Abstract:
Commercially feasible methods for lyophobic precipitation of liquid-dispersed or dissolved material (e.g., medicaments) are provided wherein a plurality of individual, open containers ( 22 ) each containing a quantity ( 84 ) of a solution or dispersion are treated within a common pressurizable chamber ( 12 ). In this process, desired near-supercritical or supercritical temperature and pressure conditions are established for a selected antisolvent gas such as carbon dioxide, and an ultrasonic device ( 14 ) is actuated to generate high energy ultrasonic waves in the chamber ( 12 ). This leads to intense mixing of the antisolvent with the liquid solution or dispersion within the containers ( 22 ), with consequent solvent removal and material precipitation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is broadly concerned with improved, commercially feasible methods for the simultaneous precipitation of material (particularly medicaments) within a plurality of containers using near-supercritical or supercritical antisolvent gas such as carbon dioxide. 
         [0003]    2. Description of the Prior Art 
         [0004]    U.S. Pat. No. 5,833,891 describes greatly improved methods for the precipitation of particles such as medicaments using near-supercritical or supercritical antisolvents. These methods generally involve spray techniques wherein the interphase mass transfer rate is maximized between small droplets of the dispersion and antisolvent gas so as to generate very small precipitated particles. This patent also teaches that medicaments can be prepared and administered to a patient without the necessity of transferring the medicament between containers. That is, a dispersion/antisolvent precipitation is carried out in a final use container which is consequently sealed to permit later withdraw of medicament doses from the use container. This technique generally involves lyophobic precipitation of medicaments on a batch or semi-batch basis. However, the methods taught for this process involve use of long glass tubes sealed at one end with glass frits. Such fritted tubes are not at all suitable for commercial production of medicaments, and thus the specific single vial techniques described in the &#39;891 patent are of limited commercial potential. 
         [0005]    U.S. Pat. No. 6,620,351 is also concerned with formation of nanoparticles using supercritical fluid antisolvents. In this case, a dispersion containing a desired material to be precipitated is applied on or very close to an ultrasonic vibrating surface to generate small droplets. An antisolvent at near-supercritical or supercritical conditions is also applied adjacent the vibrating surface in order to precipitate the desired particles. Here again, the requirement for direct or near contact between the ultrasonic vibrating surface and the material-containing dispersion means that the process cannot be effectively used on a commercial scale. This is because containers would need to be individually treated, or an individual vibratory surface would need to be provided for each container. In either case, the cost and complexity of such a system would materially detract from the usefulness of the process. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention overcomes the problems outlined above and provides greatly improved and commercially feasible methods allowing the simultaneous precipitation of liquid-dispersed or dissolved material within a plurality of individual containers or vials using antisolvent gas at near-supercritical or supercritical conditions. The methods are similar to those disclosed in U.S. Pat. No. 5,833,891, incorporated by reference herein. The present method broadly involves locating a plurality of containers within a common pressurizable chamber, each container being at least partially open to the atmosphere within the chamber and having a quantity of a liquid solution or dispersion therein containing material to be precipitated. The chamber is then heated and pressurized with the containers therein, including the step of introducing the antisolvent gas into the chamber. When appropriate temperature and pressure conditions exist within the chamber (generally near-supercritical or supercritical conditions for the selected antisolvent), ultrasonic energy waves are generated within the antisolvent in order to cause the antisolvent to rapidly mix with and dissolve the liquid therein and precipitate the material as the small particles. 
         [0007]    In one embodiment, each of the containers has a stopper loosely fitted within a mouth thereof during the solvent removal/precipitation step. Thereafter, each of the valves is sealed by fully installing each of the stoppers into the container mouths. This is preferably accomplished by a stoppering apparatus situated within the chamber. 
         [0008]    As noted, it is preferred that the temperature and pressure conditions within the chamber be at or near-supercritical or supercritical conditions for the antisolvent, and generally from about 0.7-1.4 T c  and from about 0.2-7 P c  for the antisolvent. More normally, the pressure will be less than 2 P c  for a given chamber temperature. Preferably, once the composition of the solution or dispersion is known, simple experiments can be undertaken to ascertain optimum temperature and pressure conditions that achieve maximum mixing between antisolvent and solution or dispersion while preventing overflow of liquid from the individual containers. 
         [0009]    The preferred antisolvents are selected from the group consisting of carbon dioxide, propane, butane, ethane, isobutane, nitrous oxide, sulfur hexafluoride, trifluoromethane, xenon, and mixtures thereof. Generally, carbon dioxide is the single most preferred antisolvent. The compositions treated in the invention are preferably true solutions made up of a solvent and a solute comprising a material to be precipitated. Alternatively, the composition maybe a dispersion with the dispersant comprising the material to be precipitated. Normally, the solution or dispersion should contain at least 5% by weight solute or dispersant, more preferably at least about 50% by weight solute or dispersant, and most preferably at least about 90% by solute or dispersant. The solution or dispersion may also contain other auxiliary ingredients such as adjuvants (in the case of medicaments), excipients, surface active agents, extenders, binders, and the like. 
         [0010]    The ultrasonic energy waves are preferably generated by the use of an ultrasonic probe located within the chamber at a position relatively remote from the individual containers. It has been found that even when the containers are partially stoppered, the ultrasonic waves can nonetheless enter the containers to mix with the liquid therein and effect particle precipitation. The precipitated materials can be in a variety of forms, e.g., pure crystalline or non-crystalline particles of the material or a cake containing the material along with one or more of auxiliary ingredients. 
         [0011]    In one embodiment, the resultant material is in the form of particles having an average diameter of from about 0.1-10 μm and more preferably up to about 0.6 μm. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic representation of a precipitation apparatus useful in the present invention; 
           [0013]      FIG. 2  is a schematic view of the pressure vessel forming a part of the  FIG. 1  apparatus, illustrating a plurality of open containers therein each containing a quantity of a liquid dispersion including material to be precipitated; and 
           [0014]      FIG. 3  is a view similar to that of  FIG. 2 , but illustrating the containers after precipitation of particles therein and full closure of the containers. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    Turning to the drawings, in greater detail, and initially to  FIG. 1 , an exemplary precipitation apparatus useful in the context of the invention is represented generally by the numeral  10 . Broadly speaking, the apparatus  10  includes a high pressure chamber  12  equipped with an ultrasonic transducer device  14 , a system  16  for the introduction of antisolvent into chamber  12 , and a test system  18 . 
         [0016]    In one embodiment, the chamber  12  is an upright metallic vessel of appropriate volume (e.g., 6 L) having two viewing windows (not shown). The chamber also includes an internal shelf  20  adapted to hold a plurality of containers or vials  22 . Additionally, a stoppering mechanism  24  is situated above shelf  20  for purposes to be described. The device  14  includes an external ultrasonic transducer  26  operably coupled with a probe  28  within chamber  12 . 
         [0017]    The antisolvent system  16  includes a gas cylinder  30  designed to hold a supply of antisolvent gas, with a line  32  having valves  34  and  36  and moisture trap  38  interposed therein. As shown, the line  32  intersects an outlet conduit  40  leading from chamber  12 . A bypass line  42  extends from valve  34  to the bottom of chamber  12 , and a delivery line  44  extends from valve  36  to booster pump  46 ; the line  44  is also equipped with a filter  48  and a pressure indicator  50 . The output from pump  46  is delivered via line  52  having a 4.5 L surge tank  54 , valve  56 , and temperature and pressure indicators  58  and  60  therein. As shown, the line  52  is coupled with the base of chamber  12  for delivery of antisolvent gas into the chamber. An air line  62  having valve  64  therein is also coupled with pump  46 . 
         [0018]    A safety valve  66  is operably coupled with conduit  40  and has a vent  68 . Pressure and temperature indicators  70  and  72  are respectively coupled with conduit  40  and chamber  12 . 
         [0019]    The system  18  is optional and comprises a gas cylinder  74  coupled with a line  76  having a valve  78  therein. The cylinder  74  normally holds a supply of nitrogen which is used to test the leak integrity of the chamber  12  and associated components, prior to actual use thereof. 
         [0020]    The containers  22  are entirely conventional and for purposes of illustration are shown with open mouths  80 , and stoppers  82  loosely fitted within the mouths  80  so that the interior of the containers communicate with the atmosphere within chamber  12 . As shown, each valve contains a quantity  84  of a liquid solution or dispersion having therein the material to be precipitated. After precipitation ( FIG. 3 ), a quantity  86  of precipitated material is present in each of the containers  22 . 
         [0021]    The stoppering device  24  is schematically illustrated and contains a common header  88  with a series of depending, reciprocal plungers  90  respectively situated above each stopper  82 . The plungers  90  are operable to engage the respective stoppers  82  to fully seat the latter within the container mouths  80  as illustrated in  FIG. 3 . 
         [0022]    During use of apparatus  10 , the latter is first heated to a specified temperature using a conventional heating tap coupled with a controller (not shown). The entire system is then tested for leakage using nitrogen system  18 . Following testing, a plurality of containers  22  each having a quantity  84  of the liquid solution or dispersion are placed on shelf  20  below the individual plungers  90 . The containers  22  are partially stoppered as shown in  FIG. 2 , such that the interior of the containers communicate with the chamber atmosphere. At this point, the chamber  12  is pressurized by introduction of antisolvent gas from cylinder  30  into vessel  16 . This involves opening of valves  34 ,  36  and  56  to permit antisolvent to flow through filter  48 , booster pump  46  and surge tank  54  into the interior of the vessel. The antisolvent gas is recycled through conduit  40  and lines  32 ,  44  and  52 , and moisture is removed by trap  38 . 
         [0023]    Once the vessel  12  is fully pressurized and the temperature and pressure conditions therein have reached desired stabilized levels for the antisolvent employed, the device  14  is actuated in order to generate ultrasonic energy waves within the antisolvent in chamber  12 . These waves propagate throughout the interior of the chamber and pass into the individual containers  22  past the loosely-fitted stoppers  82 . This effects intense mixing of the antisolvent and the solution or dispersion within each of the containers  20  so that the solutions or dispersions become supersaturated and the solute or dispersant is selectively extracted into the antisolvent. This effects precipitation of the material within the containers. The precipitated material may be in various forms, including small particles in crystalline form or non-crystalline form, and an amorphous mass. If auxiliary ingredients are used, these generally precipitate along with the active ingredient. During this step, temperature and pressure conditions are carefully maintained so as to eliminate the possibility of overflow of the liquid from the containers  22  with consequent loss of material. 
         [0024]    After the material has fully precipitated, the device  14  is left running for a period of 60-90 minutes with flowing antisolvent through chamber  12  and venting via vent  68 . This assures that all residual liquid solvent or dispersion medium is removed from the containers. Thereafter, the high-pressure antisolvent is drained from the chamber  12  through vent  68  and the vessel is cooled to ambient. At this point, the stoppering apparatus  24  is employed to fully stopper each of the valves  82  ( FIG. 3 ) to complete the process. If desired, the system can then be flushed by switching valve  34  to the line  42  and directing a fresh fluid such as CO 2 , or another inert gas, into chamber  12 . Preferably, the fluid is sterile. 
         [0025]    The following examples set forth preferred techniques for the precipitation of particles of material in accordance with the invention. It is to be understood, however, that these examples are provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention. 
         [0026]    In Examples 1-3 below, the lyophobic precipitation of acetaminophen, ibuprofen, hydrocortisone, phenyloin, and insulin using supercritical CO 2  antisolvent and ultrasonic energy was investigated using apparatus of the type illustrated in  FIG. 1 . 
         [0027]    The precipitation apparatus  10  included a high-pressure 6 L chamber  12  along with an ultrasonic transducer device  14  attached to the top inside of the chamber. Two view windows were provided in the chamber walls to allow visual inspection of the process. A platform  20 , sized to hold up to 10 small containers  22 , was located in the bottom of the chamber at approximately the base of the viewing windows. A 4.5 L surge tank  54  was used to control the fluctuation of CO 2  flow from the CO 2  pump  46 , and a moisture trap  38  with desiccant was used to keep moisture out of the system. The maximum allowable pressure for the system was about 2,000 psi at a temperature of up to about 70° C. 
         [0028]    In a typical lyophilization experiment, a number of containers  22 , each containing a drug in solution, were loaded onto the platform  20  within chamber  12 . The chamber was heated to a given temperature, and the entire system was tested for leakage using nitrogen gas test system  18 . LabView program software was used to monitor and record the temperatures and pressures during the lyophilization/precipitation process. 
         [0029]    After the nitrogen leak test, the chamber  12  was pressurized to a given pressure with CO 2 . When the specified temperature and pressure set points were attained and stabilized, the ultrasonic transducer device  14  was powered to effect intense mixing of the drug solution with CO 2  within the containers  22 . The pressure, temperature and ultrasonic energy were monitored to avoid overflow of the expanded drug solutions from the containers. It was found that preferred pressure and temperature values could be determined based upon the particular solvent used in the system. Once the drug was observed to precipitate and the solvent was extracted into the dense CO 2  phase, the system parameters (ultrasonic energy, temperature, pressure, CO 2  flow) were maintained for an additional 60-90 minutes to remove residual solvent from the containers. Preferably, the chamber  12  was then flushed with additional CO 2  to remove the evaporated solvent, and to effect drying of any residual solvent from the drug. The chamber  12  was then carefully depressurized and the containers containing the precipitated drugs were retrieved and cooled to ambient temperatures. Specific experimental parameters are given below. 
       Example 1 
     First Lyophobic Precipitation Experiment Using Sonicator 
       [0030]    Drug solutions of varying concentrations in ethanol were prepared according to the table below. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Concentration 
                   
               
               
                 Container 
                 Drug 
                 mg/mL, ethanol 
                 Drug Amount, mg 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Acetaminophen 
                 50 
                 99 
               
               
                 2 
                 Acetaminophen 
                 90 
                 179 
               
               
                 3 
                 Acetaminophen 
                 30 
                 61 
               
               
                 4 
                 Ibuprofen 
                 50 
                 105 
               
               
                   
               
             
          
         
       
     
         [0031]    2 mL of each test solution were transferred into a container. The containers were transferred to the platform inside the chamber. The chamber was then pressurized to 1200 psi using CO 2 , and the chamber was heated to about 62-66° C. to establish supercritical conditions. The ultrasonic transducer was then powered to about 15-70% power for about 38 minutes, during which time the drug was observed to precipitate. The power was maintained at about 50% for an additional 52 minutes to remove residual ethanol from the drug. The results are shown below. 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
               
               
                   
                   
                   
                 Weight loss, 
               
               
                 Container 
                 Drug 
                 Evaporation time, min 
                 wt % 
               
               
                   
               
             
             
               
                 1 
                 Acetaminophen 
                 38 
                 5.1 
               
               
                 2 
                 Acetaminophen 
                 38 
                 2.2 
               
               
                 3 
                 Acetaminophen 
                 30 
                 6.6 
               
               
                 4 
                 Ibuprofen 
                 N/A 
                 N/A 
               
               
                   
               
             
          
         
       
     
         [0032]    From this experiment, it was determined that drying time of a drug solution is only slightly related to the drug concentration, if at all. 
       Example 2 
     Second Lyophobic Precipitation Experiment Using Sonicator 
       [0033]    Drug solutions of varying concentrations in ethanol, or hexafluoro-2-proponal (HFIP), were prepared according to the table below. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Concentration 
                 Amount 
               
               
                 Container 
                 Drug 
                 mg/mL, ethanol 
                 Drug mg/mL solvent 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Acetaminophen 
                 104 
                 104/1  
               
               
                 2 
                 Acetaminophen 
                 100 
                   58/0.58 
               
               
                 3 
                 Hydrocortisone 
                 12.5 
                 25/2 
               
               
                 4 
                 Acetaminophen 
                 68 
                   17/0.25 
               
               
                 5 
                 Phenytoin 
                 13.6 
                 27/2 
               
               
                 6 
                 Insulin 
                 29 (in HFIP) 
                   9/0.3 
               
               
                   
               
             
          
         
       
     
         [0034]    Varying amounts of each drug solution according to the table above were transferred to designated containers. The containers were then placed on the platform in the chamber. The chamber was pressurized to 1,200 psi using CO 2 , and the chamber was heated to about 50° C. to establish supercritical conditions. The ultrasonic transducer was powered to about 15-40% power for about 60 minutes during which time the drug was observed to precipitate and the solvent evaporated into the CO 2 . The power was maintained at about 40-50% for an additional 90 minutes to remove residual solvent from the drug until dry. The results are shown below. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                 Container 
                 Drug 
                 Evaporation time, min 
                 Weight loss, wt % 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Acetaminophen 
                 60 
                 6.1 
               
               
                 2 
                 Acetaminophen 
                 60 
                 3.4 
               
               
                 3 
                 Hydrocortisone 
                 60 
                 5.6 
               
               
                 4 
                 Acetaminophen 
                 60 
                 4.1 
               
               
                 5 
                 Phenytoin 
                 60 
                 11 
               
               
                 6 
                 Insulin 
                 60 
                 0 
               
               
                   
               
             
          
         
       
     
         [0035]    From this experiment, it was determined that insulin is easily expanded, and some precipitation was observed even before the ultrasonic transducer was turned on. The acetaminophen was observed to precipitate as crystals and the phenyloin was observed to precipitate as needle-shaped crystals. 
       Example 3 
     Third Lyophobic Experiment Using Sonicator 
       [0036]    Drug solutions of varying concentrations in ethanol or HFIP were prepared according to the table below. 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Concentration 
                 Amount 
               
               
                 Container 
                 Drug 
                 mg/mL, ethanol 
                 Drug mg/mL solvent 
               
               
                   
               
             
             
               
                 1 
                 Acetaminophen 
                 100 
                  27/0.27 
               
               
                 2 
                 Phenytoin 
                  14 
                 13/0.9 
               
               
                 3 
                 Insulin 
                 34 (in HFIP) 
                 17/0.5 
               
               
                   
               
             
          
         
       
     
         [0037]    Varying amounts of each drug solution according to the table above were transferred to designated containers. The containers were transferred onto the platform in the chamber. The chamber was pressurized to 1,200 psi using CO 2 , and the vessel was heated to about 50° C. to establish supercritical conditions. The ultrasonic generator was programmed to be on for 1 second, off for 2 seconds, and the power supply was incrementally increased until the drug was fully precipitated, and the solvent evaporated. The power supply was at 15% for about 10 minutes, increased to 20% for about 65 minutes, increased to 24% for about 35 minutes, increased to 28% for about 40 minutes and finally increased to 30% for about 185 minutes, for a total of 5 hours and 30 minutes to complete the process. The power was then maintained at about 40% for an additional 50 minutes to remove residual solvent from the drug until dry. The results are shown below. 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
               
               
                 Container 
                 Drug 
                 Evaporation time, min 
                 Weight loss, wt % 
               
               
                   
               
             
             
               
                 1 
                 Acetaminophen 
                 110 
                 3.8 
               
               
                 2 
                 Phenytoin 
                 330 
                 N/A 
               
               
                 3 
                 Insulin 
                 330 
                 N/A 
               
               
                   
               
             
          
         
       
     
         [0038]    The precipitated drug particles from this experiment were observed to be larger in size than particles produced in the previous two experiments. Insulin, in particular, was observed to be much larger as precipitated in experiment three, than in experiment two. From this it was concluded that processing time correlates with particle size. Thus, shorter processing time results in smaller drug particle size. 
         [0039]    From the following example, the significant advantages of the present invention over conventional mechanical mixing are illustrated. 
       Example 4 
     Lyophobic Precipitation Using an Air-Actuated Mixing Platform 
       [0040]    In this experiment, an air-actuated shaker was employed in an attempt to effect lyophobic precipitation in a supercritical CO 2  environment via mechanical mixing. A platform was located in the high-pressure chamber at approximately the base of the viewing windows and the containers containing the drug solution were placed on the platform. Compressed air was used to shake the platform in a horizontal plane such that the contents of the container were swirled without being spilled due to motion. 
         [0041]    Two containers were each filled separately with 1 mL of a saturated drug solution and placed on the mixing platform in the vessel. The first container contained phenyloin in acetone and the second container contained hydrocortisone in acetone. The temperature of the vessel was varied between 36 and 63° C. and the vessel was pressurized with CO 2  to near/supercritical, about 910-1,220 psi. The shaking time required to precipitate the drugs was up to forty-four (44) hours. 
         [0042]    The initial experiment showed that the level of saturated solution of drug and acetone stayed virtually the same even after mechanical shaking for about 4-5 hours. While a clear meniscus was observed between the CO 2  and the drug solution at higher temperatures of about 48-63° C., no clear meniscus was observed at the lower temperatures of about 36-42° C. However, even after about 42-44 h, only 1 mL of the solvent had evaporated, even at higher temperatures. 
         [0043]    From this it was concluded that the drug solution/CO 2  interface could not be sufficiently disturbed by the mechanical shaking to cause intense mixing between the two phases, and that severe transport limitations exist for solvent diffusion into the CO 2  phase.