Abstract:
The present invention refers to an parenterally administerable aqueous formulation containing paracetamol. For enhancing stability the formulation contains a sulphur containing antioxidant, preferably sodium metabisulfite. For making the formulation more soluble it contains hydroxy propyl beta cyclodextrin. The composition is used as analgesic.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to stable pharmaceutical aqueous compositions, having analgesic activity comprising a therapeutically effective dose of paracetamol or its pharmaceutically acceptable salts, solvates, enantiomers or derivatives thereof, the processes for preparing the same and methods of use and treatment of such compositions. 
       BACKGROUND OF THE INVENTION 
       [0002]    Paracetamol (Formula I) is chemically N-(4-Hydroxyphenyl)acetamide. It is an analgesic and antipyretic agent. The mechanism of analgesic action of paracetamol has not been fully determined. Paracetamol may act predominantly by inhibiting prostaglandin synthesis in the central nervous system and to a lesser extent through a peripheral action by blocking pain impulse generation. The peripheral action may also be due to inhibition of prostaglandin synthesis or inhibition of the synthesis or actions of other substances that sensitise pain receptors. In recommended therapeutic dosage, it is usually well tolerated. However, acute overdose may cause fatal hepatic damage. The potentially toxic metabolite is said to be N-acetyl-p-benzoquinoneimine. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0003]    Formulating liquid compositions of paracetamol has critical considerations. The paracetamol in aqueous solution is liable to undergo hydrolysis to form p-aminophenol, which itself degrades to quinoneimine. Also, the stability of aqueous formulations is dependent on variables such as removal of dissolved oxygen from carrier, optional further presence of antioxidant in the formulation and adjustment to suitable pH. Hence a composition comprising an aqueous formulation of paracetamol wherein the stability of the formulation is achieved is highly desirable. 
         [0004]    Perfalgan® is a commercially available formulation which comprises a liquid formulation of paracetamol. The formulation contains buffering agents. It is available from Bristol Myers Squibb. 
         [0005]    U.S. Pat. No. 6,992,218 reports a method for preparing aqueous formulations with easily oxidizable active principles, notably phenols. The method comprises deoxygenation of the solution by bubbling it with at least one inert gas until the oxygen content is below 2 ppm. 
         [0006]    The preparation of parenteral formulations of paracetamol has been known in the art. However, the parenteral formulations of paracetamol utilize a buffer system to maintain the pH to the required value (U.S. Pat. No. 6,028,222). 
         [0007]    EP 1752139 describes liquid formulations of paracetamol for infusion, without using a buffer system. However, the formulations comprise antioxidants selected from a group of ascorbic acid, N-acetyl-L-cysteine and thiol group-containing stabilizer compounds. 
         [0008]    The use of organic solvents for the preparation of liquid formulations of paracetamol has also been reported (WO 05053747, WO 0007588). However, the prior art stabilized liquid formulation of paracetamol have the drawback of causing a potential irritant and/or allergic effect in certain patients, because of the toxicity of either the antioxidant or the organic solvent present in the formulation. 
         [0009]    Hence, the development of an aqueous parenteral formulation of paracetamol which does not contain a buffer system or an organic solvent and bypasses all the disadvantages mentioned above would be a significant improvement in the field of medical practice. Thus the present invention fills a highly desirable gap in medical art comprising stable aqueous formulations of paracetamol. 
       SUMMARY OF THE INVENTION 
       [0010]    The objective of the present invention is to provide stable parenteral compositions of paracetamol, wherein the paracetamol formulation does not contain a buffer system. 
         [0011]    Further it is an objective of the present invention to provide aqueous compositions of paracetamol, having analgesic activity, which are formulated without any organic solvent and hence to bypass any allergic, irritant or similar potential side effect caused by such solvents. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    The present invention relates to aqueous, parenteral paracetamol compositions which comprise a therapeutically effective dose of paracetamol. The paracetamol compositions as per the present invention are formulated without the addition of any organic solvent and do not contain a buffer system. 
         [0013]    In an embodiment, stable pharmaceutical aqueous compositions as disclosed in the invention are formulated as parenteral formulations, in particular infusible formulations, in a solvent. 
         [0014]    In another embodiment of the present invention, the preferable solvent is water. 
         [0015]    In another embodiment, stable pharmaceutical aqueous compositions as disclosed in the context of the present invention may optionally include a solubilising aid. 
         [0016]    By ‘solubilising aid’ is meant any compound that may assist in solubilising the active by accommodating the active in a cavity formed in the solubising aid to form inclusion complexes. 
         [0017]    Representative solubilising aids which may be used include but are not limited to cyclodextrins such as a cyclodextrin, β cyclodextrin, γ cyclodextrin; calixarenes and the like as well as their pharmaceutically useful derivatives. Combinations of more than one of these solubilising aids in different ratios or proportions as required are covered within the scope of the invention without limitation. 
         [0018]    In an embodiment, a physiologically acceptable β cyclodextrin derivative was found to be useful in the context of the present invention. 
         [0019]    In another embodiment, hydroxy propyl beta cyclodextrin, herein referred to as “HPβCD”, was found to be useful in the context of the present invention. 
         [0020]    In yet another embodiment, the w/w ratios of HPβCD to the active can range from about 0.5:1 to about 2:1, particularly from about 0.75:1 to about 1.5:1. 
         [0021]    In yet another embodiment, the present invention provides stable pharmaceutical aqueous compositions, having analgesic activity comprising a therapeutically effective dose of paracetamol with a solubilising aid with or without pharmaceutically acceptable excipients. 
         [0022]    Antioxidants may be used in the present invention to protect the active (s) from oxidative degradation. The antioxidants or free radical scavengers or combinations thereof used in various ratios are exemplified by but are not limited to sodium sulfite, sodium bisulfite, sodium metabisulfite, sodium thiosulphate, sodium formaldehyde sulfoxylate and the like in various ratios and proportions. Combinations of more than one of these antioxidants in various ratios and proportions as required are within the scope of the invention without limitation. 
         [0023]    In an embodiment, sodium metabisulfite was found to be useful in the context of the present invention. 
         [0024]    In another embodiment, sodium metabisulfite may be used in amount from about 200 mg/l to about 1 g/l. 
         [0025]    As an alternative or in addition to the use of antioxidants, the antioxidant effect may be achieved by displacing oxygen from the composition of the active(s). This may be achieved by purging the composition with a water insoluble inert gas. Inert gases which are known to a person skilled in the art may be employed. These include but are not limited to nitrogen, carbon dioxide and the like. 
         [0026]    In an embodiment, the pharmaceutical composition was purged with nitrogen to displace the oxygen from the composition. 
         [0027]    In another embodiment, the oxygen content in the composition was found to be not more than 2 ppm. 
         [0028]    Common isotonic agents may be used in the pharmaceutical compositions of the present invention to impart same osmotic pressure as the body fluid to the formulations. Isotonicity of the preparation may be achieved by adding an appropriate quantity of isotonic agent. Suitable isotonic agents which may be used in the context of the above invention may include but are not limited to sodium chloride, calcium chloride, potassium chloride, glucose, levulose and the like. 
         [0029]    In an embodiment, sodium chloride was found to be useful in the context of the present invention. 
         [0030]    The aqueous parenteral formulation of paracetamol, in the context of the present invention contains no buffer system. The pH of the formulation, according to the invention may be adjusted using chemicals such as sodium hydroxide, hydrochloric acid and the like to a value of about 4 to 8. 
         [0031]    In an embodiment, the pH of the formulation according to the invention was adjusted using NaOH. 
         [0032]    In another embodiment, the pH of the formulation according to the present invention may be between about 4 to about 8, for example about 4.5 to about 7.5, typically about 4.5 to about 6.5 and more typically about 5.5 to about 6.5. 
         [0033]    Parenteral formulations according to the invention may comprise other excipients commonly employed in parenteral formulations for intravenous administration in order to provide the required stability and/or therapeutic efficacy. This may include any other excipients commonly used in the preparation of parenteral formulations for intravenous administration. 
         [0034]    The pharmaceutical compositions according to the said invention may comprise other agents which may enhance and/or potentiate the effect of paracetamol. Such said compositions including other agents which may enhance and/or potentiate the effect of paracetamol, may optionally include a solubilising aid and/or other pharmaceutically acceptable excipients. 
         [0035]    The aqueous paracetamol formulation according to the present invention can be used in the field of medicine as a parenteral analgesic. 
         [0036]    The aqueous composition in the present invention may be prepared by processes known to one skilled in the art but is not limited to the following process:
       a) Dissolving either paracetamol or solubilising aid or both in the solvent or mixture of solvents optionally with other pharmaceutically acceptable excipients optionally under inert atmosphere.   b) Optionally adjusting the pH and/or the osmolality of the solution to suitable values.   c) Subjecting the solution to sterilization optionally using filteration sterilization.   d) Optionally deoxygenating the resultant solution using inert gas and/or optional terminal sterilization.       
 
       EXAMPLES 
       [0041]    The following examples are included to illustrate certain aspects of the invention in greater detail but are not intended to limit the scope of the invention in any way. Various examples as well as alternate embodiments will be evident to a person skilled in the art upon reference to the description and are presumed to be within the scope of the invention. 
       Example 1 
     Composition of Paracetamol Solution 
       [0042]      
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 S. No 
                 Ingredients 
                 Amount 
               
               
                   
               
             
             
               
                 1 
                 Sodium metabisulfite 
                  10.00 mg  
               
               
                 2 
                 Hydroxypropyl betacyclodextrin (HPβCD) 
                 150.00 mg  
               
               
                 3 
                 Paracetamol 
                 100.00 mg 
               
               
                 4 
                 Sodium chloride 
                  63.00 mg  
               
               
                 5 
                 Sodium hydroxide 
                 q.s to pH 5.5 
               
               
                 6 
                 Water for injection 
                 q.s to 10.00 ml 
               
               
                   
               
             
          
         
       
     
       Manufacturing Procedure: 
       [0043]    Required amounts of sodium metabisulfite, HPβCD, paracetamol and sodium chloride were dissolved in water for injection, with stirring under inert atmosphere, until each of the ingredients dissolved completely. After a clear solution was obtained, the volume was made up with water for injection and the pH of the resultant solution was adjusted with sodium hydroxide. After filtration through a sterile 0.22 μm pore size filter, the solution was purged with inert gas such as nitrogen and subsequently filled in Type II glass vials. The vials were sealed with rubber closure and aluminium caps and sterilized by autoclaving at 121° C./15 lbs for 15 minutes. 
       Example 2 
     Composition of Paracetamol Solution 
       [0044]      
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 S. No 
                 Ingredients 
                 Amount 
               
               
                   
               
             
             
               
                 1 
                 Sodium metabisulfite 
                  10.00 mg 
               
               
                 2 
                 Hydroxypropyl betacyclodextrin (HPβCD) 
                 150.00 mg 
               
               
                 3 
                 Paracetamol 
                 100.00 mg 
               
               
                 4 
                 Sodium chloride 
                  63.00 mg 
               
               
                 5 
                 Sodium hydroxide 
                 q.s to pH 5.5 
               
               
                 6 
                 Water for injection 
                 q.s to 10.00 ml 
               
               
                   
               
             
          
         
       
     
       Manufacturing Procedure: 
       [0045]    Required amounts of sodium metabisulfite, HPβCD, paracetamol and sodium chloride were dissolved in water for injection, with stirring under inert atmosphere, until each of the ingredients dissolved completely. After a clear solution was obtained, the volume was made up with water for injection and the pH of the resultant solution was adjusted with sodium hydroxide. After filtration through a sterile 0.22 μm pore size filter, the solution was purged with inert gas such as nitrogen and subsequently filled in Type II glass vials. The vials were sealed with rubber closure and aluminium caps and sterilized by autoclaving at 105° C./8 lbs for 30 minutes. 
         [0046]    The vials each from Example 1 and Example 2 were stored at 25°±2° C. and 60%±5% RH as well as 40°±2° C. and 75%±5% RH. Stability data for the vials stored at 25°±2° C. as well as 60%±5% RH and 40° C. and 75% RH indicated that the vials were stable and clear of coloured particles for at least six months. The vials each from Example 1 and Example 2 were subjected to the evaluation of the following parameters:
       1. Paracetamol assay: (%) By High Performance Liquid Chromatography (HPLC)   2. p-amino phenol titre: (%) By HPLC   3. Total Impurities: (%) By HPLC   4. Dissolved Oxygen: (ppm) By Dissolved oxygen meter
 
Vials from Example 1 Stored at 25°±2° C. and 60%±5% RH
       
 
         [0000]                                                      Sampling time                Initial                   (Time 0)   3 months   6 months               Paracetamol assay   102.4   100.8   101.0       p-amino phenol    0.008    0.007    0.01       Total Impurities    0.022    0.025    0.036       Dissolved oxygen    0.38    0.40    0.65                    
Vials from Example 1 Stored at 40°±2° C. and 75%±5% RH
 
         [0000]                                                      Sampling time                Initial                   (Time 0)   3 months   6 months               Paracetamol assay   102.4   100.4   100.3       p-amino phenol    0.018    0.017    0.02       Total Impurities    0.027    0.061    0.063       Dissolved oxygen    0.38    0.85    1.01                    
Vials from Example 2 Stored at 25°±2° C. and 60%±5% RH
 
         [0000]    
       
         
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                 Sampling time 
               
             
          
           
               
                   
                 Initial 
                   
                   
               
               
                   
                 (Time 0) 
                 3 months 
                 6 months 
               
               
                   
               
               
                 Paracetamol assay 
                 102.6 
                 102.2 
                 101.8 
               
               
                 p-amino phenol 
                 BDL* 
                  0.009 
                  0.015 
               
               
                 Total Impurities 
                  0.024 
                  0.028 
                  0.047 
               
               
                 Dissolved oxygen 
                  0.38 
                  0.31 
                  0.89 
               
               
                   
               
               
                 *BDL—Below detectable limit 
               
             
          
         
       
     
         [0051]    Vials from Example 2 Stored at 40°±2° C. and 75%±5% RH 
         [0000]    
       
         
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                 Sampling time 
               
             
          
           
               
                   
                 Initial 
                   
                   
               
               
                   
                 (Time 0) 
                 3 months 
                 6 months 
               
               
                   
               
               
                 Paracetamol assay 
                 102.6 
                 101.4 
                 101.0 
               
               
                 p-amino phenol 
                 BDL 
                  0.017 
                  0.019 
               
               
                 Total Impurities 
                  0.014 
                  0.050 
                  0.058 
               
               
                 Dissolved oxygen 
                  0.38 
                  0.52 
                  0.89