM>, thereby generating a tactile signal or clicking noise to indicate to the user that a dose is being corrected. Accordingly, the clicker body facilitates generating a tactile signal or clicking noise during both dose setting and dose correcting.

As the dose set knob <NUM> screws or advances axially out of the upper body <NUM> during the setting of a dose, the setback member <NUM> is also caused to move axially out of the body by a corresponding distance. This axial movement is caused by the engagement between the annular shoulder <NUM> on the dose set knob <NUM> pushing against the enlarged head portion <NUM> of the setback member <NUM> during its movement out of the body. Once a desired dose is set, the user pushes the push button <NUM> that is coupled to the clicker ring <NUM> that is axially connected to the setback member <NUM>. Under the force applied by the user pressing the push button <NUM>, the setback member <NUM> is moved into a locking or meshing engagement with the dose set knob <NUM> via a meshing of the respective teeth or ridges <NUM> and <NUM> provided on the dose set knob <NUM> and the setback member <NUM>, respectively. As the user continues to press the push button <NUM>, the dose set knob <NUM> is caused to rotate and screw back down into the pen upper body <NUM> via the thread engagement between the thread <NUM> on the dose set knob <NUM> and the thread <NUM> in the pen upper body <NUM>. Rotation of the dose set knob <NUM> is then transferred to the setback member <NUM> due to their locking or meshed engagement. The force of the user pressing the button <NUM> is enough to overcome the friction between the ratchet arms <NUM> on the setback member <NUM> and the teeth or splines <NUM> on the brake tower <NUM>. As a result, the setback member <NUM> is enabled to rotate in this direction. As the setback member <NUM> rotates relative to the brake tower <NUM> during injection, the ratchet arms <NUM> produce a tactile signal or clicking noise as they ratchet past the teeth <NUM> on the brake tower <NUM>. This indicates to the user that injection of the set dose is taking place. Because the dose set knob <NUM> and the setback member <NUM> rotate together during the injection, the clicker body does not rotate relative to either the dose set knob <NUM> or the setback member <NUM>. Accordingly, the clicker body <NUM> rotates with both the dose set knob <NUM> and the setback member <NUM> such that the clicker body <NUM> does not generate a tactile signal or clicking noise when injecting a set dose.

Rotation of the setback member <NUM>, as allowed during injection, is then transferred to the lead screw <NUM>, which is rotatably fixed to the setback member <NUM> via a key groove connection provided between the lead screw <NUM> and the setback member <NUM>. As shown in <FIG>, an internal surface <NUM> of the setback member <NUM> includes a groove or slot <NUM> that is engaged with a key <NUM> provided at the proximal end of the lead screw <NUM>, as shown in <FIG>. The setback member <NUM> preferably includes two oppositely disposed slots <NUM> for engaging two oppositely disposed keys <NUM> provided on the lead screw <NUM>. The setback member <NUM> moves axially relative to the lead screw <NUM> during dose setting and dose correcting, via the key <NUM> and slot <NUM> interconnection (substantially similar to <FIG>). The length of the slot <NUM> in the setback member <NUM> may be configured to correspond to a maximum dose to be injected in a single injection. The lead screw <NUM> is axially fixed with respect to the pen upper body <NUM> via a snap engagement described above with the brake tower <NUM>, which is axially and rotatably fixed to the pen upper body <NUM> as described further below. As shown in <FIG>, the lead screw <NUM> includes the inwardly disposed flange <NUM> that is received by the recess <NUM> in the brake tower core <NUM>. The flange <NUM> of the brake tower core <NUM> is received by the inwardly extending lip <NUM> of the brake tower <NUM>, thereby axially locking the lead screw <NUM> to the brake tower <NUM> and the pen upper body <NUM>.

As described above, the lead screw <NUM> includes a plurality of threads <NUM> at its distal end that are in threaded engagement with the internal threads <NUM> preferably provided along the entire length of the hollow piston rod <NUM>, as shown in <FIG> and <FIG>. The piston rod <NUM> is held non-rotatable with respect to the pen upper body <NUM> due to the engagement between the piston rod key <NUM> and the outer edges <NUM> and <NUM> of the brake tower core <NUM>, as shown in <FIG>. The piston rod key <NUM> is guided in its axial movement by the axially extending outer edges <NUM> and <NUM> of the brake tower core <NUM>, thereby preventing relative rotation therebetween while permitting the piston rod <NUM> to move axially with respect thereto. As the setback member <NUM> does not rotate during dose setting and correcting, the lead screw <NUM> does not rotate during dose setting and correcting, which prevents movement of the piston rod <NUM> during dose setting and correcting. Accordingly, rotation of the lead screw <NUM> during injection of a dose causes the threads <NUM> of the lead screw <NUM> to engage the threads <NUM> of the piston rod <NUM>, thereby axially moving the piston rod <NUM>.

During assembly, the brake tower <NUM> is inserted into the pen upper body <NUM> from the distal end. As shown in <FIG> and <FIG>, the pen upper body <NUM> includes a transverse wall <NUM> that limits the movement of the brake tower <NUM> into the body <NUM> by blocking an enlarged distal portion <NUM> of the brake tower <NUM>. Further, an inwardly protruding key <NUM> is also provided distally from the transverse wall <NUM> on an internal surface <NUM> of the pen upper body <NUM>, as shown in <FIG>. The key <NUM> engages with a slot <NUM> provided on the enlarged distal portion <NUM> of the brake tower <NUM>, as shown in <FIG> and <FIG>, to rotationally fix the brake tower <NUM> with respect to the pen upper body <NUM>. Preferably, a plurality of axially extending keys <NUM> are disposed on the inner surface of the pen upper body <NUM> to engage a plurality of slots <NUM> on the enlarged distal portion <NUM> of the brake tower <NUM>.

Because the piston rod <NUM> is non-rotatable with respect to the body <NUM>, as the lead screw <NUM> is caused to rotate during injection, as described above due to its rotational coupling with setback member <NUM>, the piston rod <NUM> through its threaded engagement with lead screw <NUM> is caused to move in the distal direction such that a piston rod flange <NUM> presses against the stopper <NUM> provided in the medicament cartridge <NUM>, thus expelling a liquid medication therefrom. The piston rod <NUM> is prevented from moving in the proximal direction because the lead screw <NUM> is rotatable in only a single direction (that which results in distal movement of the piston rod <NUM>) due to the one-way ratchet between the setback member <NUM> and the brake tower <NUM>. A mechanical advantage is preferably provided such that the dose set knob <NUM> moves further in the axial direction than the piston rod <NUM> during the injection, reducing the injection force that must be applied by the user. This is preferably accomplished by providing different pitches for the threaded connection between the dose set knob <NUM> and the pen upper body <NUM> and the threaded connection between the lead screw <NUM> and the piston rod <NUM>. The ratio between the thread pitches can vary depending on the liquid medication and the expected dose volumes. For example, the pitch ratio can be <NUM>:<NUM> or <NUM>:<NUM>, but is not limited thereto. Thus, accurate dosing can be ensured because the piston rod <NUM> maintains its engagement with the stopper <NUM> between injections.

A dose stop member <NUM>, as shown in <FIG>, is provided for last dose management, to prevent the setting of a dose that is larger than the remaining amount of medication in the cartridge <NUM>. The dose stop member <NUM> is axially slidable but rotationally fixed with respect to the setback member <NUM> by being positioned between a pair of splines <NUM> provided on the outer surface of the setback member <NUM>. The dose stop member <NUM> is a half-nut like element (<FIG>) that is threaded on its outer surface with a plurality of threads <NUM>. These threads <NUM> are configured to engage with corresponding threads <NUM> provided on the interior of the dose set knob <NUM>, as shown in <FIG>. During dose setting, as the dose set knob <NUM> rotates relative to the setback member <NUM>, and therefore also relative to the dose stop member <NUM>, the dose stop member <NUM> is caused to slide in the distal direction by a distance corresponding to the set dose due to its engagement with the threads <NUM> in the dose set knob <NUM>.

During injection, because the setback member <NUM> and the dose set knob <NUM> are rotationally coupled as discussed above, the dose stop member <NUM> will maintain its position relative to the threads <NUM> of the dose set knob <NUM>. The dose stop member <NUM> will move in the distal direction during dose setting until a distal edge <NUM> of the dose stop member <NUM> abuts an inwardly directed key <NUM> provided on the internal surface of the dose set knob <NUM>, as shown in <FIG>. In this position, the dose stop member <NUM> is prevented from further movement in the distal direction which also prevents further rotation of the dose set knob <NUM> to set an additional dose.

<FIG> illustrate an eighth exemplary embodiment of an injection pen with similar functionality to the injection pen of the seventh exemplary embodiments shown in <FIG> and <FIG>. The exemplary embodiment depicted in <FIG> includes a modified clicker body <NUM> that replaces the clicker body <NUM> of <FIG> and <FIG>. The remaining components and functions of the injection pen are substantially similar to the injection pen <NUM>.

The clicker body <NUM> is substantially ring-shaped having an upper set of teeth <NUM> and a lower set of teeth <NUM>, as shown in <FIG>. Preferably, the upper teeth <NUM> have a slope that is opposite that of the lower teeth <NUM>. Preferably, the sloped surfaces of the upper teeth <NUM> and the lower teeth <NUM> form an angle of approximately <NUM> degrees. As shown in <FIG> and <FIG>, the clicker body <NUM> is disposed between an annular shoulder <NUM> of the dose set knob <NUM> and an enlarged portion <NUM> of the setback member <NUM>. A plurality of teeth <NUM> extend axially in the proximal direction from the shoulder <NUM> of the dose set knob <NUM>. A plurality of teeth <NUM> extend axially in the distal direction from the enlarged portion <NUM> of the setback member <NUM>. A bearing insert <NUM> is received in an annular groove <NUM> of the setback member <NUM>, as shown in <FIG>. A push button <NUM> has a projection <NUM> received by an opening <NUM> in the bearing insert <NUM>. A distal skirt <NUM> of the push button <NUM> is slidably received by a recess <NUM> adjacent a proximal end <NUM> of the dose set knob <NUM>.

The clicker body <NUM> facilitates generating a tactile signal or clicking noise during dose setting. The upper teeth <NUM> of the clicker body <NUM> are locked to the teeth <NUM> (<FIG>) of the dose set knob <NUM> such that the clicker body <NUM> rotates with the dose set knob <NUM> as the dose set knob <NUM> advances out of the pen upper body. The lower teeth <NUM> slide over the teeth <NUM> (<FIG>) of the setback member <NUM>. Accordingly, a tactile signal or clicking noise is generated to indicate to the user that a dose is being set.

The clicker body <NUM> also facilitates generating a tactile signal or clicking noise during dose correcting. The lower teeth <NUM> of the clicker body <NUM> are locked to the teeth <NUM> (<FIG>) of the setback member <NUM> such that the clicker body <NUM> is rotatably locked to the setback member <NUM>. Rotation of the dose set knob <NUM> as the dose set knob <NUM> is advanced back into pen upper body to correct the dose causes the teeth <NUM> (<FIG>) of the dose set knob <NUM> to slide over the lower teeth <NUM> of the clicker body <NUM>, thereby generating a tactile signal or clicking noise to indicate to the user that a dose is being corrected. Accordingly, the clicker body <NUM> facilitates generating a tactile signal or clicking noise during both dose setting and dose correcting.

Because the dose set knob <NUM> and the setback member <NUM> rotate together during an injection, the clicker body <NUM> does not rotate relative to either the dose set knob <NUM> or the setback member <NUM>. Accordingly, the clicker body <NUM> rotates with both the dose set knob <NUM> and the setback member <NUM> such that the clicker body <NUM> does not generate a tactile signal or clicking noise when injecting a set dose.

Claim 1:
A medication injection pen (<NUM>,<NUM>,<NUM>,<NUM>), comprising:
a housing (<NUM>);
a dose set knob (<NUM>) comprising at least one internal tooth (<NUM>);
a brake member (<NUM>) having a plurality of axially extending splines (<NUM>);
a driver (<NUM>) including at least one external tooth (<NUM>) for engaging said at least one internal tooth (<NUM>) of said dose set knob (<NUM>) and at least one ratchet arm (<NUM>) engaging said plurality of axially extending splines (<NUM>); and
a lead screw (<NUM>) rotatably fixed to said driver (<NUM>),
characterized in that
during dose setting via rotation of said dose set knob and dose correcting via rotation of said dose set knob to correct said set dose, said external tooth (<NUM>) of said driver (<NUM>) is rotationally disengaged from said internal tooth (<NUM>) of said dose set knob (<NUM>) and said ratchet arm (<NUM>) is engaged with said axially extending splines (<NUM>) of said brake member (<NUM>) to prevent said driver (<NUM>) from rotating with said dose set knob (<NUM>), and
during an injection said external tooth (<NUM>) of said driver (<NUM>) is rotationally engaged with said internal tooth (<NUM>) of said dose set knob (<NUM>) causing said ratchet arm (<NUM>) to slip from said axially extending splines (<NUM>) of said brake member (<NUM>) whereby said driver (<NUM>) is allowed to rotate with said dose set knob (<NUM>), and rotation of said driver (<NUM>) is then transferred to said lead screw (<NUM>) to axially move a piston rod (<NUM>).