Asthma and other respiratory diseases have long been treated by the inhalation of appropriate medicament. For many years the two most widely used and convenient choices of treatment have been the inhalation of medicament from a drug solution or suspension in a metered dose pressurised inhaler (MDI) , or inhalation of powdered drug generally admixed with an excipient, from a dry powder inhaler (DPI) .

Inhalation activatable dispensers for use with aerosol containers which contain medicament and are pressurised with liquid propellants and are equipped with a metering valve through which a plurality of metered doses may be dispensed are known, their general purpose being to afford proper co-ordination of the dispensing of a dose of medicament with the inhalation of the patient thereby allowing the maximum proportion of the dose of medicament to be drawn into the patient's bronchial passages. Examples of such dispensers are described in British Patent Specification Nos. 1,269,554, 1,335,378, 1,392,192, 2,061,116 and 2,240,930 United States Patent Nos. 3,456,644, 3,456,645, 3,456,646, 3,565,070, 3,598,294, 3,814,297, 3,605,738, 3,732,864, 3,636,949,

3,789,843 and 3,187,748 and German Patent No. 3,040,641.

European Patent No. 147028 discloses an inhalation activatable dispenser for use with an aerosol container in which a latch mechanism releasing vane is pivotally mounted in an air passage between an aerosol outlet valve and a mouthpiece, which latch mechanism cannot be released if force to activate the dispenser is not

applied before a patient inhales.

The dispenser generally comprises a housing having a mouthpiece and an air passage therethrough terminating at the mouthpiece, the housing being adapted to receive an aerosol container and having a support block with a socket adapted to receive the stem of the valve of the aerosol container and a through orifice communicating between the socket and the air passage, and latch means having parts movable between an engaged position in which movement of the container and the support block toward each other upon the application of a force to bias the container and the support block toward each other is prevented and a release position in which movement of the container and the support block toward each other in response to said force is permitted causing the stem to move to its inner discharge position, the latch means comprising a vane mounted on the housing in the air passageway between the orifice and the mouthpiece for movement toward the mouthpiece under the influence of inhalation through the mouthpiece to release the latch means in which the vane moves toward the mouthpiece from a blocking to a non-blocking position with respect to the passageway in response to inhaling at the mouthpiece and releases the latch means only during the application of said force to bias the container and support block toward each other.

This inhalation device has been received favourably by patients and doctors since it not only overcomes the hand-lung co-ordination problem but it does so at a very low triggering flow-rate (approximately 30 litres/minute) essentially silently, and with a very compact design barely larger than a standard inhaler.

Many inhalation activatable dispensers utilise a spring to bias the container relative to the valve stem and ultimately move the container relative to the valve stem to fire the device upon inhalation. Generally the spring acts upon the base of the container and is

compressed prior to patient inhalation by a priming force generated by operation of a priming lever which may be a separate lever or connected to a pivoting mouthpiece cover. In some arrangements, after activation of the device and removal of the priming force the valve and associated triggering mechanism is reset under the influence of the internal valve spring by movement of the container relative to the valve stem. Thus, in order to ensure efficient operation of the dispenser it is necessary to carefully select the parameters of the biasing spring used to prime the device.

The spring configuration for such a dispenser must exhibit certain specific force characteristics. These characteristics are best described with reference to the three main stages of operation of the device as follows: The unprimed or at rest stage in which no priming force is applied, to the spring and the spring is applying its lowest load to the container. In this position, ideally, the force applied by the spring should be insignificant in the sense that it has no influence on the position of the aerosol container and valve thus allowing the device to reset under the influence of the internal valve spring following the previous actuation. Thus the force applied by the biasing spring must be less than the minimum valve return force.

The priming stage in which the spring is compressed. The force applied by the spring must be greater than that required to fire the aerosol valve but should be kept to a minimum as it governs the magnitude of the inspiratory flow rate required to actuate the dispenser.

The firing stage in which the container is moved relative to the valve sufficiently by the spring to actuate the valve. For correct operation, it is essential that as the spring expands from its primed position it retains sufficient force to overcome the inherent resistance to movement of the valve. Failure at

this stage would result in no delivery of medication.

The theoretical spring force profile i.e. a plot of force against spring length, is a straight line. In practice, the rate is not linear but tends to increase with compression (the softest parts of the spring compress first) . In order to achieve the parameters required for successful dispenser operation, the spring must be selected such that requirements of the unprimed and fired positions are met and in practice this can mean springs generate undesirably high forces in the primed position. Thus, spring selection and manufacturing tolerances are critical.

The present invention provides an improved spring arrangement for such dispensing devices. According to the present invention there is provided a breath-actuated aerosol dispenser comprising a housing defining a patient port and containing a pressurised container equipped with a metered dose dispensing valve, primer movable between a rest position and a priming position in which it applies a force sufficient to actuate the dispensing valve and breath- actuated trigger mechanism which prevents actuation of the dispensing valve until a triggering air flow passes through the patient port, in which the primer comprises a spring which is maintained in a partially compressed state when the primer means is in its rest position without applying any substantial force to the aerosol container, valve or breath actuated trigger mechanism.

It has been found that by utilising a spring which is maintained in a partly compressed state, e.g., by restricting the spring within a cage, it is readily possible to achieve the desired spring configuration in all three positions and greatly simplify the manufacture and selection of a suitable spring. By appropriate selection of the cage dimensions it can be guaranteed the spring will not interfere with movement of the aerosol container and valve in the rest position. Furthermore, a

spring of free length longer than the available space within the device can be used. This allows the necessary force for the firing stage to be generated at a lower spring rate, which in turn offers the opportunity of either: a) lowering the force applied in the primed position whilst maintaining the force generated in the firing stage thus lowering triggering air flow i.e. the inspiratory flow rate required to actuate the dispenser, or b) raising the force generated during the firing stage without adversely affecting the force applied in the priming stage, thus maintaining the triggering inspiratory flow rate at an acceptable level whilst allowing the device to cope with valves requiring more force to actuate.

The cage maintaining the spring in a partially compressed state may be any device having a configuration which allows further compression of the spring when the primer is moved to its priming position. For example, the cage may comprise two interengagable parts having a telescopic action. The parts may be prevented from disengagement by mechanical interlocking between the parts or by separate means e.g. a rivet. Alternatively, the spring may be held in the compressed state by a non- deformable cage provided the priming means has access to the spring. The caged spring constitutes an entirely • self-contained system and may be assembled remote from the dispenser in which it is used. The invention will now be described with reference to the accompanying drawings in which:

Figure 1 represents a plot of force applied against spring length for unrestricted and caged springs. Figures 2a to 2c represent a section through the primer means of an aerosol dispenser in the at rest, priming and firing stages respectively.

Figures 3a and 3b represent a perspective and

sectional view through a caged spring arrangement suitable for use in the invention,

Figure 4 represents a sectional view through a further caged spring arrangement in accordance with the invention, and

Figure 5 represents a sectional view through a further caged spring arrangement in accordance with the invention.

Figure 1 is a plot of force applied by a spring against spring length. The plot indicates the force to fire which is that force required to move the aerosol container relative to the valve for actuation of the valve, and the return force which is the force generated by the internal spring of the valve.

Plot A is the force profile of an unrestricted spring. In its at rest position the force applied by the spring must not exceed the return force generated by the internal spring of the valve or the device will not re- set. In the firing stage the force applied by the spring must be sufficient to move the container relative to the valve. In a theoretically perfect spring the force profile will be a straight line and accordingly, if the criteria in the at rest and fired positions are met the force applied by the spring in the primed condition will be F _A . This force should be ideally kept as low as possible in order to allow the device to be activated by low inspiratory flow rates. In practise, the profile of a spring is not often a straight line and there is a tendency for F _A to be considerably higher.

Plot B illustrates the force profile of a caged spring. The spring is maintained in a partially compressed state by a cage and accordingly in its at rest position will apply no force against the aerosol container. At its restrained length, in absence of the cage, the spring would apply a force higher than the return force and this is represented in the plot by a

step at the at rest position. The use of the caged spring allows a lower rated, longer spring to be used and thus the straight line portion of the profile may have a shallower slope than that of Plot A, retaining the necessary force to fire in the firing stage, but applying a force F _B which is considerably lower than F _A in the primed position. Thus, it is possible to maintain triggering inspiratory flow rates at lower levels using a caged spring than could be achieved using an unrestricted spring.

Figures 2a to 2c represent cross-sections through the upper part of a breath-actuated aerosol dispenser illustrating the priming means of the device. The device comprises a housing formed of parts (2 and 4) within which an aerosol container partly shown at (6) is positioned. The device additionally comprises breath- actuated trigger, (not shown), e.g., of the type disclosed in European Patent No. 147028, the full disclosure of which is incorporated herein by reference. The primer of the device comprises a priming lever

(8) which acts on spring (10) held within a cage (12).

The cage (12) comprises a base (14) and shoulder portions (16) joined by side portions (18) . The side portion (18) may be in the form of a substantially cylindrical wall or may comprise a plurality of upright portions. The distance between the base (14) and shoulder (16) is less than the unrestrained length of the spring (10) and accordingly, the spring (10) will always be in the partially compressed state when it is confined in the cage. The base portion (14) is shaped to configure to the base of the aerosol container (16) and may comprise internal lugs (20) to facilitate correct positioning of the spring within the cage. The cage may additionally comprise a circular plate or washer (22) positioned beneath the shoulder portions (16) and movable within the cage to apply pressure to the spring (10) . Figure 2a shows the device in the at rest or

unprimed position. The cage is dimensioned such that it fits in the space between the base of the aerosol container (6) and the priming lever (8) without applying pressure to the base of the aerosol container. The cage (10) may possess resilient guide portions (24) having projections (26, 28) to ensure the cage and spring are correctly aligned in the device and to prevent unwanted movement of the cage during transportation and handling of the device. Figure 2b shows the device in the primed position.

Priming is effected by upward movement of the priming lever (8) . The lever (8) comprises a cam surface (30) which engages the undersurface of the housing (2) causing the end (32) of the priming lever to move downwardly. The priming lever (8) comprises lugs (34) which engage within channels (36) within the housing (2) to control the movement of the priming lever. As the end (32) of the priming lever moves it causes movement of the washer (22) within the cage (12) which in turn causes compression of the spring (10) . In the primed position the spring will be under its maximum compression and the force applied to the aerosol container (6) will be in excess of the force required to actuate the aerosol valve. Movement of the container (6) is prevented by the breath-actuated trigger (not shown) which blocks movement of the container until patient inspiration, when a triggering air flow passes through the patient port. Those skilled in the art will recognise that the air flow that constitutes a triggering air flow will depend on the particular breath-actuated dispenser and the particular trigger. Generally, however, flow rates of 15 to about 60 L/min are sufficient to actuate a device and ensure delivery of the drug to the lung of the patient.

Figure 2c shows the device in its fired position. Upon inspiration the trigger moves to an unblocking position allowing movement of the aerosol container (6) . The aerosol container (6) is moved downwardly under the

influence of the spring (10) which acts on the cage (12) thereby actuating the valve and firing a dose of medicament. When the priming lever (8) is moved to the unprimed or rest position (Figure 2a) the force developed by the internal spring of the aerosol valve is sufficient to move the aerosol container (6) , cage (12) and spring (10) upwardly to the at rest position shown in Figure 2a.

It will be readily appreciated the cage for the spring may have numerous configurations and may be used with different types of compression spring, e.g., cylindrical, conical etc. Figures 3a and 3b illustrate an alternative embodiment of a cage and spring arrangement. The cage comprises interengaged lower (50) and upper (52) components. The lower component (50) is substantially cylindrical in shape having a base flange (54) and a plurality of feet (56) . The upper portion (52) has a stem .(58) terminating in compressible lugs (60) which are accommodated within an aperture (63) in the lower component to allow telescopic movement of the upper and lower components without separation. The upper component (52) has a shoulder region (62) and the spring (64) is held in a partially compressed state between the base flange (54) and shoulder (62) (Figure 3a) . The upper portion (52) has a plurality of guide legs- (65) and projections (66) which engage in corresponding slots in the interior of the housing of the device to facilitate correct alignment caged spring arrangement. The priming lever of the aerosol device acts on the upper component (52) pushing this component downwardly to compress the spring.

The caged spring arrangement of Figure 4 is similar to that disclosed in Figures 3a, 3b, like numerals represent like parts. The feet (56) are flexible and project downwardly in order to ensure the cage fully occupies the space between the aerosol container and priming lever so that the cage will not rattle when the priming lever is in the unprimed position

and the device is carried by a patient, e.g., in a pocket, handbag etc. A further difference is the provision of an annular wall (68) in place of the guide legs (65) . The caged spring arrangement of Figure 5 is similar to that disclosed in Figures 3a, 3b and 4. The fundemental difference is that the upper portion (52) and the lower portion (50) are held together by a rivet (70) having upper and lower flanges (74,72) engaging the upper and lower portions (52,50) preventing disengagement. The upper and lower portions are free to telescope along the length of the rivet (70) for further compression of spring (64) when the dispenser is primed.