Surgery – Liquid medicament atomizer or sprayer – Pre-pressurized container holding medicament
Reexamination Certificate
1999-10-22
2002-09-10
Dawson, Glenn K. (Department: 3761)
Surgery
Liquid medicament atomizer or sprayer
Pre-pressurized container holding medicament
C128S203120
Reexamination Certificate
active
06446627
ABSTRACT:
The present invention relates to a dose counter for a portable dispensing device of the type used for dispensing discrete amounts of a fluid or particulate material entrained in an air or other propellant stream. In particular, the invention is concerned with dose counters for portable dispensing devices of the metered dose inhaler type which are well known in the art of medicine for treatment of, or alleviation of the effects of, respiratory complaints such as asthma.
Metered dose inhalers typically consist of a medicament-containing vessel and an actuator body having a drug delivery outlet. The present invention will find utility in any type of metered dose inhaler in which the contents of the medicament reservoir are invisible to the user, including pressurised metered dose inhalers (of both manually-operable and breath-actuated types), dry powder inhalers, or such like.
The medicament-containing vessel may be a pressurised canister containing a mixture of active drug and propellant. Such canisters are usually formed from a deep drawn aluminium cup portion having a crimped lid portion which carries a metering valve assembly. The metering valve assembly is provided with a protruding valve stem which, in use, is inserted as a tight push fit into a so-called “stem block” in the actuator body.
To actuate the conventional manually-operable inhaler, the user applies a compressive force to the closed end of the canister. The internal components of the metering valve assembly are spring loaded so that, typically, a compressive force of between 15 and 30 N is required to activate the device. In response to this compressive force, the canister moves axially with respect to the valve stem by an amount varying between about 2 and 4 mm. This degree of axial movement is sufficient to actuate the metering valve and cause a metered quantity of the drug and propellant to be expelled through the valve stem. This is then released into the mouthpiece via a nozzle in the stem block. A user inhaling through the drug delivery outlet of the device at this point will thus receive a dose of the drug.
Metered dose inhalers as described above administer an accurate dose of medicament whenever required, which is particularly useful for users whose respiratory difficulties manifest themselves suddenly. Such has been the success of these devices that they are now used throughout the world, where they are exposed to a wide variety of climatic conditions.
A more recent development is the so-called “breath-operated actuator” which delivers a dose of drug through a mouthpiece in response to inhalation by the user. This type of arrangement is particularly convenient in circumstances where the co-ordination between user inhalation and manual depression of the aerosol canister is imperfect. For example, children sometimes lack the necessary co-ordination to achieve effective self-administration. At times of respiratory distress, adult users may also experience poor co-ordination.
Unfortunately, one of the drawbacks of self-administration from an inhaler is that users often experience difficulty in determining when the charge in the medicament-containing vessel has nearly run out. With aerosol canisters, part of the reason for this difficulty is that a surplus of propellant may remain in the canister even though the drug supply is nearly used up. Alternatively, the near-exhausted state may result in a surplus of drug in relation to propellant. Thus, the illusion is created that the inhaler is still capable of providing useful doses of medicament simply because the canister contains liquid. This is potentially hazardous for the user since dosing becomes unreliable and because few people routinely carry a back-up device.
Many users have several different inhalers for the treatment of a variety of conditions. Others keep inhalers at a number of different locations such as at school, home, work etc. In these circumstances it is particularly difficult for the user to keep track of the amount of usage extracted from each individual inhaler apparatus.
Clearly there is a need for a counter mechanism which enables users to assess how many doses remain in the obscured canister. Such a counter would ensure that users are warned when the inhaler nears exhaustion so that appropriate measures can be taken to avoid running out of medication. Moreover, if a dose counter can provide readability to a resolution of one dose, this can be used for compliance monitoring, either under hospital supervision or by parents and teachers assessing compliance by children in their care.
To this end, various counters have been proposed in recent times which aid the management of metered dosage. Such counters vary in complexity and sophistication, but they all have in common the feature that they detect relative movement between the medicament-containing vessel and the actuator body and increment in response to such movement.
Known dose counters can be categorised into the following types:
(a) Reservoir low indicators,
(b) Fuel gauge types (resolution limited to 10 doses or higher),
(c) Dose computers (resolution to one dose and intrinsically accurate).
An example of the first type is described in International Patent Application No. WO 86/05991 which uses a wheel carrying a coloured mark as the warning indicator. The wheel is rotated by a worm drive forming part of the metering mechanism. Actuation of the metering mechanism infers that the patient has taken a dose of medicament and, when a predetermined number of doses has been dispensed, the coloured part of the wheel becomes visible through an aperture. This indicates to the user that a replacement dispenser will be required shortly. The principles disclosed in this document would enable the system to be upgraded to a fuel gauge type display except for the fact that the worm gearing system is unsuitable for providing single dose resolution in a portable product.
International Patent Application No. WO 92/09324 discloses the use of a rotatable display means incorporating a rack of teeth which is driven by a ratchet during the dispensing of a medicament dose. Each tooth on the rack corresponds to a single dose. The disadvantage of this type of arrangement is that, for reliable operation, all of the teeth in the rack need to be perfect. One poor tooth will result in the counter display showing “half full” when the reservoir is actually empty. The document also discloses a number of gearing means to enable the display to increment for hundreds of doses. To provide a counter for the typical 200-dose portable inhaler using this invention would require a wheel with very small teeth, formation of which is beyond current manufacturing capabilities at sensible costs.
European Patent Application No. 0 480 488 discloses a similar dose counter using a rack of single-direction teeth as the recording means. This arrangement typifies the current state of the art and its inherent limitations. The display ring shows the doses remaining, but only in units of ten. Furthermore, for reasons of tooth size, the display ring limits the reservoir capacity to a total of approximately counted 120 doses. By means of further reduction in gearing it is possible for this type of system to be extended to 200 doses but only by reducing the display resolution to greater than 10 doses.
U.S. Pat. No. 4,565,302 discloses similar means to the devices discussed above, but illustrated clearly in
FIG. 6
the limitations of such mechanisms in terms of display readability and total reservoir size. To ensure readability, a large numeral 5 is shown in the device; it is clear from the Figure that no more than 30 doses could be displayed in this manner if the same style and size of indication is required for each dose dispensed i.e. 5, 4, 3 etc.
In U.S. Pat. No. 5,437,270 for a multi-dose powder device, a number of display means are disclosed, including a tape system. The system is described as a tape wound up into a roll and which is freely rotatable, the leading edge of the tape being secured to a drum coupled to the rotation of the m
Bowman Nicholas John
Holroyd Michael John
Panayi Costaninos
Treneman William Richard
Arent Fox Kintner & Plotkin & Kahn, PLLC
Dawson Glenn K.
Norton Healthcare Limited
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