Title of Invention	"INJECTABLE LIQUID PHARMACEUTICAL COMPOSITION OF PARACETAMOL"
Abstract	The invention relates to a novel injectable liquid pharmaceutical composition of paracetamol, comprising 0.1 to 5.0 g/100 ml of paracetamol; and a remaining quantity of an aqueous solvent; a buffer with a pKa of between 4.5 to 6.5; an isotonic agent such as herein described; characterized in that the paracetamol thus present comprises 0.005% to 0.73% of paracetamol dimmer of formula (I) as detected based on the ratio of the surface area of the HPLC peaks with detection at 245 ran.

Title of Invention

"INJECTABLE LIQUID PHARMACEUTICAL COMPOSITION OF PARACETAMOL"

Abstract

The invention relates to a novel injectable liquid pharmaceutical composition of paracetamol, comprising 0.1 to 5.0 g/100 ml of paracetamol; and a remaining quantity of an aqueous solvent; a buffer with a pKa of between 4.5 to 6.5; an isotonic agent such as herein described; characterized in that the paracetamol thus present comprises 0.005% to 0.73% of paracetamol dimmer of formula (I) as detected based on the ratio of the surface area of the HPLC peaks with detection at 245 ran.

Full Text	The present invention relates to a novel injectable liquid pharmaceutical formulation of paracetamol containing a dimer of this active principle, to a process for preparing this formulation, and to the use of this dimer for stabilizing a liquid pharmaceutical formulation of paracetamol. Paracetamol (INN of acetaminophen or N-(4-hydroxy-phenyl)acetamide) is an analgesic and an antipyretic widely used in hospitals. It is desirable to have available stable liquid pharmaceutical formulations of this active principle for administration by injection, in particular for intravenous infusion. It is known that paracetamol in aqueous solution is liable to undergo hydrolysis to form p-aminophenol, which is itself liable to degrade into quinoneimine (cf. for example J.E. Fairbrother, "Acetaminophen" in Analytical Profiles of Drug Substances, 1974, vol. 3, pp. 1-109). The rate of degradation of paracetamol increases with increasing temperature and light. This rate is minimal at a pH in the region of 6 (K.T. Koshy et al., 1961, J. Pharm. Sci. 50, pp. 116-118). It is known practice to add a buffer and an antioxidant or free-radical scavenger to stabilize paracetamol in solution. WO 02/072 080, for example, describes stable aqueous paracetamol solutions for infusion comprising a buffer of pH 5.5 to 6.5 and an antioxidant chosen from ascorbic acid and a derivative bearing a thiol function such as cysteine or acetyl-cysteine. EP 0 916 347 discloses paracetamol solutions based on a mixture of water and of alcoholic solvents comprising a buffer of pH 5.5 to 5.6 and metabisulf ite as antioxidant. The prior-art stabilized injectable solutions of paracetamol have the drawback of causing a potential irritant, allergenic and/or carcinogenic effect in certain patients, on account of the toxicity of the antioxidant they contain. Furthermore, their stability requires the removal of the oxygen and other oxidizing agents from the aqueous medium. These solutions therefore cannot be stored in plastic containers that are partially permeable to oxygen or that comprise traces of oxidizing residues. The as yet unpublished patent application MI2001A002135 discloses stable injectable aqueous solutions of paracetamol obtained by mixing paracetamol with water, propylene glycol and a citrate buffer, heating the solution obtained to a temperature of between 70 and 13Q°C and maintaining this solution at this temperature for at least 10 minutes. These solutions do not contain any toxic antioxidant, citric acid being a weak antioxidant widely used in the food industry. D.W. Potter et al., 1985, J. Biol. Chem. 260, 22, pp. i 12174-80 disclose the oxidation and polymerization of paracetamol in aqueous solution with hydrogen peroxide in the presence of horseradish peroxidase, isolation by semipreparative HPLC and identification by mass spectrometry and NMR spectroscopy, of two dimers, two trimers and two tetramers of paracetamol. For a paracetamol concentration of greater than 0.2 mM, the dimer of formula (I) ("compound B") is largely predominant. (Formula Removed) The problem or aim of the invention is that of finding a novel injectable liquid pharmaceutical formulation of paracetamol that is stable for a prolonged period without having the drawbacks mentioned above. This problem is solved by the invention as defined by the attached claims. The invention relates to an injectable liquid pharmaceutical formulation of paracetamol that contains paracetamol, an aqueous solvent, a buffer with a pKa of between 4.5 and 6.5, an isotonic agent and paracetamol dimer of formula (I). This paracetamol dimer, even in very small amount, appears to act as an antioxidant and makes it possible to dispense with the strong or toxic antioxidants described for the prior-art stabilized solutions of paracetamol. The formulation of the invention has excellent stability at room temperature, and even at a temperature of the order of 40°C, and may be stored in a plastic container, in particular an infusion bag, for example a bag made of polypropylene, polyethylene, polyvinyl chloride or combinations of extruded polymers. This paracetamol dimer may be replaced with another paracetamol polymerization product, for example a mixture of at least two oligomers of paracetamol chosen from the two dimers, the two trimers and the two tetramers of paracetamol described by D.W. Potter et al., 1985 in the reference cited hereinabove. In general, this formulation contains at least 0.005% and preferably at least 0.05%, as a ratio of the surface area of the HPLC peaks with detection at 245 nm, of paracetamol dimer of formula (I). The formulation of the invention may contain from 0.1 to 5.0 g/100 ml and preferably from 0.4 to 1.5 g/100 ml of paracetamol. The aqueous solvent is water, of injectable grade, or a mixture of water and of one or more other water-miscible solvent(s), for example propylene glycol, polyethylene glycol, ethanol, and/or- surfactants such as polysorbates or poloxamers. If the desired content of paracetamol in the solution exceeds 1.0 g/100 ml, the aqueous solvent will preferably be a mixture of water and of water-miscible solvent(s). The formulation of the invention contains a buffer with a pKa of between 4.5 and 6.5 and preferably between 5.0 and 6.2.. This buffer will advantageously be chosen from citrate buffer, phosphate buffer, phosphate-citrate buffer, bicarbonate buffer, tartrate buffer and acetate buffer, preferably from citrate buffer, phosphate buffer and phosphate-citrate buffer, or a mixture of these buffers. This formulation for injection contains an isotonic agent, intended to create an osmotic pressure in the region of that of physiological saline. This isotonic agent is generally chosen from sodium chloride and glucose. The formulation of the invention is generally prepared by first mixing together paracetamol, injectable-grade water, optionally one or more other water-miscible solvent(s), and/or surfactants, buffer and isotonic agent, followed by heating the solution obtained, in bulk or prefilled in containers, at a temperature of at least 70°C for at least 15 minutes. The aim of this heating is to remove any trace of nucleation that might trigger recrystallization of the paracetamol during the storage of the solution. The invention also relates to a process for preparing the formulation defined above, which includes the mixing of paracetamol, water, optionally water-miscible solvent, and/or surfactants, buffer and isotonic agent, followed by heating of the solution obtained, in bulk or prefilled in containers, at a temperature of at least 70°C for at least 15 minutes. The dimer of formula (I) appears to form spontaneously but slowly during the storage of the solution obtained above at a sufficient temperature, for example 60°C. To form the dimer of formula (I) in situ, it is practical to heat the solution at a temperature of between 100 and 130°C and preferably between 110 and 125°C for a period of at least 5 minutes. The invention also relates to a process for preparing the formulation defined above, which includes the heating of the solution at a temperature of between 100 and 130°C and preferably between 110 and 125°C for a period of at least 5 minutes. The invention also relates to a formulation as defined above that may be obtained via this process. The invention also relates to the use of the dimer of formula (I) for stabilizing a liquid formulation of paracetamol. This dimer is generally manufactured in situ within the liquid formulation of paracetamol. The invention is described in greater detail in the examples below, which are given as nonlimiting illustrations. In these examples, the temperature is room temperature or is expressed in degrees Celsius, and the pressure is atmospheric pressure. The water, the propylene glycol and all the reagents used are of injectable grade. Moreover, all the examples form an integral part of the invention, as does any characteristic of the description including the examples, which appears to be novel with respect to any prior art, in the form of a general characteristic rather than of a particular • characteristic of the example. Example 1 Preparation of liquid pharmaceutical formulations according to the invention and analysis of these formulations by HPLC Formulations 001, 002, 003, 004, 005 and 006 were prepared by mixing together paracetamol, ultrapurified injectable-grade water, optionally (formulation 004) propylene glycol, buffer (phosphate buffer, citrate-phosphate buffer or citrate buffer) and isotonic agent (sodium chloride), heating at 70-90°C for about 15 minutes to avoid the possibility of nucleation and consequent recrystallization of the paracetamol, and filling of glass bottles. These bottles were then sterilized for 15 minutes at 121°C. The solutions were analyzed, before and after sterilization, by HPLC on a column of octylsilyl silica gel and a mobile phase obtained by mixing together a solution of disodium hydrogen phosphate, a solution of sodium dihydrogen phosphate and methanol R containing a solution of tetrabutylammonium R, and detection by spectrophotometry at 245 nm, according to the method recommended in the European Pharmacopoeia (European Pharmacopoeia 4.4, pp. 3503-4, • 04/2003: 0049 Paracetamol). A peak corresponding to an unknown substance (not accounted for by the European Pharmacopoeia) was detected. This substance was identified, by mass spectrometry coupled to liquid chromatography (LC-MS) and proton nuclear magnetic resonance (NMR) at 200 MHz, as being the paracetamol dimer of formula (I), which is identical to compound B described by D.W. Potter et al., 1985, J. Biol. Chem. 260, 22, pp. 12174-80. The detection limit is about 0.005% .for p-aminophenol and the dimer of formula (I) . The difference between 100 and the paracetamol value measured is not significant and represents experimental uncertainty. The compositions of these formulations and the HPLC analysis results are collated in table 1 below. Table 1 (Table Removed) *ratio of surface area of the peak for the dimer/surface area of the peak for paracetamol, in % nd: not detected For these formulations, a content of the dimer of formula (I) of from 0.02 to 0.12 after sterilization was measured, this dimer not being .detectable before the sterilization. The presence of p-aminophenol was not detected before or after sterilization. Example 2 Study of the formation of the dimer 1) Effect of temperature and time The effect of the temperature on the formation of the dimer of formula (I) was studied on formulation 001 of example 1 after heating at 70-90°C for 15 minutes and placing it in a glass bottle. This formulation was subjected to various storage temperatures and/or to various sterilization times, and analyzed by HPLC as described above in example 1. The main results are collated in table 2 below. Table 2 - Effect of temperature and time on the formation of the dimer (Table Removed) According to the above table, the dimer forms rapidly at 121°C, with a rate of formation proportional to the sterilization time, and slowly but in measurable amount at 60°C- for 14 days. The dimer is not detectable after one hour at 70°C. p-Aminophenol is not detected under any of the conditions studied. 2) Effect of the pH The values for the content of dimer of formula (I) given in table 1 of example 1 for formulations 001, 002 and 003 of compositions that are similar but with different pHs show that the formation of the dimer depends on the pH. The more basic the pH, the larger the amount of dimer formed. The generation of the radicals is probably facilitated by the formation of the phenoxides. Example 3 Stability study The stability was studied on formulation 001 of example 1 after heating at 70-90cC for 15 minutes, put in glass bottles or polypropylene infusion containers, and sterilization at 121°C for 15 minutes for the glass bottles and at 120°C for 20 minutes for the polypropylene containers. Table 3 below collates the results obtained by HPLC analysis as described in example 1 above. Table 3: Stability of formulation 001 (Table Removed) nd: not detected This table shows that the injectable liquid formulation according to the invention maintains the same paracetamol content after storage for 10 months at 25°C or 40°C, with a slight increase in the dimer content, which is higher at 40°C than at 25°C, and higher in the glass bottles than in the polypropylene containers. The degradation of paracetamol in solution is often studied by measuring the absorbances at 500 ran according to the method described by J.E. Fairbrother "Acetaminophen", in Analytical Profiles of Drug Substances, 1974, vol. 3, pp. 1-109. Monitoring for three weeks, according to this method, of the absorbance firstly of formulation 001 and secondly of the commercial formulation Perfalgan® containing 1.0 g/100 ml of paracetamol and cysteine hydrochloride, obtained as described in WO 98/05314, shows that, at 60°C, paracetamol degrades at least ten times more quickly in the Perfalgan® formulation than in the formulation of the invention. The pharmaceutical formulation of the present invention is so designed so as to provide greater stability than the Prior Art, such stability is achieved only when all the ingredients are mixed and present in the formulation. Hence it is a synergistic composition and exhibits surprising results. We Claim: 1. An injectable liquid pharmaceutical composition of paracetamol, comprising: 0.1 to 5.0 g/100 ml of paracetamol; and a remaining quantity of an aqueous solvent; a buffer with a pKa of between 4.5 to 6.5; an isotonic agent such as herein described; characterized in that the paracetamol thus present comprises 0.005% to 0.73% of paracetamol dimmer of formula (I) as detected based on the ratio of the surface area of the HPLC peaks with detection at 245 ran. (FormulaRemoved) 2. The composition as claimed in claim 1, wherein the paracetamol is in the range of 0.4 to 1.5 g/100ml. 3. The composition as claimed in any one of the preceding claims, wherein the buffering agent is selected from the group containing citrate buffer, phosphate buffer, phosphate-citrate buffer, bicarbonate buffer, tartrate buffer and acetate buffer, and preferably from citrate buffer, phosphate buffer and phosphate-citrate buffer, or a mixture of these buffers. 4. The composition as claimed in any one of the preceding claims, wherein said formulation is obtained by a process including heating of the solution at a temperature of between 100 and 130°C and preferably between 110 and 120°C. 5. A process for preparing the composition as claimed in claim 1 wherein said process comprising mixing together paracetamol, water, optionally one or more water miscible solvent(s), buffer and isotonic agent, followed by heating the solution obtained, in bulk or prefilled in containers, at a temperature of at least 70°C. 6. The process as claimed in claim 6, wherein said process includes heating the solution at a temperature in the range of 100 to 130°C and preferably between 110 to 125°C. 7. The composition as claimed in claim 1, wherein the dimmer as an when use as a stabilizing agent for liquid composition of the paracetamol. 8. An injectable liquid pharmaceutical composition of paracetamol and a process for preparing the same substantially as herein described with reference to the foregoing examples.

Full Text

The present invention relates to a novel injectable liquid pharmaceutical formulation of paracetamol containing a dimer of this active principle, to a process for preparing this formulation, and to the use of this dimer for stabilizing a liquid pharmaceutical formulation of paracetamol.
Paracetamol (INN of acetaminophen or N-(4-hydroxy-phenyl)acetamide) is an analgesic and an antipyretic widely used in hospitals. It is desirable to have available stable liquid pharmaceutical formulations of this active principle for administration by injection, in particular for intravenous infusion.
It is known that paracetamol in aqueous solution is liable to undergo hydrolysis to form p-aminophenol, which is itself liable to degrade into quinoneimine (cf. for example J.E. Fairbrother, "Acetaminophen" in Analytical Profiles of Drug Substances, 1974, vol. 3, pp. 1-109). The rate of degradation of paracetamol increases with increasing temperature and light. This rate is minimal at a pH in the region of 6 (K.T. Koshy et al., 1961, J. Pharm. Sci. 50, pp. 116-118).
It is known practice to add a buffer and an antioxidant or free-radical scavenger to stabilize paracetamol in solution.
WO 02/072 080, for example, describes stable aqueous paracetamol solutions for infusion comprising a buffer of pH 5.5 to 6.5 and an antioxidant chosen from ascorbic acid and a derivative bearing a thiol function

such as cysteine or acetyl-cysteine.
EP 0 916 347 discloses paracetamol solutions based on a mixture of water and of alcoholic solvents comprising a buffer of pH 5.5 to 5.6 and metabisulf ite as antioxidant.
The prior-art stabilized injectable solutions of paracetamol have the drawback of causing a potential irritant, allergenic and/or carcinogenic effect in certain patients, on account of the toxicity of the antioxidant they contain. Furthermore, their stability requires the removal of the oxygen and other oxidizing agents from the aqueous medium. These solutions therefore cannot be stored in plastic containers that are partially permeable to oxygen or that comprise traces of oxidizing residues.
The as yet unpublished patent application MI2001A002135 discloses stable injectable aqueous solutions of paracetamol obtained by mixing paracetamol with water, propylene glycol and a citrate buffer, heating the solution obtained to a temperature of between 70 and 13Q°C and maintaining this solution at this temperature for at least 10 minutes. These solutions do not contain any toxic antioxidant, citric acid being a weak antioxidant widely used in the food industry.
D.W. Potter et al., 1985, J. Biol. Chem. 260, 22, pp. i 12174-80 disclose the oxidation and polymerization of paracetamol in aqueous solution with hydrogen peroxide in the presence of horseradish peroxidase, isolation by semipreparative HPLC and identification by mass spectrometry and NMR spectroscopy, of two dimers, two

trimers and two tetramers of paracetamol. For a
paracetamol concentration of greater than 0.2 mM, the
dimer of formula (I) ("compound B") is largely
predominant.
(Formula Removed)
The problem or aim of the invention is that of finding a novel injectable liquid pharmaceutical formulation of paracetamol that is stable for a prolonged period without having the drawbacks mentioned above.
This problem is solved by the invention as defined by the attached claims.
The invention relates to an injectable liquid pharmaceutical formulation of paracetamol that contains paracetamol, an aqueous solvent, a buffer with a pKa of between 4.5 and 6.5, an isotonic agent and paracetamol dimer of formula (I).
This paracetamol dimer, even in very small amount, appears to act as an antioxidant and makes it possible to dispense with the strong or toxic antioxidants described for the prior-art stabilized solutions of paracetamol.
The formulation of the invention has excellent stability at room temperature, and even at a

temperature of the order of 40°C, and may be stored in a plastic container, in particular an infusion bag, for example a bag made of polypropylene, polyethylene, polyvinyl chloride or combinations of extruded polymers.
This paracetamol dimer may be replaced with another paracetamol polymerization product, for example a mixture of at least two oligomers of paracetamol chosen from the two dimers, the two trimers and the two tetramers of paracetamol described by D.W. Potter et al., 1985 in the reference cited hereinabove.
In general, this formulation contains at least 0.005% and preferably at least 0.05%, as a ratio of the surface area of the HPLC peaks with detection at 245 nm, of paracetamol dimer of formula (I).
The formulation of the invention may contain from 0.1 to 5.0 g/100 ml and preferably from 0.4 to 1.5 g/100 ml of paracetamol.
The aqueous solvent is water, of injectable grade, or a mixture of water and of one or more other water-miscible solvent(s), for example propylene glycol, polyethylene glycol, ethanol, and/or- surfactants such as polysorbates or poloxamers. If the desired content of paracetamol in the solution exceeds 1.0 g/100 ml, the aqueous solvent will preferably be a mixture of water and of water-miscible solvent(s).
The formulation of the invention contains a buffer with a pKa of between 4.5 and 6.5 and preferably between 5.0 and 6.2.. This buffer will advantageously be chosen from

citrate buffer, phosphate buffer, phosphate-citrate buffer, bicarbonate buffer, tartrate buffer and acetate buffer, preferably from citrate buffer, phosphate buffer and phosphate-citrate buffer, or a mixture of these buffers.
This formulation for injection contains an isotonic agent, intended to create an osmotic pressure in the region of that of physiological saline. This isotonic agent is generally chosen from sodium chloride and glucose.
The formulation of the invention is generally prepared by first mixing together paracetamol, injectable-grade water, optionally one or more other water-miscible solvent(s), and/or surfactants, buffer and isotonic agent, followed by heating the solution obtained, in bulk or prefilled in containers, at a temperature of at least 70°C for at least 15 minutes. The aim of this heating is to remove any trace of nucleation that might trigger recrystallization of the paracetamol during the storage of the solution.
The invention also relates to a process for preparing the formulation defined above, which includes the mixing of paracetamol, water, optionally water-miscible solvent, and/or surfactants, buffer and isotonic agent, followed by heating of the solution obtained, in bulk or prefilled in containers, at a temperature of at least 70°C for at least 15 minutes.
The dimer of formula (I) appears to form spontaneously but slowly during the storage of the solution obtained above at a sufficient temperature, for example 60°C.

To form the dimer of formula (I) in situ, it is practical to heat the solution at a temperature of between 100 and 130°C and preferably between 110 and 125°C for a period of at least 5 minutes.
The invention also relates to a process for preparing the formulation defined above, which includes the heating of the solution at a temperature of between 100 and 130°C and preferably between 110 and 125°C for a period of at least 5 minutes.
The invention also relates to a formulation as defined above that may be obtained via this process.
The invention also relates to the use of the dimer of
formula (I) for stabilizing a liquid formulation of
paracetamol. This dimer is generally manufactured in
situ within the liquid formulation of paracetamol.
The invention is described in greater detail in the examples below, which are given as nonlimiting illustrations.
In these examples, the temperature is room temperature or is expressed in degrees Celsius, and the pressure is atmospheric pressure. The water, the propylene glycol and all the reagents used are of injectable grade.
Moreover, all the examples form an integral part of the invention, as does any characteristic of the description including the examples, which appears to be novel with respect to any prior art, in the form of a general characteristic rather than of a particular •

characteristic of the example.
Example 1 Preparation of liquid pharmaceutical formulations according to the invention and analysis of these formulations by HPLC
Formulations 001, 002, 003, 004, 005 and 006 were prepared by mixing together paracetamol, ultrapurified injectable-grade water, optionally (formulation 004) propylene glycol, buffer (phosphate buffer, citrate-phosphate buffer or citrate buffer) and isotonic agent (sodium chloride), heating at 70-90°C for about 15 minutes to avoid the possibility of nucleation and consequent recrystallization of the paracetamol, and filling of glass bottles. These bottles were then sterilized for 15 minutes at 121°C.
The solutions were analyzed, before and after sterilization, by HPLC on a column of octylsilyl silica gel and a mobile phase obtained by mixing together a solution of disodium hydrogen phosphate, a solution of sodium dihydrogen phosphate and methanol R containing a solution of tetrabutylammonium R, and detection by spectrophotometry at 245 nm, according to the method recommended in the European Pharmacopoeia (European Pharmacopoeia 4.4, pp. 3503-4, • 04/2003: 0049 Paracetamol).
A peak corresponding to an unknown substance (not accounted for by the European Pharmacopoeia) was detected. This substance was identified, by mass spectrometry coupled to liquid chromatography (LC-MS) and proton nuclear magnetic resonance (NMR) at 200 MHz, as being the paracetamol dimer of formula (I), which is

identical to compound B described by D.W. Potter et al., 1985, J. Biol. Chem. 260, 22, pp. 12174-80.
The detection limit is about 0.005% .for p-aminophenol and the dimer of formula (I) . The difference between 100 and the paracetamol value measured is not significant and represents experimental uncertainty.
The compositions of these formulations and the HPLC analysis results are collated in table 1 below.
Table 1
(Table Removed)

*ratio of surface area of the peak for the dimer/surface area of the peak for paracetamol, in %

nd: not detected
For these formulations, a content of the dimer of formula (I) of from 0.02 to 0.12 after sterilization was measured, this dimer not being .detectable before the sterilization. The presence of p-aminophenol was not detected before or after sterilization.
Example 2 Study of the formation of the dimer
1) Effect of temperature and time
The effect of the temperature on the formation of the dimer of formula (I) was studied on formulation 001 of example 1 after heating at 70-90°C for 15 minutes and placing it in a glass bottle. This formulation was subjected to various storage temperatures and/or to various sterilization times, and analyzed by HPLC as described above in example 1.
The main results are collated in table 2 below.
Table 2 - Effect of temperature and time on the formation of the dimer
(Table Removed)

According to the above table, the dimer forms rapidly at 121°C, with a rate of formation proportional to the sterilization time, and slowly but in measurable amount at 60°C- for 14 days. The dimer is not detectable after one hour at 70°C.
p-Aminophenol is not detected under any of the conditions studied.
2) Effect of the pH
The values for the content of dimer of formula (I) given in table 1 of example 1 for formulations 001, 002 and 003 of compositions that are similar but with different pHs show that the formation of the dimer depends on the pH. The more basic the pH, the larger the amount of dimer formed. The generation of the radicals is probably facilitated by the formation of the phenoxides.
Example 3 Stability study
The stability was studied on formulation 001 of example 1 after heating at 70-90cC for 15 minutes, put in glass bottles or polypropylene infusion containers, and sterilization at 121°C for 15 minutes for the glass bottles and at 120°C for 20 minutes for the polypropylene containers.
Table 3 below collates the results obtained by HPLC analysis as described in example 1 above.

Table 3: Stability of formulation 001
(Table Removed)

nd: not detected
This table shows that the injectable liquid formulation according to the invention maintains the same paracetamol content after storage for 10 months at 25°C or 40°C, with a slight increase in the dimer content, which is higher at 40°C than at 25°C, and higher in the glass bottles than in the polypropylene containers.
The degradation of paracetamol in solution is often studied by measuring the absorbances at 500 ran according to the method described by J.E. Fairbrother "Acetaminophen", in Analytical Profiles of Drug Substances, 1974, vol. 3, pp. 1-109. Monitoring for three weeks, according to this method, of the absorbance firstly of formulation 001 and secondly of the commercial formulation Perfalgan® containing 1.0 g/100 ml of paracetamol and cysteine hydrochloride, obtained as described in WO 98/05314, shows that, at

60°C, paracetamol degrades at least ten times more quickly in the Perfalgan® formulation than in the formulation of the invention.
The pharmaceutical formulation of the present invention is so designed so as to provide greater stability than the Prior Art, such stability is achieved only when all the ingredients are mixed and present in the formulation. Hence it is a synergistic composition and exhibits surprising results.

We Claim:
1. An injectable liquid pharmaceutical composition of paracetamol, comprising:
0.1 to 5.0 g/100 ml of paracetamol; and a remaining quantity of an aqueous solvent; a buffer with a pKa of between 4.5 to 6.5; an isotonic agent such as herein described; characterized in that the paracetamol thus present comprises 0.005% to 0.73% of paracetamol dimmer of formula (I) as detected based on the ratio of the surface area of the HPLC peaks with detection at 245 ran.

(FormulaRemoved)

2. The composition as claimed in claim 1, wherein the paracetamol is in the range of 0.4 to 1.5 g/100ml.
3. The composition as claimed in any one of the preceding claims, wherein the buffering agent is selected from the group containing citrate buffer, phosphate buffer, phosphate-citrate buffer, bicarbonate buffer, tartrate buffer and acetate buffer, and preferably from citrate buffer, phosphate buffer and phosphate-citrate buffer, or a mixture of these buffers.
4. The composition as claimed in any one of the preceding claims, wherein said formulation is obtained by a process including heating of the solution at a temperature of between 100 and 130°C and preferably between 110 and 120°C.

5. A process for preparing the composition as claimed in claim 1 wherein said process comprising mixing together paracetamol, water, optionally one or more water miscible solvent(s), buffer and isotonic agent, followed by heating the solution obtained, in bulk or prefilled in containers, at a temperature of at least 70°C.
6. The process as claimed in claim 6, wherein said process includes heating the solution at a temperature in the range of 100 to 130°C and preferably between 110 to 125°C.
7. The composition as claimed in claim 1, wherein the dimmer as an when use as a stabilizing agent for liquid composition of the paracetamol.
8. An injectable liquid pharmaceutical composition of paracetamol and a process
for preparing the same substantially as herein described with reference to the
foregoing examples.

Documents:

3782-DELNP-2005-Abstract-(15-04-2009).pdf

3782-DELNP-2005-Abstract-(25-03-2009).pdf

3782-delnp-2005-abstract.pdf

3782-DELNP-2005-Claims-(15-04-2009).pdf

3782-DELNP-2005-Claims-(18-11-2008).pdf

3782-DELNP-2005-Claims-(25-03-2009).pdf

3782-delnp-2005-claims.pdf

3782-DELNP-2005-Correspondence-Others-(15-04-2009).pdf

3782-DELNP-2005-Correspondence-Others-(16-04-2009).pdf

3782-DELNP-2005-Correspondence-Others-(18-11-2008).pdf

3782-DELNP-2005-Correspondence-Others-(25-03-2009).pdf

3782-delnp-2005-correspondence-others.pdf

3782-DELNP-2005-Description (Complete)-(15-04-2009).pdf

3782-delnp-2005-description (complete).pdf

3782-DELNP-2005-Form-1-(15-04-2009).pdf

3782-DELNP-2005-Form-1-(18-11-2008).pdf

3782-delnp-2005-form-1.pdf

3782-delnp-2005-form-13-(25-03-2009).pdf

3782-delnp-2005-form-18.pdf

3782-DELNP-2005-Form-2-(15-04-2009).pdf

3782-DELNP-2005-Form-2-(18-11-2008).pdf

3782-delnp-2005-form-2.pdf

3782-delnp-2005-form-26.pdf

3782-DELNP-2005-Form-3-(18-11-2008).pdf

3782-DELNP-2005-Form-3-(25-03-2009).pdf

3782-delnp-2005-form-3.pdf

3782-delnp-2005-form-5.pdf

3782-delnp-2005-pct-210.pdf

3782-delnp-2005-pct-304.pdf

3782-DELNP-2005-Petition-137-(18-11-2008).pdf

3782-denp-2005_Abstract(16-04-2009).pdf

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Patent Number

233919

Indian Patent Application Number

3782/DELNP/2005

PG Journal Number

20/2009

Publication Date

15-May-2009

Grant Date

21-Apr-2009

Date of Filing

25-Aug-2005

Name of Patentee

NGUYEN-XUAN THO

Applicant Address

LE BON PIROUZ, CH-1267 VICH, SWITZERLAND.

Inventors:

#	Inventor's Name	Inventor's Address
1	NGUYEN-XUAN, THO	LE BON PIROUZ, CH-1267 VICH, SWITZERLAND.

PCT International Classification Number

A61K 31/167

PCT International Application Number

PCT/CH2004/000085

PCT International Filing date

2004-02-16

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	FR 03/01972	2003-02-14	France