it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention claimed . as used herein , the use of the singular includes the plural unless specifically stated otherwise . as used herein , “ or ” means “ and / or ” unless stated otherwise . furthermore , use of the term “ including ” as well as other forms , such as “ includes ,” and “ included ,” is not limiting . the section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described . it is to be understood that “ 7 -[ 3 , 5 - dihydroxy - 2 -( 3 - hydroxy - 5 - phenyl - pent - 1 - enyl )- cyclopentyl ]- hept - 5 - enoic acid ” and “ bimatoprost acid ” refer to the same compound and may be used interchangeably throughout . in addition , “ crystalline form ” and “ polymorphic form ” may be used interchangeably throughout the specification . “ crystalline form i ” or “ form i ”, “ crystalline form ii ” or “ form ii ”, “ crystalline form iii ” or “ form iii ” may also be referred to as “ polymorph i ”, “ polymorph ii ”, or “ polymorph iii ”. unless specific definitions are provided , the nomenclatures utilized in connection with , and the laboratory procedures and techniques of analytical chemistry , synthetic organic and inorganic chemistry described herein are those known in the art . standard chemical symbols are used interchangeably with the full names represented by such symbols . thus , for example , the terms “ hydrogen ” and “ h ” are understood to have identical meaning standard techniques may be used for chemical syntheses , chemical analyses , and formulation . bimatoprost acid was manufactured by organic consultants , inc . the purity of the compound per coa was 100 % determined by hplc . fig9 and 10 summarize the crystallization processs . samples isolated from the experiments were immediately analyzed and the same sample was rescanned after overnight vacuum drying at 35 ° c . approximately 3 - 5 mg of the samples were gently pressed on zero background sample holders and subjected to xrpd scan . approximately 2 - 3 mg of the sample was placed in t - zero nonhermetic pan and subjected to mdsc heating ramp . the present invention provides bimatoprost acid in new polymorphic forms , designated as polymorphs i , ii , and iii . physical characterization of bimatoprost acid led to the discovery of these three polymorphs . the results of a polymorph screening study of bimatoprost acid showed that polymorph ii forms when polymorph i is maturated in diethyl ether upon thermo - cycling at 12 - 32 ° c . xrpd patterns of polymorph i , polymorph ii and polymorph iii are presented in fig1 . fig2 shows that the ftir spectra of polymorphs i and ii are identical indicating that they have the same chemical composition . the xrpd and ftir data indicate the two forms are polymorphic and not different chemical entities . polymorph i and polymorph ii have an enantiotropic polymorphic relationship . enantiotropic polymorphs are characterized by a difference in melting points and fusion enthalpies , where the higher melting polymorph has a lower fusion enthalpy . modulated differential calorimetric ( mdsc ) data in fig3 shows that polymorph i has a melting endotherm onset ( t onset ) at 63 . 2 ° c . and a fusion enthalpy ( δh f ) of 65 . 6 j / g as compared to the corresponding properties for polymorph ii ( 62 . 2 ° c . and 81 . 5 j / g , respectively ). the differences in free energy between the polymorphs were measured as a function of temperature in order to determine the transition temperature and relative stability versus temperature . isothermal competitive co - slurries of polymorph i and ii ( 1 : 1 ratio at 5 , 20 and 35 ° c .) showed that polymorph i converts to polymorph ii at all three temperatures , indicating that polymorph ii is the more stable form over the temperature range of 5 - 35 ° c . fig4 shows the thermodynamic equilibrium solubility of the anhydrous polymorphs in anisole at 6 ° c . and 25 ° c . at both temperatures polymorph ii has the lower solubility indicating that polymorph ii is the lower energy form at temperature 6 - 25 ° c . anisole was selected as solvent based on good stability and measurable solubility of bimatoprost acid polymorphs in the studied temperature range . solubility studies could not be performed at temperatures above 40 ° c . in order to determine the enantiotropic polymorph transition temperature because bimatoprost acid transforms to an oil in anisole . another solvent , nitromethane , was selected to detect the solubility of bimatoprost acid at 9 and 22 ° c . at 9 ° c ., the solubility of polymorph i ( 4 . 1 ± 0 . 3 mg / ml ) is significantly higher than the solubility of polymorph ii ( 3 . 3 ± 0 . 2 mg / ml ) which suggests the polymorph ii is more stable than polymorph i at 9 ° c . at 22 ° c ., both forms converted to oils where no comparison between the two polymorphs could be made . the crystalline monohydrate form ( designated polymorph iii ) was discovered upon vapor sorption analysis ( vsa ) of both polymorph i and polymorph ii . fig6 shows that at rh ˜ 75 % polymorph i absorbs 4 . 42 w / w % water , which is equivalent to a stoichiometric monohydrate . the conversion of polymorph i to the monohydrate form was confirmed by xrpd . the generated monohydrate converted beck to the initial polymorph 1 upon drying in vapor sorption analyzer at 25 ° c . vapor sorption analysis also showed that polymorph ii converts to a hydrated form at water activity above 85 % rh . the 2 nd adsorption cycle of polymorph ii reconfirms formation of the monohydrate again at rh ˜ 75 % ( fig7 ). at 25 ° c ., the relative humidity at which polymorph ii forms the monohydrate is greater than that for polymorph i , consistent with the assertion that polymorph ii is the more stable form at 25 ° c . the thermal analysis ( mdsc ) of the monohydrate form indicates a melting endotherm onset ( t onset ) at 53 . 9 ° c . and a fusion enthalpy ( δh f ) of 72 . 4 j / g for the monohydrate form ( see fig8 ). pharmaceutical compositions may be prepared by combining a therapeutically effective amount of polymorphs i , ii , or iii of bimatoprost acid according to the invention , or a pharmaceutically acceptable salt thereof , as an active ingredient , with conventional ophthalmically acceptable pharmaceutical excipients , and by preparation of unit dosage forms suitable for topical ocular use . the therapeutically efficient amount typically is between about 0 . 0001 and about 5 % ( w / v ), preferably about 0 . 001 to about 1 . 0 % ( w / v ) in liquid formulations or preferably about 0 . 01 - to about 0 . 1 % w / v and 0 . 01 % w / v to about 0 . 03 % w / v . an “ effective amount ” is an amount sufficient to accomplish a stated purpose ( e . g ., achieve the effect for which it is administered , treat a disease , reduce one or more symptoms of a disease or condition ). an example of an “ effective amount ” is an amount sufficient to contribute to the treatment , prevention , or reduction of a symptom or symptoms of a disease , which can be referred to as a “ therapeutically effective amount .” a “ reduction ” of a symptom or symptoms ( and grammatical equivalents of this phrase ) means decreasing of the severity or frequency of the symptom ( s ), or elimination of the symptom ( s ). the actual amount effective for a particular application will depend , inter alia , on the condition being treated . “ treatment ”, “ treat ” or “ treating ” can refer to curing any disease or condition or reducing or alleviating the symptoms of the disease or condition for ophthalmic application , preferably solutions are prepared using a physiological saline solution as a major vehicle . the ph of such ophthalmic solutions should preferably be maintained between 4 . 5 and 8 . 0 with an appropriate buffer system , a neutral ph being preferred but not essential . the formulations may also contain conventional , pharmaceutically acceptable preservatives , stabilizers and surfactants . preferred preservatives that may be used in the pharmaceutical compositions of the present invention include , but are not limited to , benzalkonium chloride , chlorobutanol , thimerosal , phenylmercuric acetate and phenylmercuric nitrate . a preferred surfactant is , for example , tween 80 . likewise , various preferred vehicles may be used in the ophthalmic preparations of the present invention . these vehicles include , but are not limited to , polyvinyl alcohol , povidone , hydroxypropyl methyl cellulose , poloxamers , carboxymethyl cellulose , hydroxyethyl cellulose cyclodextrin and purified water . tonicity adjustors may be added as needed or convenient . they include , but are not limited to , salts , particularly sodium chloride , potassium chloride , mannitol and glycerin , or any other suitable ophthalmically acceptable tonicity adjustor . various buffers and means for adjusting ph may be used so long as the resulting preparation is ophthalmically acceptable . accordingly , buffers include acetate buffers , citrate buffers , phosphate buffers and borate buffers . acids or bases may be used to adjust the ph of these formulations as needed . in a similar vein , an ophthalmically acceptable antioxidant for use in the present invention includes , but is not limited to , sodium metabisulfite , sodium thiosulfate , acetylcysteine , butylated hydroxyanisole and butylated hydroxytoluene . other excipient components which may be included in the ophthalmic preparations are chelating agents . the preferred chelating agent is edetate disodium , although other chelating agents may also be used in place of or in conjunction with it . ingredient amount (% w / w ) active ingredient about 0 . 001 - 5 preservative 0 - 0 . 10 vehicle 0 - 40 tonicity adjustor 0 - 10 buffer 0 . 01 - 10 ph adjustor q . s . ph 4 . 5 - 7 . 5 antioxidant as needed surfactant as needed purified water as needed to make 100 %. the actual dose of the active compounds of the present invention depends on the specific compound , and on the condition to be treated ; the selection of the appropriate dose is well within the knowledge of the skilled artisan . the ophthalmic formulations of the present invention are conveniently packaged in forms suitable for metered application , such as in containers equipped with a dropper , to facilitate application to the eye . containers suitable for dropwise application are usually made of suitable inert , non - toxic plastic material , and generally contain between about 0 . 5 and about 15 ml solution . one package may contain one or more unit doses . especially preservative - free solutions are often formulated in non - resealable containers containing up to about ten , preferably up to about five units doses , where a typical unit dose is from one to about 8 drops , preferably one to about 3 drops . the volume of one drop usually is about 20 - 35 ml . table 1 shows characteristic peaks of polymorphic forms i , ii and iii of bimatoprost acid . while this invention has been described with respect to these specific examples , it is understood that other modifications and variations are possible without departing from the spirit of the invention .
the invention provides new crystalline forms of 7 -- cyclopentyl ]- hept - 5 - enoic acid . this compound is commonly referred to as “ bimatoprost acid .” the novel crystalline forms are designated forms i , ii , and iii . the invention crystalline forms are useful for solid ocular implant formulations , utilized in the treatment of various ocular conditions , such as , for example , ocular hypertension . in addition , invention crystalline forms are useful for solid or semisolid dosage formulations used to treat ocular hypertension .