Abstract:
The invention relates to a trigger mechanism for a drug delivery device comprising at least one energy storing element, an actuation element and a series of cascaded trigger elements. The trigger elements are pre-stressed with increasing pre-stressing and coupled to the at least one energy storing element such that the trigger elements, upon exerting a sufficient actuation force (Fa, U) on the actuation element, cause a cascaded release of increasing portions of energy stored in the at least one energy storing device. At least one of the trigger elements is equipped with a latch element directly coupling at least two trigger elements such that the latch element restrains at least one of these trigger elements to its pre-stressed state before exerting the actuation force (Fa, U).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a trigger mechanism for a drug delivery device comprising at least one energy-storing element and to a drug delivery device with such a trigger mechanism. 
       BACKGROUND OF THE INVENTION 
       [0002]    Drug delivery devices, such as inhalers or injection devices, that can be easily operated by a patient himself are well known in the art. Generally, such devices have trigger mechanisms to actuate drug dispensing. 
         [0003]    For instance, there are trigger mechanisms designed as breath-actuation mechanisms in mechanically powered inhalers, such as a dry powder inhaler (DPI), an aqueous droplet inhaler (ADI) and/or a metered dose inhaler (MDI). 
         [0004]    US 2004 020486 A1 discloses an inhaler for delivery of medicament from a canister which is compressible to deliver a dose of medicament. The inhaler comprises a housing for holding a canister. The housing having a mouthpiece for inhalation of a dose of medicament delivered by the canister. Furthermore the inhaler includes a breath-actuated actuation mechanism for compressing a canister held in the housing in response to inhalation at the mouthpiece. The actuation mechanism includes a locking mechanism arranged to lock the canister in a compressed state. The locking mechanism has a vane in the form of a flap and being responsive to the inhalation at the mouthpiece to release the canister when the level of inhalation at the mouthpiece falls below a predetermined threshold. It is necessary for the user to take e deep breath to ensure proper inhalation of the medicament so the delay for reset of the canister is sufficient long. 
         [0005]    US 6405727 B1 discloses a dosing device comprising a dispensing means for dispensing a dose material, a first biasing means for engaging with the dispensing means, and a dose activating mechanism. The dose activating mechanism comprises a deflectable member moveable by airflow, and a series of at least two moveable elements which transmit movement of the first element in the series to the last element in the series by a cascade effect, such that movement of the deflectable member is transferred to the first element of the series and a second biasing means communicates with one the at least two moveable elements. As movement is transferred between the moveable elements, energy stored in the second biasing means is released to increase the force associated with the movement of the moveable elements. 
         [0006]    US 2007 118094 A1 discloses a needle-less injector device for delivering a dose of fluid intradermally, subcutaneously or intramuscularly to an animal or human. The device includes an inner housing having opposed ends. A syringe is disposed in one end of the inner housing. The syringe includes a nozzle for delivering a dose of fluid held within the syringe. A plunger is movably disposed within the syringe. A spring-powered hammer is movably disposed within the inner housing. The hammer cooperates with the plunger to drive the dose of medicament from the nozzle. An injection delivery spring for powering the hammer is positioned and compressed between the other vend of the inner housing and the spring powered hammer. An outer housing slideably supports the inner housing. A skin tensioning spring is mounted between the inner housing and the outer housing, the skin tensioning spring biasing the nozzle of the syringe against the animal or human. A trigger mechanism is disposed in the outer housing, the trigger mechanism cooperating with the spring powered hammer to release the injection delivery spring, wherein the size of the injection delivery spring and the length of the hammer dictate the amount of dose delivered and whether the dose is delivered intradermally, subcutaneously or intramuscularly to an animal or human. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the present invention to provide an improved trigger mechanism for a drug delivery device, in particular to actuate drug dispensing, and an improved drug delivery device. 
         [0008]    The object is achieved by a trigger mechanism according to claim  1  and by a drug delivery device according to claim  12 . 
         [0009]    Preferred embodiments of the invention are given in the dependent claims. 
         [0010]    According to the present invention there is provided a trigger mechanism for a drug delivery device comprising at least one energy storing element, an actuation element and a series of cascaded trigger elements. The trigger elements are pre-stressed with increasing pre-stressing and coupled to the at least one energy storing element such that the trigger elements, upon exerting a sufficient actuation force on the actuation element, cause a cascaded release of increasing portions of energy stored in the at least one energy storing device. Thereby at least one of the trigger elements is equipped with a latch element directly coupling at least two trigger elements such that the latch element restrains at least one of these trigger elements to its pre-stressed state before exerting the actuation force. 
         [0011]    The cascaded release of increasing portions of stored energy has the advantage that a large amount of energy can be released through a relatively small actuation force. This is particularly useful for drug delivery devices that are to be actuated by very small amount of trigger energy, for example for an inhaler that is to be actuated by a flap that is moved by a flow of inhaled air or a device to be actuated by a button pressed by a finger or an autoinjector that is actuated by pressing against a patients body. 
         [0012]    The cascaded release of increasing portions of stored energy by a cascaded series of trigger elements thereby advantageously solves the problem that stored energy usually creates resistance to the movement of a trigger, typically in the form of friction. This resistance therefore limits the amount of stored energy that a trigger can release. Using a cascade of trigger elements, one trigger element in the series can trigger a subsequent trigger element in the series using a portion of stored energy, thereby increasing successively the portion of stored energy that can be released by trigger elements. 
         [0013]    Equipping trigger elements with latch elements directly coupling trigger elements in the series simplifies the cascaded trigger mechanism as compared to indirect couplings, e.g. through intermediate coupling elements, and reduces both the manufacturing expense and the size of the trigger mechanism. Furthermore it can reduce the probability of a malfunction of the trigger mechanism due to the reduction of the number of components, which is particularly desirable when the trigger mechanism is used in drug delivery devices for life-saving drugs. In addition it can simplify the procedure to reset the trigger mechanism after drug delivery, again due to the reduction of the number of components and to the simplification of the couplings between the trigger elements. 
         [0014]    In a preferred embodiment at least one of the trigger elements is a pivoted lever. 
         [0015]    Pivoted levers are particularly suited as trigger elements as the can be easily coupled to one another and are cheap and simple components. 
         [0016]    When using pivoted levers as trigger elements, preferably at least one latch element is a protrusion, in particular designed as a ring segment, and located at a pivot of a pivoted lever. 
         [0017]    A protrusion located at a pivot of a pivoted lever is particularly suited to a cascaded coupling of trigger elements as it can restrain another trigger element from moving, and decouple this trigger element from the lever as the lever rotates, thereby supporting the cascade effect in a simple and effective manner. 
         [0018]    Furthermore, in preferred embodiment the pivots of all pivoted levers are preferably located in the same plane. 
         [0019]    This enables a particularly simple and effective construction of the trigger mechanism by a chain of pivoted levers. 
         [0020]    In another preferred embodiment, at least one latch element is a notch in the surface of a trigger element. 
         [0021]    A notch in the surface of a trigger element is another suitable means to couple two trigger elements in a simple and effective manner by engaging one trigger element in the notch of a neighbouring trigger element and disengaging it within the cascade effect. 
         [0022]    Preferably at least one energy-storing element is a spring. 
         [0023]    Springs are particularly suited as energy storing elements for the trigger mechanism for they are simple and cheap components that can store energy effectively and that can be easily reset and connected to trigger elements. 
         [0024]    Furthermore, preferably the trigger elements correspond one-to-one to energy storing elements and each trigger element is coupled to the corresponding energy storing element. 
         [0025]    In this way each trigger element is coupled precisely to one energy-storing element. This makes it particularly easy to realize a cascaded release of increasing portions of stored energy as each trigger element in the series can control its “own” energy storing element and trigger the release of energy stored in it during the cascade effect. 
         [0026]    Preferably the actuation element is equipped with a latch element directly coupling it to one of the trigger elements. 
         [0027]    In this way the actuation of the cascade effect can be easily realized by making the actuation element effectively part of the series of trigger elements. 
         [0028]    Furthermore, in a preferred embodiment the cascaded release of increasing portions of stored energy amplifies an actuation force exerted on the actuation element to a force exertable through one of the trigger elements. 
         [0029]    An amplification of the actuation force is particularly advantageous in drug delivery devices which the force required for drug delivery exceeds the actuation force exertable on the actuation element. 
         [0030]    According to the present invention, there is further provided a drug delivery device equipped with a trigger mechanism according to any one of these embodiments, in which the trigger mechanism is a release mechanism to actuate and release delivery of a dose of a drug stored in the drug delivery device. 
         [0031]    A preferred embodiment of such a drug delivery device is an inhaler, in particular an inhaler whose actuation element is a pivoted actuation flap movable by gas or fluid flow. 
         [0032]    Another preferred embodiment of such a drug delivery device is an autoinjector. 
         [0033]    The trigger mechanism is particularly suited as a release mechanism for drug delivery through inhalers and autoinjectors as these devices are typically actuated by an actuation force that is smaller than the force required for drug delivery. 
         [0034]    In a preferred embodiment of a drug delivery device at least one of the trigger elements is a piston by means of which a pressure is exertable to the drug. 
         [0035]    The use of a piston as a trigger element is particularly advantageous when the drug to be delivered by the drug delivery device is a fluid or a gas because such drugs may be best delivered by a pressure exerted to the drug. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments and accompanying drawings, in which 
           [0037]      FIGS. 1A through 1D  illustrate schematically a first embodiment of a trigger mechanism for an inhaler to actuate delivery of a dose of a drug, 
           [0038]      FIGS. 2A and 2B  illustrate schematically a second embodiment of a trigger mechanism for an inhaler to actuate delivery of a dose of a drug, and 
           [0039]      FIGS. 3A through 3D  illustrate schematically a third embodiment of a trigger mechanism for an autoinjector to actuate delivery of a dose of a drug. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0040]      FIGS. 1A through 1D  illustrate a first embodiment of a trigger mechanism according to the invention. The trigger mechanism is used in an inhaler  1  to actuate delivery of a dose of a drug stored in the inhaler  1 , for example a dry powder, aqueous droplet or metered dose inhaler. Successive stages of an actuation process for drug delivery are shown to explain the operation of the trigger mechanism. 
         [0041]    The trigger mechanism comprises an actuation flap  11 , a first lever  12 , a second lever  13 , a first spring  14  and a second spring  15 . 
         [0042]    The actuation flap  11  is located in a breathing channel  10  through which a user inhales. The actuation flap  11  and the levers  12 ,  13  are pivoted around pivots  111 ,  121 ,  131  at one of their ends respectively. The actuation flap  11  is equipped with a first ring segment  112  located at its pivot. The first lever  12  is equipped with a second ring segment  122  located at its pivot. The ring segments  112 ,  122  extend about one third of a circle around the centre of the respective pivot  111 ,  121  and extend from the surface of the respective pivot  111 ,  121 . 
         [0043]    The pivots  111  and  121  of the actuation flap  11  and of the first lever  12  are separated by a distance L 1  corresponding to a length of the first lever  12 . The pivots  121  and  131  of the levers  12 ,  13  are separated by a distance L 2  corresponding to a length of the second lever  13 . The pivots  111 ,  121 ,  131  are located in a common plane. Hence, when the actuation flap  11  and the levers  12 ,  13  are rotated to this plane and likewise oriented from their respective pivots  111 ,  121 ,  131  as shown in  FIG. 1A , the first lever  12  extends to the pivot  111  of the actuation flap  11 , and the second lever  13  extends to the pivot  121  of the first lever  12 . Furthermore, in this position the first ring segment  112  restrains the first lever  12  from rotating upwards while the second ring segment  122  restrains the second lever  13  from rotating downwards. 
         [0044]    The first lever  12  is coupled to the first spring  14  near to the pivot  111  of the actuation flap  11  at a distance X 1  to the pivot  121  of the first lever  12 . The second lever  13  is coupled to the second spring  15  near to the pivot  121  of the first lever  12  at a distance X 2  to the pivot  131  of the second lever  13 . Thereby the first spring  14  is located below the first lever  12  while the second spring  15  is located above the second lever  13 . The stiffness of the second spring  15  exceeds the stiffness of the first spring  14 . 
         [0045]      FIG. 1A  shows an initial state of the trigger mechanism with the actuation flap  11  and the levers  12 ,  13  located in the same plane as described above. In this state both springs  14 ,  15  are compressed, the second spring  15  storing more energy than the first spring  14 . When no force is acting on the actuation flap  11 , a rotation of the actuation flap  11  and the levers  12 ,  13  are restrained by the ring segments  112 ,  122  respectively. The levers  12 ,  13  are thus pre-stressed by the springs  14 ,  15  respectively, the pre-stressing of the second lever  13  exceeding the pre-stressing of the first lever  12 . 
         [0046]      FIG. 1B  shows the trigger mechanism when a user just has started to inhale. The inhaling causes an airflow B and a pressure drop P which suffices to rotate the actuation flap  11  downwards. A detailed quantitative discussion of this mechanism is given below. 
         [0047]      FIG. 1C  shows the trigger mechanism when the actuation flap  11  has been rotated sufficiently so that the first ring segment  112  releases the first lever  12 . As a consequence, the first spring  14  expands and rotates the first lever  12  upwards. This mechanism is also discussed in detail below. 
         [0048]      FIG. 1D  shows the trigger mechanism when the first lever  12  has been rotated sufficiently so that the second ring segment  122  releases the second lever  13 . As a consequence, the second spring  15  expands and rotates the second lever  13  downwards. 
         [0049]    During the actuation process illustrated by the  FIGS. 1A through 1D  an actuation force Fa exerted by the pressure drop P on the actuation flap  11  releases energy stored in the first spring  14  which in turn is used to release energy stored in the second spring  15 . Thereby the actuation force Fa can be considerably amplified to forces exerted by the springs  14 ,  15 . This will be shown in the following quantitative analysis of the trigger mechanism described qualitatively above. 
         [0050]    With A denoting the area of the actuation flap  11 , the actuation force Fa exerted by the pressure drop P on the actuation flap  11  is Fa=P·A. The actuation force Fa exerts an actuation torque Ta=P·A·Z on the actuation flap  11  where Z is the distance between the pivot  111  of the actuation flap  11  and the effective application point of the actuation force Fa. 
         [0051]    Denoting the spring force exerted by the first spring  14  on the first lever  12  by F1, a reaction force Y 1  at the pivot  111  is Y 1 =(X 1 /L 1 )·F 1 . In the initial state of the trigger mechanism shown in  FIG. 1A , the rotation of the actuation flap  11  is restrained by a static friction between the first ring segment  112  and the corresponding end of the first lever  12 . This static friction is mue Y 1 =μ·(X 1 /L 1 )·F 1  with μ a friction coefficient. Denoting the radius of the first ring segment  112  from the centre of the pivot  111  by R 1 , the rotation of the actuation flap  11  is thus restrained by a first restraining torque T 1 =R 1 ·μ·(X 1 /L 1 )·F 1 . 
         [0052]    In order for the trigger mechanism to operate according to  FIG. 1B , i.e. in order to rotate the actuation flap  11 , this first restraining torque T 1  must be exceeded by the actuation torque Ta, i.e. T 1 &lt;Ta and thus R 1 ·μ·(X 1 /L 1 )·F 1 &lt;Z·P·A. Therefore, the force F 1  of the first spring  12  that can be restrained by the trigger mechanism, and still released by actuation flap  11  is restricted by 
         [0000]        F   1 &lt; Z·P·A· ( L   1   /X   1 )/( R   1 ·μ). [1]
 
         [0000]    and the maximal amplification of the actuation force Fa provided by the first spring  14  is restricted by 
         [0000]        F   1 / Fa&lt;Z· ( L   1   /X   1 )/( R   1 ·μ).  [2]
 
         [0053]    Inserting typical values A=100 mm 2 , Z=5 mm, P=1 kPa, L 1 =40 mm, X 1 =20 mm, R 1 =1 mm and μ=0.5, this results in 
         [0000]      F 1 &lt;2 N  [3]
 
         [0000]    and 
         [0000]      F 1 /Fa&lt;20.  [4]
 
         [0054]    An analogous consideration applies to the coupling of the first lever  12  to the second lever  13  through the second ring segment  122 . 
         [0055]    Denoting the spring force on the second lever  13  due to the second spring  15  by F 2 , a reaction force Y 2  at the pivot  121  is Y 2 =(X 2 /L 2 )·F 2 . The rotation of the first lever  12  is restrained by a static friction between the second ring segment  122  and the corresponding end of the second lever  13 . This static friction is μ·Y 2 =μ·(X 2 /L 2 )·F 2 . Denoting the radius of the second ring segment  122  from the centre of the pivot  121  by R 2 , the rotation of the first lever  12  is restrained by a second restraining torque T 2 =R 2 ·μ·(X 2 /L 2 )·F 2 . 
         [0056]    In order for the trigger mechanism to operate according to  FIG. 1C , i.e. in order to rotate the first lever  12 , the second restraining torque T 2  must be exceeded by the torque X 1 ·F 1  provided by the first spring  14  on the first lever  12 , i.e. R 2 ·μ·(X 2 /L 2 )·F 2 &lt;X 1 ·F 1 . 
         [0057]    Therefore, the additional force amplification F 2 /F 1  is restricted by 
         [0000]        F   2 / F   1 &lt; X   1 ·( L   2   /X   2 )/( R   2 ·μ).  [5]
 
         [0058]    Inserting the same typical values as above with X 1 =X 2 =20 mm, L 1 =L 2 =40 mm, R 1 =R 2 =1 mm, μ=0.5, this yields 
         [0000]      F 2 /F 1 &lt;80  [6]
 
         [0000]    and 
         [0000]      F 2 &lt;160 N.  [7]
 
         [0059]    F 2  could thus be up to about 160 N. This is a significant force and the energy released from the springs  14 ,  15  can indeed be used dose delivery through the inhaler  1 . Additional cascaded trigger elements and springs could be added to enhance the force amplification even further. 
         [0060]    A further use for the trigger mechanism could be that each lever  12 ,  13  could be connected to a separate part of the inhaler mechanism. For example, the first lever  12  could trigger opening of a dose container, the second lever  13  could trigger dose delivery. By adding damping to either the first lever  12  or the second lever  13  it would also be possible to introduce a time delay between the initial breath actuation of the actuation flap  11  and the release of the second lever  13 . This could be used to introduce a “staged” response to the breath actuation. 
         [0061]    After the levers  12 ,  13  have been released the user would have to reset both levers  12 ,  13  before the trigger mechanism could be used again. The reset action could occur simultaneously when the user performs some other action with the inhaler  1 , for example opening it to remove an empty dose container or load a new dose container, or in a priming action of the inhaler  1  prior to use. The limit of how far a force could be amplified by the trigger mechanism is likely to be how much energy the user can put back into the system when resetting the trigger mechanism. 
         [0062]    The embodiment shown in  FIGS. 1A through 1D  has the disadvantage that the springs  14 ,  15  have to be reset in opposite directions. This disadvantage is overcome by an alternative embodiment of the trigger mechanism shown in  FIGS. 2A and 2B . Again, the trigger mechanism is used in an inhaler  1 . 
         [0063]    A difference of this embodiment as compared to the first embodiment is that the levers  12 ,  13  are arranged such that they are stacked one above the other in an initial state of the trigger mechanism shown in  FIG. 2A . Furthermore, the first lever  12  is fixed to the actuation flap  11 , both having the same pivot  111  so that they can only rotate simultaneously. The springs  14 ,  15  are located on the same side of the levers  12 ,  13 , and the second lever  13  is equipped with a third ring segment  133  of the same type as the ring segments  112 ,  122  of the first embodiment. The first lever  12  now extends from its pivot  111  to the pivot  131  of the second lever  13 . Again, the pivot  111  is equipped with a first ring segment  112  (not visible in the  FIGS. 2A and 2B ) to which the second lever  13  extends in its initial position. 
         [0064]    In the initial state of the trigger mechanism shown in  FIG. 2A , the third ring segment  133  restrains the actuation flap  11  and the first lever  12  from rotating through the friction between the third ring segment  133  and the corresponding end of the first lever  12  and the first ring segment  112  restrains the second lever  13  from rotating through the friction between the first ring segment  112  and the corresponding end of the second lever  13 . 
         [0065]    When a user exerts a sufficient actuation force Fa on the actuation flap  11  through inhaling, the levers  12   13  are released and both rotate upwards as shown in  FIG. 2B . 
         [0066]    In order to reset the trigger mechanism both levers  12 ,  13  are pushed downwards to reengage the ring segments  112 ,  133 . 
         [0067]      FIGS. 3A through 3D  illustrate a third embodiment of a trigger mechanism according to the invention. The trigger mechanism is used in an autoinjector  2  to actuate delivery of a dose of a drug  242  stored in a cartridge  24  through a dispensing element  243  of the autoinjector  2  located at the bottom of the cartridge  24 . The cartridge  24  is sealed by plug  241 . 
         [0068]    The trigger mechanism comprises a manually operated actuation lever  21 , an intermediate lever  22 , a piston  23 , a first spring  26  and a second spring  25 . 
         [0069]    The actuation lever  21  is pivoted around a pivot  211  at one of its ends and is equipped with a trigger button at its opposite end. The distance between the centres of the pivot  211  and of the trigger button is denoted by X 5 . The actuation lever  21  is equipped with a first ring segment  212  which is located at the pivot  211  and is of the same type as the ring segments  112 ,  122 ,  133  of the first and second embodiment. 
         [0070]    The intermediate lever  22  is hook-shaped with a bend located at the pivot  211  of the actuation lever  21 . A first end of the intermediate lever  22  is directed towards the piston  23 , the second end contains a pivot around which the intermediate lever  22  is pivoted. The intermediate lever  22  is connected to the first spring  26  at a distance X 3  from its pivot. The distance between the bend and the pivot of the intermediate lever  22  is denoted by X 4 . 
         [0071]    One end of piston  23  is directed towards the plug  241  of the cartridge  24 , the other end is connected to the second spring  25 . The surface of the piston  23  is equipped with a notch in which the first end of the intermediate lever  22  can engage. 
         [0072]    The operation of the trigger mechanism is now described first qualitatively with reference to  FIGS. 3A through 3D  and afterwards analysed quantitatively. 
         [0073]      FIG. 3A  shows an initial state of the trigger mechanism. Both springs  25 ,  26  are compressed. The first end of the intermediate lever  22  engages in the notch of the piston  23  and prevents the piston  23  from moving towards the plug  241 . The bend of the intermediate lever  22  is coupled to the first ring segment  212  which restrains the intermediate lever  22  from rotating. 
         [0074]      FIG. 3B  shows the trigger mechanism when a user presses the trigger button of the actuation lever  21  sufficiently so that the actuation lever  21  is rotates around its pivot  211 . As the actuation lever  21  rotates, the first ring segment  212  eventually disengages and releases the intermediate lever  22 . 
         [0075]      FIG. 3C  shows the trigger mechanism after the intermediate lever  22  has been released. The first spring  26  expands and rotates the intermediate lever  22 . The first end of the intermediate lever  22  disengages from the notch in the surface of the piston  23  which releases the piston  23 . The piston  23  is now free to move towards the plug  241  under the action of the fourth spring  25 . 
         [0076]      FIG. 3D  shows the trigger mechanism after the piston  23  has been released. The piston  23  has moved to the plug  241  and pressed it towards the bottom of the cartridge  24 . Thereby it exerts a pressure on the drug inside the cartridge  24  which forces delivery of the drug through the dispensing element  243 . 
         [0077]    To discuss the trigger mechanism quantitatively the spring forces of the third spring  26  and of the fourth spring  25  exerted on the intermediate lever  22  and the piston  23  in the initial state of the trigger mechanism are denoted by F 3  and F 4  respectively. 
         [0078]    Assuming that the thickness of the intermediate lever  22  thickness is negligible compared to its length, the approximate reaction force provided by the first spring  26  between the intermediate lever  22  and the second ring segment  212  in the initial state of the trigger mechanism is F 3 ·(X 3 /X 4 ). A third restraining torque T 3  caused by friction between the intermediate lever  22  and the fourth ring segment  212  is therefore approximately T 3 =R 3 ·μ·F 3 ·(X 3 /X 4 ) where R 3  is the radius of the first ring segment  212  from the centre of the pivot  211 . 
         [0079]    A user must provide a sufficient actuation force U to the trigger button to overcome this resistance. The actuation torque resulting from U is U·X 5 . 
         [0080]    The actuation lever  21  starts to rotate when this torque exceeds the third retraining torque T 3 , i.e. when U·X 5 &gt;R 3 ·μ·F 3 ·(X 3 /X 4 ). Hence, for the actuation lever  21  to rotate, the force F 3  of the third spring  26  is restricted by 
         [0000]        F   3 &lt;( X   4   ·X   5   /X   3 )· U /( R   3 ·μ).  [8]
 
         [0081]    In order to release the piston  23  the force F 3 ·(X 3 /X 4 ) provided by the first spring  26  at the bend of the intermediate lever  22  must overcome the friction between the piston  23  and the intermediate lever  22  which is μ F 4 . Therefore, the piston  23  is released if F 3 ·(X 3 /X 4 )&gt;μ·F 4 . Hence, for the trigger mechanism to operate, the force F 4  of the second spring  25  is restricted by 
         [0000]        F   4 &lt; F   3 ·( X   3   /X   4 )/μ.  [9]
 
         [0082]    Inserting typical values X 5 =25 mm, X 3 =15 mm, X 4 =30 mm, μ=0.5, R 3 =2.5 mm and U=1 N, one obtains 
         [0000]      F 4 &lt;40 N.  [10]
 
         [0083]    As compared to the actuation force U=1 N this gives a force amplification up to a factor of 40. The amplification can be further enhanced by different arrangements of the intermediate lever  22  and/or the use of further intermediate levers and springs and/or a “rolling” coupling of the intermediate lever  22  to the piston  23  in place of the coupling through the notch in the surface of the piston  23 . 
       LIST OF REFERENCES  
       [0084]      1  inhaler
 
 10  breathing channel
 
 11  actuation flap
 
 12 , 13 , 22  lever
 
 14 , 15 , 25 , 26  spring
 
 111 , 121 , 131 , 211  pivot
 
 112 , 122 , 133 , 212  ring segment
 
 2  autoinjector
 
 21  actuation lever
 
 22  intermediate lever
 
 23  piston
 
 24  cartridge
 
 241  plug
 
 242  drug
 
 243  dispensing element
 
X 1 ,X 2 ,X 3 ,X 4 ,X 5 ,L 1 ,L 2 ,Z distance
 
B air flow
 
P pressure drop
 
Fa, U actuation force
 
F 1 ,F 2 ,F 3 ,F 4  spring force
 
Y 1 ,Y 2  reaction force
 
Ta actuation torque
 
T 1 ,T 2 ,T 3  restraining torque
 
R 1 ,R 2 ,R 3  radius
 
μ friction coefficient