Patent Publication Number: US-2005123635-A1

Title: Cannabis aerosol

Description:
The invention relates to an apparatus and to a method for providing  cannabis, cannabis  oils, and  cannabis  derivatives in the form of an aerosol suitable for inhalation.  
      There is currently an increasing interest in the potential use of  cannabis  and its derivatives for therapeutic use. However  cannabis  oils are of high viscosity, so that existing nebulizer mechanisms cannot provide a high concentration of aerosol droplets. Inhalation of vapour, on the other hand, is an inefficient way of providing a therapeutic dose to the lungs because much of the vapour will condense out on other surfaces in the air passage ways or will be exhaled, while if the vapour is generated by smoking, toxic smoke components will also be generated by pyrolysis. With other pharmaceuticals it is known that provision of fine droplets, say less than 5 μm in diameter, is an efficient route to ensure delivery to the lung, so that it would be desirable to be able to generate an aerosol of particles or droplets of  cannabis  of such a size at a high concentration.  
       Cannabis  is a narcotic substance derived from the hemp plant ( Cannabis indica  or  Cannabis sativa ); the leaves and stalks of these plants may be referred to as hashish or marijuana. The term  cannabis  may refer to the female flowering heads of hemp, or to a resin obtained from the flowering heads that may also be referred to as cannabin. Derived materials include cannaboid, an alkaloid cannabine, and an oil cannabinol. In this specification these, and other derivatives, are referred to generically as  cannabis.    
      According to the present invention there is provided a method of forming an aerosol of  cannabis , the method comprising vaporising  cannabis  at an elevated temperature, causing the  cannabis  vapour to flow with a carrier gas to a region at a lower temperature at which the vapour would be supersaturated, generating seed nuclei of particle size less than 0.5 μm, and mixing the seed nuclei with the  cannabis  vapour and the carrier gas.  
      The provision of seed nuclei enables heterogeneous nucleation to occur, so that droplets of a desired diameter and concentration can be obtained. The seed nuclei may be mixed with the  cannabis  vapour before it flows to the lower temperature region.  
      The seed nuclei may for example be generated by passing air over a bath of molten sodium chloride, or molten silver, or by using an electrically heated wire for example of palladium.  
      The invention also provides an apparatus for performing this method. Preferably the  cannabis  is introduced into the region at elevated temperature at a controlled rate, for example using a syringe. When using  cannabis  oil, the boiling point of the oil is about 280° C., but the elevated temperature may be between 180° C. and 280° C., preferably between 200° C. and 260° C., for example 250° C., at which temperature the oil will evaporate. The apparatus may also include additional vaporising means for vaporising other components, such as glycerol, which are also mixed with the carrier gas so that the resulting aerosol droplets contain both  cannabis  and the other components.  
      By adjusting the flow rates, aerosol droplets of a desired size may be obtained. For example substantially monodisperse droplets have been obtained at diameters in the range 0.7 μm to 2.0 μm. The concentration of the aerosol may be up to 100 mg/litre, for example 50 mg/litre. 
    
    
      The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which:  
       FIG. 1  shows a diagrammatic view of an apparatus for generating a  cannabis  aerosol; and  
       FIG. 2  shows a particle size distribution for particles made with an apparatus as in  FIG. 1 . 
    
    
      Referring to  FIG. 1 , an apparatus  10  for generating an aerosol comprises a first gas flow line  12  along which air is caused to flow by a pump  14 , and within which is a bath  16  containing sodium chloride and heated electrically to a temperature of 850° C. at which the sodium chloride is molten. Evaporation of sodium chloride creates very small particles (typically no larger than 50 nm) of sodium chloride in the air stream emerging from the first gas flow line  12 . This air stream then flows along a duct  18  whose walls are held at a controlled temperature that decreases along its length from about 250° C. at the junction with the flow line  12 , to 15° C. at its open end  20 .  
      A second gas flow line  22  also communicates with the duct  18  near the high temperature end, and air is caused to flow along this line  22  by a pump  24 . The flow line  22  is held at a temperature of 250° C. A syringe  26  is arranged to introduce  cannabis  oil at a steady rate into the line  22 , in which it evaporates.  
      The two air flows mix within the duct  18 , the resulting mixture initially containing  cannabis  vapour and particles of sodium chloride. As the air cools the  cannabis  condenses onto the sodium chloride particles to form an aerosol in which the droplets are of substantially uniform size, and consist primarily of  cannabis . The droplet size is determined by the particle concentration, and by the vapour concentration, and can therefore be controlled by controlling the air flow through the two lines  12  and  22 , the feed rate of the  cannabis  through the syringe  26 , and the temperature of the sodium chloride bath  16 .  
      As an illustration, droplets have been made in this manner (using glycerol in place of  cannabis ) at sizes between 0.7 and 2.04 μm, the particles being substantially monodisperse in each case, and at concentrations up to 50 mg/litre; a particle size distribution for such aerosol droplets is shown in  FIG. 2 .  
      It will be appreciated that the  cannabis  might instead be supplied in the form of a solution in a suitable solvent, so that both the solvent and the  cannabis  evaporate when they are introduced into the line  22 , and as a consequence the resulting aerosol droplets emerging from the outlet  20  will be of both  cannabis  and the solvent. Alternatively the apparatus might include a third gas flow line (not shown) similar to the second gas flow line  22 , whereby a vapour of another liquid (such as glycerol) may be introduced into the duct  18 , so the resulting aerosol droplets emerging from the outlet  20  will contain both  cannabis  and this other liquid. Provision of another liquid in one or other of these ways may enable particles of a desired larger size to be generated.  
      The wall of the duct  18  may be cooled actively, using one or more heat exchange jackets through which coolant fluids are passed, or may be merely exposed to the surrounding air so the wall loses heat by natural convection.