Abstract:
A breath actuated inhaler for delivering medicament by inhalation, comprising a housing having a mouthpiece and defining an air flow path extending from the mouthpiece through the housing; the housing holding a replaceable canister of medicament actuatable to deliver a dose of medicament into the air flow path, wherein the housing defines an opening in the air flow path and the opening is closed by a closure element connected to and replaceable with the canister. The closure element acts as a safety feature because it is only closed when the inhaler is used with a canister to which a closure element is connected the closure element carries an indication of the type of medicament in the canister to allow the user to recognise the type of medicament. A plurality of inhalers may be provided in which each given inhaler has an opening with a different shape and has a closure element with a shape which conforms with the opening of the given inhaler but which does not conform with the openings of the other inhalers.

Description:
This application is a continuation of application Ser. No. 10/096,174, filed Mar. 13, 2002 now abandoned, which is a continuation of application Ser. No. 09/424,333, filed Nov. 22, 1999, now abandoned, the entire content of which is hereby incorporated by reference in this application. 
    
    
     The present invention relates to an inhaler for delivery of medicament by inhalation, particularly but not exclusively to a breath-actuated inhaler. 
     BACKGROUND OF THE INVENTION 
     Inhalers are commonly used for delivery of a wide range of medicaments. The inhaler houses a canister of medicament which is actuated to deliver a dose of medicament through a mouthpiece. Desirably the canister is replaceable so that the inhaler is re-useable after the canister is empty or can be used with different medicaments. However, this advantage can create safety problems. In particular, it is difficult to control the type of medicaments supplied by inhalers. For example, users might insert a canister containing an inappropriate medicament as different medicaments are commonly supplied in similar canisters. Users might not know whether a given inhaler which comes to hand will deliver the desired medicament. Such problems are particularly serious when the inhaler is needed to provide a particular medicament urgently in an emergency. The present invention is intended to improve safety in an inhaler with a replaceable canister. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided an inhaler for delivering medicament by inhalation, comprising a housing having a mouthpiece and defining an air flow path extending from the mouthpiece through the housing; the housing holding a replaceable canister of medicament actuatable to deliver a dose of medicament into the air flow path, wherein the housing defines an opening in the air flow path and the opening is closed by a closure element connected to and replaceable with the canister. 
     The closure element acts as a safety feature because it is only closed when the inhaler is used with a canister to which a closure element is connected. This enables better control over the type of medicament to be delivered in that valid canisters can be provided with closure elements connected thereto. The absence of the closure element may be recognised by the user on insertion. 
     Advantageously, the closure element carries an indication of the type of medicament in the canister. In this way, the closure element may provide the advantage that it enables the type of medicament to be easily recognised by a user. It is particularly advantageous that the indication is provided on an element connected to the cannister itself so the risk of confusion is reduced. 
     The indication may be printed information, such as different colours, patterns, text or numbers or the colour of the closure element itself. Desirably, the indication is a tactile surface, for example an embossed or indented pattern. This enables a user with poor eyesight to recognise the type of medicament, which would not otherwise be possible, particularly in the case of an indication visible, say, through a window. 
     Preferably, the opening is defined in the outer surface of the housing. This enables the presence or absence of the closure element to be clearly visible to a user of the inhaler with the canister fitted. 
     Desirably, the opening is provided adjacent the mouthpiece. This allows for the closure element to be easily formed with a connection to the canister which itself is normally adjacent the mouthpiece to enable engagement in a nozzle block directing medicament out of the mouthpiece. Also it assists in making the indication visible because in normal use the inhaler will be held with the mouthpiece in view, facing the user. 
     The safety may be improved further if the present invention is applied to a breath-actuated inhaler further comprising an actuation mechanism arranged to be operated to actuate the canister by a flow through the air flow path, the opening being arranged, when open, to vent the flow sufficiently to prevent operation of the actuation mechanism. In this way, the inhaler will not provide medicament if inserted with a canister without a closure element, potentially containing inappropriate medicament, or if a canister is inserted in the incorrect position. This improves safety and gives the inhaler provider better control over the proper use of the inhaler. 
     The opening may be positioned and dimensioned to prevent operation at in the absence of a closure element at an inhalation level above the maximum expected flow rate at the mouthpiece. For example, operation may be prevented at a flow rate of at least eight times a standard inhalation flow rate. Conversely, it is unnecessary for the closure element when present to completely close the opening, provided that it closes the opening sufficiently to allow operation of the inhaler. 
     Typically in a breath-actuated inhaler wherein the actuation mechanism includes a trigger disposed in the air flow path responsive to the flow to cause operation of the actuation mechanism, for example by comprising a pre-loading mechanism arranged to store a loading force for actuation of the canister, the trigger being arranged to release the stored force. 
     The trigger is preferably a vane arranged to be physically moved by a flow through the air flow path, although an electronic trigger sensing the flow is a conceivable alternative. 
     The present invention is particularly suited to a common, simple form of breath actuated inhaler in which wherein the housing has outer walls defining a space which constitutes the air flow path. 
     Desirably, the opening is disposed in the air flow path between the trigger and the mouthpiece. This is an advantageous structure, because the inhalation flow generated by inhalation at the mouthpiece is drawn through the opening without thereby limiting the flow created within the air flow path at the trigger to prevent operation of the trigger. 
     Preferably the housing defines an inlet opening for the air flow path having a smaller opening area than the opening. This increases the air flow resistance at the opening relative to the opening which assists in ensuring the inhalation flow is vented by the opening in preference to the inlet opening, hence allowing the opening to prevent operation of the actuation mechanism. 
     According to a second aspect of the present invention, there are provided a plurality of inhalers according to the first aspect wherein each given inhaler has an opening with a different shape and has a closure element with a shape which conforms with the opening of the given inhaler but which does not conform with the openings of the other inhalers. 
     This provides the inhalers with a form of canister recognition. Inhalers are to be used exclusively with canisters having a closure element with a conforming opening. Use of canisters in inhalers which do not have a conforming opening may be recognised by the different shapes and may be prevented by the shapes of the opening and the closure element of a given inhaler prevent fitting of the closure element in an inhaler other than the given inhaler. Alternatively, the different shapes may the inhalers further comprise an actuation mechanism arranged to be operated to actuate the canister by a flow through the air flow path and the shape of the closure element of a given inhaler is such that when the closure element fitting in inhaler other than the given inhaler leaves open the opening of the other inhaler sufficiently open to prevent operation of the actuation mechanism of the other inhaler. 
     Accordingly the second aspect of the present invention makes it possible to control the use of canisters in particular inhalers. For example, the different shapes of opening and closure elements may be used for respective types of medicament to reduce the chances of cross-contamination between inhalers for differing medicaments. 
     With either aspect of the present invention, the canister and the closure element are connected by a connector which is arranged to prevent reconnection after separation of the canister and the closure element, for example by the connector is formed with a weak portion arranged to be broken in preference to the remainder of the connector on application of a force to separate the canister and the closure element. This further enhances the security of the present invention because it prevents a closure element from a valid canister being removed and attached to a new canister. 
     To allow a better understanding, an inhaler which embodies the present invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of the inhaler held in a hand; 
     FIG. 2 is a side view of the inhaler, 
     FIG. 2A is a side view of the inhaler without a closure element fitted; 
     FIG. 3 is a side view of the inhaler with a lower housing portion being removed; 
     FIG. 4 is a side view of an upper housing portion of the inhaler with a canister being removed; 
     FIG. 5 is a side view of an alternative form of collar for connecting the closure element to the canister; 
     FIG. 6 is a cross-sectional view taken along line VI—VI in FIG. 5; 
     FIG. 7 is a side view of the canister mounting arrangement and actuation mechanism; 
     FIG. 8 is a view from the rear and side of the actuation mechanism; 
     FIG. 9 is a view from the rear and the opposite side from FIG. 8 of the actuation mechanism; 
     FIG. 10 is a front view of the arrangement for loading the actuation mechanism; 
     FIG. 11 is a side view of an alternative form of button arrangement for loading the actuation mechanism; 
     FIG. 12 is a view of certain parts of the actuation mechanism from the front and side; 
     FIGS. 13 to  16  are schematic views of the actuation mechanism illustrating respective states over a complete cycle of operation; and 
     FIG. 17 is a view of the electronic timer circuit. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     An inhaler  1  which embodies the present invention is illustrated in FIGS. 1 and 2, respectively showing the front view of the inhaler  1  held in a user&#39;s hand and a side view of the inhaler. 
     The inhaler has a housing  2  comprising an upper housing portion  3  and a lower housing portion  4  which are coupled together. The upper and lower housing portions  3  and  4  have outer walls which are hollow to define a space accommodating a canister  5  of medicament and an actuation mechanism  6  operatable to actuate the canister  5  to deliver a dose of medicament. 
     The upper housing portion  3  has opposed side walls  7  joined by a flat front wall  8 , a curved rear wall  9  and a top wall  10 . The lower housing portion  3  has opposed side walls  11  fitting flush with the side walls  7  of the upper housing portion  3  and a curved rear wall  12  fitting flush with the rear wall  9  of the upper housing portion  3 . The rear walls  12  and  9  together form a curved surface comfortably received in the palm of the user&#39;s hand as illustrated in FIG. 1. A mouthpiece  13  protrudes from the lower housing portion  4  and may be protected by a cap  14  hinged to the lower housing member  4  to be openable as illustrated in FIG.  2 . 
     The front of the lower housing member  4  between the side walls  11  is open to define an opening  15  in the outer surface of the housing  2  adjacent the mouthpiece  13  between the upper and lower housing portions  3  and  4 . The opening  15  is closed by a closure element  16  fitting flush with the front wall  8  of the upper housing portion  3  to form part of the outer wall of the housing  2 . 
     The upper and lower housing members are coupled by a coupling  17  allowing the lower housing member  4  to be slid off as illustrated in FIG.  3 . 
     The canister  5  fits in the upper housing portion  3  and may be slidably removed for replacement as illustrated in FIG.  4 . 
     The canister  5  comprises a generally cylindrical body  18  and a valve stem  19  which are compressible together to deliver a dose of medicament from the valve stem  19 . The canister is of a known type including a metering chamber which captures a defined volume of medicament from the body  18  of the canister  5 , which volume of medicament is delivered as a metered dose from the valve stem  19  on compression of the valve stem  19  relative to the body  18 . The valve stem  19  is weakly biassed outwardly to reset the canister  5  after compression for refilling the metering chamber. The valve stem  19  is received in a nozzle block  20  which is arranged to direct a dose of medicament delivered from the valve stem  19  out of the inhaler  1  through the mouthpiece  13 . 
     The closure element  16  is connected to the canister  5  by a collar  21  fitted around a necked portion  22  of the canister body  18 . The collar  21  is permanently fixed to the closure element  16  and may be integral therewith. The collar  21  is restrained by the necked portion  22  of the canister  5  such that the closure element  16  is removed and replaced together with the canister  5  as illustrated in FIG.  4 . The canister  5  and collar  21  have a small degree of relative movement along the axis of the canister  5 . This allows actuation of the canister by compression of the canister body  18  towards the valve stem  19  when the stem  19  is fixed relative to the inhaler  1  in the nozzle block  20  and the collar  21  is also fixed by the closure element  16  fitting as part of the housing  2  of the inhaler  1 . 
     FIGS. 5 and 6 respectively illustrate a side view and cross-sectional view and alternative collar  23  for connecting the closure element  16  to the canister  5 . The collar  23  includes a cylindrical portion  24  held on the necked portion  22  of the canister body  18  by a protrusion  25  formed in the cylindrical portion  24  by a U-shaped cut-out  26 . The cylindrical portion  24  has an extension  27  extending beyond the end of the canister body  18  to protect the valve stem  19 . The extension  27  is of reduced diameter relative to the remainder of the cylindrical portion  24  of the collar  23 . 
     The force needed to separate either collar  21  or  23  from the canister preferably exceeds the normal strength of human fingers or hands, so in normal use the closure element is effectively permanently connected. 
     Optionally, the collars  21  and  23  are formed with a weak portion constituted by two rupture lines  28  disposed on opposite sides of the collar  21  or  23  and arranged to be broken preferentially to the remainder of the collar  21  or  23  on application of a force to separate the closure element  16  from the canister  5 . After the rupture lines  28  have been broken or at least deformed to enable removal of the canister  5 , it is impossible to connect the collar  21  or  23  to a different canister. 
     The outer surface of the closure element  16  carries an indication of the type of medicament in the canister  5  to which the closure element  16  is connected. The indication may be printed information, such as text, letters or numerals, or simply coloured patterns, an embossed or indented pattern or the colour of the closure element  16 . 
     An inlet opening  29  is formed in the upper housing portion  3 , in particular in its top wall  10  and front wall  8 . The outer walls of the housing defined by the upper and lower portions  3  and  4  and the closure element  16  seal together to define a closed space which constitutes an air flow path extending from the mouthpiece  13  through the housing  2  to the inlet opening  29 . Inhalation at the mouthpiece  13  creates a pressure differential which draws air in through the inlet opening  29  through that air flow path around the canister  5  and actuation mechanism  6  encased in the housing  2 . The actuation mechanism  6  (described in detail below) has a trigger disposed in the upper housing portion  4  which, in response to a flow through the air flow path, triggers the actuation mechanism  6  to actuate the canister  5 . 
     If a canister without a closure element connected thereto is inserted into the housing  2 , then the opening  15  will remain open as illustrated in FIG.  2 A. Consequently, when a user inhales at the mouthpiece  13 , the flow resistance through the opening  15  will be much lower than the flow resistance through the remainder of the air flow path above the opening  15  from the inlet opening  29 . Accordingly, the opening  15  will act as a vent most of the flow through the mouthpiece, thereby reducing the flow in the remainder of the air flow path in the upper housing portion through. The positioning of the opening  15  in the air flow path inside the housing  2  between the mouthpiece  13  and the trigger reduces the air flow across the trigger. The opening  15  is positioned and dimensioned such that the flow at the trigger is reduced below the threshold needed to operate the trigger and therefore prevents operation of the actuation mechanism  6 . To assist in assuring that the opening  15  sufficiently vents the flow, the opening  15  is provided with a larger opening area and hence a lower flow resistance than the inlet opening  29 . The opening  15  is dimensioned so that the actuation mechanism is not operated on a flow through the mouthpiece  13  at a level above the maximum expected inhalation, for example at an inhalation of at least eight times a standard inhalation flow rate. The triggering mechanism for the actuation mechanism  6  is designed taking into account the flow generated by a standard inhalation selected by the designer. 
     The actuation mechanism  6  for actuating the canister  5  to deliver a dose of medicament is illustrated in FIGS. 7 to  9 . The elements illustrated in FIGS. 7 to  9  are accommodated in the housing  2  but are illustrated separately for clarity. The canister  5  is held with its valve stem  19  in a nozzle block  20 ′ connected to the mouthpiece  13 , both fixed relative to the lower housing portion  4 . A nozzle block  20 ′ has a slightly different structural form from the nozzle block  20  illustrated in FIGS. 3 and 4 but performs the same function. The body  18  of the canister  5  is supported by a guide block  30  fixed to the upper housing portion  3  and having a curved inner surface engaging the cylindrical surface of the canister body  18  to allow axial movement of the canister body  18  within the housing  2 . The actuation mechanism  6  operates to compress the canister body  18  relative to the valve stem  19  held in the nozzle block  20  to deliver a dose of medicament. 
     The structure of the actuation mechanism  6  is as follows. 
     The actuation mechanism  6  includes a pre-loading mechanism for loading a resilient loading element in the form of a coiled loading spring  31 . The pre-loading mechanism includes the loading member constituted by a shaft  32  encircled by the coils of the loading spring  31 . The shaft extends and is movable in a direction parallel to the cylindrical axis  80  of the canister body  18 . The loading member shaft  32  has an enlarged head  33 . 
     As illustrated in FIG. 1, two buttons  34   a  and  34   b , constituting contact members to be manually depressed, are mounted opposite one another in the side walls  7  of the upper housing portion  3  on either side of the axis  80  of the canister  5  held in the housing  2 . The buttons  34  are manually depressible in a direction substantially perpendicular to the axis  80  of the cannister  5  which makes them easy to grip and move by a finger and thumb, as can be seen in FIG.  1 . The buttons  34  load the loading member  32  and loading spring  31  through the arrangement illustrated in FIG. 10 comprising two torsion springs  35   a  and  35   b  fixed inside the upper housing portion. The torsion springs  35   a  and  35   b  engage the enlarged head  33  of the loading member  32  and respective ones of the buttons  34  to convert sideways force applied to the buttons  34  to a downwards force along the axis of the loading member shaft  32 . 
     An alternative means for converting the sideways force applied to the buttons  34  is illustrated in FIG.  11 . This consists of a double knee joint  36  fixed at its upper end  37  to the upper housing portion  3 , fixed at its lower end  38  to the enlarged head  33  of the loading member  32  and fixed at its intermediate joints  39   a  and  39   b  to the respective buttons  34   a  and  34   b.    
     The pre-loading mechanism further includes a lever  40  pivoted relative to the housing about a pivot  41 . The lever  40  has a planar canister engagement portion  42  contacting the canister body  18  adjacent the pivot  41  with a pair of arms  43  and  44  extending therefrom. One arm  43  is engaged by the loading spring  31  so that the loading spring  31 , when loaded, biasses compression of the canister through the lever  40  coupled to the canister  5  by the canister engagement portion  42 . As the loading spring  31  is further away from the pivot  41  than the cannister engagement portion  42 , this provides leverage between the loaded actuation force and the force applied to the cannister  5 . The arm  43  has a hole through which the loading member shaft  32  extends. The other arm  44  of the lever  43  has a similar hole through which extends a further shaft  78  for preventing lateral displacement of the lever  40 . 
     The actuation mechanism further includes a triggering mechanism for holding the lever  40  against compression of the canister under the biassing of the spring  31  and to release the lever  40  in response to inhalation at the mouthpiece. The triggering mechanism is constructed as follows. 
     The triggering mechanism comprises a first knee joint  45  having two links  46  and  47  connected pivotally to one another by a central pivot  50 . The upper link  46  is pivotally connected both arms  43  and  44  of the lever  40  by a pivot  48 . The lower link  47  is pivotally connected to the upper housing portion  3  by a pivot  49 . 
     Accordingly, the first knee joint  45  has a locked position illustrated in FIGS. 7 to  9  in which it holds the lever  40  against compression of the canister  5 . In the locked position of the first knee joint  45 , the central pivot  50  is substantially aligned with the pivots  48  and  49  at the ends of the links  46  and  47 . As the first knee joint  45  is connected to the lever at a position further away from the pivot  41  then the cannister engagement portion  42 , this provides leverage between the locking force provided by the first knee joint and the force applied to the cannister  5 . This leverage enhances the locking and triggering action of the triggering mechanism. 
     The triggering mechanism further includes a second knee joint  51  comprising two links  52  and  53  connected by a central pivot  54 . One link  57  of the second knee joint  51  is pivotally connected to the upper housing portion  3  by a pivot  55  and extends laterally so that it constitutes a trigger vane which is moved by a flow of air thereover. The trigger vane  52  has a counterweight portion  79  (illustrated only in FIG. 7) fixed to the opposite side of pivot  55  from the laterally extending surface. The counterweight balances the trigger vane so that its centre of mass is positioned on the axis of the pivot  55 . 
     The other link  53  of the second knee joint  51  extends from the trigger vane  52  between the arms  43 ,  44  of the lever  40  to the upper link  46  of the first knee joint  45  where it is pivotally connected by a pivot  56 . 
     Accordingly, the second knee joint  51  has a locked position illustrated in FIGS. 7 to  9 . In the locked position of the second knee joint, the central pivot  54  is substantially aligned with the pivots  55  and  56  and the ends of the links  52  and  53 . 
     The actuation mechanism  6  further includes a reset mechanism which is constructed as follows. 
     The reset mechanism employs a locking element constituted by a third knee joint  57  comprising an upper link  58  and a lower link  59  pivotally connected together by a central pivot  60 . The upper link  58  is pivotally connected to the upper housing portion  3  by the pivot  49  in common with the first knee joint  45 . The lower link  59  is pivotally connected to the loading member shaft  32  by a pivot  61 . The third knee joint  57  has a locked position illustrated in FIGS. 7 to  9  in which it holds the loading member shaft  32  in its loaded position as illustrated in FIG.  7 . In the locked position of the third knee joint  57 , the central pivot  60  is aligned with the pivots  48  and  61  at the end of the links  53  and  59 . The third knee joint  57  is also biassed into its locked position by a biassing spring  67  connected to the upper housing portion  3 . Hence the third knee joint constitutes a locking element which holds the canister in a compressed state through spring  31  and lever  40  after the full movement of the lever  40  to compress the canister  5 . 
     The reset mechanism further includes a release member  62  mounted on the loading member shaft  32  by having an aperture through which the shaft  32  extends. The release member  62  is movable relative to the shaft  32  between limits defined by a pin  63  protruding from the shaft  32  engaging in a track  64  formed in the release member  62 . A timer spring  65 , the coils of which encircle the shaft  32 , is connected between the arm  43  of the lever  40  and the release member  62 . The timer spring  65  is in a relaxed state in FIG.  7  and is provided for biassing the release member  62  when loaded by movement of the lever  40  to compress the canister  5 . 
     A protrusion  66  extends from the release member  62  (as best seen in the partial view of FIG. 12) to engage with the lower link  59  of the third knee joint  57  when the release member  62  is moved down the shaft  32 . Such engagement of the protrusion  56  with the third knee joint  57  moves the knee joint  57  against the biassing spring  67  to break the third knee joint  57  thereby releasing locking effect of the third knee joint  57 . 
     The shaft  32  is biassed upwardly by a reset spring  68  acting between the shaft  32  and upper housing portion  3  to move the shaft  32  upwardly upon breaking of the third knee joint  57 . 
     The downwards movement of the release member  62  is damped by a damping element  69  consisting of a stator  70  fixed to the upper housing portion  3  and a rotor  71  rotatable through viscous fluid provided between the rotor  71  and stator  70 . The rotor  71  is driven by a toothed rack  72  connected to the release member  62 . 
     Operation of the actuation mechanism  6  will now be described with reference to FIGS. 13 to  16  which illustrate the various parts of the actuation mechanism  6  in schematic form for ease of understanding. 
     FIG. 13 illustrates the neutral state in which the loading member shaft  32  is in its uppermost position, so that the loading spring  31  is relaxed. In this state, the first and second knee joints  45  and  51  are both in their locked positions. The timer spring  65  and the reset spring  68  are relaxed. 
     Upon depression of the buttons  34 , the loading member shaft  32  is moved downwardly to a second position illustrated in FIG. 14 loading the loading spring  31  which therefore biasses the lever  40  towards compression of the canister  5 . However, the first knee joint  45  is its locked position where it holds the lever  40  against compression of the canister  5 . The first knee joint  45  is held in its own locked position by the second knee joint  51  being in its locked position. 
     Movement of the loading member shaft  32  downwards also loads the reset spring  68  and brings the third knee joint  57  into its locked position where it is held by the spring  67 . In this loaded state illustrated in FIG. 14, the inhaler  1  is loaded ready for delivery of a dose of medicament. 
     Inhalation by the user at the mouthpiece  13  generates an air flow through the air flow path defined inside the housing  2  from the inward opening  29  to the mouthpiece  13 . This air flow acts on the trigger vane  55  of the second knee joint  51  causing it to move upwardly due to pressure drop created by the flow inside the housing  2  to the position illustrated in FIG. 15 where the second knee joint is broken. This breaks the first knee joint  45  into its broken position illustrated in FIG. 15 which releases the lever  40  and allows it to compress the canister  5  under the biassing of the loading spring  31 . 
     During compression of the canisters, the shaft  32  remains locked in position by the third knee joint  57 . This causes the canister to be held in its compressed state by the shaft  32  acting through the spring  31  and lever  40 , the spring force of the spring  31  far exceeding the internal reset biassing of the canister  5 . 
     However, movement of the lever  40  loads the timer spring  65  which accordingly biasses the release member  62  downwards. Movement of the release member  62  is delayed by the damping action of the damping element  69 . The protrusion  66  of the release element  62  engages the third knee joint  57  after a predetermined period of time after actuation of the canister  5 . This time is determined by the strength of the timer spring  65  and the damping properties of the damping element  69  and is at least 100 ms or 200 ms and up to 1000 ms or 5000 ms to allow the full dose of medicament to be delivered from the cannister  5 . Such engagement breaks the third knee joint  57  into its broken position as illustrated in FIG.  16 . Subsequently the reset spring  68  moves the loading member shaft  32  upwardly to the neutral position illustrated in FIG.  13 . At the same time the shaft  32  lifts the release member  62 , itself still damped by the damping element  69  so that the reset movement is damped. 
     Release of the shaft  32  causes the spring  31  to raise the lever  40  which has two effects. Firstly it allows the canister to reset itself. Secondly, it causes the first and second knee joints  45  and  51  to straighten, returning them to their locked position in the neutral position of the actuator mechanism illustrated in FIG.  13 . The loading spring  31  and the timer spring  65  are pre-loaded and do not work against the reset movement, so that the reset spring  68  has only to overcome friction and the weight of the component. 
     The buttons  34   a  and  34   b  protrude from the inhaler when the actuation is in its relaxed state as shown in FIG.  1  and are depressed to a position flush with the side walls  8  of the upper housing portion  3 . Accordingly, the distance between the extremities of the buttons before depression is less than the maximum length of the inhaler  1  in the direction parallel to the axis  80  of the canister  5  and less than the overall length of the canister  5  including the body  18  and the valve stem  19 . Also, the total distance over which the two buttons  34  are moved relative to one another is greater than the distance by which the body  18  and the valve stem  19  of the canister  5  are relatively compressed. This is achieved by the leverage obtained by the loading spring  31  engaging lever  40  at a point further away from the pivot  41  than the canister engagement portion  42 . 
     The actual flow recommended in order to correctly deliver a drug will depend on the manner operation of the drug, the position where it should be deposited in the mouth, lungs of the user and the manner of dispensing the drug. Some drugs are inhaled as a fine mist and transported all the way to the lungs whereas others are inhaled like a jet of liquid deposited in the mouth of the person. These different types of drugs require different types of inhalation and therefore different inhalation flows and different actions by the user. 
     It is possible to adapt each of a number of different inhalers for use with a number of different types of drug by giving each inhaler an opening with a different shape and giving different closure elements shapes which conform with a single type of inhaler. For example, a possible different shape is illustrated by the dotted line in FIG.  1 . Thus canister with differently shaped closure elements are for use exclusively with the inhaler having a conforming opening. The different shapes may prevent a closure element from being fitted in an inhaler of the inhaler having a conforming opening. Alternatively, the closure element may fail to close the vent of an inhaler having a differently shaped opening such that the remaining opening vents the flow sufficiently to prevent operation of the triggering mechanism.