nonionic surfactants are added to the ophthalmic solution according to the invention for their solubilizing effect and to prevent the absorption of pgf2α analogues to the resinous walls of the container . examples of nonionic surfactants are polyoxyethylene fatty esters such as polysorbate 80 [ poly ( oxyethylene ) sorbitan monooleate ], polysorbate 60 [ poly ( oxyethylene ) sorbitan monostearate ], polysorbate 40 [ poly ( oxyethylene ) sorbitan monopalmitate ], poly ( oxyethylene ) sorbitan monolaurate , poly ( oxyethylene ) sorbitan trioleate and polysorbate 65 [ poly ( oxyethylene ) sorbitan tristearate ], polyoxyethylene hydrogenated castor oils such as polyoxyethylene hydrogenated castor oil 10 , polyoxyethylene hydrogenated castor oil 40 , polyoxyethylene hydrogenated castor oil 50 and polyoxyethylene hydrogenated castor oil 60 , polyoxyethylene polyoxypropylene glycols such as polyoxyethylene ( 160 ) polyoxypropylene ( 30 ) glycol [ pluronic f68 ], polyoxyethylene ( 42 ) polyoxypropy lene ( 67 ) glycol [ pluronic p123 ], polyoxyethylene ( 54 ) polyoxypropylene ( 39 ) glycol [ pluronic p85 ], polyoxyethylene ( 196 ) polyoxypropylene ( 67 ) glycol [ pluronic f127 ] and polyoxyethylene ( 20 ) polyoxypropylene ( 20 ) glycol [ pluronic l - 44 ], polyoxyl 40 stearate and sucrose fatty esters . the nonionic surfactants can be used solely or in combination . a preferred example of the nonionic surfactants is polysorbate 80 [ poly ( oxyethylene ) sorbitan monooleate ]. other preferred nonionic surfactants are polyoxyethylene hydrogenated castor oil 60 and polyoxyl 40 stearate . the amount of nonionic surfactant ( s ) in the ophthalmic solution according to the invention can be chosen depending on the amount and type of prostaglandin analogue and the specific surfactant ( s ) and is within the skill of a person in the art . for pol ysorbate 80 , the concentration is for example in the range of 0 . 05 to 0 . 5 % ( w / v ), even more preferably 0 . 05 to 0 . 1 %, and most preferably about 0 . 075 %. it has also been found by the present inventors that a too high concentration of the nonionic surfactant has an irritative effect on the corneal epithelium layer and an adverse effect on the bioavailability of prostaglandin from the ophthalmic solution . for example in the case of tafluprost an upper limit of 0 . 5 % of the nonionic surfactant polysorbate 80 is possible . the ophthalmic solution according to the invention also contains stabilizing agents to inhibit decomposition of pgf2α analogues in the ophthalmic solution . preferred examples of stabilizing agents are ethylenediaminetetraacetic acid and salts thereof , such as disodium edetate , and dibutylhydroxytoluene . also other stabilizing agents , such as sodium nitrite , ascorbic acid , l - ascorbic acid stearate , sodium hydrogensulfite , alphathioglycerin , erythorbic acid , cysteine hydrochloride , citric acid , tocopherol acetate , potassium dichloroisocyanurate , 2 , 6 - di - t - butyl - 4 - methylphenol , soybean lecithin , sodium thioglycollate , sodium thiomalate , natural vitamin e , tocopherol , asco rbyl pasthyminate , sodium pyrosulfite , butylhydroxyanisole , 1 , 3 - butylene glycol , pentaerythtyl tetrakis [ 3 -( 3 , 5 - di - t - butyl - 4 - hydroxyphenyl )] propionate , propyl gallate , 2 - mercaptobenzimidazole and oxyquinoline sulphate , may be used . the amount of stabilizing agents in the ophthalmic solution according to the inve ntion can be selected depending on the specific stabilizing agent and is within the skill of a person in the art . for example , when the stabilizing agent is disodium edetate , the concentration is usually 0 . 005 to 0 . 2 % ( w / v ), preferably 0 . 01 to 0 . 1 %, even more preferably about 0 . 05 %. a preferred pgf2α analogue for use in the ophthalmic aqueous solution according to the invention is tafluprost . however , all of the known pgf2α analogues , especially other omega chain phenyl ring - substituted pgf2α analogues such as latanoprost , travoprost and bimatoprost or a mixture of two or more prostaglandins may also be used . alternative drugs for use in the ophthalmic aqueous solution according to the invention are other prostaglandins and their derivatives such as prostaglandin e and its analogues ( see u . s . pat . no . 6 , 344 , 477 and references therein ). combinations of pro staglandins or analogues and other eye drugs , for example β - blocking agents such as timolol , are also possible . the amount of pgf2α analogues in the ophthalmic solution according to the invention can be selected depending on the specific prostaglandin in question , on the diseases to be treated and their symptoms . for tafluprost , an amount of for example 0 . 0001 to 0 . 01 %, preferably about 0 . 0005 to 0 . 0025 %, even more preferably 0 . 0010 to 0 . 0025 % ( w / v ) is regarded to be sufficient . preferable concentrations of other pgf2α analogues for treating glaucoma are 0 . 001 to 0 . 004 % for travoprost , approximately 0 . 005 % for latanoprost , about 0 . 03 % for bimatoprost and about 0 . 15 % for unoprostone . the ophthalmic solution according to the invention may also comprise conventional excipients used in ophthalmic compositions , such as buffering agents , solvents , ph adjusters , tonicity agents and the like . examples of suitable buffering agents include but are not limited to sodium dihydrogen phosphate dihydrate , boric acid , borax , citric acid , or ε - aminocaproic acid . specific examples of tonicity agents include but are not limited to glycerol , sorbitol , mannitol and other sugar alcohols , propylene glycol , sodium chloride , potassium chloride and calcium chloride . the ph of the ophthalmic aqueous solution according to the invention is preferably from 4 to 8 , more prefer ably from 5 to 7 . as ph adjusters , common ph adjusting agents such as sodium hydroxide and / or hydrochloric acid may be used . the material of the resinous container consists essentially of polyethylene . the container material may contain minor amounts of other materials than polyethylene , for example polypropylene , polyethylene terephthalate , polyvinyl chloride , acrylic resins , polystyrene , polymethyl methacrylate and nylon 6 . the amount of said materials is preferably no more than about 5 to 10 % of the total co ntainer material . polyethylene is classified to several types by the density thereof , namely low density polyethylene ( ldpe ), middle density polyethylene ( mdpe ), high density polyethylene ( hdpe ), etc and these polyethylenes are included in this invention . preferable polyethylene is ldpe . containers for packaging and storing the aqueous ophthalmic solution according to the invention include all container forms suitable for user - friendly topical ophthalmic delivery . consequently , the containers may be selected for example from the group consisting of bottles , tubes , ampoules , pipettes and fluid dispensers , in single unit dose form or in multidose form . according to a preferred embodiment of the invention , the aqueous ophthalmic solution is in a single dose or unit dose form . the containers for the ophthalmic solution according to the invention are preferably manufactured by extrusion blow moulding method . extrusion blow moulding gives smoother inner surface of the container compared to injection blow moulding , which is commonly used to manufacture for example polyethylene multidose bottles . the smoother inner surface gives better chemical stability of prostaglandins in the polyethylene container compared to polyethylene container manufactured by injection blow moulding . furthermore , when single - dose containers are used , they are sterilized during the moulding process by heat and no additional sterilization of containers is needed , which also improves stability of prostaglandins in a single - dose container ( see ep 1 825 855 and ep 1 349 580 ). generally , a unit dose ophthalmic container manufactured by blow moulding method has a volume of about 1 ml and about 0 . 2 to 0 . 5 ml of solution is filled . a large variety of shapes are known in such containers . typical examples are seen in u . s . pat . no . 5 , 409 , 125 and u . s . pat . no . 6 , 241 , 124 . although unit dose containers are preferred for the purposes of the invention , the aqueous ophthalmic solution according to the invention remains soluble , stable and bioavailable also in fluid dispensers for dispensing of minute amounts of germ - free fluid or in any other container - type wherein the aqueous ophthalmic solution is in contact with container material consisting essentially of polyethylene . such fluid dispensers are disclosed for example in u . s . pat . no . 5 , 614 , 172 . the preservative - free aqueous ophthalmic solution according to the invention can be stored at room temperature in the above mentioned suitable containers , including unit dose pipettes and dispensers . stability studies have shown that a preservative - free aqueous ophthalmic tafluprost solution according to the invention is stable in a polyethylene container for a long time , at least for 12 months at 25 ° c . and at least for 30 months at 5 ° c . a preferred embodiment according to the invention is an aqueous ophthalmic solution for treating ocular hypertension and glaucoma , which comprises optionally buffering agents , ph adjusters and tonicity agents conventionally used in ophthalmic solutions , in a container consisting essentially of polyethylene . the following examples illustrate the invention without limiting the same any way . the effect of nonionic surfactant on the absorption of preservative - free tafluprost to low density polyethylene containers was studied for 20 weeks at 5 ° c ., 25 ° c . and 40 ° c . three different polysorbate 80 ( tween 80 ) concentrations , namely 0 . 05 %, 0 . 075 % and 0 . 1 % were used . the composition of the preservative - free aqueous tafluprost formulation except polysorbate 80 was 0 . 0015 % tafluprost , 2 . 25 % glycerol , 0 . 2 % sodium dihydrogen phosphate dihydrate , 0 . 05 % disodium edetate and sodium hydroxide and / or hydrochloric acid to adjust the ph to 5 . 0 - 6 . 7 . 0 . 3 ml of the composition prepared above was filled in the body part of the unit dose container ( ldpe ) and sealed by heating with the upper part of the container ( ldpe ). the inner volume of the unit dose container was ca . 1 ml . the container was packaged into paper coated aluminium - polyethylene foil and stored in refrigerator or incubator . the remaining concentration of tafluprost was measured by hplc . the results are shown in fig1 - 3 . the results show that the concentration of polysorbate has an influence to the absorption of tafluprost to polyethylene . polysorbate ( 0 . 05 to 0 . 1 %) inhibits the absorption of tafluprost , especially even at an elevated temperature ( 40 ° c .). an amount of 0 . 075 to 0 . 1 % of polysorbate shows good inhibition effect of absorption of tafluprost . the concentration of free acid of tafluprost in rabbit aqueous humor after a single instillation of 1 ) preserved 0 . 0015 % tafluprost ophthalmic solution containing 0 . 01 % bak and 0 . 05 % polysorbate 80 , or 2 ) non - preserved 0 . 0015 % tafluprost ophthalmic solution containing 0 . 20 % polysorbate 80 , or the concentrations of ingredients except polysorbate 80 in non - preserved solutions were the following : 2 . 25 % glycerol , 0 . 2 % sodium dihydrogen phosphate dihydrate , 0 . 05 % disodium edetate and sodium hydroxide and / or hydrochloric acid to adjust the ph to 5 . 0 - 6 . 7 . rabbits received the ophthalmic solutions described above . the rabbits were sacrificed at each time point ( 4 animals per treatment per time point ) and aqu eous humor sample was taken . the concentration of tafluprost acid form was measured using the validated lc - ms / ms method . the results ( n = 8 for each test solution per time point ) are shown in fig4 . from the results it can be seen that the amount of nonionic surfactant has an effect on ocular bioavailability . when the amount of the nonionic surfactant exceeds a certain limit , penetration of the active agent to the aqu eous humor starts to decrease . thus the amount of the nonionic surfactant has to be balanced , on one hand to minimize the absorption of pgf2α analogue to the container walls and , on the other hand , to maximize ocular bioavailability .
the present invention relates to an ophthalmic aqueous composition containing pgf2α analogues for treating ocular hypertension and glaucoma , to a method for treating ocular hypertension and glaucoma by administering said composition to a subject in need of such treatment , and to a method for increasing aqueous solubility and stability of pgf2α analogues in an aqueous composition .