Patent Description:
Injector pens are typically assembled from two main components. The first component is a cartridge housing that contains a drug cartridge, from which a desired dose of a drug may be expelled by driving forwards a piston located inside the cartridge. The cartridge housing also comprises an attachment for a hypodermic needle, through which the drug can be delivered from the cartridge to a subject. The cartridge may contain a single, measured dose of the drug but more commonly it contains a quantity sufficient to deliver multiple doses.

The second main component of the injector pen is a dose selector, contained in a dose selector housing, which is used in a first mode to select the desired dose of drug. In a second mode, the dose selector then delivers the drug to a patient by moving a piston rod through a distance that corresponds to the selected dose. The piston rod extends out of the dose selector housing and into the cartridge housing to engage the piston of the drug cartridge. Various mechanisms are known for selecting the dose, typically by withdrawing a dose delivery button along a linear or helical path, through an axial distance that measures the dose to be selected. The dose delivery button is then pushed forwards to return to its starting position, while a transmission mechanism converts the forward movement of the button into forward movement of the piston rod through a proportionate distance (sometimes with a simultaneous rotational movement of the piston rod). The details of the dose selection mechanism are not relevant to the present invention, which is applicable to all dose selectors of the general form described.

Some injector pens are designed so that when the supply of drug in the cartridge is exhausted a replacement cartridge can be fitted into the cartridge housing and the position of the piston rod can be reset to resume use of the pen. On the other hand, the present invention is most suitable for pens that are not reusable. The pen may be used to deliver single dose or multiple doses but when the cartridge is empty, or when less than a predetermined minimum dose remains, the pen is disposed of.

Patent application <CIT> discloses a reusable injector pen, in which an interface member is fixedly secured to the dose selector housing and provides an internal thread for removable attachment of the cartridge housing. The interface member also serves to retain a floating nut, which is threaded to the piston rod. When the cartridge housing is attached, it displaces the floating nut axially to engage a clutch and prevent rotation of the floating nut. When the cartridge housing is removed, a spring moves the floating nut axially in the other direction to disengage the clutch, which permits the piston rod to be reset for use with a full replacement cartridge.

There are various reasons why it may be undesirable to insert the drug cartridge into the injector pen when the pen is initially manufactured. Such pens are typically manufactured by a medical equipment company then supplied to a drugs company for onward distribution, and it is more efficient for the drugs company to provide and fit the drug cartridge. Alternatively, the unfilled pens and the drug cartridges can be supplied separately, for final assembly by a third party such as a drug distributor or a health service. Separating initial manufacture from final assembly in this way allows a single model of pen to be used for multiple types of drug, which simplifies both the inventory and supply chain functions. Also, certain drugs have a limited shelf-life or have particular storage requirements such as a need for refrigeration, so it is beneficial to allow the unfilled pens to be distributed and stored without being subject to such limitations. Consistently with this distribution model, it is desirable that the pens following their initial manufacture should be in a condition suitable for safe transport and storage, leaving the steps of inserting the drug cartridge and final assembly of the pens to be as simple and reliable as possible.

The invention provides a sub-assembly for an injector pen as defined in claim <NUM>.

It will be understood that the initial manufacture (claim <NUM>) and the final assembly (claim <NUM>) need not take place in the same location or the same legal jurisdiction.

In this specification, the term "distal" refers to the end of the pen at which the hypodermic needle is attached, while the term "proximal" refers to the end of the pen where the dose delivery button is located. "Forwards" refers to the direction towards the distal end of the pen. If two elements are "releasably engaged" or one is "releasably retained" in the other, then the elements are at least temporarily held together to prevent them being accidentally separated during normal use, transport or storage of the article of which they form part. However, they are designed to be separated easily when it is desired to do so, for example by applying a certain level of force or by manipulating the elements in a specific way. In contrast, if two elements are "securely engaged", then they are designed to be permanently attached to one another. The permanence of the attachment may be, among other reasons, because attempting to separate the elements would risk damaging them or because the connecting parts of the respective elements cannot be easily accessed in order to release the engagement between them.

<FIG> illustrates, in longitudinal section, an assembled injector pen according to the invention. At the distal end of the pen is a cartridge housing <NUM>, which contains a drug cartridge <NUM>. A piston <NUM> is located inside the cartridge <NUM> and can be urged forwards to displace a dose of a drug from the cartridge <NUM>. The cartridge housing <NUM> comprises a thread <NUM> or other suitable means for attaching a hypodermic needle (not shown), through which the dose of drug can be delivered into the skin of a patient or other subj ect.

At the proximal end of the injector pen is a dose selector housing <NUM>. The dose selector housing <NUM> contains a dose selector <NUM>, which is used to set and then deliver doses of the drug from the pen. The dose selector <NUM> is withdrawn in the proximal direction through a distance that determines the dose to be set. As seen in <FIG>, in the illustrated embodiment of the invention the dose selector housing <NUM> has an internal thread <NUM> to guide the movement of the dose selector <NUM> along a helical path. However, that is not essential: in other embodiments (not illustrated) the dose selector <NUM> moves along a straight, axial path. After the desired dose has been set, a dose delivery button <NUM> on the proximal end of the pen is pushed forwards to return the dose selector <NUM> to its starting position, while an internal gearing mechanism <NUM> converts the axial movement of the dose selector <NUM> into a proportionate - though not necessarily equal - degree of axial movement of a piston rod <NUM>. The details of the transmission <NUM> differ between types of pen and are not relevant to the present invention so they will not be described further.

The piston rod <NUM> protrudes from the distal end of the dose selector housing <NUM> and extends into the cartridge housing <NUM>. A distal end of the piston rod <NUM> engages the piston <NUM> so that forward movement of the piston rod <NUM> through the distance determined by the dose selector <NUM> displaces the desired dose of drug from the drug cartridge <NUM>.

A nut <NUM> is located between the cartridge housing <NUM> and the dose selector housing <NUM> and serves to couple the two housings <NUM>,<NUM> together, as described below. The nut <NUM> also guides the piston rod <NUM> as it emerges from the dose selector housing <NUM>. In the illustrated embodiment of the invention, the nut <NUM> has a threaded engagement with the piston rod <NUM> but that is not essential; in other embodiments (not illustrated) the piston rod <NUM> is in sliding engagement with the nut <NUM>. If the cartridge <NUM> contains multiple doses, the dose selector <NUM> may be operated through multiple cycles of forward and backward movement but a ratchet mechanism <NUM> acting between the nut <NUM> and the transmission mechanism <NUM> ensures that the piston rod <NUM> can only move forwards.

In the perspective view of <FIG>, the dose selector housing <NUM> has been omitted in order to show the relationship between the nut <NUM> and the cartridge housing <NUM> more clearly. It may be seen that the nut <NUM> generally cup-shaped, being open at its distal end to receive the proximal end of the drug cartridge <NUM>. The distal end of the nut <NUM> terminates in two alignment arms <NUM> that extend in the distal direction towards the cartridge housing <NUM>. Similarly, the proximal end of an outer wall of the cartridge housing <NUM> terminates in two alignment arms <NUM> that extend in the proximal direction towards the nut <NUM>. The respective pairs of alignment arms <NUM>,<NUM> have complementary shapes so that they can interdigitate and fit together when the nut <NUM> and the cartridge housing <NUM> are brought into engagement. It will be understood that in other embodiments the number of alignment arms <NUM> on the nut <NUM> and the number of alignment arms <NUM> on the cartridge housing <NUM> could be greater than two, provided the respective numbers are equal. Each alignment arm <NUM> of the nut <NUM> carries a segment of an outwardly extending lip <NUM> at or near its distal end. The lip <NUM> thus extends discontinuously around the circumference of the nut <NUM>. Two channels <NUM> are formed in an outer wall of the nut <NUM> and extend axially from the base of the nut <NUM> along part of the length of the respective alignment arms <NUM>. In other embodiments (not illustrated) the number of axial channels <NUM> could be greater than two. There is typically, but not necessarily, one channel <NUM> formed in each alignment arm <NUM>.

Each alignment arm <NUM> of the cartridge housing <NUM> comprises a recess <NUM>. The recess could be blind but preferably, as illustrated, the recess <NUM> is formed as an aperture that pierces the alignment arm <NUM>. In each gap between adjacent alignment arms <NUM> of the nut <NUM> a clip <NUM> is formed, which snaps into the corresponding recess <NUM> when the nut <NUM> and the cartridge housing <NUM> are brought together and prevents them being pulled apart again, thereby securely engaging the nut <NUM> with the cartridge housing <NUM>. In alternative embodiments the nut <NUM> could comprise the recesses and the alignment arms <NUM> of the cartridge housing <NUM> could comprise the clips. Other alternative mechanisms for providing that the nut <NUM> and the cartridge housing <NUM> can be pushed axially together but not easily pulled apart again will be apparent to the reader.

As seen in <FIG>, the dose selector housing <NUM> comprises a cavity <NUM> with an opening in its distal end for receiving the nut <NUM>. The neck <NUM> of the cavity <NUM> has a thicker wall than the main body of the dose selector housing <NUM> to constrict the opening. An annular indent <NUM> is formed within the thickened wall of the neck <NUM>. A pair of opposite, axially extending ribs <NUM> project inwards into the cavity <NUM>. The axial ribs <NUM> of the dose selector housing <NUM> correspond in number and position to the axial channels <NUM> of the nut <NUM>.

<FIG> and <FIG> show the sequence of steps by which the dose selector housing <NUM>, the nut <NUM> and the cartridge housing <NUM> are assembled to form an injector pen. Only the region around the nut <NUM> is shown in these figures; it should be understood that the dose selector housing <NUM> extends below the curved line at the bottom of each figure and that the cartridge housing <NUM> extends above the curved line at the top of <FIG>, <FIG>. The dose selector housing <NUM> is cut away on a plane along the axis to show the relationship between the various components. For clarity, the piston rod <NUM> and the cartridge <NUM> are not shown in these figures.

<FIG> shows the nut <NUM> when it is initially inserted into the opening of the cavity <NUM> in the distal end of the dose selector housing <NUM>. The piston rod <NUM> (not shown) has previously been threaded through the nut. The nut <NUM> is oriented so that its axial channels <NUM> are aligned with the axial ribs <NUM> of the dose selector housing <NUM>. The lip <NUM> of the nut <NUM> rests at the mouth of the cavity <NUM>.

<FIG> shows the nut <NUM> after the initial assembly step, when it adopts an intermediate axial position in the dose selector housing <NUM>. A jig (not shown) pushes the nut <NUM> to slide in the proximal direction from the initial position of <FIG>, the movement being guided by the axial channels <NUM> of the nut <NUM> following the axial ribs <NUM> of the dose selector housing <NUM>. The nut alignment arms <NUM> flex inwards to allow the lip <NUM> to pass through the constricted neck <NUM> of the cavity <NUM>. When the lip <NUM> reaches the annular indent <NUM> in the neck <NUM>, the resilient alignment arms <NUM> spring back outwards so that the lip <NUM> lodges in the indent <NUM>. When the jig is withdrawn, the nut <NUM> is releasably retained in the dose selector housing <NUM> to form a sub-assembly that is robust enough to be transported to another location for final assembly, while maintaining the relative positions of the various components. (Note that the sub-assembly preferably also includes the dose selector mechanism <NUM> and the piston rod <NUM> not shown in <FIG>.

<FIG> and <FIG> illustrate the first step in the final assembly of the injector pen, which involves fitting the drug cartridge <NUM> and cartridge housing <NUM> to the previously manufactured sub-assembly. The view in <FIG> corresponds to <FIG>, while the view in <FIG> is rotated through <NUM>°. The pre-filled drug cartridge <NUM> is first inserted into the cartridge housing <NUM> but for clarity it is not shown in these figures.

First the sub-assembly comprising the dose selector housing <NUM> and the nut <NUM> is firmly mounted then, using a second jig, the proximal end of the cartridge housing <NUM> is inserted into the cavity <NUM> in the distal end of the dose selector housing <NUM>. The cartridge housing <NUM> is oriented such that the cartridge housing alignment arms <NUM> enter the gaps between the nut alignment arms <NUM> and interdigitate with them. Insertion of the cartridge housing <NUM> continues, being guided by the mutually engaging alignment arms <NUM>,<NUM> until an end surface <NUM> of the cartridge housing <NUM> abuts the ends of the nut alignment arms <NUM>. In the illustrated embodiment, the interdigitating alignment arms <NUM>,<NUM> combine to form a substantially complete cylinder, which encloses the proximal end of the drug cartridge <NUM> and the distal end of the piston rod <NUM> (not shown). The clips <NUM> on the nut <NUM> snap into the recesses <NUM> of the cartridge housing <NUM> to engage the respective parts securely together. The nut <NUM> remains lodged in the intermediate axial position, with its lip <NUM> releasably retained by the annular indent <NUM>. A protrusion, such as an annular bead <NUM>, faces outwardly from an external surface of the cartridge housing and rests against the mouth of the cavity <NUM>.

<FIG> and <FIG> illustrate the final step in the assembly of the injector pen. The views are the same as <FIG> and <FIG> respectively.

The second jig (not shown) now pushes the cartridge housing <NUM> and the nut <NUM> in the proximal direction, further into the dose selector housing <NUM>. The sliding movement is guided by the axial channels <NUM> of the nut <NUM> continuing to follow the axial ribs <NUM> of the dose selector housing <NUM>. The jig is strong enough to force the lip <NUM> of the nut <NUM> out of the annular indent <NUM>, even though the nut alignment arms <NUM> are no longer able to flex inwards. The jig is also strong enough to force the annular bead <NUM> of the cartridge housing <NUM> through the constricted neck <NUM> of the dose selector housing <NUM> until the bead reaches the annular indent <NUM>. The cartridge housing <NUM> and nut <NUM> are now in their final axial position, as seen in <FIG> and <FIG>, and the jig can be withdrawn. Engagement of the annular bead <NUM> in the annular indent <NUM> resists the cartridge housing <NUM> being pulled back out of the dose selector housing <NUM> during subsequent use of the pen. As previously noted, in the illustrated embodiment the piston rod <NUM> has a threaded engagement with the nut <NUM>. When the pen has been primed for first use, the piston rod <NUM> thereafter exerts a pull on the nut <NUM> in the proximal direction, which in turn pulls the clips <NUM> tight within the recesses <NUM> of the cartridge housing <NUM>.

Claim 1:
A sub-assembly for an injector pen, comprising:
a dose selector housing (<NUM>), which comprises a distal end and a proximal end and which defines an axis from the distal end to the proximal end; and
a nut (<NUM>) for guiding a piston rod, whereby the nut comprises engagement means (<NUM>) for securely engaging a cartridge housing (<NUM>) when the sub-assembly is assembled into an injector pen;
wherein the distal end of the dose selector housing (<NUM>) defines an opening, through which the nut (<NUM>) can be inserted to move along the axis through an intermediate axial position in the dose selector housing (<NUM>) and reach a final axial position in the dose selector housing (<NUM>); and
characterized in that:
the nut (<NUM>) comprises an outwardly facing lip (<NUM>); and
the dose selector housing (<NUM>) comprises an inwardly facing indent (<NUM>);
whereby, when the nut (<NUM>) is in the intermediate axial position, the lip (<NUM>) of the nut (<NUM>) is releasably located in the indent (<NUM>) of the dose selector housing (<NUM>).