in accordance with this invention , dithranol is applied topically to the skin in a water and oil nanoemulsion which contains a plurality of bilayer vesicles dispersed therein with the vesicles having a particle size of no greater than 450 nm . these bilayer vesicles are formed with one layer being a lipid phase and the other being an aqueous phase with the lipid phase containing dithranol solubilized in a non - ionic oily liquid lipid material which forms the lipid phase . in accordance with this invention , the composition can contain either dithranol or a mixture of dithranol with salicylic acid solubilized in the lipid phase . in accordance with this invention either dithranol alone or with salicylic acid can form the active ingredient in the topical treatment of dermatological diseases such as psoriasis , etc . in accordance with this invention , the dithranol present in the system in concentrations as high as 1 . 0 % by weight of said composition can be completely solubilized in this composition . in general , these compositions contain dithranol in an amount ranging from about 0 . 1 % to about 1 % by weight based upon the weight of the composition . if it is desired to incorporate salicylic acid in the composition , the salicylic acid is present in combination with dithranol in an amount of from about 0 . 1 % to about 3 % by weight based upon the weight of the composition and preferably from about 0 . 5 % to about 1 . 5 % by weight based upon the weight of said composition . if salicylic acid is present in combination with dithranol , this combination is entrapped in the lipid phase of the bilayer vesicles within the nanoemulsion . solublization is important since dithranol is insoluble in water and sparingly soluble in hydrocarbon bases , vegetable oils and esters of fatty acids ; limiting its concentration below 0 . 1 % in soluble form . it has been very difficult to formulate preparations containing dithranol above 0 . 1 % w / w concentration in soluble form . surprisingly , it has been found that dithranol and combinations of dithranol and salicylic acid can be solubilized in non - ionic liquid lipid materials such as tocopherol acetate ( vitamin e acetate ) which can be used as a vehicle to keep the dithranol in solution in stable form even at high concentrations . in accordance with the present invention it is discovered that by using a non - ionic oily liquid lipid material which acts as a solubilizer for dithranol , such as α - tocopherol acetate , the dithranol and combinations of dithranol and salicylic acid will be kept in solution entrapped in the vesicles in this oily lipid material which forms the oily phase in both the nanoemulsion and the bilayer vesicles . any conventional in non - ionic liquid lipid materials , suitable for topical administration , which will solubilize dithranol , can be utilized in formulating the oily lipid phases of this system . among the preferred non - ionic oily liquid lipid materials are included tocopherol acetate and arlamol e ® ( polyoxypropylene - 15 - stearyl ether ) or mixtures thereof with tocopherol acetate being especially preferred . in formulating the system of this invention , the non - ionic oily liquid lipid material can be generally present in an amount of from about 3 % to 40 % by weight based upon the weight of the composition , with amounts of from about 5 % to 30 % by weight based upon the weight of the composition being especially preferred . the system of this invention achieves enhanced encapsulation of dithranol in solubilized state . furthermore the composition of the invention surprisingly has been found to be free of undesirable side effects , and provides excellent therapeutic effects in psoriasis , eczemas , dermatophytoses , alopecia areata and other skin disorders when it is administered topically . in clinical tests it has been found that the system of this invention due to the presence of micro - emulsion with mixed vesicles provides effective delivery of dithranol . these advantages are in some part due to — it is known that any active ingredient / drug present in solution form diffuses rapidly through the skin as compared to solid dispersed particulate drug . it is an object of the invention to make pharmaceutical compositions containing dithranol in soluble form even at higher drug concentrations so as to make it more effective , where by the active ingredient can penetrate into and through the skin so that the active ingredients are provided continuously and in sufficient quantity at the site of action . in accordance with this invention , the composition topical administration is in the form of a homogeneous mixture of an oral water nanoemulsion that constitutes an oil lipid phase and an aqueous phase . it can be either an oil in water or water in oil emulsion in which spherical hollow bilayer vesicles like liposomes are present in the single system wherein the dithranol or the dithranol in combination with salicylic acid is present in both the oil globules of the emulsion and in the oil or lipid phase of the bilayer vesicles in a soluble state . generally , it is preferred that the composition of this invention be a homogeneous mixture of an oil in water nanoemulsion . with the oil lipid phase which is emulsified in the aqueous phase being present in an amount of from 8 % to 50 % by weight of the composition , preferable from about 5 % to about 40 % by weight of the composition . the above mixed vesicular system of this invention which is present as a liquid , if desired , can be thickened to form a gel or cream . this can be done by adding a gelling agent which are thickening agents or viscosity modifying agent to the liquid system . any conventional gelling agent can be utilized to convert the liquid emulsion of this invention into a cream or gel . among the preferred gelling agents are included xanthan gum , ethylene oxide , carbopol , hydroxypropyl , methyl or cellulose . the amount of gelling agent to be added to the composition depends upon the ultimate viscosity of the gel or cream that is desired . in accordance with one embodiment of this invention when salicylic acid is used in combination with dithranol the salicylic acid is also retained in soluble form along dithranol in the mixed vesicular system mimicking niosomes and liposomes . it is also known in the art that pharmaceutical compositions containing dithranol are more effective in combination with salicylic acid and alcoholic extract of coal tar for the treatment of psoriasis . however such preparations are reported have some percentage of alcohol content which may be intensifying the irritation potential to the skin . in addition , if it is desired to further reduce any possible additional irritating effect of alcohol on the skin of the topical composition of this invention one can vacuum dry the alcoholic extract of coal tar and add it to the composition this invention . this vacuum dried coal tar extract is in the form of viscous slurry . generally in accordance with a preferred embodiment of this invention the coal tar extract is added in an amount of from about 0 . 1 % to about 6 . 0 %, by weight based the weight of the composition with amounts of from about 0 . 25 % to about 2 . 0 % by weight being especially preferred . it is known in the art that dithranol is very sensitive to oxidative degradation and a variety of known antioxidants such as butylated hydroxyanisole , butylated hydroxytoulene , ascorbic acid , citric acid , oxalic acid , tartaric acid , succinic acid etc . can be present in the preferred compostion of this invention in the present invention , it is preferred to use antioxidants such as bha and bht in combination with ascorbic acid to prevent oxidative degradation of dithranol . in one embodiment of the present invention dithranol alone or in combination with salicylic acid are dissolved in a mixture of tocopherol acetate and arlamol e ® ( polyoxypropylene - 15 - stearyl ether ) containing nonionic surfactant and cholesterol . thus the oily phase formed was homogenized with aqueous phase . it is known that any active ingredient / drug present in solution form diffuses rapidly through the skin as compared to solid dispersed particulate drug . in accordance with this invention topical pharmaceutical compositions are prepared containing dithranol in soluble form even at higher drug concentrations so as to make it more effective . in tis manner the active ingredients can penetrate into and through the skin so that they are provided continuously and in sufficient quantity at the site of action . the oil phase may contain lecithin ( phosphotidyl choline ) or other synthetic , semisynthetic lecithins alone or in combination such as hydrogenated phosphatidylchloine , phosphatidylethanolamine , dipalmatoyl phosphatidylchohne ( dppc ), dipalmatoyl phosphatidylethanohnine ( dppe ) distearoyl phosphatidylcholine ( dspc ), distearoyl phosphatidylethanolamine ( dspe ), dioleylphosphatidylchohne ( dopc ), dioleylphosphatidylethanolamine ( dope ), phosphatidic acid ( pa ), phosphatidylserine ( ps ), phosphatidylglycerol ( pg ) and their hydrogenated analogs . the preferred carrier for dithranol or dithranol with salicylic acid in accordance with the present invention is tocopherol acetate or mixture of tocopherol acetate . the concentration of tocopherol acetate in the system used for dissolution of dithranol may range from about 5 % to about 40 % by weight based on the weight of the total composition . the preferred concentration range , however , is from about 3 % to about 30 %. the concentration of arlamol e ® ( polyoxypropylene - 15 - stearyl ether ) may range from about 1 % to about 10 % by volume , based upon the volume of the total composition . the preferred concentration range , however , is from about 3 % to about 7 %. in the present invention non - ionic surfactant refers to fatty acid esters and ethers of triglycerides , diglycerides or monoglycerides having hlb value in the range of 4 to 16 preferably between 8 to 14 . the examples of non - ionic surfactant refers to but not limited to polyoxyl 60 hydrogenated castor oil ( cremophore ® rh - 60 ), polyoxyl 35 hydrogenated castor oil ( cremophore ® el ), polyoxyl 40 hydrogenated castor oil ( cremophore ® rh - 40 ), sorbitan monooleate ( span - 80 ), polyoxyehtylene 20 sorbitan monooleate ( tween - 80 ), span 20 , polyglyceryl - 3 - oleate ( plurol olique ®) peg - 32 glyceryl stearate ( gelucire53 / 10 ). the concentration of non - ionic surfactant may range from about 0 . 5 % to about 5 % by volume based upon the volume of the total composition . the preferred concentration range however is from about 0 . 75 % to about 3 % by volume . the concentration of cholesterol may range from about 0 . 1 to about 2 % by volume of the composition , preferably from about 0 . 5 to about 1 . 5 %. the lecithin may be present in the mixed vesicular system and the concentration may range from 0 . 2 to 10 % by volume of the total composition , preferably from about 1 % to about 6 %. in accordance with the embodiment of this invention other commonly used additives known in the art such as antioxidants , chelating agent may be present . antioxidants which can be included in accordance with an embodiment of this invention are combinations of butylated hydroxyanisole , butylated hydroxytoulene and ascorbic acid chelating agents includes disodium edta . the concentration of antioxidants and chelating agent may range from about 0 . 01 % to about 0 . 5 % by volume of the total composition , preferably about 0 . 1 % to about 0 . 5 % by volume . the particle size of the mixed vesicular system obtained by present invention is no greater than 450 nm . accordingly , another embodiment of the present invention , the mixed vesicular system is preferably gelled . among the gelling agents which can be used , cellulose derivatives such as hydroxypropyl methyl cellulose , carbopol , xanthan gum and other hydrophilic polymer such as polyethylene oxide . depending upon the desired viscose , the gelling agent may be generally added in amounts from about 0 . 1 % to about 5 % by weight based upon the weight of the composition , preferably 0 . 5 to about 3 % by weight . concentration of dithranol in the mixed vesicular system according to an embodiment of the present invention may range from 0 . 01 to about 1 . 0 % by weight in soluble form . concentration of salicylic acid in the mixed vesicular system according to an embodiment of the present invention may range from about 0 . 1 % to about 3 . 0 % in soluble form , preferably from about 0 . 5 % to 1 . 5 % by weight . the vacuum dried coal tar extract according to the present invention can be prepared by first dispersing and soaking the coal tar viscous mass in the alcoholic solution of polyoxyethylene 20 sorbitan monolaurate ( tween - 80 ) for 7 days . the extract is then filtered and alcohol is removed form the filtrate by vacuum evaporation at 35 ° c . temperature in rotary vacuum evaporator to get vacuum dried coal tar extract . concentration of vacuum dried coal tar extract in the mixed vesicular system according to the present invention may range from about 0 . 01 % to about 6 . 0 % by weight based upon the weight of the composition , preferably from about 0 . 25 % to about 2 % by weight . this invention is directed to the process for preparing an oil and water nanoemulsion with an oil and water phase wherein the nanoemulsion has dispersed therein a plurality of bilayer vesicles retaining dithranol alone or in combination with salicylic acid solubilized in the oily layers of the vesicles . in accordance with this invention , the nanoemulsion is carried out providing a solution of dithranol dissolved in the non - ionic oily liquid lipid material as well as a separate aqueous medium which may contain such excipients as stabilizers , anti - oxidants , etc . dissolved therein . the aqueous medium and the oily solution are mixed together and then homogenized to form a homogeneous emulsion which contains the oily phase and the aqueous phase . any conventional homogenizer may be used to homogenize this emulsion mixture . this emulsion is next subjected to high pressure homogenization at pressures from about 20 , 000 psi to about 30 , 000 psi . in the final step , the homogeneous mixture after being subjected to high pressure homogenization is passed through a 0 . 45 nm membrane . in this manner , the oil and water nanoemulsion is produced . the oily non - ionic lipid medium such as α - tocopherol acetate prior to mixing with the aqueous phase contains dithranol or dithranol in combination with salicylic acid solubilized in said lipid phase which preferably contains α - tocopherol acetate along with other non - ionic lipids . this homogenized mixture is then passed through high pressure homogenizer at 20 , 000 to 30 , 000 psi pressure followed by passing through 0 . 45 μm membrane . the resulting system was found to be mixed vesicular system comprising nanoemulsion with vesicles formed by combination of tocopherol acetate , nonionic surfactant , cholesterol and lecithin , encapsulating the dithranol alone or in combination with salicylic acid in soluble form . in the present invention , the oil phase composition is such that after emulsification and high pressure homogenization it forms an oil in water emulsion along with in situ formation of bilayer vesicles composed of the non - ionic oily liquid lipid material such as α - tocopherol acetate and other non - ionic surfactants . in accordance with the method of this invention , the bilayer vesicles are formed in situ after the high pressure homogenization step and are not added separately to the system . the composition according to the present invention having 0 . 5 % w / w dithranol , 1 . 15 % w / w salicylic acid and 0 . 58 %, w / w vacuum dried coal tar extract were tested clinically on 12 patients with skin psoriasis and found to as equally effective as compared to conventional dithranol ointment containing 1 . 1 % w / w dithranol , 1 . 15 % w / w salicylic acid & amp ; 5 . 3 % w / w alcoholic extract of coal tar solution . the following non - limiting examples set forth herein below illustrate the invention : example 1 part a : dithranol - 0 . 5 % w / w salicylic acid - 1 . 15 w / w α - tocopherol acetate - 15 % w / w polyoxypropylene - 15 - stearyl ether - 5 % w / w ( arlamol ®- e ) oleic acid - 0 . 5 % w / w butylated hydroxy anisole - 0 . 1 % w / w butylated hydroxy toluene - 0 . 1 % w / w cholesterol - 0 . 5 % w / w polyoxyl 40 hydrogenated castor oil - 1 . 0 % w / w egg lecithin ( lipoid ® e - 80 s )- 3 . 0 % w / w ethanol - 0 . 75 % w / w part b : glycerin - 5 . 0 % w / w disodium edta - 0 . 1 % w / w ascorbic acid - 0 . 5 % w / w demineralised water - 51 . 0 % w / w part c : xanthan gum - 2 . 0 % w / w methyl paraben - 0 . 1 % w / w propyl paraben - 0 . 02 % w / w sodium hydroxide - 0 . 06 % w / w demineralised water - 13 . 0 % w / w part d : 0 . 58 % w / w coal tar extract ( vacuum drier )- heat part a to 50 ° c . under nitrogen gas flushing and mix to get homogenous solution . then cool to room temperature . add part a into part b with homogenization . then transfer the mixture to high pressure homogenizer ( apv gaulin lab 40 ) and homogenize it for 10 - 12 passes at 30 , 000 psi pressure . the resulting dispersion is passed through 0 . 45 μm membrane to obtain the mixed vesicular system with average particle size less than 450 nm . part c , xanthan gum gel is prepared separately by hydrating xanthan gum in demineralised water containing parabens at 80 - 90 ° c . temperature and allow to cool and soak at room temperature . then add above homogenized mixed vesicular system and mix to get the gel consistency . finally add coal tar exact slurry ( vacuum dried ) and mix thoroughly to get the final composition . the mixed vesicular composition of example 1 was filled in collapsible tubes and kept at accelerated temperature conditions , 25 ° c ., 37 ° c . and 45 ° c . for 6 months . samples were periodically analyses for dithranol and salicyclic acid content by hplc analysis . the results are tabulated the following table . storage dithranol content % salicylic acid content % period temperature by weight by weight initial — 0 . 518 1 . 159 1 month 25 ° c . 0 . 521 1 . 159 37 ° c . 0 . 518 1 . 158 45 ° c . 0 . 517 1 . 156 3 month 25 ° c . 0 . 511 1 . 156 37 ° c . 0 . 509 1 . 153 45 ° c . 0 . 507 1 . 1516 6 month 25 ° c . 0 . 508 1 . 155 37 ° c . 0 . 501 1 . 1514 45 ° c . 0 . 494 1 . 148 conclusion the mixed vesicular composition is stable over 6 month even at 37 ° c . and 45 ° c . temperature storage as evidenced by it &# 39 ; s dithanol content and salicylic acid content not reducing drastically as compared to the initial value . example 2 part a : dithranol - 0 . 5 % w / w α - tocopherol acetate - 15 % w / w polyoxypropylene - 15 stearyl ether - 5 % w / w ( arlamol ®- e ) oleic acid - 0 . 5 % w / w butylated hydroxy anisole - 0 . 1 % w / w butylated hydroxy toluene - 0 . 1 % w / w cholesterol - 0 . 25 % w / w polyoxyl 40 hydrogenated castor oil - 1 . 0 % w / w egg lecithin ( lipoid ® e - 80 5 )- 3 . 0 % w / w ethanol - 0 . 75 % w / w part b : glycerin - 5 . 0 % w / w disodium edta - 0 . 1 % w / w ascorbic acid - 0 . 5 % w / w demineralised water - 51 . 58 % w / w part c : xanthan gum - 2 . 0 % w / w methyl paraben - 0 . 1 % w / w propyl paraben - 0 . 02 % w / w sodium hydroxide - 0 . 06 % w / w demineralised water - 13 . 0 % w / w heat part a to 50 ° c . under nitrogen gas flushing and mix to get homogenous solution . then cool to room temperature . add part a into part b with homogenization . then transfer the mixture to high pressure homogenizer ( apv gaulin lab 40 ) and homogenize it for 10 - 12 passes at 30 , 000 psi pressure . the resulting dispersion is passed through 0 . 45 μm membrane to obtain the mixed vesicular system with average particle size less than 450 nm . part c , xanthan gum gel is prepared separately by hydrating xanthan gum in demineralised water containing parabens at 80 - 90 ° c . temperature and allow to cool and soak at room temperature . then add above homogenized mixed vesicular system and mix to get the gel consistency . therapeutic composition similar to that described in example 1 , except α - tocopherol acetate was increased form 15 % to 20 % by weight and polyoxypropylne - 15 - stearyl ether ( arlamol ®- e ) was omitted . therapeutic composition similar to that described in example 1 , except 3 . 0 % w / w egg lecithin ( lipoid e 80 s ) was replaced by soya lecithin ( lipoid ® s75 ). therapeutic composition similar to that described in example 1 , except 3 . 0 % w / w egg lecithin ( lipoid e 80 s ) was replaced by dipalmitoyl phosphatidylcholine ( dppc ). therapeutic composition similar to that described in example 1 , except 1 . 0 % w / w polyoxyl - 40 hydrogenated castor oil was replaced by 1 . 0 % w / w / polysorbate 80 . therapeutic composition similar to that described in example 1 , except 1 . 0 % w / w polyoxyl - 40 hydrogenated castor oil was replaced by 1 . 0 % w / w span 20 ( sarbitan monolaurate ). therapeutic composition similar to that of example 1 , except 1 . 0 % w / w polyoxyl - 40 - castor oil was replaced by 1 . 0 % w / w polyglyceryl - 3 - oleate ( plurol olique ®) therapeutic composition similar to that of example 1 , except 0 . 5 % w / w dithranol was substituted by 0 . 1 % w / w dithranol and a - tocopherol acetate reduced from 15 % w / w to 10 % w / w . therapeutic composition similar to that of example 1 , except 0 . 5 % w / w dithranol was substituted by 1 . 0 % w / w dithranol . dithranol - 1 . 15 % w / w salicylic acid - 1 . 15 % w / w solution of coal tar ( alcoholic )- 5 . 3 % w / w maize starch - 12 % w / w white soft paraffin - q . s . 100 % dithranol and maize starch were finely dispersed in melted white soft paraffin at 65 - 70 ° c . temperature and cooled to room temperature with mixing . salicylic acid was dissolved in coal tar solution and added to dithranol paraffin mixture & amp ; mixed thoroughly to get ointment consistency . therapeutic compositions as described in example 1 , 2 , and 11 were tested clinically and comparison is being made . clinical test protocol was followed as described by van scott , eugene j . et al . in u . s . pat . no . 4287214 . skin involves in psoriasis is hyperplastic ( thickened ), erythematous ( red or inflamed ) and has thick adherent scales . the degree of thickening is such that lesion are elevated up to 1 mm above the surface & amp ; adjacent normal skin ; erythema is usually an intense red ; the thickened adherent scales cause the surface of involved skin to be marked by rough & amp ; uneven . these three attributes of thickness , colour & amp ; texture as described in u . s . pat . no . 4287214 were quantified to allow comparative measurement of degree of improvement from topically applied therapeutic compositions — therapeutic composition of the present invention ( example 1 & amp ; example 2 ) and conventional dithranol ointment ( example 11 ). none mid moderate substantial complete ( 0 ) ( 1 +) ( 2 +) ( 3 +) ( 4 +) thickness highly detectable readily barely normal elevated reduction apparent elevated thickness texture visibly palpably uneven slightly visibly and rough rough but not uneven palpably rough smooth colour intense red dark pink light pink normal skin red colour in order to ascertain whether the dithranol compositions of the present invention ( example 1 & amp ; example 2 ) are therapeutically more efficacious than conventional dithranol ointment ( example 11 ) for topical treatment of psoriasis , a total of more than 12 patients having psoriasis were tested in this study . the treatment areas in patients having psoriasis were localized lesions 8 - 20 cm in diameter . the therapeutic compositions were topically applied by the patient in an amount sufficient to cover the treatment . applications were made two - three times daily and without occlusive dressing . clinical evaluation of degree of improvement were made of weekly interval . the treatment was continued for 4 weeks unless clearing of disease occurred earlier & amp ; evaluation of degree improvement was made . the treatment results are summarized as follows . [ 0071 ] table 2 : staining and irritation effect of topically applied composition of skin dithranol concentration irritation staining example 1 0 . 5 %° w / w no irritation no staining example 2 0 . 5 % w / w no irritation no staining example 11 1 . 1 % w / w high irritation staining of cloth observed , sometimes and skin required for the observed removal from applied skin therapeutic compositions of the present invention were found to be nonirritating , non - staining and therapeutically more effective even at low dithranol concentration ( 0 . 5 % w / w ) as compared to conventional dithranol ointment containing 1 . 1 % w / w dithranol . shyamala , c . ; jayaraman , c . ; topical delivery of erythromycin form various formulations : an in vivo hairless mouse study ; j . pharm . sci . ; vol . 85 ; n . 10 ; october 1996 , 1082 - 84 .
mixed vesicular system containing a nanoemulsion with bilayer nanovesicles mimicking noisome and liposome for the topical delivery of dithranol alone or together with salicylic acid to treat psoriasis , eczemas , dermatophytoses , alopecia areata and other dermatological diseases and methods for producing said system .