Abstract:
A pharmaceutical composition comprising a platinum (II) complex compound in n aqueous solvent. The pharmaceutical composition is prepared by the essential steps of: (i) adding a platinum (II) complex compound to an oxygen enriched aqueous solvent to obtain a solution; (ii) Sterilizing the solution (iii) Filling the sterilizedsolution of step (ii) into suitable containers; and (iv) Sealing the containers. The oxygen enriched aqueous solvent is obtained by purging or bubbling of a gas into an aqueous solvent for 30 to 150 minutes. A device for preparing the pharmaceutical composition is illustrated in FIG.  1.  The composition is used for treatment of a human or an animal cancerous disease by the administration of pharmaceutical compositions of platinum (II) complex compounds as per the claim  1,  to the human or animal in need of said treatment.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to stabilized pharmaceutical compositions of antitumor platinum (II) complexes and a process for preparation thereof.  
       BACKGROUND OF THE INVENTION  
       [0002]     Platinum (II) complexes have found wide acceptance for treatment of variety of tumors, especially Lung cancer, Lymphoma, Ovarian cancer, Testicular cancer, Bladder cancer, Urothelial cancer and Head/neck cancer in both humans and animals. Therapeutically and commercially important platinum complexes, which are currently in clinical practice, include cisplatin (Peyrone, M.  Ann. Chemie Pharm.  1845, 51, 1-29), carboplatin (U.S. Pat. No. 4,140,707), oxaliplatin (U.S. Pat. No. 4,169,846) and miboplatin (U.S. Pat. No. 4,822,892). Other platinum (II) complexes, which are at various stages of development, include lobaplatin and enloplatin.  
         [0003]     In general, the above mentioned platinum (II) complexes are preferably administered to humans or animals affected with a tumor by an intravenous route i.e. an injectable. Such intravenous administration is essentially achieved through: 
        i) Reconstitution of a lyophilized or freeze dried powder of the requisite platinum (II) complex compound in an aqueous solvent, preferably water and administration of the solution thus obtained subsequent to dilution with dextrose or saline solutions; or     ii) Direct administration of a solution of the respective platinum (II) complex compound in an aqueous solvent, preferably water, by using recommended diluting solutions.        
 
         [0006]     The former mode of administration is, however, associated with several disadvantages such as: 
        a) Double handling: To administer a lyophilized preparation, double handling of the drug is required. The lyophilized cake has to be first reconstituted and then administered;     b) Dissolution time of the cake: In some cases, the complete dissolution of the powder may require prolonged shaking because of solubilisation problems;     c) Health Hazard: Improper reconstitution of a lyophilized powder sometimes result in the formation of air-borne droplets (“blow-back”), which, in the case of a potent antitumor agent such as platinum complexes may be a health hazard to the personnel making up the solution for injection;     d) Improper dose: There is always a problem in reconstituting a lyophilized powder in that an inappropriate quantity of diluents may be used because of a different vial size. This could result in a improper dose being administered to a patient; and     e) Cost of manufacture: The manufacture of a lyophilized formulation is quite costly, since it not only requires capital investment for installation of a lyophiliser, but also its maintenance; 
 
 even though, the stability of the reconstituted solution is not a major issue, since such solutions need to be administered immediately or within a prescribed time, generally not exceeding 8 hrs. 
       
 
         [0012]     A preformed solution of platinum (II) complex compounds in aqueous solvents, generally referred to as “ready-to-use” solution, has found wide utility in comparison to a solution reconstituted from a lyophilizate as it overcomes the limitations associated with a lyophilized composition. However, storage stability of such ready-to-use solutions are a major concern, which has vexed researchers and manufacturers of such solutions since long.  
         [0013]     There is a welter of literature, both academic and patents, which describe the studies directed towards not only understanding the mechanistic and/or kinetic pathway of the degradation of platinum (II) complex solutions but also in stabilization of such solutions. To name a few, stabilization of platinum (II) complex solutions have been reported to be achieved through: 
        a) Maintenance and/or adjustment of pH of a cisplatin solution to 3.5-5.0 and excluding any dissolved oxygen in the said solution as disclosed by Alam et. al. in U.S. Pat. No. 4,915,956.     The patent claims that for obtaining optimum stability, the level of dissolved oxygen in the solution should be less than 2 ppm.     b) Addition of aqueous polyethylene glycol, methoxy polyethylene glycol and a source of chloride ions in a cisplatin solution as disclosed by Kaplan et. al. in U.S. Pat. No. 4,451,447.     c) Adjustment of the pH of a cisplatin solution to 2.0-3.0 with acids, such as hydrochloric acid, as disclosed by Granatek et. al. in U.S. Pat. No. 4,310,515.     d) Addition of preservatives, like benzyl alcohol and mannitol, to a carboplatin solution as disclosed by Levius et. al. in EP 0,334,551.     e) Adjustment of the pH to 2.0-6.5 of a carboplatin solution by inorganic buffers as disclosed by Nijkerk et. al. in U.S. Pat. No. 5,104,896.     f) Addition of a requisite amount of 1,1-cyclobutane dicarboxylic acid to a carboplatin solution and adjusting the pH of the solution to 4.0-8.0 as disclosed by Kaplan et. al. in U.S. Pat. No. 5,455,270 or adjusting the pH to 2.0-7.0 as disclosed by Kiss et. al. in EP 0,743,854.     g) Utilization of carboplatin having less than 0.1% by weight of 1,1-cyclobutane dicarboxylic acid for preparation of a carboplatin solution as disclosed by Kysilka et. al. in U.S. Pat. No. 6,589,988.     h) Addition/utilization of oxalic acid or its salt as a buffering agent in an oxaliplatin solution as disclosed by Anderson et. al. in U.S. Pat. No. 6,306,902.     i) Addition/utilization of lactic acid or malonic acid or their salts as a buffering agent in an oxaliplatin solution as disclosed by Lauria et. al. in U.S. Pat. No. 6,476,068 or in published U.S. Application No. 2003/0,109,515 respectively.     j) Addition/utilization of a carbohydrate or an inorganic and/or organic acid in an oxaliplatin solution as disclosed by Schridde et. al in published EP Application Nos. 1,466,599 A1 and 1,466,600 A1.     k) Utilization of oxaliplatin, having not more than 0.08% by weight of oxalic acid, for preparation of an oxaliplatin solution as disclosed by Ibrahim et. al. in published U.S. Application No. 2004/0,186,172.     l) Utilization of a platinum (II) complex compound prepared under conditions which strictly exclude oxygen and utilization of the said platinum (II) compound thus obtained for preparation of the respective ‘ready-to-use solution’ as disclosed by Ohnishi et al in U.S. Pat. No. 5,959,133.        
 
         [0027]     From the abovementioned disclosures, it would be apparent that most, if not all the methods for stabilization of platinum (II) complex compound solution involve: 
        i) Utilization of additives such as physiologically acceptable acids, physiologically acceptable buffers, carbohydrates, preservatives, antioxidants, a stabilizing amount of corresponding dicarboxylic acids etc.;     ii) Adjustment and/or maintenance of the pH of platinum (II) complex compound solutions;     iii) Utilization of a platinum (II) complex active pharmaceutical ingredient (API) having very low content, generally below 0.1% by weight, of the corresponding dicarboxylic acid; and     iv) Exclusion of all dissolved oxygen from the solutions or through utilization of platinum (II) complex APIs prepared under conditions, which strictly exclude oxygen from the entire manufacturing process.        
 
         [0032]     However, the abovementioned methods suffer from one or more of the following limitations, which render such methods either not economical, convenient or commercially not particularly viable. The limitations are 
        i) Selection of an appropriate additive for stabilization. For instance, there is neither any general guideline nor can an inference be drawn that stabilization achieved in an oxaliplatin solution through addition of either oxalic acid, lactic acid, malonic acid, carbohydrates or organic and/or inorganic acid would give similar or substantially similar stabilization to a cisplatin, carboplatin or miboplatin solution through utilization of the said additive.     ii) Similarly, there is neither any general guideline nor can an inference be drawn that addition of a stabilizing amount of cyclobutane dicarboxylic acid to a carboplatin solution would result in similar or substantially similar stabilization of an oxaliplatin solution or for that matter a cisplatin or miboplatin solution by addition of the respective dicarboxylic acid solution.     iii) The disclosures in U.S. Pat. No. 4,915,956 and in U.S. Pat. No. 5,959,133 amply demonstrate that oxygen present in the system either in the dissolved state in the solution or arising and/or carried forward from the active pharmaceutical ingredient utilized for its preparation are detrimental to the stability of such solutions by virtue of the fact that oxygen present in the system actually facilitates the formation of over oxidation products which not only leads to lower potency but also imparts coloration to such solutions.        
 
         [0036]     Further, it might be mentioned that for manufacture of an active pharmaceutical ingredient having very low content of the respective dicarboxylic acid more often than not, recourse to tedious and costly purification techniques are necessary, which needless to mention, would increase the cost of manufacturing.  
         [0037]     Furthermore, for exclusion of oxygen from either the active pharmaceutical ingredient or the finished dosage forms recourse to control of systems for effecting complete or near complete exclusion of the said gas i.e. oxygen is necessary, which would increase not only the cost of manufacturing but also the hazards and operability of the methods.  
         [0038]     In addition, even though, the disclosure contained in U.S. Pat. No. 5,455,270 does mention use of oxygen or air i.e. a gaseous mixture of about 78% nitrogen and 21% oxygen in preparation of carboplatin solution, however from the teachings of the said patent it would be apparent that in preparation of such solution the gas is invariably bubbled into a solution of carboplatin in water prior to sterilization and filling the solution in vials or alternatively filling a sterilized solution of carboplatin in water in suitable vials and blanketing the free headspace of the said vial with air.  
         [0039]     However it should be noted that as per the teachings of the U.S. Pat. No. 5,455,270 bubbling of gas or blanketing the headspace with air is an optional embodiment of the invention recited therein, the eventual invention, however, comprises stabilization of a carboplatin solution through addition of requisite amount of 1,1-cyclobutane dicarboxylic acid (CBDCA).  
         [0040]     Further, the disclosure of U.S. Pat. No. 5,455,270 is not enabling enough in that it does not specify the amount of oxygen to be bubbled. Moreover, patent claims that whenever a purging technique is employed, it is preferred that the liquid in the container fill no more than 50% of its volume (half full), i.e. the unfilled air oxygen volume or headspace be more than 50% of the total volume of the container.  
         [0041]     It might be further mentioned that Health Authorities all over the world are very concerned about the level of degradation product and impurities present in a drug substance or a drug product. As a consequence, regulatory approval norms today are very stringent about the level of impurities present in a drug substance or a drug product. In view of this, it is rather intriguing how a platinum (II) complex compound solution containing more often than not amounts of additives above the limits prescribed by regulatory authorities could comply with pharmacopeial specifications, even though such solutions may be stable.  
         [0042]     From the foregoing, it would be apparent that there is no universal method or system for stabilization of a platinum (II) complex compound solution, which is simple, convenient, economical and is not dependent on the vagaries of critical parameters like pH, amount of additives specially requisite dicarboxylic acid, amount of oxygen present, quality of active pharmaceutical ingredient etc.  
         [0043]     A need, therefore, exists for a pharmaceutical composition of platinum (II) complex compounds which is universal, simple, convenient, and is not dependent on the vagaries of critical parameters like pH, amount of additives specially requisite dicarboxylic acid, amount of-oxygen present, quality of active pharmaceutical ingredient etc.  
         [0044]     The present invention is a step forward in this direction and overcomes most, if not all the limitations of the prior art methods in providing a novel and simple method for stabilization of platinum (II) complex compound solutions.  
       OBJECTS OF THE INVENTION  
       [0045]     An object of the present invention is to provide a pharmaceutical composition of platinum (II) complex compounds, which are stable on storage for pharmaceutically acceptable duration of time.  
         [0046]     Another object of the present invention is to provide a pharmaceutical composition of platinum (II) complex compounds, which are stable and undergo less degradation.  
         [0047]     Yet another object of the present invention is to provide a process for preparation of a stable pharmaceutical composition of platinum (II) complex compounds, which is simple, convenient and economical.  
         [0048]     A further object of the present invention is to provide a method for treatment of a human or an animal cancerous disease, comprising administration of such stable pharmaceutical compositions of platinum (II) complex compounds, to the human or animal in need of said treatment.  
       SUMMARY OF THE INVENTION  
       [0049]     Thus the present invention relates to a stable pharmaceutical composition comprising a platinum (II) complex compound in an aqueous solvent  
         [0050]     According to another aspect the invention relates to a process for preparing a stable pharmaceutical composition comprising a platinum (II) complex compound in an aqueous solvent obtained by a process comprising the steps of: 
        (i) adding a platinum (II) complex compound to an oxygen enriched aqueous solvent to obtain a solution;     (ii) Sterilizing the solution);     (iii) Filling the sterilizedsolution of step (ii) into suitable containers; and     (iv) Sealing the containers.        
 
         [0055]     According to a further aspect there is also provided a device for preparing the pharmaceutical composition according to the invention.  
         [0056]     According to a still further aspect there is also provided a method for treatment of a human or an animal cancerous disease, comprising administration of pharmaceutical compositions of platinum (II) complex compounds of the invention to the human or animal in need of said treatment.  
         [0057]     In their efforts to prepare a ready-to-use solution of platinum (II) complex compounds, in particular carboplatin, the present inventors have found to their surprise that such a solution could be made to stand for a pharmaceutically acceptable duration of time without significant drop in potency as well as minimizing the formation of degradation products through a simple unit operation of enriching the oxygen content of the solution.  
         [0058]     Further, the present inventors have found that other than enriching oxygen content of the solution, no additive needs to be added, no pH adjustment is required and no particular significance need to be given for active pharmaceutical ingredient specification, i.e. the dicarboxylic acid content, for stabilization of the solution. In particular, it has been found that a stable solution of carboplatin in water can be obtained by simple dissolution of carboplatin in an oxygen-enriched water, involving neither addition of any stabilization agent nor adjustment of pH with a pharmaceutically acceptable pH modifier.  
         [0059]     Furthermore, it has been found that the acceptable stability of the pharmaceutical composition of the present invention could be achieved through utilization of water, which is at least 50% saturated with oxygen, with maximum stability being observed when the water used for injection is saturated or near saturated with oxygen.  
         [0060]     The method for preparation of such stable solutions is simple and is achieved through bubbling of oxygen gas into an aqueous solvent for a suitable period of time, followed by addition of platinum (II) complex compound to obtain solutions, which can be made into a sterile form for human or animal consumption by conventional methods.  
         [0061]     Further, it has been found that instead of oxygen when any other gas like nitrogen is bubbled into an aqueous solvent, which is then utilized for the preparation of a solution of platinum (II) complex compounds, the stability profile of such solution is far inferior to those wherein no gas is bubbled. This is not surprising, since bubbling of nitrogen into an aqueous solvent actually drives out any dissolved oxygen thereby providing an oxygen depleted solution, which in turn leads to the inferior stability. The stabilizing effect of an oxygen enriched composition prepared as per the method of the present invention over that of a composition not enriched or depleted of oxygen could be best understood by a comparative stability profile of the two compositions as summarized in Table—I. Also for direct comparison the stability profile of a solution prepared by bubbling of nitrogen is summarized in Table—I.  
                                                           TABLE I                           Comparison of Stability of Carboplatin Solutions enriched       with oxygen with those not enriched with oxygen.            Solution of           Carboplatin   % Fall       carboplatin   Storage   Solution   Assay   in assay of       enriched with   conditions   Description   (mg/ml)   Carboplatin                    Nitrogen   Initial   Clear   10.20   —               colourless               solution           20 D/50° C.   Black   NE   NE               solution       None   Initial   Clear   10.53   —               colourless               solution           15 D/60° C.   Yellow   9.72   6.1               coloured               solution           30 D/50° C.   Light brown   10.13   4.0               coloured               solution       Oxygen   Initial   Clear   10.17   —               colourless               solution           15 D/60° C.   Very light   9.57   6.0               yellow               coloured               solution           30 D/50° C.   Faint yellow   9.95   2.2               coloured               solution                 D—days, NE—not evaluated, CBDCA—cyclobutane dicarboxylic acid             
 
         [0062]     D-days, NE-not evaluated, CBDCA-cyclobutane dicarboxylic acid  
         [0063]     Furthermore, the present inventors have also found that the acceptable stability of the pharmaceutical composition of the present invention is not determined by the volume of the solution filled in the container or to put in other words the stability is not dependent on the free available headspace of the container. It has been found that a container filled with an oxygen enriched carboplatin solution in an aqueous solvent less than or more than 50% of the volume of the container exhibit essentially similar stability or degradation profile.  
         [0064]     Thus, in accordance with the above:  
         [0065]     In one aspect, the present invention provides stable pharmaceutical compositions comprising a solution of platinum (II) complex compounds in an aqueous solvent.  
         [0066]     In another aspect, the present invention provides stable pharmaceutical compositions comprising a solution of platinum (II) complex compounds in an aqueous solvent having a pH from about 5.0 to 7.0.  
         [0067]     In yet another aspect, the present invention provides stable pharmaceutical compositions comprising a solution of platinum (II) complex compounds in an aqueous solvent having a pH from about 5.0 to 7.0 contained in a suitable container wherein the free headspace of the container is not blanketed with a gas.  
         [0068]     In still another aspect, the present invention provides stable pharmaceutical compositions comprising a solution of platinum (II) complex compounds in an aqueous solvent having a pH from about 5.0 to 7.0 contained in a suitable container wherein the volume of the platinum (ID) solutions is less than 50% of the volume of the container.  
         [0069]     In a further aspect, the present invention provides stable pharmaceutical compositions comprising a solution of platinum (II) complex compounds in an aqueous solvent having a pH from about 5.0 to 7.0 contained in a suitable container wherein the volume of the platinum (ID) solutions is more than 50% of the volume of the container.  
         [0070]     In yet further aspect, the present invention provides a process for preparation of stable pharmaceutical composition of platinum (II) complex compounds in an aqueous solvent having a pH from about 5.0 to 7.0 comprising the steps of: 
        i) Bubbling of oxygen gas into an aqueous solvent for a suitable period of time;     ii) Addition of platinum (II) complex compound to the solution of step (i);     iii) Mixing or agitating the mixture of step (ii) to obtain a clear solution;     iv) Sterilizing the solution of step (iii);     v) Filling the sterilized, clear solution of step (iv) into suitable containers; and     vi) Sealing the containers as prepared in step (v).        
 
         [0077]     In another aspect, the present invention provides a process for preparation of stable pharmaceutical composition of platinum (II) complex compounds in an aqueous solvent having a pH from about 5.0 to 7.0 wherein the entire process is carried out in assembly as depicted in  FIG. 1 .  
         [0078]     In yet another aspect, the present invention provides a stable pharmaceutical composition comprising a solution of carboplatin in an aqueous solvent.  
         [0079]     In still another aspect, the present invention provides a stable pharmaceutical composition comprising a solution of carboplatin in an aqueous solvent having a pH from about 5.0 to 7.0.  
         [0080]     In a further aspect, the present invention provides stable pharmaceutical compositions comprising a solution of carboplatin in an aqueous solvent having a pH from about 5.0 to 7.0 contained in a suitable container wherein the free headspace of the container is not blanketed with a gas.  
         [0081]     In yet further aspect, the present invention provides stable pharmaceutical compositions comprising a solution of carboplatin in an aqueous solvent having a pH from about 5.0 to 7.0 contained in a suitable container wherein the volume of the carboplatin solutions is less than 50% of the volume of the container.  
         [0082]     In another aspect, the present invention provides stable pharmaceutical compositions comprising a solution of carboplatin in an aqueous solvent having a pH from about 5.0 to 7.0 contained in a suitable container wherein the volume of the carboplatin solutions is more than 50% of the volume of the container.  
         [0083]     In yet another aspect, the present invention provides a process for preparation of stable pharmaceutical composition of carboplatin in an aqueous solvent having a pH from about 5.0 to 7.0 comprising the steps of: 
        i) Bubbling of oxygen gas into an aqueous solvent for a suitable period of time;     ii) Addition of carboplatin to the solution of step (i);     iii) Mixing or agitating the mixture of step (ii) to obtain a clear solution;     iv) Sterilizing the solution of step (iii);     v) Filling the sterilized, clear solution of step (iv) into suitable containers and     vi) Sealing the containers as prepared in step (v).        
 
         [0090]     In still another aspect, the present invention provides a process for preparation of stable pharmaceutical composition of carboplatin in an aqueous solvent having a pH from about 5.0 to 7.0 wherein the entire process is carried out in assembly as depicted in  FIG. 1 . 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0091]      FIG. 1  depicts a schematic description of the assembly used to carry out the process for preparation of a stable aqueous pharmaceutical composition of platinum (II) complex compounds. The assembly consists of a sparger unit, stirrer and dissolved oxygen meter probe to monitor the level of dissolved oxygen. Sparger unit consists of an oxygen cylinder, flow regulator, pressure regulator, filter, tubings and sparger. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0092]     The oxygen enriched aqueous solvent is obtained by purging or bubbling of a gas into an aqueous solvent for a suitable period of time, to which is added the platinum (II) complex compound and mixed or agitated to obtain a clear solution. Preferably, the solution has a pH of from about 5.0 to 7.0. The platinum (II) complex compound is selected from cisplatin, carboplatin, oxaliplatin, lobaplatin, enloplatin and miboplatin.  
         [0093]     The aqueous solvent is selected from the group consisting of water, aqueous polyalkylene glycols containing C 1-6  alkyl groups, aqueous carbohydrate solutions and mixtures thereof. The most preferred aqueous solvent is water.  
         [0094]     The final  1  water content in the solution of platinum (II) complex compound ranges from 0.01 to 99.99%. The gas used in the process is selected from oxygen, oxygen allotropes and combinations thereof. The purging of the gas into the aqueous solvent is carried out for a period from about 30 minutes to about 150 minutes and preferably from about 90 minutes to about 120 minutes.  
         [0095]     After the enrichment of oxygen into the aqueous solvent, the dissolved oxygen concentration is in the range from about 20 ppm to about 40 ppm. The preferred dissolved oxygen concentration is 35 ppm.  
         [0096]     As mentioned hereinbefore, the pharmaceutical compositions of the present invention comprising of an aqueous solution of a platinum (II) complex compounds is achieved by simple dissolution of the platinum (II) compounds in an oxygenated aqueous solvent.  
         [0097]     As used herein, the term “platinum (II) complex compounds” refers to platinum compounds having 2+ oxidation state in aqueous solution, which dictate the square planar sterochemical arrangement of the ligand. Examples of such platinum (II) complex compounds are, but not limited to, cisplatin, carboplatin, oxaliplatin, myboplatin, lobaplatin, enloplatin etc. While the specification illustrates the invention with particular references to carboplatin, however, it should not be construed as limiting the scope of the invention.  
         [0098]     As used herein the term “aqueous solvent” refers to water containing solvents. Water for injection is preferred solvent. Mixtures of water and one or more auxiliary carriers e.g. polyalkylene glycols and sugar solutions could be employed. Typically, the final water content in the solution of the invention could range from 0.1 to 99.9% with auxiliary carriers. Suitable glycols include polyalkylene glycols having molecular weight of about 300 to about 900 and bearing C 1-6  alkyl groups. Accordingly, polyether polyols such as polyethylene glycol, polypropylene glycol, polybutylene glycol and the like and the mixtures thereof can be used. “Sugar solution” includes solutions of pharmaceutically acceptable dextrose, sucrose, mannose or other sugars which function as isotonicity adjusting agents.  
         [0099]     As used herein the term “oxygenated or oxygen enriched” solvent means an aqueous solvent containing dissolved oxygen obtained by means of aerating the aqueous solvent with oxygen gas. The aeration of oxygen in the aqueous solvent could be attained by bubbling the oxygen gas or any allotrope of oxygen or combinations thereof.  
         [0100]     The term “bubbling” means that sparging or otherwise passing the oxygen gas through the aqueous solvent under pressure to increase the dissolved oxygen level of the aqueous solvent. The preferred dissolved oxygen level is from about 20 ppm to 40 ppm. The solution having dissolved oxygen level of around 35 ppm i.e. saturated or nearly saturated solutions are preferred.  
         [0101]     The amount of carboplatin used in the formulation according to present invention vary from about 1.0 mg to 22.0 mg/ml. The amount, which is present, is not critical and may be adjusted in accordance with the individual needs and preferences. Typically, the concentration of carboplatin will be about 10.0 mg/ml.  
         [0102]     The pharmaceutical composition of the present invention can be prepared in an assembly as depicted in  FIG. 1 . The process comprises of the following steps: 
        i) Enriching the dissolved oxygen content of an aqueous solvent     ii) Addition of platinum (II) complex compound to the solution of step (i);     iii) Mixing or agitating the mixture of step (ii) to obtain a clear solution;     iv) Sterilizing the solution of step (iii);     v) Filling the sterilized, clear solution of step (iv) into suitable containers; and     vi) Sealing the containers as prepared in step (v).        
 
         [0109]     To enrich the aqueous solvent with oxygen gas, the oxygen gas is introduced into the aqueous solvent by means of a sparger. “Sparging” is a means of bubbling of an oxygen gas through a solution under suitable pressure to get the desired level of dissolved oxygen in aqueous solvent. The sparger can be constructed from a material selected from the group consisting of carbon steel and low-alloy steels or elastomeric material. The tube sparger preferably consists of a perforated elastomer tube, or perforated/sintered steel tube. The volumetric flow rate of the oxygen gas and/or an allotrope containing gas added via the tube sparger is 0.01 to 0.4 m 3  (STP)/h per m 3 . The gas is introduced into the carrier through several, usually thousands of tiny pores, creating small fine bubbles. The sparger surface pore size can vary from 0.2 μm to the 0.31 inch. Pore size is the most important parameter to be considered in the design of the gas sparging system. This particular sparger pore size range allows to attain a sufficient sparge pressure and gas flow enhancing the mass transfer. The period for which the aqueous solvent is purged is generally between about 30 minutes and about 150 minutes. Periods of about 1.5 hrs to about 2.0 hrs are preferred. The duration of purging is not critical, however it is generally desirable to sparge in aqueous solvent to achieve half saturated or complete or near complete saturated solution with the oxygen gas i.e. having dissolved oxygen content from about 20 ppm to about 40 ppm. The optimum stability is achieved with nearly saturated solution viz. having dissolved oxygen content of about 35 ppm. Under the above mentioned conditions, the desired saturation level is achieved by bubbling the gas for around 90 minutes into an aqueous solvent.  
         [0110]     Suitable packaging for the platinum (II) complex compound solutions may be the approved containers for parenteral use, such as plastic and glass containers, ready-to-use syringes and the like. Preferably the container is a sealed glass container, e.g vial or an ampoule. A hermetically sealed glass vial is the preferred container.  
         [0111]     The pharmaceutical compositions thus prepared exhibit excellent storage stability as would be evident from the examples given hereinbelow, which are not limiting and should not be construed as limiting the scope of the invention.  
         [0112]     The pharmaceutical compositions are highly effective for treatment in both human and animal hosts, of tumors, such as sarcomas, carcinomas of prostate, lung, breast, head and neck, bladder, urothelium, thyroid, ovary, testes, etc., lymphomas including Hodgkin and no-Hodgkin, neuroblastoma, leukaemias including acute lymphoblastic leukemia and acute myeloblastic leukemia, Wilm&#39;s tumor, melanoma, myeloma etc.  
         [0113]     The pharmaceutical compositions can be administered by rapid intravenous injection or infusion. For e.g. a composition containing carboplatin can be administered by an intravenous infusion of 175 to 600 mg/m 2  given in a single infusion on day 1 every 4 weeks.  
       EXAMPLE—1  
       [0114]     A carboplatin solution having a concentration of around 10 mg/ml was prepared as follows: First, the oxygen enriched aqueous solvent was prepared by purging (bubbling) oxygen gas into water for 1.5 hour with the help of assembly shown in  FIG. 1 . Then, the requisite amount of carboplatin was added to the oxygen enriched water thus obtained to get a solution of carboplatin having concentration of 10 mg/ml. Sparging and agitation was continued throughout the addition operation and until the carboplatin was observed to be visibly dissolved. The clear solution was then passed through a sterile filter under positive pressure and then aseptically filled into vials. The carboplatin solution filled vials were stored at various storage conditions. The pH of each solution was measured and the content of carboplatin and cyclobutane dicarboxylic acid were determined by HPLC. This was done with the solution as originally prepared and after various storage conditions. The results of all these studies are summarized in Table—II.  
                                                   TABLE II                           Carboplatin Physical and Chemical stability at 25° C.,       30° C., 40° C. and 60° C.            Storage           Carboplatin       Conditions   Description   pH   assay %                    Initial   Clear colorless solution   5.80   103.9       2 W/60° C.   Light yellow coloured solution   5.78   96.9       1 M/50° C.   Clear colorless solution   5.70   93.5       1 M/40° C.   Clear colorless solution   5.90   95.1       2 M/50° C.   Yellow colored solution   5.70   95.2       2 M/40° C.   Clear colorless solution   5.86   98.4       2 M/30° C.   Clear colorless solution   6.00   101.9       3 M/25° C.   Clear colorless solution   5.80   97.5       3 M/30° C.   Clear colorless solution   5.78   97.1                  
 
       EXAMPLE—2  
       [0115]     To determine the effect of oxygen gas on stability of platinum (II) complex compound solutions, carboplatin solutions enriched with oxygen, and not enriched with oxygen were prepared. The oxygen enriched solution was prepared in a manner similar to that described in Example—1. The carboplatin solutions not enriched with oxygen were prepared as follows: Nitrogen gas was purged into water for 1.5 hour with the help of assembly as shown in  FIG. 1 . Then the requisite amount of carboplatin was added to the nitrogen purged solution to get the final concentration of 10 mg/ml. Sparging and agitation was continued throughout the addition operation and until the carboplatin was observed to be visibly dissolved. The clear solution was sterilized and filled into vials in a manner similar to that described in Example—1.  
         [0116]     Similarly, carboplatin solution was prepared without purging any gas into the water. All the solutions were stored at various storage conditions and the stability of these solutions were determined. The results are given in Table—I.  
                                                           TABLE I                           Comparison of Stability of Carboplatin Solutions enriched       with oxygen with those not enriched with oxygen.            Solution of           Carboplatin   % Fall       carboplatin   Storage   Solution   Assay   in assay of       enriched with   conditions   Description   (mg/ml)   Carboplatin                    Nitrogen   Initial   Clear   10.20   —               colourless               solution           20 D/50° C.   Black   NE   NE               solution       None   Initial   Clear   10.53   —               colourless               solution           15 D/60° C.   Yellow   9.72   6.1               coloured               solution           30 D/50° C.   Light brown   10.13   4.0               coloured               solution       Oxygen   Initial   Clear   10.17   —               colourless               solution           15 D/60° C.   Very light   9.57   6.0               yellow               coloured               solution           30 D/50° C.   Faint yellow   9.95   2.2               solution                 D—days, NE—not evaluated, CBDCA—cyclobutane dicarboxylic acid             
 
       EXAMPLE—3  
       [0117]     The effect of vial fill volume i.e. headspace on the stability of aqueous solution of carboplatin was also determined at 50° C. and 60° C. Carboplatin solutions having concentration 10 mg/ml were prepared by using oxygen saturated water in a manner similar to that of Example—1. After preparation, solutions were sterilized by filtration and filled aseptically into glass vials with headspace variation of more than and less than 50% of the volume of the container. Samples were assayed after 15 and 30 days. The stability data of these solutions is given in Table—III and IV.  
                                                                   TABLE III                           Effect of Headspace and Oxygen sparging on carboplatin solution stability                                Color ratio (Initial                           absorbance to                           exposed sample       Headspace   Condition   Description   Assay   % Fall in assay   absorbance)                    ≦50%   Initial   Clear colorless   10.17   —   0.002               solution free from               any visible particles           1 M/40° C./   Clear colorless   9.95   2.2   0.006           75% RH   solution free from               any visible particles       ≧50%   Initial   Clear colorless   10.00   —   &lt;0.001               solution free from               any visible particles           1 M/40° C./   Clear colorless   9.88   1.2   0.011           75% RH   solution free from               any visible particles                  
 
         [0118]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE IV 
               
             
             
               
                   
               
               
                   
               
               
                 Effect of Headspace and Oxygen sparging on carboplatin solution stability. 
               
             
          
           
               
                   
                   
                   
                   
                   
                 Color ratio (Initial 
               
               
                   
                   
                   
                   
                   
                 absorbance to 
               
               
                   
                   
                   
                 Assay 
                   
                 exposed sample 
               
               
                   
                 Condition 
                 Description 
                 (mg/ml) 
                 % Fall in assay 
                 absorbance) 
               
               
                   
                   
               
             
          
           
               
                 Headspace 
                 Initial 
                 Clear colorless 
                 10.17 
                 — 
                 — 
               
               
                 ˜10% 
                   
                 solution 
               
               
                   
                 15 D/60° C. 
                 Clear faintly 
                 9.57 
                 6.0 
                 10 
               
               
                   
                   
                 yellow solution 
               
               
                   
                 30 D/50° C. 
                 Clear faintly 
                 9.95 
                 2.2 
                 5.5 
               
               
                   
                   
                 yellow solution 
               
               
                 Headspace 
                 Initial 
                 Clear colorless 
                 10.39 
                 — 
                 — 
               
               
                 ˜45% 
                   
                 solution 
               
               
                   
                 15 D/60° C. 
                 Clear faintly 
                 9.74 
                 6.5 
                 9.5 
               
               
                   
                   
                 yellow solution 
               
               
                   
                 30 D/50° C. 
                 Clear faintly 
                 9.99 
                 4.0 
                 5.2 
               
               
                   
                   
                 yellow solution