Methods and Apparatus for Storing Chemical Compounds in a Portable Inhaler

The invention relates generally to the field of inhalation drug therapy, and in particular to the inhalation of aerosolized chemical substances. In one aspect, the invention provides a portable inhaler having a cartridge for storing a chemical substance in a dry state and a liquid dispenser to introduce a liquid to the substance to form a solution. Immediately after formation of the solution, the inhaler aerosolizes the solution so that it may be administered to a patient.

The atomization of liquid medicaments is becoming a promising way to effectively deliver many medicaments to a patient. In particular there is a potential for pulmonary delivery of protein peptides and other biological entities. Many of these are easily degraded and become inactive if kept in a liquid form. Proteins and peptides often exhibit greater stability in the solid state. This results primarily from two factors. First, the concentration of water, a reactant in several protein degradation pathways, is reduced. See Stability of Protein Pharmaceuticals, M. C. Manning, K. Patel, and R. T. Borchardt, Pharm. Res. 6, 903-918 (1989), the complete disclosure of which is herein incorporated by reference. Second, the proteins and other excipients are immobilized in the solid state. Water is a reactant in hydrolysis reactions, including peptide change and cleavage, and deamidation. Reducing the water concentration by freeze-drying or spray drying, reduces this reactant concentration and therefore the rates of these degradation pathways.

The mobility of the peptides or proteins, as well as other molecules in the formulation, are reduced in the solid or dry state. See Molecular Mobility of Amorphous Pharmaceutical Solids Below Their Glass Transition Temperatures, B. C. Hancock, S. L. Shamblin, and G. Zografi, Pharm. Res. 12, 799-806 (1995), the complete disclosure of which is herein incorporated by reference. For the peptides or proteins, this reduces the rate of intermolecular interactions as well as intramolecular conformational changes or fluctuations in conformation. Minimization of intermolecular interactions will reduce protein and peptide aggregation/precipitation, and will also reduce the rate of diffusion of chemical reactants to the protein or peptide which will slow the rate of chemical degradation pathways. Reduction in intramolecular conformational changes reduces the rate at which potentially reactive groups become available for chemical or intermolecular interaction. The rate of this reaction may decrease as the water concentration, and mobility of the protein, is reduced.

One way to produce protein in solid or dry state is to transform the liquid into a fine powder. When used for inhalation delivery, such powders should be composed of small particles with a mean mass diameter of 1 to 5 microns, with a tight particle size distribution. However, this requirement increases the processing and packaging cost of the dry powder. See also U.S. Pat. No. 5,654,007 entitled "Methods and System for Processing Dispersible Fine Powders" and U.S. Pat. No. 5,458,135 entitled "Methods and Devices for Delivering Aerosolized Medicaments", the disclosures of which are incorporated herein by reference.

An easier way to transform a liquid solution to solid or dry form is to use a freeze drying process where a liquid solution is converted to a solid substance that can be readily reconstituted to a liquid solution by dissolving it with a liquid, such as water. Hence, one object of the present invention is to provide a way to store a solid substance and combine the solid substance the with a liquid to form a solution. Once the solution is formed, it is another object of the invention to rapidly transport the solution to an atomization device to allow the solution to be aerosolized for administration. In this way, the solution is aerosolized immediately after its reconstitution so that the degradation rate of the substance is reduced.

A variety of nebulization devices are available for atomizing liquid solutions. For example, one exemplary atomization apparatus is described in U.S. Pat. No. 5,164,740, issued to Ivri ("the '740 patent"), the complete disclosure of which is herein incorporated by reference. The '1740 patent describes an apparatus which comprises an ultrasonic transducer and an aperture plate attached to the transducer. The aperture plate includes tapered apertures which are employed to produce small liquid droplets. The transducer vibrates the plate at relatively high frequencies so that when the liquid is placed in contact with the rear surface of the aperture plate and the plate is vibrated, liquid droplets will be ejected through the apertures. The apparatus described in the '740 patent has been instrumental in producing small liquid droplets without the need for placing a fluidic chamber in contact with the aperture plate, as in previously proposed designs. Instead, small volumes of liquid can be placed on the rear surface of the aperture plate and held to the rear surface by surface tension forces.

A modification of the '740 apparatus is described in U.S. Pat. Nos. 5,586,550 ("the '550 patent") and 5,758,637 ("the '637 patent"), the complete disclosures of which are herein incorporated by reference. These two references describe a liquid droplet generator which is particularly useful in producing a high flow of droplets in a narrow size distribution. As described in the '550 patent, the use of a non-planar aperture plate is advantageous in allowing more of the apertures to eject liquid droplets. Furthermore, the liquid droplets may be formed within the range from about 1 .mu.m to about 5 .mu.m so that the apparatus will be useful for delivering drugs to the lungs.

Hence, it is a further objective of the invention to provide devices and methods to facilitate the transfer of liquid solutions (preferably those which have just been reconstituted) to such aerosolizing apparatus so that the solution may be atomized for inhalation. In so doing, one important consideration that should be addressed is the delivery of the proper dosage. Hence, it is still another object of the invention to ensure that the proper amount of liquid medicament is transferred to an aerosol generator so that a proper dosage may be delivered to the lungs.

The invention provides exemplary systems, apparatus and methods for reconstituting a solid phase substance, e.g., a substance that is in a dry state, with liquid to form a solution and for transporting the solution to an aerosol generator for subsequent atomization. In one exemplary embodiment, the system comprises a liquid dispenser, a cartridge containing a substance in a dry state, and an aerosol generator. In use, the cartridge is coupled to an outlet of the dispenser and the dispenser is operated to dispense liquid from the outlet and into the cartridge. The liquid then flows through the substance and exits the cartridge as a solution.

In an exemplary aspect, the cartridge is replaced and disposed after each use. After removal of the cartridge the user may optionally operate the liquid dispenser to deliver liquid to the aerosol generator for a subsequent cleaning cycle. In another exemplary aspect, a liquid outlet of the cartridge is positioned near the aerosol generator such that the solution is dispensed onto the aerosol generator and is readily available for atomization.

The Liquid Dispenser

In an exemplary embodiment, the liquid dispenser comprises a mechanical pump that is attached to a canister. The liquid dispenser is disposed within a housing of the inhaler and is configured to deliver a predetermined volume of liquid each time the mechanical pump is operated. The dispensed liquid then flows directly from the pump to the cartridge to form a solution which in turn is deposited on the aerosol generator.

In one particular aspect, the liquid is a saline solution or sterile water and may optionally contain an anti-microbial additive. As previously mentioned, the solid substance in the cartridge preferably comprises a chemical that is in the dry state which is reconstituted into a solution upon introduction of the liquid from the liquid dispenser.

In one particularly preferable aspect, the mechanical pump comprises a piston pump that is connected to the canister. The piston pump comprises a spring-loaded piston member that is slidable within a cylindrical member which defines a metering chamber. When the piston member is moved to a filling position, the metering chamber is filled with liquid from the canister. When released, the piston member moves to a dispensing position to dispense a known volume of liquid from the metering chamber. In this way, each time the pump is operated, a unit volume of liquid is dispensed from the piston pump.

In one particularly preferable aspect, movement of the piston member toward the filling position creates a vacuum inside the cylindrical member that gradually increases until the piston member reaches a point where a passage is provided between the piston member and the cylindrical member. At this point, the piston member has reached the filling position to allow liquid from the canister to be drawn by the vacuum into the metering chamber of the cylinder. At this point, the piston member is released and returns by the force of the spring back to the dispensing position. During the return travel of the piston member to the dispensing position, the liquid in the metering chamber is displaced through an outlet of the pump.

In another particular aspect, the piston pump is configured to deliver volumes of liquid in the range of about 10 .mu.L to about 50 .mu.L each time the pump is operated. In another aspect, the piston pump is configured such that it will dispense a full unit volume only if the user fully depresses the piston to the filling position. If the piston member is only partially depressed, no liquid will be dispensed. In this manner, partial dosing is prevented.

In still yet another aspect, the liquid dispenser further includes a valve which serves to eliminate the dead volume in the piston pump, thereby inhibiting microbial inflow into the liquid dispenser. The valve preferably comprises a tubular valve seat that is slidably disposed about a distal end of the piston member. In this way, the liquid within the metering chamber moves the tubular valve seat distally over the piston member to allow the liquid in the metering chamber to be dispensed by flowing between the piston member and the tubular valve seat when the piston member is moved toward the dispensing position. The tubular valve seat is also slidable within the cylindrical member, and the cylindrical member defines a stop to stop distal movement of the tubular valve seat relative to the piston member after the unit volume of liquid has been dispensed from the metering chamber. Further, when the spring forces the distal end of the piston member into a distal end of the tubular valve seat, a seal is provided between the piston member and the tubular valve seat to prevent microbial inflow into the piston pump. Hence, use of the tubular valve seat in combination with the piston member and the cylindrical member allows for a unit volume of the liquid within the piston pump to be dispensed and further provides a seal to prevent microbial inflow into the piston pump.

The Drug Cartridge

The cartridge of the invention allows for the storage of a chemical in a dry state. When a liquid is introduced into the cartridge, the chemical substance dissolves within the liquid to form a solution just prior to aerosolization of the solution.

In one exemplary embodiment, the cartridge comprises a housing having an inlet opening and an outlet opening. Disposed in the housing is a chemical substance which is in a dry state. As liquid flows through the housing, the substance dissolves and flows through the outlet opening as a solution.

The chemical substance may be any one of a variety of chemical substances, such as proteins, peptides, small molecule chemical entities, genetic materials, and other macromolecules and small molecules used as pharmaceuticals. One particular substance is a lyophilized protein, such as interferon alpha or alpha 1 prolastin. The lyophilized substance is preferably held in a support structure to increase the surface area that is in contact with the liquid, thereby increasing the rate by which the substance is dissolved. The support structure is preferably configured to hold the lyophilized substance in a three-dimensional matrix so that the surface area of the substance that is contact with the liquid is increased. Exemplary types of support structures include open cell porous materials having many tortuous flow paths which enhance mixing so that the solution exiting from the outlet end is homogenized. Alternatively, the support structure may be constructed of a woven synthetic material, a metal screen, a stack of solid glass or plastic beads, and the like.

When used in connection with the aerosolizing apparatus of the invention, actuation of the liquid dispenser introduces liquid into the inlet opening, through the support structure to dissolve the substance, and out the outlet opening where it is disposed on the aerosol generator as a solution. The aerosol generator is then operated to aerosolize the solution. In this way, the substance is stored in a solid state until ready for use. As previously described, the flow of liquid from the liquid dispenser is produced during the return stroke of the piston member, i.e. as the piston member travels to the dispensing position. Since the return stroke is controlled by the spring, it is not dependent on the user. In this way, the flow rate is the same each time the liquid dispenser is operated, thereby providing a way to consistently and repeatedly reconstitute the solution.

In one particular aspect, the cartridge includes a coupling mechanism at the inlet opening to couple the cartridge to the liquid dispenser. In this way, the cartridge is configured to be removable from the liquid dispenser so that it may be removed following each use and discarded. In still another aspect, the cartridge is filled with the chemical substance while in a liquid state. The substance is then freeze dried and converted to a solid state while in the cartridge.

The Aerosol Generator

In an exemplary embodiment, the aerosol generator that is employed to aerosolize the solution from the cartridge is constructed in a manner similar to that described in U.S. Pat. Nos. 5,586,550 and 5,758,637, previously incorporated herein by reference. In brief, the aerosol generator comprises a vibratable member having a front surface, a rear surface, and a plurality of apertures which extend between the two surfaces. The apertures are preferably tapered as described in U.S. Pat. No. 5,164,740, previously incorporated herein by reference. In one particular aspect, the vibratable member is preferably hemispherical in shape, with the tapered apertures extending from the concave surface to the convex surface. In use, the solution from the cartridge is supplied to the rear surface of the vibratable member having the large opening. As the vibratable member is vibrated, the apertures emit the solution from the small openings on the front surface as an aerosolized spray. The user then simply inhales the aerosolized spray to supply the chemical to the patient's lungs.

FIG. 1 illustrates a partial cutaway view of an exemplary apparatus having an aerosol generator for aerosolizing liquids according to the invention.

FIG. 2 is a schematic diagram of an inhalation flow sensor for detecting when a patient begins to inhale from an aerosolizing apparatus according to the invention.

FIG. 3 is a cross-sectional side view of an aerosol generator of the aerosolizing apparatus of FIG. 1.

FIG. 4-9 illustrate cross-sectional side views of a container and a piston pump used in the apparatus of FIG. 1 to deliver a predetermined volume of liquid to the aerosol generator. The views illustrated in FIGS. 4-9 show various states of the piston pump when metering and transferring liquids from the container to the aerosol generator.

FIG. 10 is a schematic view of an aerosolizing system having a removable cartridge holding a substance that is in a solid state according to the invention.

FIG. 11 illustrates the aerosolizing system of FIG. 10 having the cartridge removed for cleaning of the aerosol generator according to the invention.

The invention provides exemplary systems, apparatus and methods for reconstituting a solid substance that is in a dry state with liquid, such as water, to form a solution and for transporting the solution to an aerosol generator for subsequent atomization. In one exemplary embodiment, the system comprises a liquid dispenser, a cartridge containing the substance that is in the dry state, and an aerosol generator. In use, the cartridge is coupled to an outlet of the dispenser. The user then actuates the liquid dispenser so that liquid is dispensed from the dispenser and enters into the cartridge. As the liquid flows through the cartridge, the dry substance is dissolved into the liquid and exits the cartridge as a solution. Preferably, the cartridge is replaced and disposed after each use. In a preferred embodiment, an outlet end of the cartridge is positioned near the aerosol generator so that the solution disposed on the aerosol generator is readily available for atomization.

In one alternative, a two step process is employed to reconstitute the solution and deliver the solution to the aerosol generator. First, a portion of a unit volume of liquid, such as one-half a unit volume, is supplied to the cartridge when the liquid dispenser is operated. The user then waits a predetermined amount of time, such as about 10 seconds, and again operates the liquid dispenser to deliver sufficient liquid into the cartridge to force a unit volume of solution from the cartridge an onto the aerosol generator. In this way, a period of time is provided to allow more of the substance to dissolve in the liquid.

In another aspect of the invention, exemplary systems and methods are provided for metering relatively small volumes of liquid directly from a container and for delivering the metered volume to an atomizer. The systems and methods are configured to precisely meter and deliver relatively small volumes of liquid, typically in the range from about 10 .mu.L to about 100 .mu.L. When delivering volumes in the range from about 10 .mu.L to 50 .mu.L, the invention preferably employs the use of a piston pump that is connected to a canister as described in greater detail hereinafter. For volumes in the range from about 50 .mu.L to about 100 .mu.L, a pharmaceutical pump is preferably employed, such as metered dose S4 pump, commercially available from Somova S. p.A. Milano, Italy. Optionally, such pharmaceutical pumps may also contain a pharmaceutical medicament which may be delivered directly to the aerosol generator. As one example, the pharmaceutical medicament may comprise a suspension of colica steroid for treatment of asthma.

Another feature of the liquid dispensers of the invention is that they are configured to prevent or substantially reduce the possibility of contamination. In this way, each subsequent dosage delivered by the liquid dispenser is not contaminated when delivered to the atomizer.

Referring now to FIG. 1, an exemplary apparatus 10 for atomizing a liquid will be described. Apparatus 10 comprises a housing 12 which is configured to hold the various components of apparatus 10. Housing 12 is preferably constructed to be lightweight and pocket-sized, typically being molded of a plastic material. Housing 12 is divided into two separable portions. A first portion 14 includes an electronics compartment and a second portion 16 includes a liquid holding compartment for holding a canister 18, an aerosol generator 22, and a mouthpiece 20 through which the atomized liquids are dispensed to the patient. Conveniently, second portion can be separated from first portion 14 by sliding a knob 23. Optionally, second portion 16 having the liquid holding component may be disposed following separation from first portion 14. Second portion 16 may be disposed along with canister 18, or canister 18 may be disposed separately.

Apparatus 10 further includes an inhalation flow sensor 24 which detects the inhalation flow produced by the patient when inhaling from mouthpiece 22. Upon detection of the inhalation, sensor 24 sends an electrical signal to an electronic circuit (not shown) which in turn sends an alternating voltage to vibrate a piezoelectric member 26 of aerosol generator 22 to aerosolize a liquid. Sensor 24 preferably comprises a flexure foil and an electro-optical sensor. The flexible foil deflects in response to the inhalation airflow produced when a patient inhales from mouthpiece 20. The optical sensor is configured to detect deflection of the flexible foil so that a signal may be produced to vibrate piezoelectric member 26.

Referring now to FIG. 2, a schematic diagram of an inhalation flow sensor 24 will be described. Flow sensor 24 comprises a flexible foil 28 having an extension 30. Inhalation flow sensor 24 further includes an optical sensor 32 which includes a light emitting diode (LED) 34 and a light sensitive transistor 36 placed in apposition to LED 34 so that LED 34 continuously transmits a light beam 38 to transistor 36. When the patient inhales, the inhalation airflow causes flexible foil 28 to deflect and move extension 30 downward until it crosses light beam 38 and causes an optical interruption that is detected by transistor 36. Transistor 36 then sends a signal to trigger activation of an aerosol generator to produce an aerosol.

By configuring inhalation flow sensor 24 in this manner, aerosol generator 22 is actuated only in response to the detection of an inhalation airflow produced by a patient. In this way, the patient may be administered a single dose using either a single inhalation or multiple inhalations. Preferably, inhalation flow sensor 24 is triggered at an inhalation flow rate of at least 15 liters per minute. However, it will be appreciated that sensor 24 may be constructed to trigger at either lower or higher flow rates. Adjustment of the actuation point may be accomplished by altering the flexible stiffness of foil 28, by selecting different materials for constructing foil 28 or by changing the thickness of foil 28.

Alternatively, the inhalation flow sensor may be constructed from a piezoelectric film component. The piezoelectric film component produces an electrical signal when it deflects. The magnitude of the electrical signal is proportional to the magnitude of deflection. In this way, the electrical signal that is produced by the piezoelectric film component can be used to detect the magnitude of the inhalation flow. In this manner, the output of the aerosol generator may be adjusted in proportion to the inhalation airflow. Such a proportional output from the aerosol generator is particularly advantageous in that it prevents the coalescence of particles and controls the aerosol production according to the inhalation flow. Control of the aerosol output may be adjusted by turning the aerosol generator on and off sequentially. The ratio between the on time and the off time, generally defined as the duty cycle, affects the net flow. An exemplary piezoelectric film component with such characteristics is commercially available from ATO Autochem Sensors, Inc., Valley Forge, Pa.

Referring back to FIG. 1, the electronic circuit (not shown) within first portion 14 includes electrical components to detect the presence of liquid on aerosol generator 22 and to send a signal to the user indicating that all of the liquid has been aerosolized. In this way, the user will know if additional inhalations will be required in order to receive the prescribed amount of medicament. The sensing circuit preferably comprises a voltage sensing circuit (not shown) which detects the voltage across piezoelectric element member 26. Since the voltage across piezoelectric member 26 is proportionally related to the amount of liquid in surface tension contact with an aperture plate 40 (see FIG. 3) of aerosol generator 22, it can be determined, based on the voltage, whether any liquid is left remaining. For example, when aerosolization is initiated, the voltage is high. At the end of aerosolization, the voltage is low, thereby indicating that the aerosolization process is near completion. Preferably, the sensing circuit is configured to be triggered when about 95% of the liquid has been aerosolized. When triggered, the sensing circuit turns on a light emitting diode (LED) 42 indicating that the prescribed dosage has been delivered.

Referring now to FIG. 3, construction of aerosol generator 22 will be described in greater detail. As previously described, aerosol generator 22 includes a vibratable aperture plate 40 and annular piezoelectric member 26. Aerosol generator 22 further comprises a cup-shaped member 44 to which piezoelectric member 26 and aperture plate 40 are attached as shown. Cup-shaped member 44 includes a circular hole 46 over which aperture plate 40 is disposed. Wires (not shown) connect piezoelectric member 26 to the electrical circuitry within portion 14 (see FIG. 1) which in turn is employed to vibrate piezoelectric member 26.

Cup-shaped member 44 is preferably constructed of a low damping metal, such as aluminum. Aperture plate 40 is disposed over hole 46 such that a rear surface 48 of aperture plate 40 is disposed to receive liquid from canister 18 (see FIG. 1). Although not shown, aperture plate 40 includes a plurality of tapered apertures which taper from rear surface 48 to a front surface 50. Exemplary aperture plates which may be used with the invention include those described the '740 patent, the '550 patent, and the '637 patent, previously incorporated by reference.

Aperture plate 40 is preferably constructed of a material that may be produced by a metal electroforming process. As an example, aperture plate 40 may be electroformed from palladium or a palladium alloy, such as palladium cobalt or palladium nickel. Aperture plate 40 may further be gold electroplated to enhance its corrosion resistance. Alternatively, aperture plate 40 may be constructed of nickel, a nickel-gold alloy, or a combination of nickel and nickel-gold alloy arranged such that the nickel-gold alloy covers the external surfaces of the aperture plate. The nickel-gold alloy may be formed using a gold electroplating process followed by diffusion at an elevated temperature as described generally in Van Den Belt, TGM, "The diffusion of platinum and gold in nickel measured by Rutherford Fact Scattering Spectrometry", Thin Solid Film, 109 (1983), pp. 1-10. The complete disclosure of this reference is incorporated herein by reference. A small amount of manganese may also be introduced to the nickel during the electroforming process so that the nickel can be heat treated at an elevated temperature as described generally in U.S. Pat. No. 4,108,740, incorporated herein by reference. The gold-nickel alloy is particularly useful in protecting the nickel components, and particularly the electroformed nickel components, from corrosion caused by plating porosity. The diffusion process may be useful for other applications which require corrosion protection for nickel components, and particularly nickel electroformed components, such as, for example, inkjet aperture plates, other spray nozzle plates, and the like.

As another alternative, corrosion resistance of the aperture plate may be enhanced by constructing the aperture plate of a composite electroformed structure having two layers, with the first electroformed layer comprising nickel and the second electroformed layer comprising gold. The thickness of the gold in the composite in preferably at least two microns, and more preferably, at least five microns. Alternatively, the second layer may be electroformed from palladium or another corrosive-resistant metal. The external surfaces of the aperture plate may also be coated with a material that prevents bacteria growth, such as polymyxin or silver. Optionally, other coatings that enhance wetability may be applied to the aperture plate.

Cup-shaped member 44 is disposed within a housing 52 which prevents liquids from coming into contact with piezoelectric member 26 and with cup-shaped member 44. Cup-shaped member 44 is suspended within housing 52 by two elastic rings 54 and 56. Ring 54 is positioned between housing 52 and the circumference of cup-shaped member 44. Ring 56 is positioned between the inner diameter of piezoelectric member 26 and a shield member 58. Such an arrangement provides a hermetic seal that prevents the contact of liquids with the piezoelectric member 26 without suppressing the vibratory motion of cup-shaped member 44.

Referring back now to FIG. 1, aerosol generator 22 is axially aligned with mouthpiece 20 so that when piezoelectric member 26 is vibrated, liquid droplets are ejected through mouthpiece 20 and are available for inhalation by the patient. As previously described, disposed within second portion 16 is a canister 18 which holds the liquid medicament to be atomized by aerosol generator 22. Canister 18 is integrally attached to a mechanical pump 60 which is configured to dispense a unit volume of liquid through a nozzle 62 to aerosol generator 22. Pump 60 is actuated by pressing a knob 64 which pushes canister 18 downward to generate the pumping action as described in greater detail hereinafter. Pressing on knob 64 also puts pressure on an electrical microswitch 66 within second portion 16. When actuated, microswitch 66 sends a signal to the electrical circuit within first portion 14 causing a light emitting diode (LED) (not shown) to blink indicating that apparatus 10 is ready for use. When the patient begins to inhale, the inhalation is sensed causing actuation of the aerosol generator.

As illustrated in FIG. 3, pump 60 delivers a unit volume of liquid 68 (shown in phantom line) to rear surface 48 of aperture plate 40. The delivered volume 68 adheres to aperture plate 40 by solid/liquid surface interaction and by surface tension forces until patient inhalation is sensed. At that point, piezoelectric member 26 is actuated to eject liquid droplets from front surface 50 where they are inhaled by the patient. By providing the delivered volume 60 in a unit volume amount, a precise dose of liquid medicament may be atomized and delivered to the lungs of the patient. Although canister 18 of FIG. 1 is shown as being configured to directly deliver the dispensed liquid to the aperture plate, pump 60 may alternatively be configured to receive a cartridge containing a chemical in a dry state as described in greater detail hereinafter.

Referring now to FIGS. 4-10, a schematic representation of a canister 138 and a piston pump 140 will be described to illustrate an exemplary method for dispensing a unit volume of a liquid medicament to an aperture plate, such as aperture plate 40 of apparatus 10 (see FIGS. 1 and 3). Canister 138 comprises a housing 142 having an open end 144 about which a cap 146 is placed. Disposed against open end 144 is a washer 148 which provides a seal to prevent liquids from escaping from housing 142. On top of washer 148 is a cylindrical member 150. Cap 146 securely holds cylindrical member 150 and washer 148 to housing 142. Cylindrical member 150 includes a cylindrical opening 151 which allows liquids to enter from canister 138. Cylindrical member 150 in combination with washer 148 also serve to securely position a holding member 152 about which a compression spring 154 is disposed.

Piston pump 140 comprises a piston member 156, cylindrical member 150, a valve seat 158 and compression spring 154. Piston member 156 has a frontal end 156A and a distal end 156B, with frontal end 156A providing the piston action and distal end 156B providing the valve action.

Piston pump 140 is configured such that every time valve seat 158 is depressed toward canister 138 and then released, a unit volume of liquid is dispensed through a tapered opening 161 in valve seat 158. Valve seat 158 includes a valve seat shoulder 158A which is pressed to move valve seat inwardly, causing valve seat 158 to engage with distal end 156B to close tapered opening 161.

As shown in FIG. 5, as piston member 156 is further depressed into cylindrical member 150, spring 154 is compressed and a metering chamber 168 begins to form between frontal end 156A and cylindrical member 150. Frontal end 156A and distal end 156B are preferably constructed from a soft elastic material which provides a hermetic seal with cylindrical member 150 and valve seat 158, respectively. Due to the seal between frontal end 156A and cylindrical member 150, a vacuum is created within metering chamber 168 upon depression of piston member 156.

As piston member 156 is further moved into cylindrical member 150 (see FIG. 6), spring 154 is further compressed and frontal end 156A moves past cylindrical opening 151 so that a gap is provided between frontal end 156A and cylindrical member 150. As frontal end 156A passes the edge of cylindrical member 150, liquid from canister 138 is drawn into cylindrical member 150 by the vacuum that was created within metering chamber 168. In FIG. 6, piston member 156 is in the filling position.

At the end of inward travel, the user releases the pressure on valve seat 158, allowing spring 154 to push piston member 156 back toward its starting position. As illustrated in FIG. 7, upon the return travel of piston member 156 to the starting position, frontal end 156A again engages cylindrical member 150 and forms a seal between the two surfaces to prevent any liquid within metering chamber 168 from flowing back into canister 138.

Since the liquid within metering chamber 168 is generally incompressible, as spring 154 pushes on piston member 156, the liquid within metering chamber 168 forces valve seat 158 to slide distally over piston member 156. In so doing, the liquid within metering chamber 168 is allowed to escape from the metering chamber through tapered opening 161 of valve seat 158 as illustrated in FIG. 8.

As illustrated in FIGS. 7-9, liquid from metering chamber 168 is dispensed from tapered opening 161 as frontal end 156A travels length L. As frontal end 156A passes through length L, it is in contact with cylindrical member 150. In this way, the liquid within metering chamber 168 is forced out of tapered opening 161 during this length of travel. After passing through Length L, frontal end 156A passes out of sealing relationship with cylindrical member 150 so that no further liquid is dispensed from tapered opening 161. Hence, the amount of liquid dispensed is proportional to the diameter of cylindrical member 150 over length L. As such, piston pump 140 may be designed to dispense a known volume of liquid each time piston member 156 travels from the starting position to the filling position and then back to the starting position. Since piston member 156 must be fully depressed to the filling position in order to create a gap between frontal end 156A and cylindrical member 150, a way is provided to ensure that partial volumes can not be dispensed.

As shown in FIG. 9, valve seat 158 includes a shoulder 170 which engages a stop 172 on cylindrical member 150 to stop distal movement of valve seat 158 relative to cylindrical member 150. At this point, piston pump 140 is at an ending dispensing position which corresponds to the starting position as initially illustrated in FIG. 4. In this position, spring 154 forces distal end 156B of piston member 156 into tapered opening 161 to provide a seal and prevent contaminants from entering into piston 140.

Valve seat 158 is preferably coated with a material that inhibits proliferation of bacteria. Such coatings can include, for example, coatings having a positive electric charge, such as polymyxin, polyethylinimin, silver, or the like.

The invention further provides a convenient way to store chemical substances in the solid or dry state and then to dissolve the chemical substance with liquid from the canister to form a solution. In this way, chemical substances that are otherwise susceptible to degradation can be stored in the dry state so that the shelf life of the product is extended. An exemplary embodiment of a cartridge 180 for storing such chemical substances that are in the dry state is illustrated in FIG. 10. For convenience of illustration, cartridge 180 will be described in connection with piston pump 140 and canister 138, which in turn may be coupled to an aerosolization apparatus, such as apparatus 10, to aerosolize a medicament as previously described. Cartridge 180 comprises a cylindrical container 182 having an inlet opening 184 and outlet opening 186. Inlet opening 182 is sized to be coupled to piston pump 140 as shown. Disposed within container 182 is a first filter 188 and a second filter 190. Filter 188 is disposed near inlet opening 184 and second filter 190 is disposed near outlet opening 186. A chemical substance 192 which is in a dry state is disposed between filters 188 and 190. Chemical substance 192 is preferably held within a support structure to increase the rate in which the chemical substance is dissolved.

The support structure may be constructed of a variety of materials which are provided to increase the rate in which the chemical substance is dissolved. For example, the support structure may comprise an open cell material such as a polytetrafluoroethylene (PTFE) matrix material commercially available from Porex Technologies, Farburn, Ga. Preferably, such an open cell material has a pore size in the range from about 7 .mu.m to about 500 .mu.m, and more preferably about 250 .mu.m. Alternatively, various other plastic materials may be used to construct the open cell matrix, including olyethylene (HDPE), ultra-high molecular weight polyethylene (UHMW), polypropylene (PP), polyvinylidene fluoride (PVDF), nylon 6 (N6), polyethersulfone (PES), ethyl vinyl acetate (EVA), and the like. Alternatively, the support structure may be constructed of a woven synthetic material, a metal screen, a stack of solid glass or plastic beads, and the like.

An exemplary method for placing chemical substance 192 into container 182 is by filling container 182 with the chemical substance while the chemical substance is in a liquid state and then lyophilizing the substance to a dry state while the substance within the cartridge. In this way, filling of cartridge 180 with a chemical substance may be precisely and repeatedly controlled. However, it will be appreciated that the chemical substance may be placed into cartridge 180 when in the solid state.

Lyophilization is one exemplary process because it will tend to reduce the rate of various physical and chemical degradation pathways. If the substance comprises a protein or peptide, both the lyophilization cycle (and resulting moisture content) and product formulation can be optimized during product development to stabilize the protein before freezing, drying and for long term storage. See Freeze Drying of Proteins, M. J. Pikal, BioPharm. 3, 18-26 (1990); Moisture Induced Aggregation of Lyophilized Proteins in the Solid State, W. R. Liu, R. Langer, A. M. Klibanov, Biotech. Bioeng. 37, 177-184 (1991); Freeze Drying of Proteins. II, M. J. Pikal, BioPharm. 3, 26-30 (1990); Dehydration Induced Conformational Transitions in Proteins and Their Inhibition by Stabilizers, S. J. Prestrelski, N. Tedeschi, S. Arakawa, and J. F. Carpenter, Biophys. J. 65, 661-671 (1993); and Separation of Freezing and Drying Induced Denaturation of Lyophilized Proteins Using Stress-Specific Stabilization, J. F. Carpenter, S. J. Prestrelski, and T. Arakawa, Arch. Biochem. Biphys. 303, 456-464 (1993), the complete disclosures of which are herein incorporated by reference. Adjustment of the formulation pH and/or addition of a wide variety of additives including sugars, polysaccharides, polyoles, amino-acids, methylamines, certain salts, as well as other additives, have been shown to stabilize protein towards lyophilization.

As an example, which is not meant to be limiting, a cartridge was packed with small glass beads having a diameter of approximately 0.5 mm. The cartridge was filed with a solution of lysozyme at a concentration of 10 mg/ml. To enhance its stability, the solution was combined with a form of sugar and with a buffer solution. The buffer solution was sodium citrate, and the sugar was mannitol. A twin 20 surfactant was also added to the solution. The solution was then lyophilized in the cartridge.

The lyophilized substance may optionally contain a solubility enhancer, such as a surfactant as described in Journal of Pharmaceutical Science Technology which is J.Pharmsei. Technology, 48; 30-37 (1994) the disclosure of which is herein incorporated by reference. To assist in protecting the chemical substance from destructive reactions while in the dry state, various sugars may be added as described in Crowe, et al., "Stabilization of Dry Phospholipid Bilayer and Proteins by Sugars", Bichem. J. 242: 1-10 (1987), and Carpenter, et al. "Stabilization of Phosphofructokinase with Sugars Drying Freeze-Drying", Biochemica. et Biophysica Acta 923: 109-115 (1987), the disclosures of which are herein incorporated by reference.

In use, cartridge 180 is coupled to piston pump 140 and piston pump 140 is operated as previously described to dispense a known volume of liquid into cartridge 180. The supplied liquid flows through chemical substance 192 and chemical substance 192 dissolves into the liquid and flows out of outlet opening 186 as a liquid solution 194. Outlet opening 186 is spaced apart from an aperture plate 196 of an aerosol generator 198 so that liquid solution 198 will be deposited on aperture plate 196 as shown. Aerosol generator 198 further includes a cup shaped number 200 and a piezoelectric member 202 and operates in a manner similar to the aerosol generator 22 as previously described. Hence, when aerosol generator 198 is operated, liquid solution 194 is ejected from aperture plate 196 in droplet form as shown.

One important feature of the invention is that cartridge 180 is removable from piston pump 140 so that cartridge 180 may be discarded following each use. As illustrated in FIG. 11, after cartridge 180 has been removed, the user may optionally actuate piston pump 140 to again deliver a volume of liquid 204 directly to aperture plate 96. Aerosol generator 198 is then operated so that, similar to an ultrasonic cleaner, the vibratory action removes any residual solution from aperture plate 196. Liquids that may be held within canister 138 to form the solution and to clean aperture plate 196 include sterile water, a mixture of water with ethanol or other disinfectant, and the like.

In summary, the invention provides a portable aerosolizing apparatus that is able to store a chemical substance in the dry state, and to reconstitute the chemical substance with liquid to form a solution just prior to administration. The invention further provides techniques for aerosolizing the solution and for cleaning the aerosol generator. Also, it will be appreciated that the aerosolization apparatus as described herein may be used to aerosolize a liquid medicament that is not stored within a cartridge so that the liquid medicament is passed directly from the piston pump and on to the aperture plate for aerosolization.

Apparatus 10 may optionally be configured to warn the user when cleaning is needed. Such a feature is best accomplished by providing a processor within second portion 14 which is programmed to include an expected amount of time required to aerosolize a dose received from canister 18. If the expected amount of time exceeded before the entire dose is aerosolized, it may be assumed that the apertures in the aperture plate are clogged, thereby requiring cleaning to clear the apertures. In such an event, the processor sends a signal to an LED on apparatus 10 indicating that cleaning is needed.

To determine whether all of the liquid has been aerosolized in the expected time period, the processor records the amount of time that the aerosol generator is actuated. When the aerosol generator has been actuated for the expected time, the voltage sensing circuit is actuated to detect whether any liquid remains on the aperture plate as previously described.

The invention has now been described in detail, however, it will appreciated that certain changes and modifications may be made. For example, although illustrated in the context of delivering liquid to an aperture plate, the apparatus and methods may be employed to deliver known quantities of liquid to other types of atomization devices. Therefore, the scope and content of this invention are not limited by the foregoing description. Rather the scope and content are to be defined by the following claims.