Abstract:
The invention provides a method for increasing the solubility of nevirapine, including the steps of rendering nevirapine in a gaseous phase; and rendering the gaseous phase in a relatively more soluble solid particulate form. The invention further provides for a crystalline Form-VI ( 36 ) of nevirapine having an X-ray diffraction pattern of (2-theta values in degrees) 9.2953, 11.2023, 12.7019, 12.9796, 13.5273, 15.4670, 17.2597, 19.1038, 19.7267, 21.1303, 22.9381, 25.5589, 26.4913, 27.2150, 27.7283, 29.7134, and 33.8343 degrees two theta. The invention further provides for the preparation of microspherical and/or nanospherical Form-V ( 34 ) and crystalline Form-VI ( 36 ) of nevirapine as well as novel dosage forms including parenteral-, inhalant-, transdermal- and oral dosage forms.

Description:
RELATED APPLICATION 
     This application is a nationalization under 35 U.S.C. 371 of PCT/IB2010/055077, filed Nov. 9, 2010 and published as WO 2011/058498 A2 on May 19, 2011, which claimed priority under 35 U.S.C. 119 to South African Patent Application Serial No. 2009/07879, filed Nov. 10, 2009; which applications and publication are incorporated herein by reference and made a part hereof. 
     BACKGROUND TO THE INVENTION 
     This invention relates to method for increasing the solubility of a transcriptase inhibitor composition and a transcriptase inhibitor composition prepared in accordance with such a method. More particularly, but not exclusively, this invention relates to a method for increasing the solubility of nevirapine to increase the bioavailability and efficacy thereof. This invention further relates to new forms of nevirapine. 
     The present invention further relates to novel crystalline forms of 11-cyclopropyl1-5,11-dihydro-4-methyl-6H-dipyrido[3,2-b: 2′,3′-e][1,4]diazepin-6-one, generically known as nevirapine. More specifically, the present invention provides novel microspherical and/or nanospherical Form-V and crystalline Form-VI of nevirapine. 
     Nevirapine is a well-known anti-retroviral drug used in the treatment of HIV-1 infection and AIDS. It is a non-nucleoside reverse transcriptase inhibitor and, structurally, it is a member of the dipyridodiazepinone chemical class of compounds. 
     A first disadvantage experienced with commercially available nevirapine is that it is highly hydrophobic and very poorly water soluble. Although comprehensive solubility and permeability data for nevirapine is lacking, the FDA classifies nevirapine as a Class II (high permeability, low solubility) drug. nevirapine&#39;s water solubility at neutral pH is ˜1 mg/ml, and is only highly soluble at pH&lt;3. 
     Nevirapine is currently available in two dosage forms, namely tablets (anhydrous form) and in suspensions (hemi-hydrate form). The mean maximum particle sizes of commercially available nevirapine are generally larger than 50 μm. 
     A further disadvantage experienced with nevirapine is that there are no parenteral dosage forms available, because of the relatively large particle size and poor water solubility. Particle sizes of commercially available nevirapine raw materials are unsuitable for parenteral administration in suspension. Further owing to the particle sizes, nevirapine in inhalant and transdermal dosage forms are also not available. 
     Yet another disadvantage experienced with known forms of nevirapine is that bioavailability thereof decreases at higher doses due to absorption being solubility rate-limited. 
     US patent application number 2005/0059653 describes crystalline Form-II and Form-III of nevirapine. A disadvantage of both these forms is that they are also suffering from poor solubility. 
     Applicant is the co-applicant of a separate patent application in respect of another form of nevirapine, namely Form-IV. The novel forms of nevirapine referred to herein are thus designated Form-V and Form-VI respectively. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide novel forms of nevirapine. Another object of the invention is to provide a method for increasing the solubility of a transcriptase inhibitor composition. Yet another object of the invention is to provide a medicament and dosage forms prepared in accordance with such a method with which the aforesaid disadvantages may be overcome or at least minimised. 
     According to the first aspect of the invention there is provided a crystalline Form-VI of nevirapine having an X-ray diffraction pattern of (2-theta values in degrees) 9.2953, 11.2023, 12.7019, 12.9796, 13.5273, 15.4670, 17.2597, 19.1038, 19.7267, 21.1303, 22.9381, 25.5589, 26.4913, 27.2150, 27.7283, 29.7134, and 33.8343 degrees two theta. 
     The crystalline Form-VI of nevirapine may have an X-ray powder diffraction pattern of at least 25% similarity to the X-ray diffraction pattern depicted in  FIG. 7 . 
     Preferably, the crystalline Form-VI of nevirapine has the X-ray powder diffraction pattern depicted in  FIG. 7 . 
     Further according to the invention the crystalline Form-VI of nevirapine is in a particulate form, wherein the particles have a mean maximum diameter of less than 50.0 μm. 
     The particles of crystalline Form-VI of nevirapine may have a mean maximum diameter of less than 4.0 μm, preferably between 0.1 to 4.0 μm. 
     The crystalline particles of the crystalline Form-VI of nevirapine may aggregate in the form of nanospheres and/or microspheres (Form-V). 
     The nanospheres and/or microspheres of the Form-V of nevirapine may be coated with a protective layer. 
     According to a second aspect of the invention there is provided a method for increasing the solubility of a transcriptase inhibitor composition, including the steps of:
         rendering the composition in a gaseous phase; and   rendering the gaseous phase in a relatively more soluble solid particulate form.       

     Further according to the invention the transcriptase inhibitor composition is of the type that sublimes. 
     Further according to the invention, the step of rendering the composition in a gaseous phase includes the further steps of sublimating the composition and depositing the gaseous phase in a relatively more soluble solid particulate form onto a surface. 
     The step of allowing the composition to sublimate may include the further step of elevating the temperature of the composition. Preferably the temperature of the composition is increased to above 150 degrees Celsius at atmospheric pressure. Alternatively or in addition, the step may include the further step of subjecting the composition to sublimation at a pressure relatively lower than atmospheric pressure. 
     Alternatively, the step of rendering the composition in a gaseous phase may include the step of evaporating the composition. 
     Further according to the invention the step of rendering the gaseous phase in a relatively more soluble solid particulate form may include the step of depositing the composition onto a surface such that the particles have a mean maximum diameter of less than 50.0 μm. 
     Preferably, the composition is deposited in a solid particulate form such that the particles have a mean maximum diameter of less than 4.0 μm, further preferably between 0.1 to 4.0 μm. 
     Further according to the invention the composition is deposited in a crystalline form and the method includes the further step of allowing the crystalline particles to aggregate to form microspheres. 
     The method may include the further step of coating the microspheres with a protective layer. 
     Further according to the invention the transcriptase inhibitor is in the form of nevirapine. 
     According to a third aspect of the invention there is provided a transcriptase inhibitor composition prepared in accordance with the method of the second aspect of the invention. 
     The transcriptase inhibitor may be provided in a parenteral dosage form. 
     Alternatively, the transcriptase inhibitor may be provided in the form of an inhalant. 
     Further alternatively, the transcriptase inhibitor may be provided in an oral dosage form. 
     Yet further alternatively, the transcriptase inhibitor may be provided in a form suitable for transdermal administration. 
     According to the fourth aspect of the invention there is provided use of a transcriptase inhibitor composition, according to the first aspect of the invention and prepared in accordance with the method of the second aspect of the invention, in the preparation of a medicament for use in a method of treating a patient suffering from an immune deficiency condition. 
     According to the fifth aspect of the invention there is provided use of a transcriptase inhibitor composition, according to the first aspect of the invention and prepared in accordance with the method of the second aspect of the invention, in a method of treating a patient suffering from an immune deficiency condition, including the step of administering to such a patient a pharmaceutically effective amount of such composition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described further, by way of example only, with reference to the accompanying drawings wherein: 
         FIG. 1 : is a diagrammatical representation of apparatus for preparing a medicament in accordance with a preferred embodiment of the invention on a non-commercial scale; 
         FIG. 2 : is a Scanning Electron Microscope (SEM) photo of bladed crystals of anhydrous nevirapine recrystallised from 20:80 ethanol:water according to the prior art; 
         FIG. 3 : is a SEM photo of platy crystals of hemi-hydrate nevirapine recrystallised from 40:60 ethanol:water according to the prior art (STIEGER, N., et al. 2010. Influence of the Composition of Water/Ethanol Mixtures on the Solubility and Recrystallization of Nevirapine.  Crystal Growth  &amp;  Design,  10(9):3859-3868); 
         FIG. 4 : is a SEM photo of microspherical novel Form-V of nevirapine prepared in accordance with the invention; 
         FIG. 5 : is a SEM photo of microspherical novel Form-V of nevirapine prepared in accordance with the invention; 
         FIG. 6 : is a graph depicting Fourier Transform Infrared Spectroscopy (FT-IR) traces of three forms of nevirapine, namely microspherical-, anhydrous and hemi-hydrate forms; 
         FIG. 7 : is an X-ray power diffractometry (XRPD) overlay comparing regular anhydrous nevirapine to the crystalline Form-VI thereof; and 
         FIG. 8 : is a SEM photo of the microspherical Form-V of nevirapine depicting the respective sizes of two particles as 0.17 and 0.88 μm. 
     
    
    
     DESCRIPTION 
     Referring to  FIG. 1 , apparatus for use in a method according to one aspect of the invention, for increasing the solubility of a transcriptase inhibitor composition that sublimes, is generally designated by numeral  10 . 
     The apparatus  10  comprises a conventional sublimation finger which includes a tubular outer glass container  12  for containing a transcriptase inhibitor in the form of nevirapine  14 . The apparatus  10  further includes a tubular inner glass container  16  disposed concentrically within the outer container  12 . 
     The outer container  12  includes an upper mouth  18  (wherein the inner container  16  is flushly and sealingly received by means of a collar  20 ); and a port  21 . 
     The inner container  16  is provided with an inlet tube  22  extending concentrically with the inner container  16  and providing an outlet opening  24  towards the lower end of the inner container  16 . The inner container  16  is further provided with an outlet tube  26  towards an opposite upper end of the inner container  16 . A passage  28  for coolant  30 , such as water below 10 degrees Celsius, is thus defined by the inlet tube  22 , the inner container  16  and the outlet tube  26 . The inner container  16  further defines an outer condensation surface  31  disposed above the nevirapine  14 . 
     In use, conventional nevirapine  14  in a solid anhydrous form is disposed in the bottom of the outer container  12  via the mouth  18  and heated to a temperature above 150 degrees Celsius. The nevirapine  14  sublimates into a gaseous phase  32  filling a sublimation zone A in the outer container  12  above the solid nevirapine  14 . The said coolant  30  is simultaneously passed along the passage  28 , as indicated by arrows B, to cool the inside of the inner container  16  and thus the outer condensation surface  31  thereof. 
     The condensation surface  31  is thus cooled whilst in contact with the gaseous phase  32  of the nevirapine in the sublimation zone A, so that the nevirapine in the gaseous phase  32  condensates and is thus deposited on the condensation surface  31  in solid particles in the form crystalline nevirapine (Form-VI). 
     In accordance with an alternative embodiment of the invention, the pressure inside the outer container  12  is reduced below atmospheric pressure, by connecting the inlet  21  to a vacuum pump (not shown). In doing so, the nevirapine  14  would commence sublimation at temperatures below 150 degrees Celsius, and, which the applicant foresees, could lead to a relatively higher yield of pharmaceutically active final product. 
     Applicant has found that the nanospheres and microspheres  34  (Form-V) that form on the condensation surface  31  have a mean maximum diameter of less than 50 μm, which is substantially smaller than the mean maximum diameter of commercially available nevirapine. More specifically, it was found that the nanospheres and microspheres  34  have mean maximum diameters ranging between 0.1 to 4.0 μm. Applicant has found that by manipulating the production parameters, such as by reducing the temperature of the condensation surface  31  further, even smaller nanospheres having a mean maximum diameter of 0.17 and 0.88 μm are formed (as depicted in  FIG. 8 ). The formation of microspheres and/or nanospheres unexpectedly substantially increases the water solubility and thus the bioavailability and efficacy thereof, relative to prior art anhydrous and hemi-hydrate forms of nevirapine. FT-IR analysis proved the final product to be nevirapine of a relatively very high chemical purity, and not a degradation product. 
     Applicant prepared SEM photos ( FIGS. 4 and 5 ) showing crystalline nevirapine (Form-VI), aggregated into nanospheres and microspheres  34  (Form-V) with average sizes in the order of 0.1 μm to 4 μm. A preliminary solubility experiment showed the nanosphere and microsphere aggregation to be at least 30% more soluble than the conventional anhydrous form of nevirapine, and 140% more soluble than the conventional hemi-hydrate form. 
     Applicant further prepared a SEM photo ( FIG. 8 ) of nanospheres (Form-V) with average sizes in the order of 0.17 and 0.88 μm. 
     It was further surprisingly observed, subject to the temperature of the condensation surface  31 , that additional nanocrystals  36  (Form-VI) form on the surface of the nanospheres and microspheres  34  and that these nanocrystals, dependant on the preparation conditions also aggregate to form the nanospheres and/or microspheres. The nanospheres and/or microspheres tend to form an aggregate with one another and hence it is proposed to coat the nanospheres and/or microspheres with a protective coating shortly after formation, to limit such aggregation, thus to further increase the solubility and bioavailability thereof. Such a coating could be in the form of shellac or biocompatible water soluble polymer. Coating of the spheres with polymers or other bio-compatible substances is used to limit the aggregation between spheres, to improve powder characteristics and to improve or prohibited solubility. Further application is to ensure pH-dependant solubility and targeted drug delivery, for example to the small intestines or colon. 
     The individual crystals  36  have individual mean maximum diameters that are substantially smaller than that of the nanospheres and microspheres  34 . Thus, in accordance with a further step of the invention, crystal aggregates form of which the maximum mean diameters of the individual crystals  36  are less than 0.5 μm. It is expected that the nanocrystalline (Form-VI) of nevirapine would display an even further increase in water solubility and bioavailability/efficacy. 
     It is foreseen that various methods could be employed to remove the microspheres, nanospheres, or crystals as they are formed, to limit clustering or aggregation thereof. 
     It is further foreseen that instead of having a condensation surface  31 , alternative collection methods could be employed such as collecting the gaseous phase in a liquid trap, alternatively with electrostatic charge or further alternatively by means of a vortex (all not shown). 
     A FTIR overlay was prepared for comparing Form-V to two known commercially available forms of nevirapine ( FIG. 6 ) namely anhydrous and hemihydrous nevirapine.  FIG. 6  shows that the spectra of the microspheres  34  and the anhydrous form are similar. This is an indication that the microspheres  34  contain pure nevirapine and that no degradation took place during the preparation of nevirapine Form-V. 
     Applicant further prepared an X-ray diffraction pattern of the crystals  36  and found that the crystals displayed the X-ray diffraction pattern depicted in  FIG. 7 . 
     It is foreseen that nevirapine in microspherical and nanospherical form (Form-V) or micro/nano-crystalline form (Form-VI) could present substantial advantages over prior art forms. For example, it was found that a method according to the invention renders the final product in a form suitable for administration in ways not previously possible. For example, the nevirapine in crystalline form could be administered to a patient suffering from an immune deficiency condition such as HIV infection or AIDS in a parenteral dosage form and, specifically, by way of injection. Alternatively, it could be administered in the form of an inhalant. Further alternatively, the medicament could be provided in an oral dosage form. Yet further alternatively, it could be provided in a form suitable for transdermal administration. 
     It will be appreciated that the apparatus  10  is suitable for preparing a medicament according to the invention merely on an experimental basis in a laboratory and that entirely different apparatus would have to be designed and developed for the production of a medicament according to the invention on a commercial or industrial scale. It is foreseen that the main elements for the successful production of the medicament of the invention are the elevation of temperature of the composition to establish an acceptable level of sublimation and the reduction of pressure in the sublimation zone, to expedite sublimation at relatively lower temperatures; and a surface having a temperature which is relatively lower than the temperature of the sublimation zone. In addition, it is foreseen that deposition of the composition from the gaseous phase could also be achieved by using a static charge; a vortex; or that the product may be collected in a liquid trap. 
     In the case of a liquid trap, the gaseous phase may be bubbled through a liquid in which nevirapine is poorly soluble. This liquid might be cooled to relatively lower temperature than the gaseous phase, so that the microspheres would form within the liquid. 
     In the case of using an electrostatic charge, the gaseous phase is attracted to a statically charged object (cooled or otherwise) to collect in particulate form. 
     In the case of a vortex, the gaseous phase is continually extracted by means of air/gas flow and collected in a receptacle with or without the use of baffles. The vortex could be combined with cooling to relatively lower temperature than the nevirapine gaseous phase. 
     It is also foreseen that the above methods could be used in various combinations. 
     It will be appreciated further that variations in detail are possible with the invention described herein without departing from the scope of the appended claims.