the present invention is directed to compositions comprising bendamustine and one or more amphiphilic anionic compounds . the composition forms self - assembled aggregates in aqueous media , which aggregates exhibit enhanced stability in aqueous solutions , including plasma . as is employed herein , the term “ amphiphilic ” refers to a compound which has at least one hydrophilic moiety and at least one hydrophobic moiety . the hydrophilic moiety of the amphiphilic compounds useful in the practice of this invention preferably comprises one or more sulphate and / or sulfonate anionic groups . such anionic groups are typically in the form of pharmaceutically acceptable salts . it is preferred that the salts are sodium , magnesium , calcium , or ammonium salts . the hydrophobic moiety of the amphiphilic compounds useful in the practice of this invention comprises a hydrocarbon chain . the chain may be an aliphatic chain , or a mixed aliphatic - aromatic chain . the aliphatic chain can be linear or branched although it is preferred that the chain is linear . the amphiphilic anionic compound may comprise one or more anionic groups per molecule . the ratio of the total number of anionic groups to the total number of carbon atoms is generally between about 1 : 4 and about 1 : 30 . it is preferred that the ratio of anionic groups to the total number of carbon atoms is between about 1 : 8 and 1 : 18 . the anionic group may be directly attached to the hydrocarbon chain . alternatively , the anionic group may be attached to the hydrocarbon chain by a linker . accordingly , in one embodiment , the amphiphilic anionic compound comprises a sulfonate group attached directly to an aliphatic hydrocarbon chain . preferably , the anionic agent is an alkanesulfonate . in a preferred embodiment , the hydrocarbon chain of the alkanesulfonate contains between 10 and 18 carbon atoms . in another embodiment , the amphiphilic anionic compound comprises a sulfonate group attached directly to an aromatic ring . preferably , in this embodiment , the amphiphilic anionic compound is an alkylbenzenesulfonate . in a more preferred embodiment , the alkyl chain of such alkylbenzenesulfonate contains between 8 and 14 carbon atoms . a particularly preferred amphiphilic anionic compound is dodecylbenzenesulfonate . in yet another embodiment , the amphiphilic anionic compound comprises a sulfate group attached directly to an aliphatic chain . the amphiphilic anionic compound may be an alkyl sulfate . in a preferred embodiment , the alkyl fragment in the amphiphilic anionic compound is linear 1 - hydroxyalkane composed of between 10 and 18 carbon atoms . particularly preferred amphiphilic anionic compounds are dodecyl sulfate and tetradecyl sulfate . another particularly preferred amphiphilic anionic compound is caeliferin a . in another embodiment , the amphiphilic anionic compound is a polysulfonated polyethylene , wherein the molecular weight of such polymer is about 100 , 000 daltons or less . in a further embodiment , the amphiphilic anionic compound is a polysulfated polyethylene polyol , wherein the molecular weight of such polymer is about 100 , 000 daltons or less . in another embodiment , the amphiphilic anionic compound is a hydrophobically modified polysulfated polysaccharide . in one embodiment , the linker is an ether comprising a chain of oxyethylene groups , oxypropylene groups , and / or oxybutylene groups . the total number of such groups in the chain is not more than 4 . the amphiphilic anionic compound may be an alcohol ether sulfate . in a preferred embodiment , the alcohol in the agent is linear 1 - hydroxyalkane composed of between 10 and 18 carbon atoms , and the ether is composed of 1 , 2 , or three oxyethylene groups . in another embodiment , the linker is a sugar , or a polyol , linear or cyclic , comprising between 3 and 6 hydroxyl groups , where some of the hydroxyl groups are used to form ether or ester bonds to one or two hydrocarbon chains , and to one or two sulfate groups . it is preferred that each of said hydrocarbon chains contain between 8 and 18 carbon atoms . in one preferred embodiment , the amphiphilic anionic compound is an o - sulfoglyceryl fatty acid ester . in another preferred embodiment , the amphiphilic anionic compound is an o - sulfoglyceryl alkyl ether . in another preferred embodiment , the amphiphilic anionic compound is an o - sulfosorbitan fatty acid ester . in another preferred embodiment , the amphiphilic anionic compound is a glycolipid sulfate . in another embodiment , the linker is an amide . in a preferred embodiment , the amphiphilic anionic compound is an amide of alkanoic acid and n - methyl - n - alkylsulfonic acid . a particularly preferred amphiphilic anionic compound is an amide of alkanoic acid comprising between 8 and 18 carbon atoms and n - methyl - taurine or n - methyl - 3 - aminopropylsulfonic acid . particularly preferred amphiphilic anionic compounds are n - methyltaurolipids . other particularly preferred amphiphilic anionic compounds are dialkyl sulfosuccinates . it is known to those skilled in art that the anionic agents described above are usually manufactured not as unique chemical entities of exactly defined structure , but rather as mixtures of isomeric and homologous chemical compounds of related structures . a mixture of one or more of the amphiphilic anionic compounds described above can be used to prepare the aggregates of the present invention . the aggregates of the present invention are typically prepared by mixing the amphiphilic anionic compound with bendamustine . the anionic agent is a chemical , the molecules of which self - assemble to form aggregates in aqueous media . such aggregates have lipophilic core and ionic outer layer . the weight ratios of bendamustine to amphiphilic anionic compound may range from about 1 : 2 to about 1 : 1000 ; is preferably between about 1 : 5 and about 1 : 500 ; and is most preferably between about 1 : 10 and about 1 : 100 . as will be recognized by those of skill in the art , the concentration of the amphiphilic anionic compound must be at or above the critical micelle concentration during application . the critical micelle concentration will depend upon a number of factors , including the composition of the amphiphilic anionic compound , ph , ion strength , etc ., but can easily be determined by routine experimentation for any given composition employing procedures well known to one of skill in the art . the compositions of this invention may further contain pharmaceutically acceptable excipients , such as sugars , polyalcohols , soluble polymers , salts and lipids . sugars and polyalcohols which may be employed include , without limitation , lactose , sucrose , mannitol , and sorbitol . illustrative of the soluble polymers which may be employed are polyoxyethylene , poloxamers , polyvinylpyrrolidone , and dextran . useful salts include , without limitation , sodium chloride , magnesium chloride , and calcium chloride . lipids which may be employed include , without limitation , fatty acids , glycerol fatty acid esters , glycolipids , and phospholipids . compositions of bendamustine and amphiphilic anionic compounds may disperse and release the drug upon dilution in aqueous media . the composition of bendamustine with amphiphilic anionic compounds renders the bendamustine sufficiently chemically stable . the compositions of the present invention are suitable for injection or infusion into patients in need for treatment with bendamustine . the invention can be further illustrated by the following examples thereof , although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated . all percentages , ratios , and parts herein , in the specification , examples , and claims , are by weight and are approximations unless otherwise stated . 1 g sodium dodecyl sulfate was dissolved in 100 ml water . this solution was used to dissolve solid mixture of 60 mg of bendamustine and 102 mg of d - mannitol . the composition was thoroughly mixed . bendamustin chemical stability in various formulations comprising amphilphilic anionic agents and phosphate buffer formulations were prepared by dissolving bendamustine hydrochloride in pre - equilibrated 1 % ( w / v ) aqueous solution of amphiphilic anionic agent containing 6 mm phosphate buffer , ph 7 . 2 . the final concentration of bendamustine was 0 . 6 mg / ml . the formulations were incubated at 25 ° c ., and were periodically analyzed by hplc as follows . 10 μl samples were separated using waters symmetryshield rp - 18 3 . 5 μm column ( 4 . 6 × 50 mm ) at the flow of 1 . 5 ml / min of acetonitrile - water gradient containing 0 . 1 % tfa . peak detection has been performed with means of uv absorption detection at 260 nm . the area of the peak of bendamustine was used to evaluate the rate of drug decomposition in the first order kinetics model . the results expressed as decomposition half times ( t½ ) are presented in table 1 below . it is to be understood that the above - described embodiments are illustrative of only a few of the many possible specific embodiments , which can represent applications of the principles of the invention . numerous and varied other arrangements can be readily devised in accordance with these principles by those skilled in the art without departing from the spirit and scope of the invention .
the present invention is directed to pharmaceutical compositions comprising bendamustine and one or more amphiphilic anionic compounds and self assembled aggregates , which aggregates exhibit enhanced stability in aqueous solutions , including plasma , are disclosed . the unexpectedly enhanced stability afforded by such aggregates permits patients to be treated with bendamustine in lower and / or with less frequent dosages or to improve its therapeutic effect while using the same as presently used treatment protocol .