the gelling agents of the invention include sorbitan monostearate and / or sorbitan monopalmitate . both of these materials are available from a number of suppliers commercially for topical or oral use . sterile material free from foreign particulates is not available and is difficult to produce . it is now possible to produce such sterile , foreign particulate free material through the use of aseptic precipitation and drying alone or in conjunction with gamma irradiation . it is essential that the process used for the preparation of a sterile bulk does not introduce any change in physicochemical properties of the gelling agent which will in turn cause a change in the gelling potential of the gelling agent . the process to provide a foreign particulate free , sterile bulk gelling agent comprises the steps of : 1 . dissolution of the gelling agent ( s ) in volatile organic solvents , if required at an elevated temperature , followed by filtration of the solutions also at the elevated temperature and subsequent evaporation to obtain a dry product or 2 . dissolution of the gelling agent ( s ) in water - miscible organic solvents at an elevated temperature followed by filtration of the solutions also at the elevated temperature , precipitation of the gelling agents from solution either through addition of a non - solvent or cooling the solution to a lower temperature to cause phase - separation , filtration to recover the wet bulk and subsequent evaporation to obtain a dry product and 3 . subjecting the foreign particulate - free gelling agent obtained from steps 1 and 2 to sterilization by gamma irradiation the gelling agents of the invention viz . sorbitan monostearate or sorbitan monopalmitate are soluble in a variety of organic solvents including volatile organic solvents such as methylene chloride , ethyl acetate , benzene , petroleum ether , carbon tetrachloride , methanol , acetonitrile , acetone , ethanol , tetrahydrofuran and other volatile solvents , at elevated temperatures . non - volatile organic solvents in which the gelling agents are soluble include nn ′- dimethylacetamide ( dma ), dimethylsulfoxide ( dmso ), n - methyl - 2 - pyrrolidone mp ), triacetin , triethyl citrate , benzyl alcohol , propylene carbonate , decylmethylsulfoxide , dimethylformamide ( dmf ), glycofural , benzoyl benzoate , alkyl esters of aromatic acids , polyethylene glycols ( peg ), propylene glycol and the like , also at elevated temperatures . the solvents for the invention should be biocompatible and not pose toxicity issues . such solvents may be completely water - miscible , partially water - miscible or completely water - immiscible . water - immiscible organic solvents such as dichloromethane , chloroform , ether , benzene , hexane and the like though otherwise used in the preparation of pharmaceutical compositions are generally toxic and require exotic methods such as lyophilization and the like for removal . also , there are very strict guidelines for the levels of such residual solvents allowable in pharmaceutical compositions , especially so for parenteral administration . water - miscible organic solvents are preferred . more specifically , such water - miscible organic solvents are chosen from dma , dmso , nmp , triacetin , triethyl citrate , benzyl alcohol , propylene carbonate , decylmethylsulfoxide , dmf , glycofural , benzoyl benzoate , alkcl esters of aromatic acids , peg , propylene glycol , isopropanol , methanol , acetonitrile , acetone , ethanol , tetrahydrofuiran and the like . a specially preferred volatile water - miscible solvent is ethanol because of its proven antiseptic properties , its complete water - miscibility , its volatile nature , its biocompatibility and low toxicity potential , its solvating capability for the gelling agents of the invention at elevated temperatures and its known use in the pharmaceutical industry for parenteral administration of solution dosage forms . preferred non - volatile water - miscible oraganic solvents include dma , dmso , dmf , nmp , peg among others . in one embodiment of the novel process of the invention , the sterile bulk gelling agent is prepared by dissolution in volatile water - miscible organic solvents specifically chosen from ethanol , methanol , acetonitrile , acetone , ethanol , tetrahydrofuran at a temperature above ambient , filtered through a sterilizing grade filter membrane at the elevated temperature and dried under vacuum at the elevated temperature . in another aspect of this embodiment of the invention the solution of the gelling agent which has been filtered through a sterilizing grade filter membrane , is cooled to room temperature or lower to cause gelation of the solvent and the same solvent is added to the gel to cause precipitation of the gelling agent . this suspension is then filtered through a further sterilizing grade filter membrane and the wet mass which is substantially free from the organic solvent is then dried under vacuum at an elevated temperature . this procedure has the advantage of removal of a large percentage of the organic solvent from the gelled bulk which would otherwise be lost under vacuum . this solvent can then further be used in processing of a separate lot of the gelling agent . the term “ substantially free ” indicates that a large percentage of the organic solvent is removed when compared with the situation where all of the solvent is bound to the gelling agent in the form of a gel . in a further embodiment of the invention , the solution of the gelling agent which has been filtered through sterilizing grade filter membranes at elevated temperatures is then added to a non - solvent to cause precipitation of the gelling agent . the non - solvent can be an organic solvent or can be water . the precipitated gelling agent is then treated further as in the earlier embodiment described above with the same advantages . in a further aspect of this embodiment , the water - miscible organic solvent is non - volatile chosen from dma , dmso , nmp , triacetin , triethyl citrate , benzyl alcohol , decylmethylsulfoxide , dmf , glycofural , peg , propylene glycol and the like . upon precipitation from a non - solvent such as water , the gelling agent is subjected to drying to remove water . the residual organic solvent should be chosen advantageously to be the same as the one to be used in the final gelled polymeric dispersion . in an additional embodiment of the invention , the sterile dried bulk gelling agent is subjected to sterilization by gamma irradiation . surprisingly , the gelling agents are not degraded by this procedure . other materials in the gelled polymeric dispersion can be processed by other techniques as described above and generally known in the art of preparation of sterile dosage forms . the concentration of the gelling agent in the water - miscible solvent can be from 5 % w / w to 80 % w / w , preferably from about 10 % w / w to 70 % w / w and even more preferably from about 20 % w / w to 60 % w / w . the concentration of the gelling agent in the final solution will be dependent on the solvent chosen , the gelling agent solvent interactions , the processing temperature and of course the solubility of the gelling agent in the solvent . of particular importance is the concentration of the gelling agent in the solvent , which allows filtration through a sterilizing grade membrane filter . the higher the concentration of the gelling agent in the solution the greater the yields and smaller the amounts of the expensive solvents that are used . when a solvent / non - solvent type of precipitation is to be used , the ratio of the solvent to the non - solvent may be adjusted so that complete precipitation occurs to ensure maximum yields . the temperature of preparation of the solution and also the processing will of course depend on the solvent to be used with a temperature below the boiling point of the solvent being preferred . thus , for example , for a solvent such as ethanol a clear solution can be prepared at a temperature of 35 - 40 ° c . and higher at concentrations as high as 50 % w / w , which can be filtered through a sterilizing grade 0 . 22 μn filter at the same temperature . but , for a solvent such as dma , a solution with the same concentration needs to be processed at a higher temperature because of the viscosity imparted by the gelling agent . the gelling agents of the invention are known to gel the solvents of the invention at high concentrations . each gelling agent - solvent system will have a different temperature range at which the gelation occurs which will also - affect the processability of the solution . the sterilizing grade filter can be any membrane , which has the capability to remove foreign particulates and also microorganisms to ensure sterility . such filters usually have a pore size of 0 . 22 μm . any membrane filter is acceptable for the practice of this invention as long as it can filter the solution and is compatible with the solvents of the invention . such membranes include those made from nylon 66 , cellulose acetate , cellulose nitrate , polytetrafluoroethylene ( ptfe ), silver membrane , gold membrane , polysulfone , polycarbonate and other known in the art and supplied by various manufacturers . the sterilizing grade filter could be preceded by a cleaning filter such as a 0 . 45 μm , 5 μm or 8 μm filter which can take up much of the burden from the sterilization filter . the choice of filters is within the scope of a person skilled in the art of development of pharmaceutical injectable dosage forms . any mode of filtration is acceptable as long as a sterile product is produced . such methods include , vacuum filtration , filtration under positive pressure using compressed air or nitrogen and the like . also , the use of cartridge filters or filter candles and the like are well within the scope of this description . the drying of the sterile gelling agent bulk obtained after the above described processes can be conducted by any means known in the art , including for example tray drying in an oven with or without the application of vacuum and with or without heating , lyophilization , simple vacuum drying and other methods known to a person skilled in the art of processing pharmaceutical dosage forms . where heating is required it is preferable to heat at a temperature above the boiling point of the solvent to be evaporated to ensure complete removal of the organic solvent . further , for the preparation of a sterile in - situ microcarrier forming gelled polymeric dispersion composition , the preparation of sterile solvents , polymers , oil and bioactive agents can be as per known procedures in the art such as aseptic filtration of the solvents and oil , gamma irradiation of the polymer or aseptic filtration of the polymer solution in a volatile organic solvent followed by evaporation of the solvent and the like and are well known to persons skilled in the art of manufacture of parenteral controlled release dosage forms . the bioactive agents which can be incorporated into the sterile in - situ microcarrier forming gelled polymeric dispersion compositions can be chosen from peptide drugs , protein drugs , desensitizing agents , antigens , vaccines , anti - infectives , antibiotics , antimicrobials , antineoplastics , antitumor , antiallergenics , steroidal anti - inflammatory agents , analgesics , decongestants , miotics , anticholinergics , sympathomimetics , sedatives , hypnotics , antipsychotics ,- psychic energizers , tranquilizers , androgenic steroids , estrogens , progestational agents , humoral agents , prostaglandins , analgesics , antispasmodics , antimalarials , antihistamines , cardioactive agents , non - steroidal anti - inflammatory agents , antiparkinsonian agents , antihypertensive agents , beta - adrenergic blocking agents , nutritional agents , antivirals , dna fragments , nucleic acids , genetic material , oligonucleotides , radioisotopes , or combinations of these classes of compounds . to those skilled in the art , other drugs or biologically active agents that can be released in an aqueous environment can be utilized in the described delivery system . also , various forms of the drugs or biologically active agents may be used . these include , without limitation , forms such as uncharged molecules , molecular complexes , salts , ethers , esters , amides , and other chemically modified forms of the biologically active agent which are biologically activated when injected into a body . in a further embodiment , the sterile bioactive agent may also be added to the oil phase as a suspension to enhance the loading of the bioactive agent in the delivery composition . whatever the final composition that is arrived at the process allows a sterile composition to be prepared . also , the further behavior of the delivery composition in forming a delivery system and the subsequent release of the bioactive agent is as described in u . s . 20030049320 a1 , au 0222505 a5 and wo 02 / 49573 a3 to bhagwatwar et al . and are all incorporated herein by reference . the term “ parenterally ” as used herein is intended to include routes such as intramuscular , intravenous , subcutaneous , subdermal , intralesional , intratumoral , intracavitary , peritumoral , intraarticular , vaginal , intraperitoneal , intraabdominal , intrathecal , intraorgan and the like or on open wounds , fractures , ulcers , cancerous lesions and the like and is not to be construed as limiting on the scope of the invention . thus , the composition can be used for the immediate or controlled release or both of bioactive agents or bioinactive agents wherever the use of a sterile composition is called for . the following examples describe the invention in further detail and are not to be construed as limiting on the scope of the invention . examples 1 - 5 describe different methods for preparation of sterile sorbitan monostearate . the same methods can be applied to the preparation of other sterile gelling agents including sorbitan monopalmitate . sorbitan monostearate ( sanyo , japan ) was subjected to sterilization by dry heat at a temperature of 180 ° c . for 2 hours . a dark brown colored mass was obtained . the material thus obtained though it would pass the test for sterility renders the final product unacceptable for pharmiaceutical use because of the dark brown color it imparts . preparation of sterile sorbitan monostearate by direct evaporation of the solvent from a solution in a volatile organic solvent sorbitan monostearate ( sanyo , japan ) was dissolved in ethanol ( 50 % w / v ) by heating upto 60 - 65 ° c . in a water bath to form a clear solution . the hot solution was filtered through a 0 . 2 μm nylon 66 ( pall gelman ) sterilizing grade membrane filter under vacuum using a specially fabricated jacketed stainless steel filtration assembly , which was also maintained , at the elevated temperature . the filtrate was dried in a vacuum oven at 40 ° c . and 760 mm vacuum for 48 hours . the dried material was crushed and stored in a sterile container free from moisture . preparation of sterile sorbitan monostearate by dissolving in a hot volatile water - miscible solvent and precipitating by mixing with the same solvent which is cold sorbitan monostearate ( sanyo , japan ) was dissolved in ethanol ( 50 % w / v ) by heating upto 60 - 65 ° c . in a water bath to form a clear solution . the hot solution was filtered through a 0 . 2 μm nylon 66 ( pall gelman ) sterilizing grade membrane filter under vacuum using a specially fabricated jacketed stainless steel filtration assembly , which was also maintained , at the elevated temperature . the filtered solution was kept at 37 ° c . for 60minutes and was then slowly added into cold , sterile , particulate free ethanol at 2 - 8 ° c . the sorbitan monostearate precipitated as a fine powder at the bottom of the beaker . the precipitated sorbitan monostearate was collected and dried . preparation of sterile sorbitan monostearate by dissolving in a volatile water - miscible organic solvent and precipitating from a non - solvent sorbitan monostearate ( sanyo , japan ) was dissolved in ethanol ( 50 % w / v ) by heating upto 60 - 65 ° c . in a water bath to form a clear solution . the hot solution was filtered through a 0 . 2 μm nylon 66 ( pall gelman ) sterilizing grade membrane filter under vacuum using a specially fabricated jacketed stainless steel filtration assembly that was also maintained at the elevated temperature . the sorbitan monostearate was precipitated by drop - wise addition of the filtered ethanolic solution into sterile water for injection . the supernatant was decanted off and the precipitated sorbitan monostearate was collected on a filter paper and dried under vacuum at an elevated temperature . the dried material was crushed and stored in a sterile container free from moisture . preparation of sterile sorbitan monostearate by dissolving in a non - volatile water - miscible solvent and precipitating from a non - solvent sorbitan monostearate ( sanyo , japan ) was dissolved in dma ( fluka ) by heating upto 60 - 65 ° c . in a water bath to form a clear solution . this solution was slowly added into sterile water for injection to cause precipitation of sorbitan monostearate , which was collected and dried . sorbitan monostearate prepared in example 1 was exposed to gamma irradiation at a dose of 25 kgy using a 60 cobalt source at a contract irradiation laboratory . a dose of 25 kgy is accepted internationally to be sufficient to ensure sterility ( british pharmacopoeia ). there was no change in appearance of the gelling agent . these examples demonstrate that sterile sorbitan monostearate can be prepared by these techniques without any change in properties . the same techniques may be used to prepare sterile sorbitan monopalmitate . the further examples describe the use of the sterile sorbitan monostearate in the preparation of the gelled polymeric dispersions .
this invention is directed to sterile gelling agents , which retain their physico - chemical properties so that they can be used in drug delivery systems . also described are the processes for obtaining a sterile gelling agent .