Abstract:
An inhalation device for delivering doses of medicament to a user comprising:—a canister ( 5 ), said canister being adapted to accommodate the medicament to be dispensed to a user, and—a counter ( 15 ) which is connected to the canister ( 5 ). According to the invention—the canister ( 5 ) is adapted to receive the counter ( 15 ) on a base end ( 6   a ),—the counter and/or the canister further having contact parts ( 18, 20 ) for their attachment having means for increasing the friction and thereby allowing the counter to fixedly be attached onto the canister in a range of different positions in the lengthwise direction,—the counter further being adapted to during the process to assemble the counter to the canister, be urged onto the canister until the length of the counter and canister together is within a predefined tolerance of a predefined length.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to an inhalation device for delivery of a medicament by inhalation according to the preamble of claim  1 . It further relates to a canister and a counter assembly according to the preamble of claim  15  adapted to be positioned in an inhalation device and to a method for assembling said canister and said counter according to the preamble of claim  8 . 
       BACKGROUND OF THE INVENTION AND RELATED ART 
       [0002]    Inhalers are commonly used for delivery of a wide range of medicaments. The inhaler holds a canister of medicament, the canister being actuated by compression to deliver a dose of medicament through a mouthpiece to a user. 
         [0003]    Canisters for holding a suspension or solution of a pharmaceutical substance in a propellant under pressure are well known. One such known canister to be used in an inhalation device comprises a can coupled with a valve. The valve consists of a body comprising a chamber, a valve stem (which extends from a head of the body) and a metering chamber, selectively communicable by the valve stem to the atmosphere via an L-shaped conduit within the valve body. The valve stem is axially displaceable between a first, extended position in which the metering chamber, and hence the canister, is closed to the atmosphere (since the L-shaped conduit is disposed wholly outside the metering chamber), and a second, depressed position, in which the metering chamber is in open communication with the outlet provided by the L-shaped conduit in the valve stem and through which a metered dose of propellant containing pharmaceutical substance is delivered. The valve stem is inserted into a stem body component, which is part of the mouthpiece and housing of the device. The patient applies a compressive force between the base of the canister, held in an inverted position in the housing, and the stem body which forces the valve stem into the canister. When the valve stem has been depressed sufficiently to open the metering channel, the inhaler will discharge a single dose. This is known as the firing point. This technology is well known and described in many parts of the prior art. For example in Respiratory Drug delivery, Ed Peter Byron, CRC press, 1991, and in Lung Biology in Health and Disease, Vol 94, Inhalation Aerosols, A J Hickey, Publisher Marcel Decker, 1996 and in Pharmaceutical Preformulation and Formulation, Ed Mark Gibson, Chapter 10, Inhalation Dosage Forms, IHS Health Group, 2001. 
         [0004]    It is important for the patient to be able to ascertain the level of medicament remaining in the canister. This requirement is met by the use of a dose counter accessory either attached to or part of the inhaler device. It is obvious that this counter must be accurate in that over-counting results in medicament being left in the inhaler unnecessarily resulting in more repeat prescribing with their resultant costs and inconvenience to patient. It also means that in an emergency situation the patient may not use the inhaler in the belief that it is empty when it is not. Conversely, undercounting could result in the inhaler being empty of medicament before the patient has a replacement, which could be dangerous for the patient and reduce patient compliance. Regulatory guidelines require the over and undercounting errors to be minimised. 
         [0005]    An inhaler traditionally contains from 120 to 200 doses (shots) so any counter must be reliable, accurate and easy to read. There are many examples of dose counters in the prior art, some located near the valve region of the canister and some attached to the base of the canister which due to the fact that the canister is in an inverted position in the inhaler mouthpiece means that the counter is on the top of the assembled inhaler and can be easily viewed. 
         [0006]    In U.S. Pat. No. 6,446,627 a dose counter attached to the base of the actuator is described. The counter measures the displacement of the top of the canister relative to the valve stem. The counter is not attached to the canister and therefore a problem is that the user can swap canisters between actuators and that would cause the indicator of the counter to display the incorrect number of doses remaining in the canister. Furthermore a problem with the inhalation device according to U.S. Pat. No. 6,446,627 is that the actuator and counter assembly are difficult to clean and are vulnerable to damage with water and cleaning products. 
         [0007]    In U.S. Pat. No. 4,817,822 a counter attached to the base of the canister, i.e. on the top of the inhalation device, is disclosed. One embodiment of this inhalation device measures the displacement of the canister base relative to the actuator body. A problem with the counter disclosed in U.S. Pat. No. 4,817,822 is miscounting since the counter relies on the displacement of the canister and the canister length due to manufacturing variables is a length with a variable tolerance. A large tolerance of the canister length has the potential to cause miscounting. 
         [0008]    In U.S. Pat. No. 6,082,358 a counter attached to the base of the canister is disclosed where the counter counts when a certain force is reached. The counter is attached to the canister but does not require alignment with the actuator body since it relies on the force of the spring in the counter mechanism being less than the force of the spring in the metering valve, such that the counting occurs before firing. A problem with such a counter is that the force of the counting spring and the metering valve need to be accurately controlled, and may vary with use. 
         [0009]    However positioning the counter on the base of the canister would be preferred since the visibility of the counter would be good and furthermore the counter could be securely fixed to the canister. 
         [0010]    In this text we will refer to a fire point, which is the amount of compression of the canister that is necessary for delivering a dose of medicament and a count point, which is the amount of compression of the canister that is necessary for affecting the counter to count one dose. 
       SUMMARY 
       [0011]    An object of the invention is to provide an inhalation device with a dose counter counting the delivered doses of medicament in a secure and reliable way. 
         [0012]    A further object of the invention is to provide an inhalation device where a counter is securely fixed to the canister. 
         [0013]    This is achieved in an inhalation device according to claim  1  and in a canister and counter assembly according to claim  15 . It is further achieved by a method for assembling the counter and the canister according to claim  8 . 
         [0014]    Hereby the counter is securely fixed to the canister and the length tolerance of the canister and counter is limited by the controlled fixing of the counter to the base of the canister. Hereby it is possible to provide the counter on the base of the canister (i.e. the top of the inhalation device) and keep the count point close to the fire point and avoid miscounting. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]      FIG. 1  shows one embodiment of an inhalation device according to the invention. 
           [0016]      FIG. 2   a  shows schematically a diagram of the relation between displacement of the canister and the fire and count points in an inhalation device not using the assembly process according to the invention. 
           [0017]      FIG. 2   b  shows schematically the same as  FIG. 2   a  but for an inhalation device using the assembly process according to the invention. 
           [0018]      FIG. 3  shows schematically one embodiment of the canister and the positioning of a roughened surface on the canister base. 
           [0019]      FIG. 4  shows how the counter is attached to the canister. 
           [0020]      FIG. 5   a  shows schematically a cross section of one embodiment of the counter and deformable ribs provided on the inside of the counter base before assembly to the canister. 
           [0021]      FIG. 5   b  shows schematically the deformable ribs of  FIG. 5   a  when the counter is assembled to the canister. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0022]    In  FIG. 1  an inhalation device  1  according to one embodiment of the invention is shown. It comprises a housing  3 , which encloses a canister  5  holding the medicament. The canister comprises a base end  6   a  and a valve end  6   b . The medicament is delivered to the user through a valve stem  7  connected to the valve end  6   b  of the canister (lower part of the canister in the figure due to the invert position of the canister in the inhalation device). The medicament is inhaled by the user through a mouth piece  13  that is a part of the housing  3 . The mouthpiece is in connection with the valve stem  7  for receiving the medicament to be delivered. Furthermore a dose counter  15  is provided on the base end  6   a  of the canister, i.e. in the opposite end to the valve stem  7 . When a dose of medicament should be delivered to the user the canister  5  is pressed downwards whereby the valve stem is forced into a position where it delivers a dose of medicament. This is in conformity with many inhalation devices according prior art will not be described in more detail here. The dose counter  15  is attached to the canister and will be pressed down together with the canister. The counting is related to the downward motion of the canister and counter. See more detailed description below. The dose counter  15  should increase the number of counted doses by one every time a dose has been delivered. Since undercounting is not to recommend due to the risk that the user believes that there is medicament left in the canister when it actually is empty, the counter usually is affected to count one count only when the canister has been pressed down a distance less than is needed for delivering the dose of medicament. Hereafter the position to where the canister is needed to be pressed down for affecting the counter to count one dose is called the count point and the position to where the canister is needed to be pressed down to deliver one dose is called fire point. 
         [0023]    According to the invention the counter is provided onto the base of the canister  5 . The counter  15  is attached to the canister  5  in an assembling process and it can be attached to the canister  5  at any one of numerous points along the base part of the canister, i.e. the part of the canister opposite from the valve stem, from the outermost edge of the counter to its inside base giving ranges of variation of positions and varying lengths of canister tolerances. I.e. the counter can be attached anywhere on the base of the canister. The contact areas between the counter and the canister, i.e. the inside of the counter  18  and/or the outside surfaces of the base of the canister  20  (see  FIG. 5   a ), are provided with means for enhancing the friction and ensuring that the counter is fixedly attached to the counter. Different alternatives for this are described in relation to  FIGS. 3 ,  4  and  5  below. In the assembly process the counter  15  is pressed down onto the canister  5  and at the same time the length of the canister together with the counter is measured. The counter  15  is pressed down until a predefined length of the canister and counter together is achieved and this length should also be within a predefined tolerance interval. 
         [0024]    Hereby an inhalation device  1  is achieved having a counter securely fixed to the canister and the canister and counter together having a predefined length within a predefined tolerance interval. This is preferred since this allows the control of the distance the canister needs to be depressed before a dose of medicament is delivered and thus also how much the canister needs to be depressed before the counter counts a dose. 
         [0025]      FIG. 2   a  shows schematically how the fire point  21  (dose delivering) and the count point  22  are related to the compression of the canister in an inhaler device where the counter is attached to the base of the canister but the method according to the invention for assembling the counter and canister to achieve a small length tolerance is not used. Hereby the length tolerance of the canister and counter is large. This large length tolerance results in a range of possible counting points  24 . This is illustrated in  FIG. 2   a  in that the range of possible count points  24  is larger than the range of possible fire points  23 . The range of fire points is only dependent on the valve tolerances and not on the canister length tolerance. The given lengths in  FIG. 2   a  and b for input displacement of the canister are only examples. In reality these could vary for different products. To be absolutely sure that the count point  22  is before the fire point  21  to avoid miscounting, the whole tolerances need to be considered when the position of the count point  22  is decided. The result of this is that the count point  22  needs to be positioned relatively far away from the fire point  21  and in reality this means that the dose counter will count one dose when the canister is pressed down much less than is needed for delivering a dose. This in turn results in a tendency for the counter to overcount the doses and there will actually be medicine remaining when the counter says the canister is empty. 
         [0026]      FIG. 2   b  shows schematically the same as  FIG. 2   a  but for an inhalation device according to the invention. Here the length tolerance of the canister and counter together is much smaller giving a smaller range of possible count points  28 . Therefore the count point  26  can be positioned closer to the fire point  25 . Hereby there is less tendency for overcounting. 
         [0027]    The counter should be a displacement counter, i.e. a counter that is affected by the displacement of the canister and counts one count each time the canister is pressed down for delivering a dose. As described in the related art chapter there are different examples of such counters available today. One example of a counter that could be positioned onto the base of the canister according to the invention comprises a mechanism to convert longitudinal compression of the canister to a rotational, horizontal movement of an indicating mechanism of the counter. One example of such a counter is described in WO 01/37909. Displacement counters with other kinds of indicating mechanisms are also possible. 
         [0028]    To ensure that the counter is fixedly attached to the canister and that the counter can be attached in a range of different positions to the canister one or more of the contact surfaces between the counter and canister ( 18 ,  20   FIG. 5   a ) are provided with means for increasing the friction. The means for increasing the friction can be for example roughened areas or deformable means or both. Preferably roughened areas are provided onto the base of the canister. Deformable means can in one embodiment be provided on the inside base of the counter. 
         [0029]      FIG. 3  shows schematically where roughened areas  37  on the base end  6   a  of the canister  5  can be provided. Preferably the outer side wall at the base of the canister and more preferably the widest part of the wall nearest the base is roughened and the inside of the counter is smooth plastic that deforms into the roughened surface and thereby provides a secure grip. Hereby the counter is securely fixed onto the base of the canister and furthermore the counter may, during the assembly process when the counter is fitted onto the canister, be pressed onto the canister to fit in a range of different positions. The area that should be provided with a roughened surface can vary between different types of canisters but should preferably be provided on the widest part of the base. In another embodiment, the inside of the counter, i.e. the contact surface of the counter ( 18  in  FIG. 5 ), could also be provided with some kind of roughened surface for increasing the friction. A roughened surface could be produced by for example mechanical working of the surface, knurling the surface, forming grooves into the surface, chemically etching the surface or by laser marked hatching of the surface. 
         [0030]    The roughened surface, more precisely, is in one embodiment positioned on the outer wall of the canister at the base end and circumvents the canister, ie it is all the way around the canister side at the widest point of the canister length, see  FIG. 3 . 
         [0031]    The friction between said canister and said counter could also be further increased by means of adhesive. Furthermore the inner surface of the counter could be co-moulded with a high friction coefficient material. 
         [0032]    Another possible way of attaching the counter to the base of the canister fixedly to a predefined position is to melt the plastic into a close fit to the canister. An example of this is to use ultra sonic welding or other heating process. 
         [0033]      FIG. 4  shows how the counter  15  is attached to the canister  5 . 
         [0034]      FIG. 5   a  shows schematically a cross section of one embodiment of a counter  15  according to the invention before assembly to the canister  5 . In this embodiment deformable means  52  in the form of ribs are provided around the inside of the counter base. 
         [0035]      FIG. 5   b  shows schematically the deformable ribs of  FIG. 5   a  when the counter  15  is assembled to the canister. 
         [0036]    The deformable ribs  52  are provided for improving the possibility to control the position of the counter on the base of the canister in a range of different positions. When the counter is pressed onto the base of the canister during the assembly process the deformable ribs are deformed (can be seen in  FIG. 5   b ) until the predefined length of the counter and canister together is achieved and then the pressing process is stopped. The force to deform the ribs is higher than the maximum force a patient can apply to the device therefore the canister remains in a fixed position. 
         [0037]    The deformable means could be shaped differently and also be positioned in other positions along the inside of the counter than what is shown in  FIG. 5 . The deformable means could for example be spike shaped features, foam material etc. The deformable means should deform in a controlled manner. 
         [0038]    The deformable means could for example be of a rubber material or a polymer material. They could also be co-moulded from two or more materials. 
         [0039]    Another method for preventing movement of the counter and canister when assembled is to use a quick setting polymer to deform and fill the space between the counter and canister during the assembly process. 
         [0040]    All these different described methods provide a possibility to attach the counter in a range of different positions on the canister and can be used alone or in any combination. 
         [0041]    In summary, correct depth alignment of the canister into the counter is achieved by controlling the distance the canister travels into the counter during the assembly process and thereby controlling the overall length tolerances. This is vital to the correct firing and count ratios of the device, encompassing the strict requirements of the regulatory bodies for under and over counting of said counting devices when used in conjunction with a metered dose inhaler system.