Medication delivery pen with variable increment dose scale

A medication delivery pen is provided having a pen body assembly and a cartridge assembly that are threadedly engageable with one another. The pen body assembly includes a rotatable driver for driving a cartridge plunger preselected distances that are in accordance with a desired dose of medication to be delivered. The driver providing different preset rates of injection.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The subject invention relates to medication delivery pens having a 
cartridge holder assembly and a pen body assembly removably mounted to the 
cartridge holder assembly for delivering medication having an improved 
dose setting device. 
2. Description of Related Art 
Hypodermic syringes are used to deliver selected doses of medication to 
patients. The prior art hypodermic syringe includes a syringe barrel 
having opposed proximal and distal ends. A cylindrical chamber wall 
extends between the ends and defines a fluid receiving chamber. The 
proximal end of the prior art syringe barrel is substantially open and 
receives a plunger in sliding fluid tight engagement. The distal end of 
the prior art syringe barrel includes a passage communicating with the 
chamber. A needle cannula is mounted to the distal end of the prior art 
syringe barrel, such that the lumen of the needle cannula communicates 
with the passage and the chamber of the syringe barrel. Movement of the 
plunger in a proximal direction draws fluid through the lumen of the 
needle cannula and into the chamber. Movement of the plunger in a 
proximal-to-distal direction urges fluid from the chamber and through the 
lumen of the needle cannula. 
Medication to be injected with the prior art hypodermic syringe often is 
stored in a vial having a pierceable elastomeric seal. Medication in the 
prior art vial is accessed by piercing the elastomeric seal with the 
needle cannula. A selected dose of the medication is drawn into the 
chamber of the syringe barrel by moving the plunger a selected distance in 
a proximal direction. The needle cannula is withdrawn from the vial, and 
the medication is injected into a patient by moving the plunger in a 
distal direction. 
Some medication, such as insulin is self-administered. The typical diabetes 
patient will require injections of insulin several times during the course 
of the day. The required dose of insulin will vary from patient to 
patient, and for each patient may vary during the course of the day and 
from day to day. Each diabetes patient will establish a regimen that is 
appropriate for his or her own medical condition and for his or her 
lifestyle. The regimen typically includes some combination of a slow or 
medium acting insulin and a faster acting insulin. Each of these regimens 
may require the diabetes patient to periodically self-administer insulin 
in public locations, such as places of employment or restaurants. The 
required manipulation of the standard prior art hypodermic syringe and 
vial can be inconvenient and embarrassing in these public environments. 
Medication delivery pens have been developed to facilitate the 
self-administration of medication. One prior art medication delivery pen 
includes a vial holder into which a vial of insulin or other medication 
may be received. The vial holder is an elongate generally tubular 
structure with proximal and distal ends. The distal end of the prior art 
vial holder includes mounting means for engaging a double-ended needle 
cannula. The proximal end also includes mounting means for engaging a 
driver and dose setting apparatus as explained further below. A disposable 
vial for use with the prior art vial holder includes a distal end having a 
pierceable elastomeric seal that can be pierced by one end of a 
double-ended needle cannula. The proximal end of this prior art vial 
includes a plunger slidably disposed in fluid tight engagement with the 
cylindrical wall of the vial. This prior art medication delivery pen is 
used by inserting the vial of medication into the vial holder. A prior art 
pen body then is connected to the proximal end of the vial holder. The pen 
body includes a dose setting apparatus for designating a dose of 
medication to be delivered by the pen and a driving apparatus for urging 
the plunger of the vial distally for a distance corresponding to the 
selected dose. 
The user of the pen mounts a prior art double-ended needle cannula to the 
distal end of the vial holder such that the proximal point of the needle 
cannula pierces the elastomeric seal on the vial. The patient then selects 
a dose and operates the pen to urge the plunger distally to deliver the 
selected dose. The dose selecting apparatus returns to zero upon injection 
of the selected dose with this prior art medication delivery pen. The 
patient then removes and discards the needle cannula, and keeps the prior 
art medication delivery pen in a convenient location for the next required 
medication administration. The medication in the vial will become 
exhausted after several such administrations of medication. The patient 
then separates the vial holder from the pen body. The empty vial may then 
be removed and discarded. A new vial can be inserted into the vial holder, 
and the vial holder and pen body can be reassembled and used as explained 
above. 
The above described medication delivery pen is effective and much more 
convenient for self-administration of medication than the typical 
hypodermic syringe and separate medication vial. However, prior art 
medication delivery pens are limited to a particular range of dosage 
amounts because of the fairly complex dosage selecting and driving 
mechanisms within the delivery pens. To vary the dosage amounts available 
to a user would require more complex devices that are costly to 
manufacture. Hence, it is necessary to provide a medication delivery pen 
at a reasonable cost having a wider range of doses and more flexibility 
when setting doses for drug delivery. 
SUMMARY OF THE INVENTION 
The subject invention relates to a medication delivery pen having a 
medication cartridge assembly that is selectively engageable with and 
disengageable from a pen body assembly. The medication cartridge assembly 
is an elongate generally cylindrical structure having opposed proximal and 
distal ends. The distal end of the medication cartridge assembly includes 
needle mounting means for securely but releasably receiving a needle 
cannula assembly, the distal end being characterized by a pierceable 
elastomeric seal that may be repeatedly and resealable pierced by the 
proximal end of a double-ended needle cannula. The proximal end of the 
medication cartridge assembly includes body mounting means for securely 
but releasably mounting the medication cartridge assembly to the pen body 
assembly. The body mounting means may comprise an array of threads 
extending distally from the proximal end of the medication cartridge 
assembly. 
The medication cartridge assembly further includes plunger means slidably 
disposed in fluid tight engagement therein. The plunger means may 
initially be disposed in a proximal position within the medication 
cartridge assembly and may be moved in a distal direction by a driver 
projecting from the pen body assembly. The medication cartridge assembly 
further comprises anti-rotation means for preventing rotation of the 
driver. 
The pen body assembly of the subject invention comprises an array of 
mounting threads to enable threaded engagement of the pen body assembly 
and the medication cartridge assembly and an actuator button rotatably 
mounted on its proximal end. Thus, axial forces exerted on the actuator 
button cause the pen body assembly to threadedly engage the medication 
cartridge assembly. 
The pen body assembly further includes a lead screw for selectively 
engaging the plunger of the cartridge assembly and for urging the plunger 
of the cartridge assembly in a distal direction. At least a portion of the 
lead screw includes driving threads engaged with other portions of the pen 
body assembly that may be operative to achieve axial movement of the lead 
screw in response to axial forces exerted on the rotatable actuator 
button. The pen body assembly further comprises dose setting means for 
establishing and precisely controlling the amount of medication to be 
delivered in response to each actuation of the actuator button. The dose 
setting means may be any of several structures as described in greater 
detail below. 
A cartridge assembly that is filed with medication is mounted to the pen 
body assembly and the initial response to forces on the actuator button 
cause the lead screw to move in a proximal direction toward its starting 
position, while the remaining portions of the pen body assembly move 
distally toward the vial assembly. Further forces exerted on the actuator 
button cause the mounting means of the pen body to engage the mounting 
means of the cartridge assembly. Continued axial forces on the actuator 
button cause the mounting threads to engage the cartridge assembly and 
continue the proximal movement of the driver. The pen body assembly is 
fully but releasably engaged with the cartridge assembly at the same time 
that the driver is at its proximal extreme position and is then in 
position to begin delivering selected doses of medication from the pen. 
Doses of medication can be dispensed as needed over time, and the 
cartridge assembly is removed and discarded when the medication therein 
has been exhausted. A new medication cartridge assembly may then be 
mounted to the pen body assembly as described above. 
The driving means in the pen body assembly of the present invention 
includes a dose setting knob having a helical groove with three different 
regions of operation, each region having a different pitch to provide 
three different types of dosage increments. For example, the dose setting 
increments in the first region are 0.5 within a dose range of 0 to 10 
units, 1.0 in the 10 to 30 unit range of the second region, and 2.0 for 
doses above 30 units in the third region. This approach to dose setting 
and the associated resolution (ability to select a particular dose) is 
believed to be more consistent with the way insulin doses are prescribed 
by physicians and the way patients are instructed to adjust their own 
insulin dose,

DETAILED DESCRIPTION 
A medication delivery pen in accordance with the subject invention is 
identified generally by the numeral 10 in FIG. 1. Medication delivery pen 
10 includes a pen body assembly 12, a cartridge assembly 14, a needle 
cannula assembly 16 and a cap 17. Cartridge assembly 14 includes opposed 
proximal and distal ends 18 and 20, respectively. Proximal end 18 of 
cartridge assembly 14 is dimensioned and configured to threadedly engage 
pen body assembly 12, as explained further herein. Distal end 20 of 
cartridge assembly 14 is configured to securely but releasably engage 
needle cannula assembly 16 and a shield 130 is provided to cover a distal 
end 126 of a needle cannula 122 in needle cannula assembly 16. 
The preferred embodiment of pen body assembly 12 is illustrated in greater 
detail in FIG. 2. It is understood, however, that variations from this 
preferred embodiment is provided, and are considered to be within the 
scope of the subject invention. Pen body assembly 12 includes a generally 
cylindrical housing 22 having opposed proximal and distal ends 24 and 26, 
and a substantially hollow throughbore 28 extending axially therethrough. 
An array of external threads 30 extends proximally from distal end 26 for 
threaded engagement with proximal end 18 of cartridge holder assembly 14. 
Portions of hollow throughbore 28 of housing 22 adjacent distal end 26 are 
characterized by an array of clutch teeth (not shown) molded therein. 
Proximal end 24 of housing 22 is characterized by a cut-out 33 formed 
therein for receiving a window insert 78. 
Pen body assembly 12 includes a nut 34 having opposed proximal and distal 
ends 36 and 38, respectively. Exterior surface regions of nut 34 between 
proximal and distal ends 36 and 38 define a plurality of longitudinally 
extending splines 39. Proximal end 36 of nut 34 also includes a plurality 
of longitudinally extending resilient fingers 40 with enlarged ends that 
enable snap engagement of nut 34 into other portions of pen body assembly 
12, as explained further herein. Distal end 38 of nut 34 is radially 
enlarged to limit axial movement of nut 34 in distal end 26 of housing 22. 
Thus, nut 34 is axially constrained within housing 22, however, the 
dimensions and configurations of nut 34 and housing 22 permit free 
relative rotation therebetween. 
Pen body assembly 12 includes a clutch assembly 42 mounted therein. Clutch 
assembly 42 includes a proximal clutch 44, a distal clutch 46 and an 
annular spring 48 biasingly engaged therebetween. Proximal and distal 
clutches 44 and 46 each are configured for non-rotatable engagement over 
splines 39 of nut 34. Distal clutch 46 includes an army of distally facing 
saw teeth dimensioned, disposed and configured for engagement with clutch 
teeth (not shown) on the interior distal end of housing 22, such that 
distal clutch 46 can rotate only in one direction relative to housing 22. 
Proximal clutch 44 includes an army of proximally facing teeth which are 
also configured for unidirectional rotation, as explained further herein. 
Pen body assembly 12 includes a generally cylindrical driver 50 having 
opposed proximal and distal ends 52 and 54. Driver 50 is slidably inserted 
into housing 22 of pen body assembly 12 such that distal end 54 of driver 
50 is snap fit over the enlarged ends of resilient fingers 40 at proximal 
end 36 of nut 34. This snap fit engagement prevents axial movement between 
nut 34 and driver 50, but permits free relative rotational movement within 
housing 22. Distal end 54 of driver 50 is also characterized by an army of 
saw teeth 49 that engage with the saw teeth on proximal clutch 44. Outer 
surface regions of driver 50 are characterized by splines 56 extending 
radially outwardly thereon and along a substantial portion of the length 
of driver 50. 
Pen body assembly 12 includes a dose knob 58 which is a hollow generally 
cylindrical structure having opposed proximal and distal ends 60 and 62 
and opposed inner and outer surfaces 64 and 66. Inner surface 64 is 
characterized by longitudinally extending grooves 68 which are disposed 
and dimensioned for engagement with splines 56 on driver 50. More 
particularly, dose knob 58 is spline mounted over driver 50 within housing 
22 of pen body assembly 12. Thus, axially extending grooves 68 in dose 
knob 58 engage splines 56 of driver 50 to prevent relative rotation 
therebetween, but permitting relative axial movement. 
FIGS. 3-5 are side views of the periphery of dose setting knob 58 projected 
on a plane and show button 86 operating in a first, second and third 
region, respectively. As shown in FIGS. 3-5, outer surface 66 of dose knob 
58 is characterized by a groove 70 comprised of three regions, each region 
having a helical component 174, 184, 194. Each helical component has a 
different pitch to provide different dose increments in each region of 
dose setting knob 58 and thereby improve resolution and provide a greater 
range of potential dosage settings for the pen. Outer surface 66 adjacent 
each helical component 174, 184, 194 of groove 70 is provided with dosage 
indicia to define dose setting increments corresponding to each region of 
groove 70. For example, the dose setting increments are 0.5 in the dose 
range 0 to 10 units of helical component 174, 1.0 in the 10 to 30 unit 
range of helical component 184, and 2.0 for doses above 30 units in 
helical component 194. The present invention provides dosage resolution 
very consistent with the way insulin doses are prescribed by physicians, 
and the way patients are instructed to adjust their own insulin dosages. 
Proximal end 60 of dose knob 58 is characterized by a gnarled exterior 
surface to facilitate manipulation for setting a selected dose. An 
actuator button 76 is snapped into engagement with proximal end 60 of dose 
knob 58 to pennit relative rotation therebetween. An insert 78 is snapped 
into engagement with cut-out 33 in proximal end 24 of housing 22, insert 
78 including opposed inner and outer surfaces 82 and 80 and a window 84 
extending therebetween. Inner surface 82 of insert 78 includes a 
projection 86, shown in FIGS. 3-5, on inner surface 82 dimensioned and 
disposed to engage in groove 70 of dose knob 58. Projection 86 and window 
84 are also disposed to enable the indicia on dose knob 58 to be visible 
through window 84. 
Pen body assembly 12 further includes a lead screw 88 with opposed proximal 
and distal ends 90 and 92 and an array of external threads 94. External 
threads 94 are characterized, however, by a pair of opposed axially 
extending grooves 96 which extend from distal end 92 substantially to the 
proximal end 90. Threads 94 are engaged in nut 34, such that proximal end 
90 of lead screw 88 is within housing 22 and distal end 92 projects 
distally beyond housing 22. Threads 94 on lead screw 88 have exactly the 
same pitch and the same hand as threads 30 on distal end 26 of housing 22. 
Pen body assembly 12 is assembled by placing nut 34 into housing 22 from 
distal end 26. Clutch assembly 42 then is mounted over splines 39 on nut 
34. Driver 50 is then inserted into proximal end 24 of housing 22, and is 
urged sufficiently in a distal direction for snap fit engagement with nut 
34. In this snapped engagement, the saw teeth of distal clutch 46 will be 
secured in engagement with the teeth in housing 22, and the saw teeth of 
proximal clutch 44 will be engaged with saw teeth 49 at distal end 54 of 
driver 50. Spring 48 will maintain constant selected pressure between 
these interengaged saw teeth. Insert 78 then is positioned over dose knob 
58 such that projection 86 of insert 78 is engaged in groove 70 in dose 
knob 58. The temporarily assembled insert 78 and dose knob 58 then are 
urged into housing 22. Lead screw 88 then is threaded into nut 34, and 
actuator button 76 is snapped into engagement with proximal end 60 of dose 
knob 58. 
The assembled pen body assembly 12 and cartridge assembly 14, shown in FIG. 
1, is stored until a selected dose of medication is required. Just prior 
to use, needle cannula assembly 16 is threadedly engaged to distal end 20 
of cartridge assembly 14. This threaded engagement will cause a proximal 
tip 124 of needle cannula 122 to pierce a pierceable eleslomeric seal 112 
on the medication cartridge and provide communication with medication 
therein. Shield 130 may then be removed. A desired dose of medication is 
set by rotating dose knob 58 until indicia corresponding to the desired 
dose appears in window 84 of insert 78. The engagement of projection 86 on 
insert 78 in helical portions 174, 184, 194 of groove 70 in dose knob 58 
causes a threaded retraction of dose knob 58 relative to housing 22 of pen 
body assembly 12. This threaded retraction of dose knob 58 will cause a 
simultaneous rotation of driver 50 splined thereto. However, nut 34 will 
not rotate because the saw teeth on distal clutch 46 and the saw teeth on 
interior portions of housing 22 are locked to prevent rotation in that 
direction. Proximal clutch 44 is splined to nut 34, and hence also will 
not turn. However, saw teeth 49 at distal end 54 of driver 50 are shaped 
to allow rotation relative to proximal clutch 44, and provide an audible 
click for each unit of medication in the selected dose. This is helpful 
for visually impaired patients who may be required to set doses and 
administer insulin or other medication to themselves. Annular spring 48 
contributes to the engagement that provides these audible clicking sounds. 
When the desired dose is set, injection is achieved by merely pushing on 
actuator button 76. This causes dose knob 58 to turn about helixes 174, 
184, 194 relative to pen body housing 22, so that driver 50 rotates 
through the same number of degrees. As dose knob 58 turns about helixes 
174, 184, 194, projection 86 travels through helix 174 in the first region 
when dispensing 1 to 10 units of medication, helix 184 in the second 
region when dispensing 11 to 30 units of medication, and helix 194 in the 
third region when dispensing 31 to 50 units of medication. Dose setting 
knob 58 of the present invention therefore provides a wider range of 
dosages for the user than previously known dose setting knobs because of 
the different pitch of each helix, as shown in FIGS. 3-5. Rotation of dose 
setting knob 58 is opposite to the rotation generated during the dose 
setting procedure, when the rotational freedom of clutch assembly 42 is 
reversed. As dose setting knob 58 tums during injection the previously 
clicking proximal clutch 44 is locked to and tums with driver 50. This 
driving movement of proximal clutch 44 causes a corresponding rotational 
movement of nut 34 because of the splined engagement therebetween. Distal 
clutch 46 is therefore free to rotate against the saw teeth in housing 22, 
and makes an audible clicking indication during injection of medication. 
Rotation of lead screw 88 is prevented by grooves 96 and tabs unitarily 
molded within cartridge holder assembly 14. Therefore, as nut 34 rotates 
under the driving action of proximal clutch 44 and driver 50, lead screw 
88 will be advanced axially into cartridge holder assembly 14. This axial 
advancement of lead screw 88 causes distal end 92 thereof to urge plunger 
118 distally into cartridge 108, and hence causes a particular amount of 
medication 110 to be injected through needle cannula 122 depending upon 
the dosage set using dose setting knob 58. Injection is terminated when 
proximal end 60 of dose knob 58 engages against proximal end 24 of pen 
body housing 22. 
Upon completion of the injection, needle cannula assembly 16 may be 
disengaged from cartridge holder assembly 14 and safely discarded. Cap 17 
may be mounted over cartridge holder assembly 14, and pen 10 may be stored 
or carried in a convenient location until the next dose of medication is 
required. A subsequent dose of medication will be set in exactly the 
manner as described above. However, for such a subsequent dose, lead screw 
88 will be in a partly advanced position as a starting point. Dose setting 
and injections can be carried out until all of the medication has been 
used. Cartridge holder assembly 14 may then be threadedly disengaged from 
pen body assembly 12, and slidably separated from lead screw 88. The 
separated cartridge holder assembly may then be discarded and replaced as 
described above. 
While the invention has been described with respect to a preferred 
embodiment, it is apparent that various changes can be made without 
departing from the scope of the invention as defined by the appended 
claims. In particular, the pen body assembly may have other driving and/or 
clutch mechanisms. Additionally, different means for preventing and/or 
enabling rotation during the dose setting and injection phases may be 
provided. Similarly, other means for mounting needle cannula to the 
cartridge assembly may be provided. These various optional constructions 
will be apparent to those skilled in the art after having read the subject 
disclosure.