Abstract:
A dose indicator device for a pressurized metered dose inhaler comprises an inner wheel, annular outer wheel, actuator and housing;
       the inner wheel comprising primary indexing teeth and a flexible drive arm;   the outer wheel comprising secondary indexing teeth on an outer face of the outer wheel;   the inner wheel and outer wheel located at least partially within the housing such that the inner wheel and outer wheel are rotatable about a common longitudinal axis of rotation;   the actuator movable in a plane perpendicular to the axis of rotation to engage the primary indexing teeth to rotate the inner wheel;   the housing being fixed relative to the axis of rotation and comprising a deflector;   the deflector configured such that, on rotation of the inner wheel, the drive arm is intermittently deflected and brought into contact with the secondary indexing teeth to rotate the outer wheel about the axis of rotation.

Description:
The present disclosure relates to a dose indicator device and apparatus comprising such devices, and in particular to a dose indicator device for use with, or incorporated as part of a pressurised metered dose inhaler. 
     BACKGROUND 
     It has been recognised that there is a need to provide accurate information to a user of a dispensing apparatus, such as a pressurised metered dose inhaler, concerning the quantity of doses delivered from, or remaining in, the dispensing apparatus. Without such information, there is a danger that a user may be unaware that the dispensing container of the dispensing apparatus is empty or close to empty. This is especially dangerous where the dispensing apparatus is for use in delivering medicinal compounds for the treatment of chronic or acute symptoms, for example, as in the case of a pressurised metered dose inhaler used for treating asthmatic reactions. 
     It is known to provide a dispensing apparatus with a dose indicator device. Typically such dose indicator devices are triggered by movement of the dispensing container wherein the movement either directly or indirectly provides the motive force for incrementing or decrementing the dose indicator device. EP1758631 disclose one example of a dose indicator device. This device, while accurate and robust, comprises a relatively large number of separate components. 
     It would be desirable to produce a dose indicator device that requires fewer components. 
     SUMMARY OF THE DISCLOSURE 
     According to the present disclosure there is provided a dose indicator device for a pressurised metered dose inhaler comprising: 
     an inner wheel, an annular outer wheel, an actuator and a housing; 
     the inner wheel comprising a plurality of primary indexing teeth and a flexible drive arm; 
     the annular outer wheel comprising a plurality of secondary indexing teeth on an outer face of the annular outer wheel; 
     the inner wheel and outer annular wheel being located at least partially within the housing such that the inner wheel and annular outer wheel are rotatable about a common longitudinal axis of rotation; 
     the actuator being movable in a plane perpendicular to the longitudinal axis of rotation to engage the primary indexing teeth of the inner wheel to rotate the inner wheel; 
     the housing being fixed relative to the longitudinal axis of rotation and comprising a deflector; 
     the deflector being configured such that, on rotation of the inner wheel, the flexible drive arm is intermittently deflected by the deflector and is thereby brought into contact with the secondary indexing teeth so as to rotate the annular outer wheel about the axis of rotation. 
     Advantageously, the dose indicator device comprises a relatively small number of separate components and is suitable to form a compact, space-saving design. 
     The inner wheel may be cylindrical in shape and may be solid or may be provided with a central bore. The inner wheel may have a stepped diameter with portions of different diameter. 
     The annular outer wheel may have the form of a ring and may be circular in shape. 
     The inner wheel may be at least partially nested within the longitudinal extent of the annular outer wheel. By arranging the inner wheel at least partly within the annular outer wheel the ‘depth’ of the dose indicator device measured in a direction along the longitudinal axis of rotation may be minimised, since it is not necessary to stack the two wheels one upon the other. 
     The deflector may be configured such that, on rotation of the inner wheel, the flexible drive arm is intermittently deflected by the deflector inwardly towards the longitudinal axis. 
     In one aspect a proximal end of the flexible drive arm of the inner wheel may be located closer to the longitudinal axis than the secondary indexing teeth and a distal end of the flexible drive arm may be located further from the longitudinal axis than the secondary indexing teeth when not in contact with the deflector. Thus, the flexible drive arm is enabled to engage the secondary indexing teeth on the outer face of the annular outer wheel. 
     The housing may further comprise a first flexible restraint which engages the inner wheel to restrain rotation of the inner wheel when not being rotated by the actuator and a second flexible restraint which engages the annular outer wheel to restrain rotation of the annular outer wheel when not being rotated by the inner wheel. 
     The restraints advantageously serve to restrain movement of the inner wheel and annular outer wheel other than when the wheels are being positively driven during a counting action. This helps to minimise the chances of the dose indicator device changing the displayed indication if the device is dropped, shaken or otherwise knocked. 
     The inner wheel may comprise a plurality of indentations on an outer face of the inner wheel which are engagable by the first flexible restraint. The plurality of indentations may be located circumferentially around the inner wheel with the primary indexing teeth located to one side of the plurality of indentations. The indentations may have a cross-sectional shape that is part-circular or otherwise smoothly curved and the portion of the first flexible restraint that engages the indentations may have a matching circular shape. 
     The second flexible restraint may be engagable with the secondary indexing teeth of the annular outer wheel. The secondary indexing teeth may have a cross-sectional shape that is part-circular or otherwise smoothly curved and the portion of the second flexible restraint that engages the secondary indexing teeth may have a matching circular shape. 
     The housing may comprise a mounting aperture for the inner wheel enabling the inner wheel to rotate therein relative to the housing. Advantageously the housing may function to mount and locate the annular outer wheel and the inner wheel relative to one another while allowing both wheels to rotate. 
     In one aspect the inner wheel may comprise a plurality of indentations on an outer face of the inner wheel which are engagable by the first flexible restraint and wherein the plurality of indentations form the bearing surface of the inner wheel in the mounting aperture. In this aspect, a portion of a boundary of the mounting aperture may comprise a first flexible restraint which is engagable with the plurality of indentations of the inner wheel to restrain rotation of the inner wheel when not being rotated by the actuator. 
     In one aspect the actuator may be provided on an actuator member, said actuator member being movable by a dispensing container of a pressurised metered dose inhaler into an indexing position on actuation of the pressurised metered dose inhaler to engage the actuator with the primary indexing teeth of the inner wheel to rotate the inner wheel; wherein said actuator member may be biased away from the indexing position such that the actuator is disengaged from the primary indexing teeth when the pressurised metered dose inhaler is in a non-dispensing position. 
     The actuator member may take the form of a plunger or carriage which is slidable relative to an actuator housing of the pressurised metered dose inhaler. The actuator member may comprise a head part that in use is contacted by a part of the dispensing container of the pressurised metered dose inhaler (such as the valve ferrule), a stem part that movably mounts the actuator member to the housing of the pressurised dispensing container and the actuator itself which may be in the form of a flexible arm. The actuator member may comprise an aperture into or through which a portion of the inner wheel extends so as to locate the primary indexing teeth in alignment with the actuator. Again, this allows for a more compact arrangement of the components. The biasing of the actuator member may be achieved by providing a compression spring between the stem part and the actuator housing or by integrating a flexible, sprung leg into the actuator member that is compressed and strained during actuation of the pressurised metered dose inhaler. In one aspect, the head part of the actuator member comprises an annular yoke through which on assembly a valve stem of the pressurised dispensing container projects. In this aspect the stem part may comprise a carriage that slides within a C-section channel provided on the actuator housing. The stem part may comprise at least one downwardly extending leg on which is provided the flexible arm actuator. The C-section channel comprises the aperture allowing the inner wheel to project therethrough. 
     The intermittent engagement of the one or more secondary indexing teeth of the inner wheel and the indexing teeth of the annular outer wheel serve to enable the annular outer wheel to be incremented only after a plurality of rotational increments of the inner wheel. For example, the inner wheel and the annular outer wheel may have a gear ratio such that for every 10 incremental rotations of the inner wheel the annular outer wheel is incrementally rotated once. Consequently, for every 10 actuations of the inner wheel by the actuator the inner wheel will rotate through 360° and the flexible drive arm of the inner wheel will be deflected to engage the secondary indexing teeth of the annular outer wheel once to rotate it one increment. In another example, a gear ratio of 10:1 can be achieved by providing two flexible drive arms on the inner wheel at 180° spacing, two deflectors on the housing at 180° spacing and 20 primary indexing teeth. Other gear ratios can be used as desired. For example, the annular outer wheel can be arranged to incrementally rotate every 20 actuations of the pressurised dispensing container by providing one flexible drive arm and 20 primary indexing teeth on the inner wheel. 
     The housing may comprise a first housing part which is engagable with a wall portion of an actuator housing of a pressurised metered dose inhaler to define a housing enclosure containing the inner wheel and annular outer wheel. Advantageously, the components of the dose indicator device are kept in correct alignment by being held between the housing of the dose indicator device and the actuator housing which therefore requires fewer components than needed for a dose indicator housing that itself fully defines the housing enclosure. 
     The first housing part may comprise the deflector. 
     The inner wheel and/or annular outer wheel may comprise dosage indicia. The dosage indicia may be in the form of numbers, words, letters, colours, pictograms or similar. For example a decreasing series of numbers can be displayed: 200, 190, 180, 170, etc. where a gear ratio of 10:1 is used between the inner wheel and the outer annular wheel. Alternatively, where it is not desired to show a numerical count but simply to indicate to a user that the end of the useful life of the pressurised metered dose inhaler is approaching, the indicia could be in the form of a changing colour, e.g. a display that changes from green, through orange to red, or in the form of words which are displayed near or at the end of the pack life such as “Order replacement now” and “Empty”. 
     Dosage indicia may be presented only on the annular outer wheel where individual dosage counts are not to be displayed to a user. Alternatively, the inner wheel may also be provided with dosage indicia where individual dosage counts are desired to be displayed. 
     The dosage indicia may be provided on an end face of the inner wheel and/or outer wheel, the end faces being perpendicular to the longitudinal axis. 
     The present disclosure also relates to a pressurised metered dose inhaler comprising an actuator housing, a pressurised dispensing container received in the actuator housing and a dose indicator device as described in any of the aspects above. 
     The pressurised metered dose inhaler may comprise a housing enclosure containing the inner wheel and annular outer wheel, the housing enclosure being defined by a first housing part of the dose indicator device and a wall portion of the actuator housing. 
     The wall portion may comprises a rear wall of the actuator housing such that the housing enclosure is located between a stem block and the rear wall of the actuator housing. Advantageously, positioning the dose indicator to the rear of the stem block permits a clear airway to be provided between the stem block and the front of the actuator housing. 
     In one embodiment, the actuator housing may be formed from two mouldings, comprising a front case and a rear case. The front case may comprise the dispensing orifice (mouthpiece or nasal piece for example). The actuator housing may have a split line between the front and rear cases that runs down the length of the actuator housing to split the compartment receiving the pressurised dispensing container in two. The front and rear cases may be joined by a snap-fit arrangement. 
     In an alternative embodiment, the actuator housing may be formed from two mouldings, comprising a top case and a bottom case. The bottom case may comprise the dispensing orifice (mouthpiece or nasal piece for example). The top and bottom cases may be joined by a snap-fit arrangement. 
     The pressurised metered dose inhaler may further comprise a window in the actuator housing for viewing the inner wheel and/or outer wheel therethrough. 
     The window may be sized so as only to show the annular outer wheel and to obscure view of the inner wheel. Alternatively both wheels may be visible. 
     The components of the dose indicator device and actuator housing are preferably formed from plastics mouldings, except for the compression spring (when present) which may be metal or plastic. 
     Rigid components of the dose indicator device may be formed from, for example, polyester, nylon, polypropylene, polyacetal, ABS or similar. 
     Preferably, the flexible drive arm, flexible restraints and the actuator drive arm are formed from an elastic material such that imparted strains during normal actuation are recoverable elastically. A suitable example is polyacetal (POM). 
     The dose indicator device may be used with, or form a part of a pharmaceutical dispensing device, such as, for example, a pulmonary, nasal, or sub-lingual delivery device. A preferred use of the dose indicator device is with a pharmaceutical pressurised metered dose aerosol inhaler device. The term pharmaceutical, as used herein, is intended to encompass any pharmaceutical, compound, composition, medicament, agent or product which can be delivered or administered to a human being or animal, for example pharmaceuticals, drugs, biological and medicinal products. Examples include antiallergics, analgesics, bronchodilators, antihistamines, therapeutic proteins and peptides, antitussives, anginal preparations, antibiotics, anti-inflammatory preparations, hormones, or sulfonamides, such as, for example, a vasoconstrictive amine, an enzyme, an alkaloid, or a steroid, including combinations of two or more thereof. In particular, examples include isoproterenol [alpha-(isopropylaminomethyl) protocatechuyl alcohol], phenylephrine, phenylpropanolamine, glucagon, adrenochrome, trypsin, epinephrine, ephedrine, narcotine, codeine, atropine, heparin, morphine, dihydromorphinone, ergotamine, scopolamine, methapyrilene, cyanocobalamin, terbutaline, rimiterol, salbutamol, flunisolide, colchicine, pirbuterol, beclomethasone, orciprenaline, fentanyl, and diamorphine, streptomycin, penicillin, procaine penicillin, tetracycline, chlorotetracycline and hydroxytetracycline, adrenocorticotropic hormone and adrenocortical hormones, such as cortisone, hydrocortisone, hydrocortisone acetate and prednisolone, insulin, cromolyn sodium, and mometasone, including combinations of two or more thereof. 
     The pharmaceutical may be used as either the free base or as one or more salts conventional in the art, such as, for example, acetate, benzenesulphonate, benzoate, bicarbonate, bitartrate, bromide, calcium edetate, camsylate, carbonate, chloride, citrate, dihydrochloride, edetate, edisylate, estolate, esylate, fumarate, fluceptate, gluconate, glutamate, glycollylarsanilate, hexylresorcinate, hydrobromide, hydrochloride, hydroxynaphthoate, iodide, isethionate, lactate, lactobionate, malate, maleate, mandelate, mesylate, methylbromide, methylnitrate, methylsulphate, mucate, napsylate, nitrate, pamoate, (embonate), pantothenate, phosphate, diphosphate, polygalacturonate, salicylate, stearate, subacetate, succinate, sulphate, tannate, tartrate, and triethiodide, including combinations of two or more thereof. Cationic salts may also be used, for example the alkali metals, e.g. Na and K, and ammonium salts and salts of amines known in the art to be pharmaceutically acceptable, for example glycine, ethylene diamine, choline, diethanolamine, triethanolamine, octadecylamine, diethylamine, triethylamine, 1-amino-2-propanol-amino-2-(hydroxymethyl)propane-1,3-diol, and 1-(3,4-dihydroxyphenyl)-2 isopropylaminoethanol. 
     The pharmaceutical will typically be one which is suitable for inhalation and may be provided in any suitable form for this purpose, for example as a solution or powder suspension in a solvent or carrier liquid, for example ethanol, or isopropyl alcohol. Typical propellants are HFA134a, HFA227 and di-methyl ether. 
     The pharmaceutical may, for example, be one which is suitable for the treatment of asthma. Examples include salbutamol, beclomethasone, salmeterol, fluticasone, formoterol, terbutaline, sodium chromoglycate, budesonide and flunisolide, and physiologically acceptable salts (for example salbutamol sulphate, salmeterol xinafoate, fluticasone propionate, beclomethasone dipropionate, and terbutaline sulphate), solvates and esters, including combinations of two or more thereof. Individual isomers such as, for example, R-salbutamol, may also be used. As will be appreciated, the pharmaceutical may comprise of one or more active ingredients, an example of which is flutiform, and may optionally be provided together with a suitable carrier, for example a liquid carrier. One or more surfactants may be included if desired. 
    
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
       Embodiments of the present disclosure will now be described, by way of example, with reference to the accompanying drawings, in which:— 
         FIG. 1  is a perspective view of a pressurised metered dose inhaler comprising a dose indicator device according to the present disclosure and including a pressurised dispensing container; 
         FIG. 2  is an exploded perspective view of the pressurised metered dose inhaler of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of the pressurised dispensing container of  FIG. 1  from another angle; 
         FIG. 4  is an exploded perspective view of the pressurised dispensing container of  FIG. 1  from another angle; 
         FIG. 5  is a side elevation of a portion of a dose indicator device according to the present disclosure; 
         FIG. 6  is a cross-sectional view of the portion of the dose indicator device of  FIG. 5 ; 
         FIG. 7  is an end elevation of the portion of the dose indicator device of  FIG. 5 ; 
         FIG. 8  is an exploded perspective view of the portion of the dose indicator device of  FIG. 5 ; 
         FIG. 9  is an exploded perspective view of the portion of the dose indicator device of  FIG. 5  from another angle; 
         FIG. 10  is a perspective view of another embodiment of pressurised metered dose inhaler comprising a dose indicator device according to the present disclosure and including a pressurised dispensing container; 
         FIG. 11  is a rear view of the pressurised metered dose inhaler of  FIG. 10 ; and 
         FIG. 12  is a cross-sectional view of the pressurised metered dose inhaler of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a pressurised metered dose inhaler  1  which comprises an actuator housing  2  that contains a pressurised dispensing container  3 . 
     The actuator housing  2  comprises a generally tubular body  7  and a depending mouthpiece  6  at one end covered by a dust cap  106 . The tubular body  7  may have a generally circular cross-sectional shape. However, in the illustrated example the tubular body  7  comprises a squarer cross-sectional shape with a front wall  7   a , side walls  7   b  and rear wall  7   c . A stem block  8  is provided at a basal end of the tubular body  7  nearest the mouthpiece  6 . The actuator housing  2  may be formed from two mouldings comprising a front case  17   a  and a rear case  17   b . The front case  17   a  comprises the mouthpiece  6  and a portion of the tubular body  7  comprising the front wall  7   a  and half of each side wall  7   b . In addition; the front case  17   a  comprises a base  7   d  of the actuator housing  2  from which project the stem block  8 , a C-section channel  8  and a tubular extension  10  defining a bore. The C-section channel  80  comprises an aperture  81 . The rear case  17   b  comprises the rear wall  7   c  and the remainder of the side walls  7   b . A rim  71  provided on an inner face of the rear case  17   b , as shown in  FIG. 4 , defines a cavity  71   a  the function of which will be described below. The rim  71  is generally circular except for a flattened section  71   a . The front and rear cases  17   a ,  17   b  may be snap-fit together by means of formations  7   e  on each casing. A viewing window  62  in the form of a cut out is provided in the rear wall  7   c  of the actuator housing  2 . A lock-out aperture  61  is provided in the front wall  7   a  just above the mouthpiece  6 . The dust cap  106  is provided with a body that encloses the mouthpiece  6  and a tang  161  that in use can protrude through the lock-out aperture  61  when the dust cap  106  is in position on the mouthpiece  6 . 
     The pressurised dispensing container  3  typically comprises a canister  4  and a valve (not shown). To assemble the pressurised metered dose inhaler, the dispensing container  3  is inserted into an open end  7   f  of the tubular body  7  of the housing  2  such that a valve stem of the valve is received in the stem block  8 . 
     According to the present disclosure, the pressurised metered dose inhaler  1  includes a dose indicator device marked generally by reference  9 . The dose indicator device is located towards the mouthpiece end of the tubular body  7  situated between the stem block  8  and the rear wall  7   c.    
     In general the dose indicator device  9  comprises an inner wheel  11 , an annular outer wheel  12 , an actuator member  13 , a cup-shaped housing  70  and a spring  15 . The cup-shaped housing  70  of the dose indicator device  9  defines, together with the rear wall  7   c , a housing enclosure of the dose indicator device  9  which locates and aligns the inner wheel  11  and annular outer wheel  12 . 
     In the following description, unless the context otherwise requires, the term “inwardly-facing” refers to a direction which is inwards towards the pressurised dispensing container  3  within the tubular body  7 . The term “outwardly-facing” refers to a direction which is outwards away from the pressurised dispensing container  3  within the tubular body  7 . Further, unless the context otherwise requires, terms such as “upwards” refer to the direction towards the open end  7   f  of the tubular body  7  while terms such as “downwards” refer to the opposite direction. 
     The inner wheel  11  comprises a generally solid cylindrical body  20  that is mounted in use to rotate about a first rotational axis  21  as marked on  FIG. 5 . The body  20  is provided with three layers which are positioned adjacent to one another in a direction along the first rotational axis  21 . The first layer comprises a plurality of primary indexing teeth  22 . In the example shown there are 10 primary indexing teeth  22 . Adjacent the primary indexing teeth  22  is the second layer which comprises a plurality of indentations  24 . Each indentation  24  takes the form of a part circular cut out in the body  20  of the inner wheel  11 . In the example shown there are 10 indentations  24 ,  1  for each of the primary indexing teeth  22 . Adjacent the indentations  24  is the third layer which comprises a flexible drive arm  23 . The flexible drive arm  23  comprises an arm portion  23   a  that depends from the body  20  and terminates at a distal end with a circular pin  23   b . As shown most clearly in  FIG. 9 , an end face  20   a  of the body  20  of the inner wheel  11  comprises a peripheral rebate  25 . 
     The annular outer wheel  12 , as shown in  FIG. 8 , has a generally annular body  30  which in use is rotatable about the longitudinal axis  21 . The body  30  comprises an annular portion  38  a dependent flange  36 . The annular body  30  defines a central aperture  31  which accommodates on assembly as described below a portion of the inner wheel  11 . The flange  36  extends both radially outwards of the annular portion  38  and also for a distance radially inwardly of the annular portion  38  to define an annular shoulder  39  as shown in  FIG. 8 . A plurality of indexing teeth  33  are provided around an outer face of the annular portion  38 . In the example shown  21  indexing teeth  33  are provided. As well as the indexing teeth  35 , the outer face of the annular portion  38  is provided with a land  33   a  the function of which will be described below. 
     An outwardly-facing face  36   a  of the flange  36  and/or the end face  20   a  of the inner wheel  11  are provided with one or more indicia to provide information to a user of the pressurised metered dose inhaler  1  regarding the number of doses dispensed from the inhaler or remaining in the inhaler. For example, the indicia may comprise a set of increasing or decreasing numbers, a series of pictograms, a series of words or a band of changing colour—e.g. a band which changes from green to red around the circumference of the annular outer wheel  12 . 
     As shown in  FIGS. 2 to 4 , the actuator member  13  comprises a yoke  41  at its upper end from which depend two legs  42  defining a channel  44  therebetween. An actuator drive arm  45  in the form of a flexible extension is provided on one of the legs  42  facing, and extending into, the channel  44 . In use, as described below the actuator drive arm  45  drives the rotation of the inner wheel  11 . Also depending from the yoke  41  is a plunger rod  46 . 
     The cup-shaped housing  70  is shown most clearly in  FIGS. 8 and 9 . The cup-shaped housing  70  comprises a body  50  which has a generally disc-shaped planar portion  51  and a dependent rim  52  which is generally circular except for a flattened section  52   a . A projection  74  located at one point of the periphery of the body  50  projects perpendicularly to the planar portion  51 . The disc-shaped portion  51  of the body  50  comprises a centrally-located aperture  54  bounded by a rim  54   a  which, as described below, in use accommodates a portion of the inner wheel  11 . A portion of the rim  54   a  is interrupted and in the gap is provided a first flexible restraining arm  57  in the form of a flexible arm portion which has a circular pin at its distal end. A second flexible restraining arm  55  that again has a circular formation at its distal end is provided on the inner face of the rim  52 . Opposite the restraining arm  55  is provided on the inner face of the rim  52  a deflector  59  the function of which will be described below. 
     To assemble the pressurised metered dose inhaler  1 , the annular outer wheel  12 , inner wheel  11  and cup-shaped housing  70  are first nested together. When nested the primary indexing teeth  22  of the inner wheel  11  project through the aperture  54  with the indentations  24  being aligned with and bearing against the inner face of the rim  54   a . Also the peripheral rebate  25  of the inner wheel  11  engages against the shoulder  39  of the annular outer wheel  12 . With the inner wheel  11  and annular outer wheel  12  nested together the pin  23   b  of the flexible drive arm  23  lies radially just outwards of the location of the indexing teeth  33  of the annular outer wheel  12  but extends in the direction of the longitudinal axis  21  to be in line with the plane of the indexing teeth  33  as shown in  FIG. 6 . As such, the arm portion  23   a  of the flexible drive arm  23  spans the annular portion  38 . At the same time, the restraining arm  55  of the cup-shaped housing  70  is engaged with one of the indexing teeth  33 . The flange  36  is fully received within the cavity of the cup-shaped housing  70 . As such, a very compact arrangement is obtained as shown in  FIG. 5  where the depth of the inner wheel  11  and annular outer wheel  12  are fully contained within the depth of the cup-shaped housing  70 . 
     The nested annular outer wheel  12 , inner wheel  11  and cup-shaped housing  70  are then inserted into the cavity  71   a  defined by the rim  71  of the rear case  17   b . The rim  71  serves to locate the other components and prevent rotation of the cup-shaped housing  70  relative to the rear case  17   b  by virtue of the inter-engagement of the flattened sections  52   a  and  71   b.    
     Next, the spring  15  is inserted into the bore of the tubular extension  10 . The actuator member  13  is then inserted with the two legs  42  being slidingly received in the C-section channel  80 . At the same time the plunger rod  46  is engaged in the open end of the bore of the tubular extension  10  so as to contact and rest on the upper end of the spring  15 . 
     The front and rear cases  17   a  and  17   b  are then fastened together. Once fastened the cup-shaped housing  70  is abutted against the rear face of the C-section channel  80  such that the indexing teeth  22  of the inner wheel  1  project through the aperture  81  in the C-section channel  80  into alignment with the legs  42  and flexible drive arm  45  of the actuator member  13 . The abutment prevents any of the components becoming disengaged from one another. In addition, when abutted the projection  74  of the cup-shaped housing spans across the top of the C-section channel  80  preventing the actuator member  13  from becoming detached from the C-section channel is the actuator housing is inverted. 
     A pressurised dispensing container  3  can now be inserted through the open end  7   f  of the tubular body  7  such that a leading face of a ferrule of the dispensing container  3  contacts the yoke  41  of the actuator member  13 . The aperture in the middle of the yoke  41  accommodates the valve stem to enable it to project beyond the yoke  41  into engagement with the stem block  8 . The action of the spring  15  on the base of the plunger rod  46  ensures that in the rest position, the yoke  41  is held in face to face contact with the ferrule of the dispensing container  3 . 
       FIGS. 6 and 7  illustrate the relative positions of the inner wheel  11 , annular outer wheel  12  and cup-shaped housing  70  at the rest position. At rest, the distal end of the actuator drive arm  45  is out of contact with the primary indexing teeth  22  of the inner wheel  11 . Also, in this rest position, the first flexible restraining arm  57  is engaged with one of the indentations  24  of the inner wheel  11  and the second flexible restraining arm  55  is engaged with one of the indentations  33  of the annular outer wheel  12 . The purpose of the first and second flexible restraining arms is to restrain inadvertent rotation in either direction of either the inner wheel  11  or the annular outer wheel  12  other than when the components are being actively driven on actuation of the dispensing container  3  as will be described below. In other words, the action of the flexible restraining arms helps to prevent actuation of the dose indicator device  9  if the device is dropped, shaken or knocked. 
     In operation, as is normal for a pressurised metered dose inhaler, the dispensing container  3  is depressed relative to the housing  2  such that the canister  4  moves downwardly within tubular body  7  towards the stem block  8  to actuate the valve. 
     On actuation of dispensing container  3 , downward movement of the canister  4  and valve  5  within the tubular body  7  causes the actuator member  13  to be moved downwardly within the tubular body  7  so as to compress spring  15  due to contact between the yoke  41  and the ferrule. At the same time, the legs  42  and thus the actuator drive arm  45  are moved downwardly relative to the C-shaped channel  80  and the inner wheel  11 . This brings the distal end of the actuator drive arm  45  into contact with one of the primary indexing teeth  22  and onward movement of the actuator arm  45  causes the inner wheel  11  to be rotated by one increment. Rotation of the inner wheel  11  is accommodated by radially-outward flexing of the first flexible restraining arm  57  such that the circular formation at the distal end of the first flexible restraining arm  57  is displaced from its initial indentation  24  and then re-engages into a neighbouring indentation  24  associated with a neighbouring primary indexing tooth  22  to that being engaged by the actuator drive arm  45 . During rotation of the inner wheel  11  the pin  23   b  moves around the annular gap between the teeth  33  of the annular outer wheel  12  and the rim  52  of the cup-shaped housing  70 . This movement of the pin  23   b  does not interact with the teeth  33  until contact with the deflector  59  as described below. 
     On release of the dispensing container  3 , the dispensing container  3  moves back upwardly within the tubular body  7  under the internal spring bias of the valve  5 . This upward movement allows the actuator member  13  to move back upwardly within tubular body  7  under action of spring  15 . This causes in turn the legs  42  and yoke  41  to move back upwardly relative to the inner wheel  11  back into the at rest position. Depending on the number of primary indexing teeth  22  and their relative spacing, this upward movement may be accommodated by the actuator drive arm  45  flexing and riding back over the neighbouring primary indexing tooth  22 . In such a situation, the engagement of the first flexible restraining arm  57  in the indentation  24  prevents any back rotation of the inner wheel  11 . 
     Thus, on each actuation of the dispensing container  3 , the inner wheel  11  is rotated by one increment. Successive actuations of the dispensing container  3  continue to rotate the inner wheel  11  until the point that the pin  23   b  moves round into engagement with the deflector  59 . At this point, on actuation of the dispensing container  3 , the inner wheel  11  is rotated as described above and at the same time the pin  23   b  is deflected radially inwardly into engagement with one of the teeth  33  of the annular outer ring such that the annular outer wheel  12  is rotated by one increment. Advantageously, no transmission cog is required to transfer the motive force from the inner wheel  11  to the annular outer wheel  12 . As with the movement of the inner wheel  11 , the rotation of the annular outer wheel  12  is accommodated by radially-outward flexing of the second flexible restraining arm  55  to move the circular formation at the distal end of the second flexible restraining arm from its tooth  33  on to a neighbouring tooth  33 . Both the inner wheel  11  and the annular outer wheel  12  rotate in the same sense, which may be designed to be either clockwise or anti-clockwise. 
     In this way, reciprocal longitudinal movement of the dispensing container  3  can be used to create rotational movement of the inner wheel  11  and the annular outer wheel  12  to change display of dosage indicia provided on the inner wheel  11  and or annular outer wheel  12 . 
     At the end of life of the pack the rotation of the inner wheel  11  will bring the pin  23   b  into contact with the land  33   a  of the annular outer wheel  12 . At this point further rotation of the annular outer wheel  12  is prevented since the pin  23   b  is unable to engage with a tooth  33  to rotate the annular outer wheel  12 . 
     When not in use the dust cap  106  can be placed on the mouthpiece  6 . The tang  161  projects through the lock-out aperture  61  to prevent actuation of the counter by contacting and blocking downward movement of the yoke  41 . 
       FIGS. 10 to 12  show another embodiment of pressurised metered dose inhaler  1  according to the present disclosure. The structure and function of this embodiment is similar to that of the embodiment of  FIGS. 1 to 9  and in the following only the differences will be described in detail. Equivalent features have been referenced using equivalent reference numerals. 
     The tubular body  7  of the actuator housing  2  of this embodiment is formed from two mouldings comprising a top case  117   a  and a bottom case  117   b . The bottom case  117   b  fully defines the mouthpiece  6 , the stem block  8  and the base  7   d  of the actuator housing. In addition, the C-section channel  80  and the tubular extension  10  form part of the bottom case  117   b . As can be seen in  FIG. 12 , the bottom case  117   b  fully houses the dose indicator device  9 . The top case  117   a  in this embodiment shields the majority of the body of the pressurised dispensing container  3 . The top case  117   a  may be formed from a transparent or translucent material to allow markings or writing on the pressurised dispensing container  3  to be read without the need to remove the container from the actuator housing  2 . 
     The top and bottom cases  117   a ,  117   b  may be snap-fit together by means of formations on each casing. 
     As before, the pressurised dispensing container  3  is inserted into the actuator housing  2  through the open upper end  7   f —in this embodiment fully defined by the top case  117   a.    
     Operation of the pressurised metered dose inhaler  1 , including actuation of the dose indicator device  9  is the same as in the previous embodiment.