Abstract:
A disposable inhaler that includes a deagglomeration section is disclosed. The deagglomeration section has a section inlet, a section outlet, and a divider for splitting the stream of air into two flow parts. The divider has a surface that faces the section inlet at an angle substantially perpendicular to the stream of air passing through the section inlet, and the walls of the inhalation channel within the inhaler are shaped so as to cause substantially no resistance to or turbulence in the air flow through the inhaler.

Description:
BACKGROUND 
     The present invention relates to a disposable inhaler, particularly for administering powder by inhalation. 
     Previously, as described in WO93/17728 and illustrated in FIGS. 1 to  3  of the accompanying drawings, there was known a disposable inhaler constructed from two parts  1  and  2 . The lower part  2  includes a recesses  3  in which a dose of powder is stored and the two parts together define a channel through which a stream of air may be drawn by a user from an air inlet  4  to a mouthpiece  5 . A tape  6  is provided to cover the recesses  3  and is additionally bent around the outside of the part  2  to cover an aperture  8  in the bottom of the recess  3 . In use, the tape  6  is pulled away from the lower part  2  so as to expose both the aperture  8  and the recess  3 . Projections  7  are provided to keep the loose tape out of the way of the air flow and a depression  9  directs the air flow to pick up the powder in the recess  3  more effectively. The channel defined by parts  1  and  2  also includes a deagglomeration section  10  having a section inlet  11 , a section outlet  12  and a divider  13 . The divider  13  splits the stream of air into two flow paths and powder is caused to impact on internal surfaces. In this way, powder is effectively deagglomerated. 
     In use, a patient inhales through the mouthpiece  5  causing an air stream to pick up the powder stored in recess  3 . As the air/powder mixture flows through the inhaler, powder is deagglomerated then passes out of the mouthpiece  5  and into the lungs of the patient. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide improved deagglomeration of powder, in other words to increase the fine particle fraction and fine particle dose. 
     Another object of the present invention is to minimize retention of powder within the inhaler. 
     With regard to these two objects, the prior art of FIGS. 1 to  3  included an inhalation channel which directed the air flow along a path with walls that change direction. The changes in the direction of the walls results in powder impacting with those walls and a generally turbulent air flow which assists in deagglomeration of powder. 
     The present invention is based on the realization that the effects of deagglomeration of powder by the channelling surfaces or any of the surfaces facing downstream of the surfaces of the divider  13  are relatively insignificant. 
     According to the present invention there is provided an inhaler for administering powder by inhalation, the inhaler comprising: 
     a channel through which a stream of air may be drawn by inhalation of a user; and 
     a powder dispenser for providing said powder in said stream of air for inhalation by the user; wherein 
     said channel includes at least one deagglomeration section with a section inlet, a section outlet downstream of said section inlet and a divider between said section inlet and said section outlet for dividing said stream of air either side of said divider; and wherein 
     said divider has a surface opposite said section inlet and said surface is oriented at an angle substantially perpendicular to the flow of said stream of air passing through said section inlet. 
     In this way, powder carried in the air stream is more effectively deagglomerated and the final air/powder mixture inhaled by the user has a higher fine particle fraction and fine particle dose. By providing a perpendicular surface to the divider, there is greater impact of powder with the surface of the divider causing improved deagglomeration throughout the air/powder mixture. Furthermore, impact of the powder with the surface of the divider, together with the air flow past the surface prevents undue retention of powder on the surface. When a large powder particle impacts with the surface, it breaks into smaller particles which rebound back into the airflow and are carried on through the inhaler by that air flow. 
     Preferably, the surface of the divider extends over at least the area corresponding to a projection of the section inlet on to said divider. 
     By providing a perpendicular surface over the entire width of the section inlet, the effects and advantages discussed above are maximised. 
     According to the present invention there is also provided an inhaler for administering powder by inhalation, the inhaler comprising: 
     a channel through which a stream of air may be drawn by inhalation of a user; and 
     a powder dispenser for providing said powder in said stream of air for inhalation by the user; wherein 
     said channel includes at least one deagglomeration section with a section inlet, a section outlet downstream of said section inlet and a divider between said section inlet and said section outlet for dividing said stream of air either side of said divider, said divider having a surface substantially opposite said section inlet for dividing the air flow entering through said section inlet and affecting deagglomeration of powder in the air flow; and wherein 
     surfaces of the at least one deagglomeration section are shaped and spaced apart so as substantially not to cause any restriction to or turbulence in the stream of air through the inhaler. 
     According to the present invention, it has been recognized that most of the deagglomeration occurs on the surface of the divider opposite the section inlet and that, with the same size of inhaler and same fine particle fraction/dose, the shape of the walls defining the channel through the inhaler may be modified to reduce the flow resistance and retention of the inhaler. 
     In particular, with a particular shape and size of divider surface opposite the section inlet for deagglomeration of powder, the remaining surfaces of the deagglomeration section should be shaped to follow the natural flow path of the air deflected either side of the divider. Clearly, this results in reduced deagglomeration effects in the rest of the inhaler other than the deagglomeration surface. However, as mentioned above, the present invention recognizes that the effects of deagglomeration in these parts are relatively insignificant. The advantages of the present invention are that, with reduced disturbance, restriction, turbulence etc. of the stream of air, there is less opportunity for powder to be deposited in the inhaler and the flow resistance experienced by the user inhaling through the inhaler is minimized. 
     Each section inlet may be fed by one or more substantially straight sections or channels. 
     The advantage of this is that the powder particles carried in the stream of air then have a well defined momentum towards the facing surface of the deagglomeration divider. This maximizes the number of larger powder particles which leave the direction of flow of the stream of air and which continue straight on to impact with the divider. 
     Preferably, two deagglomeration sections are provided with the section outlet of one deagglomeration section being in fluid connection with the section inlet of the other deagglomeration section. 
     The channels formed either side of the divider of one deagglomeration section may feed directly into the section inlet of the next deagglomeration section or they may first join to form a single straight section feeding that section inlet. 
     The use of two deagglomeration sections provides further improvement in deagglomeration with further increases in the fine particle fraction and fine particle dose. In particular, the fine particles in the air/powder mixture will be carried by the airstream around the surface of the divider. However, those larger heavier particles which escaped deagglomeration by the first divider will have sufficient momentum to leave the flow of air and impact with the surface of the second divider. As with the first divider, the particles break into smaller particles which rebound back into the airstream and are carried on through the inhaler. Of course, the exact shape and size of the second deagglomeration section may differ from that of the first deagglomeration section. 
     According to the present invention, there is also provided a method of optimizing the characteristics of an inhaler including a channel through which a stream of air may be drawn by inhalation of a user and a powder dispenser for providing said powder in said stream of air for inhalation by the user, said channel including at least one deagglomeration section with a section inlet, a section outlet downstream of said section inlet and a divider between said section inlet and said section outlet for dividing said stream of air either side of said divider, the method comprising: 
     providing a surface for deagglomeration of the powder on the divider opposite said section inlet and extending over an area corresponding to a projection of the section inlet onto said divider; and 
     choosing dimensions for the rest of the deagglomeration section which cause substantially no restriction to or turbulence in the stream of air through the inhaler. 
     According to the present invention, there is also provided a method of optimizing the characteristics of an inhaler including a channel through which a stream of air may be drawn by inhalation of a user and a powder dispenser for providing said powder in said stream of air for inhalation by the user, the method comprising: 
     shaping and sizing the channel so as to cause substantially no restriction to or turbulence in the stream of air in the channel; and 
     causing the channel to change direction with a sufficient angle such that the momentum of particles of powder in the air stream requiring deagglomeration will cause the particles to leave the air flow and impact walls of the channel. 
     According to the present invention, there is also provided a method of providing deagglomerated powder at the outlet of a channel guiding a stream of air, the channel including at least one deagglomeration section with a section inlet, a section outlet downstream of said section inlet and a divider between said section inlet and said section outlet for dividing said stream of air either side of said divider, the method comprising: 
     providing powder in said channel upstream of said section inlet; and 
     providing a surface on said divider which is opposite said section inlet and which is orientated at an angle substantially perpendicular to the flow of the stream of air passing through said section inlet. 
     According to the present invention, there is also provided a method of providing deagglomerated powder at the outlet of a channel guiding a stream of air, the channel including at least one deagglomeration section with a section inlet, a section outlet downstream of said section inlet and a divider between said section inlet and said section outlet for dividing said stream of either side of said divider, said divider having a surface substantially opposite said section inlet for dividing the air flow entering through said section inlet and affecting deagglomeration of powder in the air flow, the method comprising: 
     providing powder in the channel upstream of said section inlet; and 
     shaping and spacing the surfaces of the channel so as substantially not to cause any restriction to or turbulence in the stream of air through the inhaler. 
     Medicaments suitable for administration by using the present invention are any which may be delivered by inhalation. Suitable inhalable medicaments may include for example β2-adrenoreceptor agonists for example salbutamol, terbutaline, rimiterol, fenoterol, reproterol, adrenaline, pirbuterol, isoprenaline, orciprenaline, bitolterol, salmeterol, formoterol, clenbuterol, procaterol, broxaterol, picumeterol, TA-2005, mabuterol and the like, and their pharmacologically acceptable esters and salts; anticholinergic bronchodilators for example ipratropium bromide and the like; glucocorticosteroids for example beclomethasone, fluticasone, budesonide, tipredane, dexamethasone, betamethasone, fluocinolone, triamcinolone acetonide, mometasone, and the like, and their pharmacologically acceptable esters and salts; anti-allergic medicaments for example sodium cromoglycate and nedocromil sodium; expectorants; mucolytics; antihistamines; cyclooxygenase inhibitors; leukotriene synthesis inhibitors; leukotriene antagonists, phospholipase-A2 (PLA2) inhibitors, platelet aggregating factor (PAF) antagonists and prophylactics of asthma; antiarrhythmic medicaments, tranquilisers, cardiac glycosides, hormones, antihypertensive medicaments, antidiabetic- antiparasitic- and anticancer-medicaments, sedatives and analgesic medicaments, antibiotics, antirheumatic medicaments, immunotherapies, antifungal and antihypotension medicaments, vaccines, antiviral medicaments, proteins, polypeptides and peptides for example peptide hormones and growth factors, polypeptides vaccines, enzymes, endorphines, lipoproteins and polypeptides involved in the blood coagulation cascade, vitamins and others, for example cell surface receptor blockers, antioxidants, free radical scavengers and organic salts of N,N′-diacetylcystine. 
     The present invention will be more clearly understood from the following description, given by way of example only, with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a prior art inhaler; 
     FIG. 2 illustrates the prior art inhaler of FIG. 1 separated into two parts; 
     FIGS. 3 a,    3   b  and  3   c  illustrate a cross-section of the prior art inhaler of FIG. 1; 
     FIG. 4 illustrates the air flow path through one half of an inhaler; 
     FIG. 5 illustrates an inhaler according to the present invention; 
     FIG. 6 illustrates the inhaler of FIG. 5 separated into its component parts; 
     FIG. 7 illustrates the main two parts of FIG. 5 from below; 
     FIG. 8 illustrates a cross-section of the inlet of the inhaler of FIG. 5; 
     FIG. 9 illustrates the shape of the channel section through the inhaler of FIG. 5; 
     FIGS.  10 ( a ) to ( d ) illustrate the dimensions of the channel section of FIG. 9; 
     FIG. 11 illustrates the flow path through half of the channel section of FIG. 9; 
     FIG. 12 illustrates the channel section of an alternative inhaler; 
     FIG. 13 illustrates schematically a side view of the inhaler of FIG. 6; and 
     FIG. 14 illustrates an inhaler according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As illustrated in FIGS. 5,  6  and  7 , the inhaler is constructed from a first part  20  and a second part  22  which together define an inhalation channel  24  joining an air inlet  26  and an outlet  28 . In this illustrated embodiment, the outer shape of the inhaler corresponds to the inner channelled shape. Clearly, however, this is not necessary and the outer shape may take any other form. 
     At an inlet end of the inhaler, a plate  30  is provided. The plate  30  has a depression  32  in which a dose of powder is stored. The use of a separate plate  30  in which the depression  32  is formed is particularly advantageous, since it allows the depression  32  to be made from a material different from that of the two parts  20  and  22 . In particular, it is advantageous to make the depression  32  from a strong water impermeable material such as aluminium or aluminium laminate, whereas the first and second parts  20  and  22  may be constructed of transparent plastics material, such that the inhalation channel maybe inspected before and after use. 
     As illustrated in FIG. 8, the plate  30  is secured to the first part  20  by means of a support  36 . Preferably, the plate  30  is also secured to the first part  20  along its edges  37  so as to form an enclosed cavity  38  underneath the depression  32 . 
     As illustrated in the Figures, two tapes  40 , 42  are provided respectively for sealing the upper open portion of depression  32  and an aperture  44  provided in the bottom of the depression  32 . Preferably, as illustrated, the free ends of the two tapes  40  and  42  are joined together. 
     In use, the two tapes  40  and  42  are simultaneously pulled out of the air inlet  26  so as to be peeled back from the depression  32 , thereby exposing the open upper surface of depression  32  and the aperture  44  in the bottom of depression  32 . When the user inhales through the outlet  28  of the inhaler, air is drawn into the air inlet  26 , picking up powder  34  from the depression  32 . Furthermore, a pressure difference is created between the channel above the plate  30  and the cavity  38  formed below the plate  30 . In this way, air is drawn in the lower part of the air inlet  26  and through the aperture  44  in the bottom of the depression  32 . This assists in ensuring that the powder contained in the depression  32  is transferred into the stream of air flowing through the inhaler. 
     By providing the depression  32  in a plate  30  housed within the inhaler as described above, the depression  32  is protected from being damaged and there is less chance of the depression  32  being accidentally opened, particularly by removal of the tape covering the aperture  44  in the bottom of depression  32 . Furthermore, this arrangement allows additional air to be drawn into the system through the aperture  44  in the bottom of the depression  32  whilst ensuring that all air entering the system enters via the air inlet  26 . In this way, there is less likelihood of the user accidentally blocking the aperture  44 . 
     FIG. 4 illustrates the streamlines which occur in one half of an inhaler where the angles of the walls of the inhalation channel have been optimized and a second divider has been introduced. Even though this inhaler gives excellent results, it is now realized that the impact of the airstream with walls of the channel downstream of the dividers gives little significant improvement in deagglomeration of powder. 
     FIG. 9 illustrates a preferred shape of the walls of the channel resulting from the present invention and FIG. 11 illustrates the resulting streamlines. 
     Firstly, a general explanation of the flow of the air and powder will be given with reference to FIG.  9 . 
     As explained before, air enters through the air inlet  26  and picks up powder  34  from the depression  32 . The air powder mixture is then channelled by walls  50  into a first acceleration section  52 . In the acceleration section  52 , powder in the air/powder mixture, particularly the larger particles of powder, are brought into a stable axial flow before entering the first deagglomeration section  54 . Opposite the section inlet  56  of the first deagglomeration section  54 , a deagglomeration surface  58  of the first divider  60  is orientated perpendicular to the flow of the air/powder mixture as it passes through the section inlet  56 . Preferably, and as illustrated, the deagglomeration surface  58  is generally planar, extends to the width of the section inlet  56  and is in alignment with the section inlet  56 . 
     As illustrated in FIG. 11, the stream of air flows either side of the divider  60  with a smooth curved flow path. However, the particles of powder in the air stream, particularly the heavier particles of powder have sufficient axial momentum that they continue in a substantially straight line so as to impact with the deagglomeration surface  58 . Upon impact, the particles break up into smaller constituent particles and rebound back into the air stream where they continue to flow with the air around the two side channels  62  and  64  of the first deagglomeration means  54 . 
     At the section outlet  66  of the first deagglomeration section  54 , the airflows of the two side channels  62  and  64  are recombined and enter into the second acceleration section  68 . 
     In the second acceleration section  68 , just as with the first acceleration section  52 , the powder particles are once again brought into a stable flow with a strong axial momentum. At the section inlet  70  of the second deagglomeration section  72 , once again the air flows smoothly either side of the second divider  74  along the two side channels  76  and  78 . However, particles with sufficient axial momentum will leave the airstream and impact upon the deagglomeration surface  80  of the second divider  74 . Just as with the deagglomeration surface  58  of the first divider  60 , particles which impact the deagglomeration surface  80  will be broken down into smaller particles and rebound into the airstream to be carried down the side channels  76  and  78 . 
     It will be appreciated that in the case of both the first and second deagglomeration sections, powder of sufficiently small size will be carried by the air flow around the respective divider  60 ,  74  without impacting upon the deagglomeration surface  58 ,  80 . It will only be the larger particles which require deagglomeration that will have sufficient momentum to leave the airstream and impact with the deagglomeration surfaces  58  and  80 . Thus, it will be appreciated that the acceleration section  68  will contain a higher proportion of fine particles than the accelerations section  52  and, therefore, a larger number of powder particles will be deflected around the second divider  74  without impacting its deagglomeration surface  80  than will be deflected around the divider  60  without impacting its deagglomeration surface  58 . It will also be appreciated that the second deagglomeration section  72  acts to deagglomerate large particles which escaped deagglomeration by the first deagglomeration section  54 . Particles which were deagglomerated by the first deagglomeration section  54  should merely flow around the second divider  74  without impacting upon its deagglomeration surface  80 . 
     It is possible to provide third or subsequent deagglomeration sections similar to that of the first deagglomeration section  54 . However, this results in an increase of the overall size of the inhaler, together with increased flow resistance through the inhaler for little improvement in deagglomeration. 
     As illustrated in FIG. 9, the second deagglomeration section  72  preferably comprises a section outlet made up of respective outlets from the side channels  76  and  78 . By providing an outlet in this way, the size of the inhaler may be reduced with no adverse effect to its characteristics. Preferably, the section outlet  82  and, therefore, the inhaler outlet  28  is formed at a position where the air/powder mixture flow in the side channels  76  and  78  is substantially axial. This provides the best flow into the mouth of the user. 
     The preferred shape and size of the inhaler of FIG. 9 is best described with reference to FIGS.  10 ( a ), ( b ), ( c ) and ( d ). These Figures illustrate the various parts of FIG. 9, but, rather than being annotated with reference numerals, are annotated with the preferred dimensions given in millimeters and, in one case, degrees. Where a number is prefixed by the letter R, the number refers to the radius of curvature of the indicated portion given in millimeters. 
     For the avoidance of doubt, FIG.  10 ( a ) illustrates all of the channel illustrated in FIG. 9, FIG.  10 ( b ) illustrates the lower channel wall of the inhaler as illustrated in FIG. 9 where the upper wall has identical dimensions, but symmetrically reversed, FIG. ( c ) illustrates the first divider  60  of the inhalation channel of FIG.  9  and FIG.  10 ( d ) illustrates the second divider  74  of the inhalation channel of FIG.  9 . 
     The inhalation channel defined by FIGS.  10 ( a ) to ( d ) produces the streamlines illustrated in FIG.  11 . As illustrated, there is virtually no disruption to the flow of air through the inhaler, such that, apart from powder being caused to impact with the deagglomeration surfaces of the dividers  60  and  74 , powder will be smoothly carried through the inhaler such that deposition and retention of powder is minimized. Similarly, with a smooth disturbance free flow, the flow resistance is minimized, thereby making inhalation easier for the user and maximizing the transfer of his or her effort in inhalation into lifting, carrying and deagglomerating powder in the inhaler. 
     It will be appreciated that many of the dimensions illustrated in FIGS.  10 ( a ) to ( d ) may be changed without departing from the present invention. Nevertheless, many of the dimensions are strongly interrelated such that changing one dimension may require many other dimensions to be changed similarly to achieve the effects described above and illustrated in FIG.  11 . FIG. 12 illustrates an alternative embodiment where the side channels  84  of the first divider  86  themselves form an acceleration section. As illustrated, the two side channels  84  recombine at the second section inlet  87  so that there are two air flows at the section inlet  87  inclined relative to one another at a small angle. Nevertheless, the deagglomeration surface  88  of the second divider  89  is still substantially perpendicular to these two flows, since the angle between the two flows is relatively small. In the illustrated embodiment, the two flows enter the second deagglomeration section through a section inlet  87  with a single opening. However, it is also possible to provide two closely spaced separate openings, though this might make construction more difficult and, in some cases, promote retention downstream of the adjoining wall. In either case, the two air flows form a single air flow which projects powder towards the perpendicular deagglomeration surface  88 . 
     The construction of an inhaler channel such as illustrated in FIGS. 9 and 10 or in FIG. 12 is dictated by many conflicting factors. For example, by introducing further deagglomeration sections, deagglomeration may be improved, but the size of the inhaler is increased, flow resistance is increased and retention is also likely to be increased. By increasing the cross-sectional area of the channel, the flow resistance can be reduced, but the flow velocity will also be reduced, such that it is difficult to achieve sufficient deagglomeration. Furthermore, the overall size of the inhaler is increased. By decreasing the cross-sectional area of the inhaler, the size of the inhaler would be reduced and the flow velocity would be increased, thereby potentially assisting in deagglomeration. However, flow resistance would be increased and there comes a point where, in small channels, it becomes extremely difficult to achieve a smooth undisturbed flow as illustrated in FIG.  11 . 
     It is also possible to vary individual features of the inhaler. For instance, by shortening the lengths of the acceleration sections  52 ,  68  and  84 , the inhaler size can be reduced, but at some point, the acceleration sections  52 ,  68  and  84  will become less effective in imparting the correct momentum to the carried particles. Similarly, the width of the acceleration sections  52  and  68  could be increased relative to the dividers  60  and  74 , but, at some point, powder particles at the edges of the acceleration sections  52  and  68  will pass around the dividers  60  and  74  without impacting upon them. In contrast, if the dividers  60  and  74  are increased in width to correspond to the width of the acceleration sections  52  and  68 , there will come a point when flow around the deagglomeration surfaces  58  and  80  of the dividers  60  and  74  will create an unacceptably large dead space from which powder particles will not rebound and retention will occur. 
     Thus, from the above, it will be appreciated that the present invention can be applied and can give rise to great advantages with a whole range of shapes of inhalation channel, the actual shape being determined by the start parameters for that channel. It will also be appreciated that, from the selection described above, the particular choice of parameters by which to optimize the inhalation channel and the inhaler as a whole would not be obvious. 
     As illustrated, the acceleration sections preferably have a cross-sectional area of the order of 16 mm 2  and, again as illustrated, are preferably formed as an approximate square. It is believed that the cross-sectional area could be increased to approximately 30 mm 2  before the inhaler became too large and particle speed too low and could be reduced to a cross-sectional area of approximately 9 mm 2  before the flow resistance became too great and the flow patterns too difficult to control. To optimize the deagglomeration of powder, the surface of each divider  60  and  74  facing its corresponding section inlet  56  and  70  should be substantially perpendicular to the air flow in the acceleration sections  52  and  60  across the entire width of the section inlets  56  and  70 . This ensures that any large particle being carried in the flow in the acceleration sections  52  and  68  and which continues to travel generally in a axial direction will hit a divider  60 ,  74  in a generally perpendicular direction. This provides the maximum amount of energy to break up the particle. The rest of the shape of the side channels  62 ,  64 ,  76 ,  78  and the dividers  60  and  74  can then be determined to minimize the disruption and turbulence caused to the flow of air and powder. 
     FIG. 13 illustrates schematically a side view of an inhaler such as described with reference to FIGS. 5 to  12 . As is clear from FIG. 13, the inhaler extends in a generally first direction between the air inlet  26  and the outlet  28 . Furthermore, the inhaler is of a generally flat construction, such that it extends in an elongate manner in a direction perpendicular to the first direction or, in other words, has a shallow extended rectangular or oval shape. 
     As illustrated in FIG. 13, unlike previous inhalers of this general form, the inhaler is not completely flat along its length, but, at position  90 , is deflected downwards, such that it is displaced in a third direction perpendicular to both the first and second directions. This deflection or displacement provides a downwardly extended wall  92 , which, in use, may be pressed against the lower lip of the user. In this way, the user can assuredly insert the inhaler into his or her mouth by the correct amount. Indeed, because of the shape of the inhaler, it will feel strange to insert the inhaler by less than the correct amount. In this way, the inhaler will be inserted with the outlet  28  over and clear of the user&#39;s tongue, rather than in a position where the user&#39;s tongue could still impede the flow of air/powder from the outlet into his or her lungs. 
     It is desirable that the inhaler retains its generally flat form. Therefore, at position  94 , the inhaler is deflected back upwardly such that it is displaced or bent in a direction opposite to the third direction. In this way, the inhaler may have the required function and yet retain a pleasing gentle S-bend form. 
     In the preferred embodiment illustrated in FIG. 13, at position  90 , the lower section has a radius of curvature of approximately 5 mm and the upper section a radius of curvature of approximately 8 mm and at the second position  94 , the lower section has a radius of curvature of approximately 8 mm and the upper section a radius of curvature of approximately 5 mm. 
     Preferably, the downward bend occurs at approximately 30 mm from the outlet  28 . 
     As also illustrated in FIG. 13, a plane  96  exists which passes within the inhaler. Shaping the inhaler with such a plane is highly advantageous, since, as illustrated, the inhaler can be more easily formed from only two moulded parts which are subsequently joined together along a flat surface. 
     This construction is particularly advantageous, since it does not require the use of a separate or special mouthpiece or any special indication on the inhaler. The inhaler comprises the same number of parts as an entirely flat inhaler, with no significant modification. Nevertheless, it provides a clear indication to the user as to how far it should be inserted into his or her mouth. 
     FIG. 14 illustrates an inhaler which could embody the various aspects of the present invention. It will be appreciated that the outer shape of the inhaler has no direct relevance on the present invention, though of course the design of an inhalation channel meeting the requirements of the present invention might necessarily put certain constraints on that outer shape.