unexpectedly , we have found that the difficulties experienced by others in formulating loratadine are overcome by the present invention , which delivers loratadine in an aqueous ophthalmic emulsion composition . in the present invention , the loratadine is dissolved in the oil phase of an oil - in - water emulsion system . this confers three main advantages to this invention over previous topical ophthalmic loratadine products . these advantages are higher drug absorption , minimal decomposition of loratadine by hydrolysis , and lubrication and improved comfort to the eye . we have found that the solubility of loratadine in vegetable oils is great enough to formulate an effective amount of the agent into an ophthalmic emulsion formulation ( see table 1 ) to be used for allergic conjunctivitis and related conditions . the solubility of loratadine in vegetable oils is comparable to or better than its solubility in a surfactant . in particular , castor oil dissolves more than three times as much loratadine as polysorbate 80 , a commonly used surfactant in ophthalmic solutions . by contrast to the irritation to the eye caused by the surfactant alone , it has been shown in commonly assigned u . s . pat . no . 5 , 668 , 133 , incorporated herein by reference , that an emulsion actually provides lubrication and improved comfort to the eye . it has also been shown , in european patent no . 1044678 , that an emulsion of vegetable oil and water delivers a higher concentration of the drug cyclosporin a to the conjunctiva of a rabbit eye than the individual oil . additionally , dissolving the hydrophobic loratadine in the oil phase of an emulsion significantly reduces the contact of the hydrophobic loratadine with water , enabling a formulation to be prepared in the ophthalmically useful ph range of 6 - 8 . this is in contrast with aqueous solutions where the loratadine is readily hydrolyzed in the desired ophthalmic ph range , greatly reducing the activity and the shelf life of the product . the present invention is directed to an ophthalmic formulation which comprises a therapeutically effective amount of loratadine , a fatty acid ester , and a surfactant . in the preferred embodiment of this invention , the fatty acid ester is a vegetable oil . a fatty acid ester has the meaning commonly understood in the art , being an ester formed between an alcohol and a fatty acid . while not intending to limit the scope of this invention , some examples of readily available fatty acid esters are triglyceride esters commonly known as vegetable oils , mono and diglyceride esters of fatty acids , and fatty acid methyl esters . the fatty acid ester may be a mixture of several chemical compounds or an essentially pure compound . preferably , the fatty acid ester is a vegetable oil . examples of vegetable oils include castor oil , sesame oil , soybean oil , cottonseed oil , olive oil , peanut oil , safflower oil , sunflower oil , palm oil , palm kernel oil , canola oil , and miglyol oil . most preferably , the fatty acid ester is castor oil . the determination of a therapeutically effective amount of loratadine used in this formulation can be readily determined by one skilled in the art . preferably , the concentration of loratadine is between about 0 . 01 % and about 1 . 5 %. more preferably , the concentration of loratadine is about 0 . 0125 % or about 0 . 0625 %. the term surfactant used in this invention has the meaning commonly understood in the art . surfactants are used to both help facilitate the formation of the emulsion and improve its stability . anionic , cationic , amphoteric , zwitterionic , and nonionic surfactants may all be used in this invention . preferably , a nonionic surfactant is used in this invention . while not intending to limit the scope of the invention , some examples of useful nonionic surfactants are polysorbates , poloxamers , alcohol ethoxylates , ethylene glycol - propylene glycol block copolymers , fatty acid amides , alkylphenol ethoxylates , and phospholipids . most preferably , polysorbate 80 is used as the surfactant . polysorbate 80 is a mixture of oleate esters of sorbitol and sorbitol anhydrides , consisting predominantly of the monoester , condensed with approximately 20 moles of ethylene oxide . it conforms generally to the formula : where w + x + y + z has an average value of 20 . polysorbate 80 is available from ici americas , inc ., wilmington , del . in another preferred embodiment of this invention , an emulsion stabilizing polymer is used . while not intending to limit the scope of the invention , emulsion stabilizing polymers generally contain hydrophilic groups such as cellulose , sugars , ethylene oxide , hydroxide , carboxylic acids or other polyelectrolytes . while not wishing to limit the scope of the invention by theory , it is believed that these polymers help to stabilize emulsions by increasing the viscosity of the formulation as well as by reducing the interfacial tension . while not intending to limit the scope of the invention , some examples of emulsion stabilizing polymers useful in this invention are carbomers , pemulen ®, sodium carboxymethylcellulose , hydroxypropylmethylcellulose , povidone , polyvinyl alcohol , and polyethylene glycol . in the most preferred embodiment of this invention , pemulen ® is used as the polymeric based stabilizer . pemulen ® is a registered trademark of b . f . goodrich for polymeric emulsifiers and commercially available from b . f . goodrich company , specialty polymers & amp ; chemicals division , cleveland , ohio . pemulens ® are acrylates / c10 - 30 alkyl acrylate cross - polymers . they are high molecular weight co - polymers of acrylic acid and a long chain alkyl methacrylate cross - linked with allyl ethers of pentaerythritol . they contain not less than 52 . 0 percent and not more than 62 . 0 percent of carboxylic acid groups . the viscosity of a neutralized 1 . 0 percent aqueous dispersion is between 9 , 500 and 26 , 500 centipoises . in the preferred embodiment of this invention the weight ratio of castor oil to polysorbate 80 is from about 0 . 3 to about 30 . in a more preferred embodiment of this invention , the weight ratio is from about 0 . 5 to about 12 . 5 . in another preferred embodiment of this invention , a buffering agent is used to maintain the ph in the therapeutically useful range of about 6 - 8 . buffering agents used are those known to those skilled in the art , and , while not intending to be limiting , some examples are acetate , borate , carbonate , citrate , and phosphate buffers . in the most preferred embodiment of this invention , boric acid is the buffering agent . in another preferred embodiment of this invention , a tonicity agent is used to adjust the composition of the formulation to the desired isotonic range . tonicity agents are known to those skilled in the ophthalmic art , and , while not intending to be limiting , some examples include glycerin , mannitol , sorbitol , sodium chloride , and other electrolytes . in the most preferred embodiment of this invention , the tonicity agent is glycerin . in another preferred embodiment of this invention , a preservative is used . preservatives are used to prevent bacterial contamination in multiple - use ophthalmic preparations , and , while not intending to be limiting , examples include benzalkonium chloride , stabilized oxychloro complexes ( otherwise known as purite ®), phenylmercuric acetate , chlorobutanol , benzyl alcohol , parabens , and thimerosal . in the most preferred embodiment of this invention , the preservative is purite ®. in another preferred embodiment of this invention , a chelating agent is used to enhance preservative effectiveness . suitable chelating agents are those known in the art , and , while not intending to be limiting , edetate salts like edetate disodium , edetate calcium disodium , edetate sodium , edetate trisodium , and edetate dipotassium are examples of useful preservatives . the best mode of making and using the present invention are described in the following examples . these examples are given only to provide direction and guidance in how to make and use the invention , and are not intended to limit the scope of the invention in any way . ophthalmic formulations 1 and 2 containing loratadine were formulated with the compositions shown in table 2 . emulsions were prepared according to the method described in u . s . pat . no . 5 , 981 , 607 , incorporated herein by reference , with the loratadine being added to the castor oil before introducing the oil into the emulsion . the physical stability of the example loratadine emulsion formulations was monitored and the results are provided in table 3 . the emulsions were allowed to stand for 5 . 5 months at 20 - 25 ° c ., and the emulsion droplet sizes were measured . the emulsion droplet sizes within experimental error , were identical at 5 . 5 months to those measured right after the emulsions were prepared , suggesting that there was no significant coalescence of the emulsion droplets . additionally , no creaming of the formulations or precipitation of solid loratadine was observed . these results demonstrate that the emulsions prepared in these formulations have superior physical stability . several drops of formulations 1 are administered to the eyes of a patient suffering from allergic conjunctivitis . reduction of the symptoms becomes noticeable within one hour . the treatment is repeated one or more times daily while the condition persists .
the present invention is directed to an ophthalmic formulation which comprises a therapeutically effective amount of ethyl 4 - cycloheptapyridin - 11 - ylidene )- 1 - piperidinecarboxylate , known as loratadine , a fatty acid ester , and a surfactant , which has been found to be useful in treating ocular allergies , especially allergic conjunctivitis , and related conditions .