HK1193778B - Dose counter for a metered-dose inhaler - Google Patents

Description

Dose counter for a metered-dose inhaler

The present application is a divisional application of an invention patent application entitled "dose counter for metered dose inhaler", international application date 28/7/2010, international application number PCT/EP2010/004792, national application number 201080040988.4.

Technical Field

The present invention relates to a dose counter adapted to be fitted in a metered-dose inhaler. The invention also relates to a metered-dose inhaler incorporating such a dose counter and a method for counting doses dispensed from a metered-dose inhaler.

Background

Metered dose inhalers include both pressurized metered dose inhalers (both manually operated and breath actuated) and dry powder inhalers. These metered-dose inhalers typically comprise a medicament-containing vessel and an actuator body having a medicament delivery outlet. The charge container may be a pressurised canister containing a mixture of active drug and propellant. Such pressurized cans are typically formed from deep drawn aluminum cups having a crimp band for carrying a metering valve assembly. The metering valve assembly is provided with a projecting valve stem which, in use, is inserted in a tight push fit into a so-called "stem post" in the body.

To actuate a conventional manually operated inhaler, the user applies pressure to the closed end of the canister. The internal components of the metering valve assembly are spring loaded, requiring a compressive force of about 15 to 30N to actuate the device. In response to the compressive force, the canister moves axially relative to the valve stem in an amount varying from about 2 to 4 millimeters. This degree of axial movement is sufficient to actuate the metering valve to expel a metered quantity of drug and propellant through the valve stem. The drug is then released into the mouthpiece through a nozzle in the stem. The user inhaling through the drug delivery outlet of the device will thus receive a dose of the drug.

The metered-dose inhalers described above administer a precise dose of medicament whenever required, which is particularly useful for users who experience sudden breathing difficulties. This is where these devices are currently used throughout the world.

A more recent development is the so-called breath-actuated metered dose inhaler which delivers a dose of medicament through a mouthpiece in response to the inspiratory action of a user. This arrangement is particularly convenient in situations where the user does not have good coordination between the inhalation and manual depression of the aerosol canister. For example, children sometimes lack the necessary coordination to achieve effective self-administration, while adult users may experience poor coordination when breathing is difficult.

One drawback of self-administration from an inhaler, whether manually operated or breath actuated, is that it is often difficult for a user to determine when the charge in the charge container is nearly exhausted, as the user is typically not able to see the contents of the drug reservoir. Part of the reason for this difficulty with aerosol canisters is that, even if the supply of medicament is nearly exhausted, there remains propellant in the canister. Otherwise a near-end condition may result in an excess of drug relative to propellant. Thus, the inhaler can still be provided with useful doses of medicament by simply filling the canister with liquid. This presents a potential hazard to the user as dosing becomes unreliable and few users carry spare devices on a daily basis. Many users have several different inhalers to treat various conditions. There are also users who place the inhaler in many different places, such as schools, homes, offices, etc. In these cases, it is particularly difficult for the user to grasp the dose drawn from each individual inhaler device.

WO98/28033 discloses a dose counter suitable for use with the metered dose inhaler described above. The dose counter enables a user to estimate how many doses remain in the opaque canister. Such counters can provide a warning when the inhaler is running low so that appropriate measures can be taken to avoid running out of medication. Furthermore, since the dose counter has a count resolution of one dose, it can be used for compliance monitoring, for surveillance in hospitals or for evaluation of compliance of children under their care by parents and teachers. In addition, there are regulatory requirements in many countries for metered-dose inhalers to have a dose counter.

Figures 1 to 3 of WO98/28033, again appearing herein, show the lower part of a metered-dose inhaler. The inhaler comprises a body 2 having a drug delivery outlet 4. An aerosol canister 6 extends into the lower portion of the main body 2. The aerosol can 6 is formed from a deep drawn aluminium can 8 to which is attached by crimping a collar 10.

The cap 10 carries a metering valve assembly having a projecting valve stem 12, the end of which is received in a close push-fit manner in a stem post 14 of the body 2. The stem 14 has a nozzle 16 in communication with the drug delivery outlet 4 such that upon actuation of the metering valve assembly, a dose of drug is ejected through the nozzle 16 into the drug delivery outlet 4. Actuation of the metering valve assembly is achieved by moving the aerosol canister 6 downwardly relative to the main body 2. This may be achieved by the user applying manual pressure against the upturned bottom of the aerosol canister 6 (not shown) or by automatic depression of the aerosol canister 6 in response to inhalation by the user in a breath-actuated inhaler. This actuating mechanism does not form part of WO98/28033 or the present invention and will not be described in further detail. A user inhaling through the drug delivery outlet 4 when pressing the aerosol canister 6 will receive a metered dose of medicament.

Referring to these figures, the counter mechanism 18 comprises an actuator shaft 20 moulded from a plastics material (such as nylon) the actuator shaft 20 having a boss 22 integrally formed at its base. The underside of the boss 22 is formed with a blind bore which receives a compression spring 24 mounted on an upstanding latch member 26 formed on the lower element of the counter chassis.

A driver 28 for driving a turning gear in the form of a ratchet wheel 30 is integrally moulded with the boss 22 of the actuator shaft 20 and comprises a transverse hook-shaped element mounted between two arms (only one of which is visible in figure 2) the bases of which are connected together with the boss 22. The transverse hook is sized and oriented to engage ratchet teeth 32 formed around the periphery of the ratchet-gear 30 to rotate the ratchet-gear in a forward direction.

The ratchet gear 30 is integrally moulded with a first hollow shaft 34 which is rotatably supported on a first main shaft 36 which projects laterally from a chassis sub-element 38. The chassis sub-element 38 also has a second main shaft 40 extending transversely therefrom, on which a second hollow shaft 42 is rotatably supported. A flexible strip 44 is wound around the second hollow shaft 42, which serves as a supply reel, and leads to the first hollow shaft 34, which serves as a take-up reel (storage reel). A guide plate 46 forming part of the chassis sub-element 38 helps to guide the strip 44 in a smooth path from the supply spool to the take-up spool. The surface of the strip 44 is marked with successively decreasing numbers indicating the number of doses remaining in the aerosol canister. Typically, the starting count is 200, and subsequent marks on the strip are decremented one by one. The markings on the strip may be reduced by 2 for each two metered dispense to enable a greater number for more convenient viewing. The spacing between subsequent markings coincides with the indexing movement of the ratchet-toothed wheel 30 so that a new number appears in the window 48 provided in the body 2 for each subsequent actuation or for each double actuation.

The reverse rotation of the ratchet-gear 30 and the integrally formed first hollow shaft 34 is limited by a wrap spring clutch 50 which surrounds the hollow shaft 34 at the end thereof remote from the ratchet-gear 30. One end (not shown) of the wrap spring clutch 50 bears against the counter chassis. The windings of wrap spring clutch 50 are oriented such that rotation of first hollow shaft 34 in the forward direction is not impeded by the coils. However, reverse rotation of the hollow shaft 34 winds the coils so that the first hollow shaft 34 is caught by the inner surface of the wrap spring clutch 50 and thus cannot rotate in the reverse direction.

Fig. 3 shows more details of the main elements of the dose counter 18. It can be seen that the actuator 28 comprises a transverse hook 52 mounted between a pair of arms 54, 56 which are connected at their bases by a web. The web is connected to a projection 22 of the actuator shaft 20. The combined actuator and driver assembly may be integrally formed from a material such as a plastic material (e.g., nylon).

In use of the dose counter 18, depression of the canister 6 causes the collar 10 to engage with the actuator shaft 20, which actuator shaft 20 moves downwardly against the compression spring 24. The transverse hook 52 in turn engages the ratchet teeth 32 of the ratchet-toothed wheel 30 mounted on the hollow shaft 34 which serves as a take-up reel for the flexible strip display 44. At the end of the hollow shaft 34 remote from the ratchet-toothed wheel 30 is a clutch 50 which serves to prevent reverse rotation of the shaft 34 and thus reverse travel of the counter strip 44.

The control surface 58 is depicted in fig. 3 as a see-through element so that the operation of the dose counter can be seen more clearly. The control surface 58 extends parallel to the direction of travel of the actuator shaft 20 and is located adjacent the ratchet-toothed wheel 30 at a position that marks the projection of the chord onto one of the wheel faces. One of the support arms 56 of the actuator 28 is in sliding contact with a control surface 58. This sliding contact serves to inhibit the natural tendency of the driver 28 to flex radially inwardly toward the axis of rotation of the ratchet-gear 30. By preventing such radially inward flexing, the control surface 58 limits the engagement and disengagement of the driver 28 with the ratchet-toothed wheel 30, thereby limiting the distance that the ratchet-toothed wheel 30 can be rotated to one pitch. This is observed regardless of the linear travel range or stroke of the actuator shaft 20.

Fig. 4 shows a schematic diagram of an alternative arrangement of a ratchet gear and driver for use in the dose counter 18 described in WO 98/28033. This alternative arrangement employs a reciprocating driver 28 acting in a pushing manner to rotate a ratchet-toothed wheel 30 in the direction indicated by arrow 31. The fixed pawl 60 serves to prevent reverse rotation of the ratchet-toothed wheel 30 by engaging on the trailing edge 62 of the ratchet teeth 32. However, as the ratchet-gear 30 rotates forward in the direction of arrow 31, the fixed pawls 60 can deform radially outward under the urging of the front edges 63 of the ratchet teeth 32.

In this arrangement, if the ratchet-toothed wheel 30 rotates more than a single pitch but less than two pitches for each reciprocation of the driver 28, there is a degree of counter-rotation until the pawl 60 becomes engaged by the trailing edge 62 (opposite the leading edge 63) of the ratchet teeth 32. Thus, the rotation of the ratchet-toothed wheel 30 can be said to be "stepped".

The components of the metered-dose inhaler are manufactured to high specifications. However, inevitable variations in component tolerances may in some cases lead to errors in dose counters of the type disclosed in WO 98/28033. In the known error mode, the reciprocating stroke of the canister is insufficient to adequately increment the dose counter. This can result in a low count, especially where the rotation of the ratchet-toothed wheel is stepped as shown in fig. 4.

Another problem relates in particular to manually operated metered-dose inhalers. In such inhalers, the user cannot be relied upon to repeatedly actuate the inhaler with the full reciprocating stroke of the canister. Rather, the user will at some point release the canister immediately after the "start point" of the metering valve, i.e. the point at which the medicament is dispensed on-stroke. This reduced canister stroke, which can be used to increment the dose counter, can exacerbate the problems described above.

Thus, there is a need in the art for a dose counter with a lower error rate. There is a particular need for such a dose counter which can be manufactured efficiently and incorporated into known metered-dose inhalers.

Disclosure of Invention

According to a first aspect of the present invention there is provided a dose counter for counting doses of medicament dispensed from or remaining in a metered-dose inhaler, the dose counter comprising:

a rotatably mounted first gear having a circular arrangement of ratchet teeth;

a display member coupled to the first gear, the display member having a visible array of dose counting indicia indexable in response to rotation of the first gear; and

an actuator mechanism having a first drive pawl for engaging the ratchet teeth of the first gear in response to dispensing of a dose of medicament,

wherein the actuator mechanism further comprises a second drive pawl for engaging the ratchet teeth of a gear wheel connected to the display and wherein the actuator mechanism is configured such that when the dose counter is used for counting a dispensed dose, the first drive pawl engages and rotatably drives a first ratchet tooth of the first gear wheel and then the second drive pawl engages and rotatably drives a second ratchet tooth of the gear wheel connected to the display.

The counter of the present invention thus provides an actuator mechanism capable of sequentially driving the display member with a pair of drive pawls. In this way, the amount of travel of the gear in response to dispensing of medicament can be increased compared to conventional dose counters having a single drive pawl. Alternatively, the travel of the gear wheel may remain constant, but the movement required for the first driving pawl may be reduced.

The reduction in the required movement of the first drive pawl can be sufficient to reliably increment the dose counter even when the user releases the medicament canister immediately after the firing point, and even when there is a large degree of accumulated variation or tolerance stack-up in the components of the inhaler. Miscounting or non-counting of doses can thereby be avoided, which in turn significantly reduces the failure rate of the dose counter. It has been found that a dose counter of the type disclosed in WO98/28033 is particularly suitable for modification in accordance with the principles of the present invention.

In operating the dose counter, a small increase in actuation force is required compared to a dose counter of the type disclosed in WO 98/28033. For metered dose inhalers comprising a pressurised medicament canister, this increase in actuation force is still substantially insignificant compared to the force required to overcome the internal valve spring of the canister.

In an embodiment of the invention, the gear arranged for engagement by the second ratchet drive pawl may be the first gear or a different gear. In a most preferred embodiment, the gear arranged for engagement by the second driving pawl is the first gear, so that only one gear is required. In case the gears arranged for engagement by the second driving pawl are different gears, these gears may be mounted on opposite sides of the display member.

In a first set of embodiments, the gear arranged for engagement by the second driving pawl is a first gear, and the first and second driving pawls are defined by a single driving member. The drive member may be pivotally mounted such that only one of said first and second drive pawls is engaged with the ratchet teeth of the first gear wheel at any one time. In this way, the drive member can follow the rocking motion that the drive pawl sequentially drives the first gear. The driving member may for example have a "balance" shape, whereby the driving pawls may substantially face each other.

In these embodiments, the actuator mechanism may further comprise an actuator shaft mounted for linear reciprocating movement in response to dispensing of a dose of medicament. The drive member is then coupled to the actuator shaft such that forward and reverse travel of the actuator shaft causes the drive member to rotate in first and (different) second directions, respectively.

In a second set of embodiments, the gear arranged to be engaged by the second driving pawl may be the first gear or a different gear. The actuator mechanism further comprises an actuator shaft mounted for linear reciprocating movement in response to dispensing of a dose of medicament. The actuator shaft carries the first drive pawl, for example in a similar arrangement to that described above with reference to fig. 3. The first drive pawl is disposed between a pair of spaced apart support arms. The second driving pawl is a separate member that is mounted separately from the first driving pawl. A control surface is provided to accurately control the engagement point and the disengagement point between the first drive pawl and the first gear.

In these embodiments, the second drive pawl may be resiliently biased into contact with a ratchet tooth of a gear wheel arranged for engagement therewith, such that the pawl may be moved away from the gear wheel against the biasing force. In particular, the second drive pawl may be carried by a flexible arm. The second driving pawl may be configured with a biasing force sufficient for the second driving pawl to drive a gear arranged to mesh therewith.

In particular, the actuator mechanism may be configured such that, when the dose counter is used for counting a dispensed dose, the first drive pawl engages and rotatably drives the first ratchet tooth of the first gear wheel until the second drive pawl has passed the tip of a second ratchet tooth of the gear wheel arranged to engage therewith (during which the second drive pawl may move against its bias); the second pawl then engages and rotatably drives the second pawl of the gear (during or after which the first pawl may return to the starting position).

In the case where the gear arranged to be engaged by the second driving pawl is the first gear, the second driving pawl may need to be biased in a direction that does not pass through the rotational axis of the gear. In the case where the gear arranged to be engaged by the second driving pawl is a different (second) gear, the second driving pawl is biased in a direction that does not pass through the rotational axis of the gear. However, it will be appreciated that the direction of the biasing force is primarily dependent upon the particular geometry of the ratchet teeth of the second gear and the second drive pawl.

In any of the above sets of embodiments, the actuator shaft may be resiliently biased towards the starting position. The actuator shaft can then be moved against the resilient bias to actuate the dose counter. The bias may be provided by a compression spring arranged to press against the underside of the actuator shaft. The actuator shaft may be arranged to perform a downward stroke and an upward stroke, i.e. a reciprocating motion, in response to the dispensing of each dose of medicament. In this case, the dose counter may be actuated on the downward or upward stroke of the actuator shaft.

The second driving pawl may be arranged such that it prevents a reverse movement of the gear wheel. Alternatively, the dose counter may be provided with a separate means for preventing counter-rotation of the gear wheel, such as another pawl arranged to engage with the ratchet teeth of the gear wheel.

The display includes a flexible strip disposed between the index spool and the storage reel. The dose counting indicia of the display may include unique indicia for display after each dose is dispensed. The dose counting indicia may comprise at least 50 single dose counting indicia representing the number of doses dispensed by or remaining in the inhaler.

According to a second aspect of the present invention there is provided a metered-dose inhaler, such as a manual metered-dose inhaler, comprising:

a medicament canister;

an actuator body for receiving the canister and having a drug delivery outlet; and

the dose counter described above.

According to a third aspect of the present invention there is provided a method of counting doses of medicament dispensed from or remaining in a metered-dose inhaler, the dose counter comprising:

a rotatably mounted first gear having a circular arrangement of ratchet teeth;

a display member coupled to the first gear, the display member having a visible array of dose counting indicia indexable in response to rotation of the first gear; and

an actuator mechanism having a first drive pawl for engaging the ratchet teeth of the first gear wheel in response to dispensing of a dose of medicament and a second drive pawl for engaging the ratchet teeth of a gear wheel connected to the display, the method comprising:

a first ratchet tooth engaged with and rotatably driving the first gear with the first driving pawl; and is

A second ratchet tooth of the gear is engaged and rotatably driven with the second driving pawl.

A third aspect of the invention corresponds to the use of a dose counter or metered-dose inhaler as described above. Thus, the method may include employing any of the features of the dose counter described above.

Drawings

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

figures 1 to 4 are views of a dose counter for a metered-dose inhaler according to prior art document WO 98/28033;

fig. 5 is a perspective view of a first dose counter according to the present invention;

fig. 6 is a perspective view showing in greater detail the elements of the first dose counter shown in fig. 5;

fig. 7a to 7d are schematic views for explaining the operation of the first dose counter shown in fig. 5;

figures 8a to 8c are schematic views of the amount of medicament canister travel during actuation of three metered-dose inhalers;

FIG. 9 is a schematic side view of a second dose counter according to the present invention;

fig. 10a to 10e are schematic views for explaining the operation of the second dose counter shown in fig. 9; and is

Fig. 11 is a view of a metered-dose inhaler according to the present invention.

Detailed Description

The dose counter of the present invention is based on the dose counter shown in figures 1 to 4 described above, except that the actuator mechanism is modified. Accordingly, the present invention generally provides a dose counter comprising a rotatably mounted gear wheel having a circular arrangement of ratchet teeth and a display coupled to the gear wheel. The display member has an array of visible dose counting indicia which are indexable in response to rotation of the gear. The dose counter further comprises an actuator mechanism having a first drive pawl for engaging the ratchet teeth of the first gear wheel in response to dispensing of a dose of medicament.

According to the invention, the actuator mechanism further comprises a second driving pawl for engaging a ratchet tooth of a gear wheel connected to the display member. The actuator mechanism is configured such that, in use of the dose counter for counting dispensed doses, the first drive pawl engages and rotatably drives a first ratchet tooth of the first gear wheel, and then the second drive pawl engages and rotatably drives a second ratchet tooth of a gear wheel coupled to the display.

A first dose counter according to the present invention will now be described with reference to figures 5 to 7 d. The actuator mechanism 118 of the dose counter is shown schematically in figure 5, when the first gear is in the form of a ratchet-toothed wheel 30. The first counter display is substantially the same as that shown in fig. 1-3 and includes a flexible strip 44 disposed between the index spool 34 and the storage reel 42.

The ratchet-gear 30 has the same structure as the corresponding wheel 30 shown in fig. 1 to 4. Thus, a plurality of ratchet teeth 32 are arranged around the circumference of the wheel 30. The ratchet gear 30 is integrally molded with a hollow shaft 34 that serves as an indexing spool for the display. The hollow shaft 34 is rotatably supported on a spindle extending from the chassis of the dose counter.

The actuator mechanism 118 of the first dose counter according to the present invention is similar in many respects to the actuator mechanism shown in figures 1 to 4. The mechanism 118 thus includes an actuator shaft 20 mounted for reciprocating linear motion in a longitudinal direction. Like the shaft shown in fig. 1 and 2, the top part (not shown) of the actuator shaft 20 is arranged to be engaged by a medicament canister of a metered-dose inhaler for use with a dose counter. The actuator shaft 20 has a projection 22 integrally formed at the bottom thereof, and a blind hole for receiving a compression spring is formed at the lower portion thereof. The compression spring serves to bias the actuator shaft 20 into the upward (start) position as shown in fig. 5.

A driver in the form of a drive pawl 28 is integrally formed with the projection 22 of the actuator shaft 20 for driving the ratchet gear 30. The driver includes a first driving pawl 28 extending in the lateral direction and supported by a pair of arm portions. The first driving pawl 28 is sized and oriented to properly engage the ratchet teeth 32 of the ratchet-toothed wheel 30.

The actuator mechanism 118 of the first dose counter differs from that shown in figures 1 to 4 in that there is no fixed pawl to prevent reverse rotation of the ratchet-toothed wheel 30. Instead, the mechanism 118 is provided with a second driving pawl 132 arranged to mesh with the second gear wheel 130, as shown more clearly in fig. 6.

Like the ratchet gear 30, the second gear 130 is integrally molded with the hollow shaft 34 serving as an index spool of the display. The ratchet gear 30 and the second gear 130 are arranged at opposite ends of the hollow shaft 34 on either side of the flexible display strip 44, so that either wheel 130, 30 can be used to drive the display. In this embodiment, the second gear 130 has triangular teeth. It will be appreciated that the teeth on gear 130 may have various shapes that also facilitate rotation.

The second drive pawl 132 not only prevents the ratchet gear 30 (indirectly) and the second gear 130 from rotating in opposite directions, but is also configured to drive the second gear 130 (and thus the display member) in response to dispensing of a dose of medicament. Thus, second pawl 132 is sized and oriented to properly engage the teeth of second gear 130, and the engaging portion of second pawl 132 is wedge-shaped.

The second driving pawl 132 is provided with a resilient mounting portion to bias it into contact with the teeth of the second gear 130. The resilient mount comprises a flexible arm (not shown) which is mounted at its proximal end to the dose counter chassis and carries a second drive pawl 132 at its distal end. The resilient mounting portion is configured to bias the force in a direction substantially toward the axis of rotation of the second gear 130. The second driving pawl 132 may move away from the second gear 130 against the resilient bias.

It will be appreciated that the mounting portion of the second driving pawl 132 is completely independent of the mounting portion of the first driving pawl 28 described above.

The use of a first dose counter for counting doses dispensed from a metered-dose inhaler according to the present invention will now be described with reference to figures 7a to 7 d. Fig. 7a to 7d are schematic views showing the components shown in fig. 5 at different stages of the actuation cycle. The left hand side of each figure shows the ratchet-toothed wheel 30 and the first driving pawl 28. The right hand side of each figure shows the second gear 130 and the second drive pawl 132.

The user actuates the metered-dose inhaler by applying a manual compressive force to the closed end of the medicament canister (not shown). In response to this compressive force, the canister moves axially downward relative to its valve stem by an amount varying from about 2 to 4 millimeters. A displacement of approximately 2 mm is required to actuate the valve and dispense a dose of medicament. After the medicament has been dispensed, the user releases the compression force and the canister returns to its starting position under the action of the internal valve spring. The dose counter is driven by the reciprocating linear motion of the canister when a dose of medicament is dispensed.

Figure 7a shows the start position of the dose counter. In this position, the actuator shaft 20 is biased upwardly to its starting position. The first driving pawl 28 is disposed a small distance above one tooth of the ratchet-toothed wheel 30, and the second driving pawl 132 is disposed between two adjacent gear teeth of the second gear 130.

Downward movement of the medicament canister during dispensing of a dose of medicament causes the canister's collar to engage and linearly move downward with the actuator shaft 20. Movement of the actuator shaft 20 causes the first driving pawl 28 to move downwardly a small distance until the pawl 28 engages the teeth of the ratchet-toothed wheel 30. The ratchet gear 30 and the second gear 130 are rotatably driven by this meshing action by approximately half the angle required for reliable indexing of the dose counter, as shown in figure 7 b. Rotation of second gear 130 causes second drive pawl 132 to move away from second gear 130 against the resilient bias as the leading edge of pawl 132 slides along the first surface of the gear teeth. At the end of the downward stroke of the actuator shaft 20, the leading edge of the second drive pawl 132 passes just beyond the tip of the teeth of the second gear wheel 130 (the schematic of fig. 7b shows the second drive pawl 132 to be fixed, but in practice it will move to the right).

At this stage, the resilient mounting portion of the second drive pawl 132 urging the pawl 132 against the second face of the gear teeth of the second gear 130 is sufficient to drive the second gear 130 and (indirectly) the ratchet-toothed wheel 30 past the remaining angle required for reliable indexing of the dose counter. As shown in fig. 7c, the rotation of the second gear 130 is terminated when the leading edge of the second driving pawl 132 is located between two adjacent gear teeth of the gear 130. Thus, it can be said that the second driving pawl 132 provides a "stepped" rotation of the second gear 130 and the ratchet-toothed wheel 30.

Fig. 7d shows the configuration of the actuator mechanism 118 after the actuator shaft 20 has been allowed to return to its starting position. Basically, the actuator shaft 20 moves upward with the first driving pawl 28, and the first driving pawl 28 bends away from the ratchet gear 30 when moving upward.

By using two drive pawls 28, 132 to drive the display, the required linear displacement of the actuator shaft 20 can be reduced. This reduces the risk of miscounting, especially under counting, and in turn reduces the failure rate of the dose counter. The reduction of the required linear displacement of the actuator shaft 20 is particularly advantageous for manual metered dose inhalers, since the linear inlet stroke of such inhalers is as small as 1.5 mm when the medicament canister is released immediately after the actuation point of the valve has been reached.

As will be described with reference to fig. 8a to 8c, the reduction in the required stroke of the actuator shaft can also reduce the risk of miscounting due to cumulative tolerance stack-up and lost motion.

Fig. 8a is a graphical diagram illustrating the amount of travel 80 of a medicament canister of a first inhaler having a usable dose counter of the type shown in fig. 1-4. The first portion of travel 82 absorbs the accumulated tolerances and any lost motion of the manufactured components. The second portion 84 of the stroke amount is the amount of stroke required to increment the dose counter. The third portion 86 of the stroke amount is the "excess" stroke amount available with greater accumulated tolerance or lost motion.

Fig. 8b is a graphical diagram showing the amount of stroke 80 of a medicament canister of a second inhaler having a non-usable (malfunctioning) dose counter of the type shown in fig. 1-4. The total canister stroke amount 80 is the same as for the first inhaler shown in fig. 8 a. Also, the first portion 82 of the stroke amount absorbs the accumulated tolerances and any lost motion of the manufactured components. The accumulated tolerance and lost motion are significantly greater in the second inhaler than in the first inhaler, so that the first portion 82 of the stroke amount is correspondingly greater. The second portion 84 of the stroke amount, which is the same stroke required to increment the dose counter, is the same as for the first inhaler shown in figure 8 a. However, the amount of canister travel 80 left is not sufficient to increment the dose counter, which causes the dose counter to malfunction.

Figure 8c is a graphical diagram showing the amount of stroke 80 of a medicament canister of a third inhaler having a dose counter according to the invention shown in figure 5. The total canister stroke 80 is the same as for the first and second inhalers shown in fig. 8a and 8 b. Also, the first portion 82 of the stroke amount absorbs the accumulated tolerances and any lost motion of the manufactured components. The accumulated tolerances and lost motion are the same as those of the second inhaler, which results in failure of the dose counter of the second inhaler. The second portion 84 of the stroke amount is the amount of stroke required to increment the dose counter. The second portion 84 of the stroke amount is significantly smaller than the corresponding formation amounts of the first and second inhalers shown in fig. 8a and 8b, because the second portion 84 of the stroke amount is reduced due to the action of the second drive pawl. Thus, the remaining canister stroke 80 is sufficient to increment the dose counter and the dose counter will not malfunction. The third portion 86 of the stroke amount is the "excess" stroke amount available with greater accumulated tolerance or lost motion.

Thus, it can be seen that the action of the second drive pawl of the present invention results in reduced failure due to excessive accumulated tolerances and lost motion.

A second drive pawl provided in accordance with the principles of the present invention will result in a slight increase in the force required to depress the medicament canister. However, the force required to operate the dose counter is still generally small compared to the force required to overcome the internal valve spring of the medicament canister.

A second dose counter according to the present invention will now be described with reference to figures 9 to 10 e. The actuator mechanism 218 of the dose counter is shown schematically in figure 9, when the first gear is in the form of a ratchet gear 230. The dose counter display is substantially the same as that shown in figures 1 to 3 and comprises a flexible strip (not shown) arranged between the index spool 34 and the storage reel 42.

The ratchet gear 230 has the same configuration as the corresponding gear 30 shown in fig. 1 to 4. Thus, a plurality of ratchet teeth 232 are arranged around the circumference of the ratchet-toothed wheel 230. The ratchet gear 230 is integrally molded with the hollow shaft 34 serving as an index spool of the display. The hollow shaft 34 is rotatably supported on a spindle extending from the dose counter chassis. The teeth 232 of the ratchet-toothed wheel 230 are altered as compared to the ratchet-toothed wheel 30 shown in fig. 1 to 4, as will be described in more detail below.

The actuator mechanism 218 of the second dose counter is similar in some respects to the actuator mechanism shown in figures 1 to 4. Thus, the mechanism 218 includes an actuator shaft 220 mounted for linear reciprocating movement in a longitudinal direction. Like the actuator shaft shown in fig. 1 and 2, the top part (not shown) of the actuator shaft 220 is arranged to be engaged by a medicament canister of a metered-dose inhaler employing the dose counter. The bottom of the actuator shaft 220 is formed with a blind hole for receiving the compression spring 24. The compression spring 24 serves to bias the actuator shaft 220 to an upward (starting) position, as shown in FIG. 9.

The actuator mechanism 218 of the second dose counter differs from the actuator mechanism shown in figures 1 to 4 in that there is no fixed pawl to prevent reverse rotation of the ratchet-toothed wheel 230. Rather, the mechanism 218 is provided with a pivotally mounted drive member 240 defining first and second drive pawls 242, 244. The drive member 240 is connected to the actuator shaft such that forward (downward) and reverse (upward) travel of the actuator shaft 220 causes the drive member to rotate in the counterclockwise and clockwise directions, respectively (as viewed in fig. 9). In other words, the reciprocating motion of the actuator shaft 220 causes the driving part 240 to perform a wobbling motion. Suitable mechanisms for converting reciprocating motion into rocking motion are well known to those of ordinary skill in the art. The pivot axis of the driving part 240 is parallel to the rotation axis of the ratchet-gear 230.

The drive part 240 is a plate-like member molded from a rigid plastic material. This component has a "wobbler" configuration whereby only one of the first and second drive pawls 242, 244 can engage the ratchet teeth of the first gear 230 at any one time. The driving pawls 242, 244 substantially face each other and are equidistant from the pivot axis of the driving part 240. The driving pawls 242, 244 are sized and shaped such that the teeth of the ratchet-toothed wheel 230 can drive the ratchet-toothed wheel in a clockwise direction (as viewed in fig. 9) by engagement of either pawl 242, 244. Thus, the rocking motion of the drive member 240 will cause the drive pawls 242, 244 to sequentially drive the ratchet-toothed wheel 230 and, hence, the dose counter display. The driving pawls 242, 244 also serve to prevent the reverse rotation of the ratchet-gear 230.

The use of a second dose counter for counting doses dispensed from a metered-dose inhaler according to the present invention will now be described with reference to figures 10a to 10 e. Fig. 10a to 10e are schematic views showing the components shown in fig. 9 at different stages of the actuation cycle.

The metered dose inhaler is actuated by a user applying manual pressure to the closed end of a medicament canister (not shown). In response to this pressure, the canister moves axially downward relative to its valve stem by an amount varying from about 2 to 4 millimeters. A displacement of about 2 mm is required to actuate the valve and dispense a dose of medicament. After the medicament has been dispensed, the user releases the compression force and the canister returns to its starting position under the action of the internal valve spring. The dose counter is driven by the reciprocating linear motion of the canister as a dose of medicament is dispensed.

Fig. 10a shows the start position of the dose counter. In this position, the actuator shaft 230 is biased upward to its starting position. The driving part 240 is rotated to a maximum clockwise amplitude such that the first driving pawl 242 is disposed away from the teeth of the ratchet-toothed wheel 230 and the second driving pawl 244 is located between two adjacent teeth of the ratchet-toothed wheel 230.

Downward movement of the medicament canister during dispensing of a dose of medicament causes the ferrule of the medicament canister to engage and linearly move the actuator shaft 220 downward. As shown in fig. 10b, the downward movement of the actuator shaft 220 causes the drive member 240 to move in a counterclockwise direction. Thus, the first driving pawl 242 moves to engage the teeth of the ratchet-toothed wheel 230, while the second driving pawl 244 moves away from the teeth of the ratchet-toothed wheel 230. The engagement of the first drive pawl 242 drives the ratchet gear 230 to rotate in a clockwise direction by approximately half the angle required to reliably index the dose counter, as shown in figure 10 c. Fig. 10c shows the drive member 240 rotated to a maximum counterclockwise amplitude and corresponds to the position at which the actuator shaft 220 reaches the end of its travel.

After dispensing a dose of medicament, the user releases the compressive force on the canister and the canister returns to its starting position under the action of the internal valve spring, causing the actuator shaft 220 to move upwardly. The upward movement of the actuator shaft 220 causes the drive member 240 to move in a clockwise direction, as shown in fig. 10 d. Thus, the second driving pawl 244 moves to engage the teeth of the ratchet-toothed wheel 230, and the first driving pawl 242 moves away from the teeth of the ratchet-toothed wheel 230. The engagement of the second drive pawl 244 further drives the ratchet-toothed wheel 230 in a clockwise direction for the remaining angle required for reliable indexing of the dose counter. It will be appreciated that the first and second drive pawls 242, 244 are arranged to correspondingly engage and drive the same surface of the teeth of the ratchet-toothed wheel 230.

Fig. 10e shows the dose counter after it has returned to its starting position. The actuator shaft 220 is then biased upwards into its starting position. The driving part 240 is rotated to a maximum clockwise amplitude such that the first driving pawl 242 is disposed away from the teeth of the ratchet-toothed wheel 230 and the second driving pawl 244 is disposed between two adjacent teeth of the ratchet-toothed wheel 230. Thus, it can be said that the drive member 240 provides a "stepped" rotation of the ratchet-gear 230.

By using two drive pawls 242, 244 to drive the display, the required linear displacement of the actuator shaft 220 can be reduced. This reduces the risk of miscounting, especially under counting, and in turn reduces the failure rate of the dose counter. The reduction of the required linear displacement of the actuator shaft 220 is particularly advantageous for manual metered dose inhalers, since the linear input stroke of such inhalers can be as small as 1.5 mm when the medicament canister is released immediately after the actuation point of the valve has been reached. The reduction in the required travel of the actuator shaft also reduces the risk of miscounting due to accumulated tolerances and lost motion.

The present invention also provides a metered-dose inhaler 72 as shown in figure 11. The inhaler comprises a medicament canister 6, an actuator body 74 for receiving the medicament canister 6 and having a medicament delivery outlet, and a dose counter as described above. The actuator body 74 has a window 76 for viewing the display. In a preferred embodiment, the actuator body 74 comprises a dimple, preferably a smooth circular dimple. The circular depression may have a substantially cylindrical upper portion and a substantially hemispherical lower portion. By providing smooth dimples, the inner surface is completely free of protrusions, so that the medicament will not substantially adhere thereto during normal use.

The medicament canister 6 may contain medicament in the form of an aerosol. The medicament may be any medicament suitable for delivery to a patient by a metered dose inhaler. Specifically, drugs delivered in this manner for the treatment of a wide variety of respiratory distress include antiallergic drugs (e.g., cromoglycate, ketotifen, and nedocromil), anti-inflammatory steroids (e.g., beclomethasone dipropionate, fluticasone, budesonide, flunisolide, ciclesonide, triamcinolone acetonide, mometasone furoate); bronchodilators are, for example: beta 2-agonists (e.g., fenoterol, formoterol, pirbuterol, reproterol, salbutamol, salmeterol, and terbutaline), non-selective beta-stimulants (e.g., isoproterenol), and xanthine bronchodilators (e.g., theophylline, aminophylline, and choline theophylline); and anticholinergics (e.g., ipratropium bromide, oxitropium bromide, and tiotropium bromide).

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

For example, the dose counter described above is configured to actuate the dose counter on the forward (downward) stroke of the medicament canister. The dose counter according to the present invention may alternatively be configured as a dose counter that actuates a reverse (upward) stroke.

The embodiment shown in fig. 5 is provided with a (separate) second gear wheel with which the second driving pawl is arranged to mesh. In a variant, the second gear is omitted and the second driving pawl is arranged to mesh with the ratchet gear.

Claims (4)

1. A dose counter for counting doses of medicament dispensed by or remaining in a metered-dose inhaler, the dose counter comprising:

a rotatably mounted first gear having a circular arrangement of ratchet teeth;

a display member coupled to the first gear, the display member having a visible array of dose counting indicia indexable in response to rotation of the first gear; and

an actuator mechanism having a first drive pawl for engaging the ratchet teeth of the first gear wheel in response to dispensing of a dose of medicament,

wherein the actuator mechanism further comprises a second drive pawl for engaging ratchet teeth of a gear wheel connected to the display and is configured such that, when the dose counter is used for counting a dispensed dose, the first drive pawl engages and rotatably drives a first ratchet tooth of the first gear wheel and the second drive pawl then engages and rotatably drives a second ratchet tooth of the gear wheel connected to the display,

wherein the actuator mechanism further comprises an actuator shaft mounted for linear reciprocating movement in response to dispensing of a dose of medicament, the drive member being pivotally mounted to the actuator shaft.

2. A dose counter according to claim 1, wherein the gear arranged for engagement by the second drive pawl is the first gear.

3. A dose counter according to claim 2, wherein the first and second ratchet drive pawls are defined by a single drive member, the drive member being pivotally mounted such that only one of the first and second ratchet drive pawls can engage with the ratchet teeth of the gear wheel at any one time.

4. A dose counter according to claim 1, wherein the drive member is pivotally mounted to the actuator shaft such that reciprocation of the actuator shaft causes rocking movement of the drive member.