Note: Descriptions are shown in the official language in which they were submitted.
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BREATH ACTUATED MEDICAMENT DISPENSING DEVICES
This invention relates to breath actuated medicament dispensing devices of the
type where
a metered dose of medicament is administered to the respiratory system of a
patient in
response to the inhalation of the patient.
Metering valves are a common means by which aerosols are dispensed from
aerosol
containers. Metering valves are particularly useful for administering
medicinal
formulations that include a liquefied gas propellant and are delivered to a
patient in an
aerosol.
In some metering valves, the metering chamber fills with the medicinal
formulation prior
to the patient actuating the valve stem and thereby releasing the dose. The
metering
chamber is refilled with formulation after dispensing one dose so that the
metering valve is
ready to discharge the next dose. Consequently, the metering chamber contains
formulation at all times except for the brief time during which the valve stem
is depressed
by the user to discharge a dose.
In other metering valves the metering valve is designed such that the metering
chamber
does not materialise unless and until the valve stem is actuated. Examples of
such valves
are disclosed in U.S. 4,19,834. Actuation of these valve stems can be divided
into a
filling stage and a discharge stage. The filling stage begins as the valve
stem is depressed
during actuation. The action of depressing the valve stern causes the
formation of a
transient metering chamber, which is in fluid communication with the residual
metering
volume defined by the small annular gap. As the valve stem is depressed, the
transient
portion of the metering chamber expands and formulation enters the metering
chamber.
As displacement of the valve stem continues, a stage is reached at which
filling of the
transient metering chamber stops.
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Eventually, displacement of the valve stem continues to the discharge stage,
in which the
metered formulation is discharged. In these valves, a single actuation thus
causes rapid
filling of the transient metering chamber followed by discharge of the
formulation to the
patient. Generally, metered formulation does not reside for any appreciable
amount of
time in the metering chamber in these metering valves.
While a metering valve having a transient metering chamber provides advantages
over
other types of metering valves for the delivery of aerosol formulations, it
has now been
appreciated that the flow of formulation from the container to the metering
chamber may
be disrupted or impeded. Flow through regions of significantly restricted
access, such as
narrow annular passageways and/or entrance ways to the metering chamber, may
be
impeded sufficiently to give rise to substantially incomplete filling of the
metering
chamber. If this happens, formulation may be delivered in inconsistent or
inaccurate
doses. In particular, it has now been appreciated that the time available for
filling the
metering chamber also has a significant effect on the ability to completely
fill the transient
metering chamber. The time available for filling depends on the speed at which
the valve
stem is depressed. In the so-called "press-and-breathe" devices in which the
patient
manually depresses the aerosol container relative to the valve stem to fire
the valve the
speed at which the valve stem is depressed is generally not more than
100mm/sec.
However, breath actuated inhalers typically fire the valve more rapidly than
manual firing
e.g. with valve stem speeds in the range 165 to 330 mm/sec. Thus, there are
difficulties
associated with the use of metering valves having a transient metering chamber
with
breath actuated devices.
A common feature of many known breath actuation devices is that they involve
two stages
of operation: a priming stage in which a priming force is applied to the valve
stem but
actuation of the valve stem is prevented; and a firing stage in which the
priming force is
released resulting in movement of the valve stem to fire the valve. The
priming stage is
generally a manual operation and may involve some movement of the valve stem
but not
sufficient to fire the valve. Any movement of the valve stem in the priming
stage tends to
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be at relatively low speed. ~nce the device is triggered by inhalation there
is high speed
displacement of the valve stem under the priming force.
It has now been found that if the metering and firing stages of operation of a
metering
valve of the type having a transient metering chamber are synchronised with
the priming
and firing stages of a breath actuated device, any difficulties or problems
associated with
flow of formulation to fill the metering chamber may be overcome or at least
significantly
reduced.
Therefore according to the present invention there is provided a breath
actuated
medicament dispensing device comprising:
an aerosol container containing a pressurised medicament formulation equipped
with a metered dose dispensing valve having a movable valve stem;
a housing disposed about the aerosol container;
a patient port in communication with the dispensing valve;
priming means adapted to apply a bias to the valve stem relative to the
aerosol
container sufficient to move the valve stem to fire the valve; restraining
means
movable between a blocking position in which it prevents said bias firing the
valve and a
release position in which it allows said bias to fire the valve;
trigger means responsive to inhalation through the patient port to cause the
restraining means to move from its blocking position to its release position;
wherein the aerosol valve comprises:
a valve housing;
a tank component positioned within the valve housing; and
a valve stem mounted within said valve housing and tank component sequentially
movable between a first position, a second position and a third position as
the valve stem
is depressed in a single direction;
such that:
as the valve stem is moved from said first position towards. said second
position a
metering chamber is formed and defined between the valve stem and tank
component and
formulation flows from the aerosol container into the metering chamber;
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in said second position the metering chamber has a predetermined volume and is
sealed from the aerosol container; and
in said third position formulation is released from the metering chamber
through
the valve stem;
and wherein:
the priming means is constructed and arranged such that as the device is
primed by
operating said priming means the valve stem is moved from its first to its
second position
to allow formation and filling of the metering chamber;
the restraining means is constructed and arranged such that in its blocl~ing
position
it maintains the valve stem in its second position until the trigger means is
actuated by
inhalation through the patient port.
The invention provides a simple effective means of overcoming problems
associated with
filling the metering chamber of an aerosol valve of the type having a
transient metering
chamber by controlling the movement of the valve stem from its first to second
position by
the priming and restraining means of a breath actuated device. When the breath
actuated
device has been primed the valve stem is held in its second position with the
metering
chamber completely full of formulation ready to be dispensed. The priming
stage of the
breath actuated device is sufficiently slow to allow the metering chamber to
be filled as it
is created by movement of the valve stem.
The invention is applicable to a wide range of breath actuated devices
including those in
which the restraining means comprises a latch mechanism and those in which the
restraining means comprises means for applying a resisting pneumatic force.
In general, the aerosol container will be mounted in the dispensing device
with the valve
stem located in a fixed nozzle block. A priming force is applied to the base
of the aerosol
container e.g. by compression of a spring. When the device is primed by
compressing the
spring e.g. by moving a lever to an over centre position, there is movement of
the aerosol
container relative to the valve stem causing the valve stem to be partially
depressed before
the restraining means is engaged to prevent further movement. The device is
arranged
such that this initial movement of the valve stem relative to the aerosol
container is
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sufficient to form and completely fill the metering chamber in the valve. The
valve is held
in its second position until the device is actuated by the patient inspiring
through the
patient port. Patient inspiration actuates the trigger which allows movement
of the
restraining means to its release position and thereby allows relative movement
of the valve
stem and aerosol container under the influence of the bias causing the valve
to fire.
In another embodiment of the invention the aerosol container is fixed within
the housing
and the priming force is applied to the valve stem e.g. to a movable nozzle
block which is
mounted on the valve stem.
The invention will now be described with reference to the accompanying
drawings in
which:
Figure lA represents a vertical cross-section through an embodiment of a
dispensing
device in accordance with the invention in its first position,
Figure 1B shows the restraining and triggering means of the device and
Figure 1C is a cross-section through the aerosol valve in its first position;
Figures 2A, 2B and 2C represent similar views to Figure 1 with the device in
its primed
position and the aerosol valve in its second position; and
Figure 3A shows the device of Figure 1 in its fired position and
Figure 3B shows the aerosol valve in its third (fired) position.
The invention will be described with reference to a breath actuated device
which is
described in EP 0147028. However, it will be appreciated that the invention
may use
other variants of breath actuated devices, such as those described in GB
1288971, GB
1297993, GB 1335378, GB 1383761, GB 1392192, GB 1413285, W085/01880, GB
2204799, US 4,803,978, EP 0186280, GB 1269554, US 5,447,150 and WO 01/93933.
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In the drawings, like references represent lilce parts.
Figure 1A shows a cross section through a breath actuated device in its rest
position. The
device comprises an aerosol container (2) containing a pressurised medicament
formulation and equipped with a metered dose dispensing valve (4) having a
movable
valve stem (6). A housing (8) is disposed about the aerosol container (2) and
comprises a
sleeve (10), body (12), top (14) and a mouthpiece cover (16) which covers the
patient port
(18). The valve stem (6) is positioned within a nozzle block (20) which
directs
formulation from the valve stem towards the patient port (18).
The priming means comprises a priming lever (22) which is pivotally mounted
about axis
(23) to act upon priming spring (24) secured within a cage (26). In the rest
position shown
in Figure lA, the priming spring (24) exerts little or no bias on the aerosol
container (2).
The restraining means comprises a rocker (28) pivotally mounted about axis
(30). One
end of the rocker is attached to tension spring (32) and the other is
pivotally connected to
catch (34). The other end of catch (34) rests on a cam surface of vane (36)
which acts as
the trigger mechanism. Vane (36) is pivotally mounted at axis (38).
In the rest position shown in Figure 1B there is a clearance (40) between the
upper surface
(42) of the rocker (2.8) and the lower surface (44) of the valve ferrule.
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Figure 1C is on an enlarged scale compared with Figure 1A and shows a cross-
section
through the aerosol valvelin its first position when the device is in its rest
position as
shown in Figure lA.
The valve (4) comprises a valve housing (46), a tank component (48) positioned
within the
valve housing and a valve stem (6) mounted within the valve housing and tank
component.
The valve comprises outer seal (50) and inner seal (52). The valve stem (6) is
biased
towards its first position shown in Figure 1C by compression spring (54) held
within
spring retaining sleeve (56).
The outer portion of the valve stem (6) comprises a discharge passage (58) and
side pierce
(60). The inner portion of the valve stem is shaped to completely fill the
tank component
(48) when the valve stem is in its first position. The inner portion of the
valve stem is
hollow, in communication with the aerosol container and comprises sampling
ports (62).
When the valve stem is in its first position shown in Figure 1C there is no
metering
chamber formed.
Figures 2A and 2B show the device in its primed position. Priming lever (22)
is pivoted
upwardly causing spring (24) to be compressed applying a bias to the aerosol
container
(2). The aerosol container moves downwardly under the influence of the bias
until the
lower surface (44) of the valve ferrule contacts the upper surface (42) of the
rocker (28).
The rocker (28) is unable to pivot since it is blocked by the catch (34) that
engages the
vane (36). During the priming operation the aerosol container moves by the
distance of
the clearance (40) shown in Figure 1B.
During the priming operation the valve moves from its first position shown in
Figure 1C to
its second position shown in Figure 2C. During movement of the valve stem from
its first
to its second position a metering chamber (64) is formed between the inner
portion of the
valve stem (6) and the tank component (48). The metering chamber is filled
with
formulation from the aerosol container passing through the sampling port (62)
and
through a small annular gap (not shown) between the inner portion of the valve
stem (6)
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and the tank component (48) into the metering chamber (64). Formulation is
prevented
from exiting the metering chamber (64) by the outer seal (50) that is in
sealing
engagement with the valve stem and between the tank component (48) and the
valve
housing (46). In the second position of the valve stem shown in Figure 2,
inner seal (52)
is in sealing engagement with the valve stem thereby preventing formulation
passing
through the sampling port (62). In the second position of the valve stem shown
in Figure
2C the metering chamber has been fully formed and completely filled with the
formulation.
Figure 3Ashows the device in its fired position. Inhalation through the
patient port (18)
causes vane (36) to pivot upwardly. Movement of the vane (36) displaces the
end of catch
(34) from the vane thereby moving the constraint on rocker (28). Rocker (28)
pivots due
to the force exerted on it by the valve ferrule under the influence of the
priming spring
(24) thereby allowing the aerosol container (2) to move downwardly, causing
the valve to
fire.
Figure 3B shows the valve in its firing position. The valve stem (6) has moved
inwardly
such that the side pierce (60) passes through the outer seal (50) thereby
allowing the
contents of the metering chamber to pass through the side pierce (60) and
discharge
passage (58). The inner seal (52) remains in sealing engagement with the inner
portion of
the valve stem preventing communication between the metering chamber (64) and
the
aerosol container.
It will be appreciated that the speed of movement during the firing, i.e.
movement of the
valve stem from its second to its third position, will not affect the
performance of the valve
since the metering chamber was formed and completely filled during the priming
stage.
Thus high speed movement under the influence of the priming spring during the
firing
operation has no effect on the volume of formulation dispensed.
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It will be understood that the present disclosure of particular embodiments in
accordance
with the invention is for the purpose of illustration only and the invention
extends to
modifications, variations and improvements thereof.
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