Dispensing – With discharge assistant – Fluid pressure
Patent
1997-10-29
2000-03-07
Bomberg, Kenneth
Dispensing
With discharge assistant
Fluid pressure
B65D 8316
Patent
active
060328363
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and apparatus for dispensing a material in aerosol form. It is particularly, though not exclusively, concerned with metered dose medicament aerosols, for example metered dose inhalers (MDIs).
BACKGROUND OF THE INVENTION
Aerosol type dispensers are used throughout the world for dispensing a wide range of products, for example hair lacquer, furniture polish, cleaners, paint, insect killers and medicaments.
Liquefied compressed gases are invariably used as the propellant for aerosol dispensers for inhalation therapy in preference to non-liquefied compressed gasses such as nitrogen or carbon dioxide, as they confer the following critical advantages: particle size inhaler vapour pressure is maintained at an almost constant level by progressive propellant evaporation metering chamber causes efficient discharging of the metered valve contents and accurate dose delivery and resistance to microbial growth.
FIGS. 1A and 1B of the accompanying drawings show the valve and lower portion of a typical MDI aerosol dispenser in closed and open positions respectively. Such dispensers generally comprise a small aluminium shuttle valve 1 which is crimp fitted to the can 2 containing the drug and chlorofluorocarbon (CFC) propellants. The valve is activated by manually pressing shuttle pin 3 such that it moves a small distance into the can 2. In order to do this it is necessary to overcome the force exerted on the pin 3 by virtue spring 4 and of the pressure within the container. Pressures within such dispensers are typically around 8 bar which is sufficient to maintain CFC propellants in a liquid state at ambient temperatures.
Until recently, CFCs were the most common of the propellant gases used in aerosols because they are inert, miscible with a wide range of products, are easily liquefied under low pressures, give a substantially constant product flow-rate, and can produce sprays of droplets having mean diameters in the range of 3 to over 100 micrometers. However, in the 1970's it was proposed that CFCs were probably responsible for depleting the Earth's protective ozone layer, and in 1987, most countries signed the Montreal Protocol to phase out the use of CFCs and have since agreed to stop use of CFCs for non-essential applications by the end of 1995. One notable exemption to this deadline for cessation of use is in relation to MDIs for medicaments, which are regarded as an essential use of CFCs, but even this use of CFCs will be phased out as acceptable alternatives are developed.
Many companies are now working to develop alternative CFC--free propellants for use in aerosol spray devices including MDIs to overcome the ozone destructing properties of conventional CFC containing propellants. A class of propellants which are believed to have minimal ozone-depleting effects in comparison to conventional CFCs comprise fluorocarbons and hydrogen-containing fluorocarbons (commonly known as HFA propellants), and a number of medicinal aerosol formulations using such propellant systems are disclosed in, for example European Patent Application Publication No. 0372777 and PCT Patent Application Nos. WO91/04011 WO91/11173, WO91/11495 and WO91/14422. These applications are all concerned with the preparation of pressurised aerosols for the administration of medicaments and seek to overcome the problems associated with the use of the new class of propellants, in particular the problems of stability associated with the pharmaceutical formulations prepared. The applications all propose the addition of one or more of adjuvents such as alcohols, alkanes, dimethyl ether, surfactants and even conventional chlorofluorocarbon propellants in small amounts to minimise potential ozone damage. Surfactants are added to make the suspension formulations stable. However, whilst surfactants may conveniently be used in MDIs which use CFC propellants, surfactants are not generally solvent in HFA propellants and so require the use of additional co-solvents.
Attempts have also been made to develop devices which produce
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Gee David Laurence
Hiscocks Peter Gerard
Bomberg Kenneth
Glaxo Group Limited
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