STABLE AMORPHOUS AMIFOSTINE COMPOSITION, AND PREPARATION THEREOF

Abstract: The present invention relates to a sterile, stable dosage forms suitable for reconstitution and parenteral administration to a patient, said dosage form comprising and amorphous aminoalkyl dihydrogen phosphorothioate, and of amifostine in particular. The invention further relates to a method of preparing such a dosage form, which typically exhibits enhanced thermal stability as compared to existing vacuum dried amorphous amifostine.

Description: STABLE AMORPHOUS AMIFOSTINE COMPOSITION, AND PREPARATION THEREOF 1. FIELD OF INVENTION 5 The present invention iclates to thermally-stablr, dosage forms of S-2-(3- aminoproμylamino)ethyl dihydrogen phosphorothioate (amifnstine) . and to methods of making same. The reconstituted dosage fnππiϊ of the invention are suiinlilc for administration to human., for example, as a radio- <n chemoprotectant agent. lϋ 2. BACKGROUND OF THE INVENTION the compound 5.-2-(3-amin(-proρyIamitιo)ethyl dihydrogen phosphπrut ioate (which is also known as anπfi.stinc, cthiotoε. Ethyo , NSC 296961, and " WF.-2721 ..(. which will lieit.iiuf.cr be referred to «:> "Amifostine") and other aminothiol compounds are disclosed in U.S. Patent No. 3,892,b'24. These compounds were originally nVv oped s__ 15 antiradiation agents (radio-piutcet<mt3), in particular to In. ustd πor vo xpos re <<> x-.ay or πt-clc. : ladiation. to protect against the harmful effects of such exposure which n_3y be encountered during military conflicts. In addition to iι.. utility aa o militaiy antirvuliation agent, amifostine as demonstrated excellent utility as a non-mιht3ry radioprotc Unt and chcmoprotectant. \ κ_, a.. (1 a pro. eciant administered prior to ther. to reduce the undesirable, adverse effects which tn.e dunng the use of chemotherapy and radiation therapy in the treatment yf i.Λnoer. Nyg-ϋr ct al.. e ≤, Academic freεε, lnc , Kt-w York, pp. 73-85 (lyK ' iJ; Grdina et v) , Carci no genesis <London) 6-929-931 (1985). In addition, the.r [-..impounds have been reported lo afford protection against tht. :.ιi verse ctlccts of 5 chemother. pr.iitic agcnta, tor example, alkyl.iting agents cuch as cisplsrin. when administered bcfυικ nr concurrently with the chemolherapeutic a^ent. Jordan et ;d.. EX D . Mol. Pathol. 36:297 (19S2); Ϊ . eJji Cancer Chen-odi™ Pharmacol. 28:3υ 8 (L g l) Similarly, it has been reported that ainifi. .tine has been ueed exp rimcπ illy prior to therapy to protect RIV-iπfcctcd patient. (AIDS) fnmi the harmlul side effects of 0 3'-£2ido-_V-ιle .x thymidine (AZ l ' J therapy. International Published Applicaiion WO 90/14007, published November 29, 1990 Amifostine and it; derivatives liavc beer, shown to exert ilif.se reported protective effrr-.is without affecting the beneficial pπipt-πic ? of ilie administered therapeutic agents. J'his is, in the case of chemotherapy, believed to be due to the selective uptake of the μioteetivc thiol and ol.ir.i metabolites into nom.nl tissue. Yuhas, Cancer Rc_. 40:1519 1524 (1930), Yuhaό, Cancer Treat Rep. 6 :971-y7o " (1979). Amitostine and related aminothiol compounds have also been shown to stimulate bone maπ w growth, gee, e.g . IπLeuiational Published Application WO 96/2504 . published August 22, 19%; and List et .1 . Vχoc. Am. Soc. Clin Oncol. 15Λ4 [1403] [Abstract]. Currently, amifostine is in Phase IT olinioal tπais as a bone marrow stimulant in patients suffering from myelodysplastic syndrome. Pie-exposure with amiπuthiol compounds is capable of causing the bone marrow function to more rapidly recover following chemotherapy. List et al. Srmin. Oncol. 2J (4) Supp. 8.58-63 (iy ). Presently, arnifi istine is indicated to reduce the cumulative renal loAΪt.i_y associated with i epcatcd administration nf splatin in patients with advanced ovanan or non-small cell lung cancer. Physiciana' Peek Pr fe nce 52 nd cd., p. i>00-502 (1998). Amifosiiue is considered a prodnig. Amifostine is metabolized to the cyroproteciive free thiol by dephosphoiylation catalyzed by alkaline phosphatase. &e , Ryan. S. V., et aL, J. Clin. Phaππ, ><5(4)-->ό5-'.7_t (1996), Amifostine exerts protective effects without significantly affecting the beneficial properties ot the administered therapeutic agents largely because of the selective uptake of the ihiol into normal tissue. In its most common use, amifostine is administered parenterall , including by bo)u3 iπjei.lii.n and intravenous infusion. Amifostine is also heing developed for subcutaneous administration- Since these route", ciicumvcnt the protective.1. I . icrs of the human body, exceptional purity of the dosage form must be achieved. Because the dosage form must be free ol microogani-ms and insoluble pa_ticulatκ.x, die procc33 used in prepm iπg it must embody Good Manufacturing Pιacticc3 ("GMP") that will produce and maintain the required quality of the product in terms of sterility and therapeutic effectiveness. Sterility is especially important in the treatment o cancer and AIDS patients, because in many instances they arc a cady immuno-comproniised and therefor highl> wiM.uptiblc to infections. The amifostine bulk drug (which is distinct from the dosage tormj can exist ;.% _. bulk crystalline tnhydrai? which iβ believed to be relati . r.ly temperature .table. Sυr-.h u crystalline form is described by g mlc el al- Acta rvst C .1 _5-13S ( 19S8), l ' he bulk drug, h ever, is not eterile, and _.ύ cannot be reconstituted into α pharmacrutica ' t product suitable for arfiπleial administration to humans. Several methods of sterilizing bulk ώ tigs arc described in Remington's Pharmaceutical Sciences, lδ' h ed. (19901. ϊ hese include, for example, steam sterilization, wherein a drug is exposed to high pisssurc steam at a minimum temperature of 121 °C This and other metho . that require heatinv, however, cannot effectively be ωed to εterilur bulk r-iystallinc amifostine This is because crysralliuc amitostine loses water at about 70°C to about 75 S C. The lo . of water facilitates degradation by a hydrolv-is reaction that forms phosphoric acid and 2-((3-aminoρropyl)amlnoJfc-tl._ιιιe thiol. See . e_g κ Risley, J.M. and Van Etteii, R. ., Biochem. Pharmacol. 35:1433 1458 (l.xWi). Amifostine has thus been sterilized by dissolving it in an aqueous solution which is then sterilized by membrane filtn.ii.-n. Substantial practical problemε related rn the packaging of bulk, yilid amifostine using thr..so-called "dry filling" or "powder filling" method were thus avoided Thr e problems include producing sterile amifostine bulk, the difficulty in the manual manipulation of powderc, the nenl to mill the powders m acceptable particle size And flowability, difficulty in maintaining p? rticle-free. aseptic conditions, and the difficulty in supplying the precise dosdgcs into individual V IS. In solution, however, amifostine is again susceptible to degradation by hydrolysis. For this reason, a prior process has ilerilizcd an amifostinr solution by filtration, mid then lyophihzed (frette-dricd) the amifostinr. solution under the following conditions: about 5 L of a solution of lflO mg/mL amifostine and 100 g'mj-. mannitol placed in vtal was loaded into a freese-drier at 0 °C and then εolidified Λt -45 U C. fhe vials wn c kept fit -15 "C for 2 hours, after which time thr fi ccze ryin- . chamber .is evacuated to 100 μm Hg. The self temperaOu e was then raised to 0 "C uvcr 12 hours and then maintained at 0°C for ? hours, ' the shelf temperature was finally raised to 25 "C, at which inmperature the vials were kept tor 2 hours This method produced v >,terilc amorphous form o f .uiπfostine suitable for parenteral adminisliation to a patient (whirl ι is hereinafter referred in as "Amorphous AmifostmB r"). Physii ian;' Peak Reference. 1 i! ed. 1997) p.485-486. This method also allowed easy production nl " . ials containing predetermined amounts of eterile, lyoph ized amifostine. JnfortunHit:ly, Amorphous Amifnsii.ie 1 wa3 thermally unstable and hydrolyzed over time at tempered... es above 0"C. For rxam lϊ,, a ty ical sample of Amo hous Amifostine I -.evpl at 25°C for about one month formed about to 7 weight percent oi the degradation product 2-[( -aminop:opyl)amino]ethane tlύul. This was the state of i r. art when the amorphous l mi of amifo. I me was approved by regulatory authorities as having a shelf life of 24 πu fhs when stored at terαpwatures of between about ? "C and 8 U C. See. £_£_. F-ΦV"^ Knropean Sumπiat v of Product Chafacteriviic? (19971 ("EthyolΦ SmPC"). In fact, the Amo hous Amifostine ϊ dosage form WOE Renerally ackaged, shipped, and stored at temperatures below about 8 U C, Further, in die United States, the amo ψbous form of amiioεtine was approved by the Food and Drug Administration as having a shrlf life of 15 months when stored at temper atures of between about 2 T and 8 D C. Temperature instability impose" ; upon manulacturere and users packaging, storage and shipping requireniKivts that increase the cost υf handling e drug and make it_. use by hospitals and clinics more difficult, and may even prevent its use in developing counιrir_, which (iften lack temperature contrail. .! storage maintenance capabilities. In recognition of the need for a dos^e form of amitostine that is muie thermally-stable than Amorphous Amifostine I, resw-ich has been directed at finding new stable and sterile doεage form, of amifostine, tor example, Jahdiisouz and coworkers studied The stability of amifostine and suggested that temperature insiwl.ility ot Amoφhous Amifostine I is related to its degree of water .intent. Jahansouz, ft., et al. Pharm. Res. 7(yV.S195 (1990) [Abstract . . Recently, instead of attempting to increase the stability of dosage formε of ammphous amitostine εuch as Aim u hous Amifostine 1. researchers focused on creating stable and sterile crystalline dosage forms. Fυi example, it v/as reported ilwt amifostine '"undergoes solid stair, tiansitions tro the amorphous to crystalline phase? by treatment of the frcczc-dried products with varying humidity." Further, the stability ot rehydrated forms of amifostine v/as allegedly iπcrea πl by the addition of certain w-ipients. Zadeii, J. M., et __L : fharm Res. 8(10.:S 172 (1991) [Abstract], This abstract does not, hov. «vcr, descnbe the rehydration process in any detail, nor provided by the two c *. ipicnts it di3θloεeϊ In addition, the abstract provides no detail as TO how and when particular vripieui, should be combined with am ' .fnstine to yield tne alleged more stable rehydrated forms (ι_κ , whether the exeipicnts were combined with amitostine psiu. io, during, or alter its rehydraiioπ). ui whether the process should differ for different excipientj. Finally, a novel dosage form ofsterϊtr, thermally stable crystalline amifostine was discovered. U.S. Patent Kus. 5,424.4 / 1 and 5,591 ,7 " .1. presently, that stenle crystalline dosage foπn of amifostme is sold undet the trade name bthyθl s . Physicians' Dc3k Reference. 52^ ed. (19 « . p. 500-502 A crystal structure *ϊ and preparation of a dosagr. foπn, which exhibits reater thermal stability than Amorphous Amifnstine I, is described by U.S. Patent Nos. 5,424,471 and 5,591,731. (generally, thi. thermally-stable crystalline doeage form is made by dissolving hulk amifostine in a solvent solution (that allows piecipitation of amifostinr, upon cooling below Q°C), followed by str.iil ' iTa- tion, precipitation and lyophilization of the compound. Decause the cryεtalliniiy, \ti and h nre the stability, of this amifostine dosage torm requires tin ec water molecule- per molecule, the lyophilization used to provide tbe final product must be carefully controlled to ensure the required, ilr.yce of hydrahon. Once made, die stable crystalline dαs^e form ma be stored at room temperaturr with minimal degradation it exhibits less than 2 weight percent deviadation when kept at 40"C for 14 days U.S. Patent No. -3,591,731. 15 Although nrwly developed stenle crystalline dosage lormfi of amifosiine. leducc or eliminate many of the problems associated with Amorphuns Amifostine 1, production of such ran be costly, difficult and'oi dangerous. For example, the piuduction ot crystalline Ethyol ® piiics the use ot explosive solvents which must be handled ith care and strictly isolated from oxygen Such solvents also contain im urities not typically found πt water 2 ( 1 that mu3t be removed to r.πsuie that the dosage form is •suitable for reconstitution and Hdiiiiiiistrat.on to a patient For example, ethanol often contains sn.etcme, mcthanol, H ,( S0 4 , MnO„, anil utlier toxic residues. See, e_ϋ.. Λ l_-_llCattϊlo≤ (.199S-1999), ages 746-747. the production uf crystalline αrnifo-tine dosa?c funns further requires long lyophilization dryine times in order ω ensure precise amifostine hytl ration. 25 In view of the above-described and other difficulties associated with the production crystalline dosage forms nf amifostine, there remains a ner fur a stable, sterile amoφhous dosage form, as well as an effu-.ir.nt and inexpensive mean; of its piuduction. The invent inn also cncompa.se. non-sterile and/or bulk thermally-stable ? πmrphous αmitostins. To applicants' knowledge, to date an amαrp.inu≤ thermallv-stable am'ifo-tins 30 baa not been previously disclosed. In preiened embodiments, the invention encompass.. ' 1 , thermally stable osag forms uf amifostine. 3. SUMMARY OF THE INVENTION The [ iicscnt invention encompa .scs non-sterile and'or bulk liiemiallv-stαble amorphous amifosiine. To applicants' knowledge, amorphous thermal ly-si*lιlc amifostine has not been previously disclosed. In preferred embodiments, the invention encompasses thermally-stabl. forms of ainifostinc. Thr. invention encompasses the following thermally-stable and sterile dosage forms: a dosage form which comprises amorphous smiifosύne . an amorphous dosage foπn which comprises amifostine; mi a dosage form that is suitable for reconstitution with H ph d i maceutically acceptable vehicle into an injectable particul ate-fi.ee drug product suitable for parenteral administration to a subject, which comprises amorphous amifostine. The invention also encompasses a room ir.mpcraturc stable dosage form eouiprisine sterile amoφhous amifostine. The invention also iπchntr.s a room temperature siablr. amorphous dosage form comprising, sterile, amorphous amifu..tin«. This invention is further directed to ... refrigerated stable dosage form comprising sterile amorphous amifostine. The dosage forms of this invention may comprise a star.iliz.ei. It is prcleπed that the molar π.ιio of stabilizer to amifostine he between about 0.05 and abom . 0, more preferably between ah.m 0.1 and about 1.0, and most prefeiably between about ύ 1 and about 0.5. Preferred stabili-r.is are compounds having amide or Λiiiino acid moieties. A spπ-.ϊric preferred stabilizer is nirotirramide. The dosage form of the present invention may also co pri _c an cxαpicnt. Suitable excipients include, but are not limited to, sodium chlondc, citric acid, tartarir. -Aci , gelatin, polyvinylpyrrolidcme (PVP), dictylenetriamine-peπiJiacetic acid (DTP A), etliyleπrdia ine- tciraacetic acid (EDTA), sodium dcoxychoUte, sodium laurocholate, and carbohydrates such as, but not limited to, dextrose, sucrose, -orbitol, inαsiinl, dcxtran. mαnnitoL and e__boxymcthγl cellulose sodium salt. Finally, tlw dosage forms may also contain up to about ?(. percent water without sitπufi..-_n_ loss of thermal stability A pr p fr.πed dosage form of the invention comprises amorphous amifostinr, nicotinamide, and PVP. The preseni invention .3 further directed to a process of making a thermally-si. Mr. and clcnls amorphous dosage form ot anύfo-tinc, and m ι , products of that process. 3.1 DEFINITIO S Av used herein, the terms "bulk amil ' ostine'Or ' hulk drug ' mean a form of amifostine which is used in preparing dusage forms, but is not suitable for parenteral administration to a patient. The term encompasses amitostine as disclosed by U.S. Patent 5 Ni i. 3 . S92.!- ' 24, including, hut not limited to, mono-, di- and trihydrate for JI is of amifostme. As used herein, the term "crystalline." when usr-1 to describe a component ui product, means that the component or piod ct is crystalline as determined by x-ray diffraction. See, e^, Remington's Pharmaceutical Sciences. 18 ώ ed. page 173; The United States Pharmacopeia, IV* ed (1995) paε;θs 1S43-1844. 10 As used herein, the teπn "amorphous" means that thr. component or product in question is not crystalline as determined by χ-ray diftraction. It should be remgnizcd that a multi-component product, gj , a product having ami fhstinc and excipients and/ui stabilizers, may have, crystalline and amorphous component.. r_ „ amorphous amiD. iae and crγGtalline excipients and'or stabilizers. 15 As used herein, the terms "de rad tion' 1 and "decomposition" when used in connection with amifostine refer to the production of 2-[(3-ammopropyl)amiιιo]ethane thiol (\V 1065) and phosphoric acid from amitostine As used herein, the term "Amorphous Amifostinr T" means a dosage form nf amifostine thπt contained amorphous xuiifostinc and which gave ai average o about 3 5% W degradation product (i^..2-[(3-an_ιnoproρyl)atιιino]ethane thiol) at about 5 °C for 2 years. Atr example of thepreparatiim of Amorphous Amifustinc I is described in the Background of thr Invention section above. As used herein, the terra "Amorphous Amifostine IT' refer. Lυ a dosaζc torm of this invention whirvh I . suitable for reconstitminn and parenteral adminisiw.i.m to a patient. In 15 particular, Amorphous Amifostine fi refers to dosage form ol amorphous amifostine as dr.scribed herein. As used herein, the term . "stability" and • thermal si ability" refer to the ability nfa. composition in withstand degradation ui decomposition when ke.pt. at a particular temperature , I ' m _. specified period of tirnfc, preferably under inert aimosphr.i c. Appropπate 30 mcane of determining stability are defined hr.ie ' m. As used herein, the term "thermally-stable" means more stable than Amorphous Aπiifostinc I (t^, the previously commercial mo hous dosage form described in the Background of the Invention section above), As used herein, the term "stabilizer" mcjn . a compound or mixture o f compounds that v, hen mixed in a suffir.le.iit amount with bulk amifosi'me, and used in the production uf Mn f_mifo5t.no osage form. Hir-mases the thermal-stability of the dosage form, for example by reducing the amount of 2-[(3-aminiipic.pyl)amino]e_hane thiol funned by it over time. As used herein, a ranε;e of numbers ι n values defined by the USP of die term ' ■ between" includes thr particular numbers or values used to describe that range. As used herein, the term "month" means o period of lime: of between about 26 days and about 33 days. As used hr.i em, the term "weight percent" when used to describe the aπn unit of degradation product in v dusagc form means the weigh, .if degradation product b?<:r,d upon the weight ot amifostine originally in that dosage form As known to those skilled in the ait, accelerated studies can br, used for the determination of s liilities and the e temper- unrs. Ssς, e.g., . Lachman, et al The Theory t Practice of Industrial Pharmacy nages; . t.6-67 (19R6), The lcS3 a compound or mi irtu.e of compounds degrades when kept at a particular temperature f< » a particular time, the more therπwlly-stablc it 13. As u ed herein, the terms "refngerauυu" or "refrigeration conditions" mean the maintenance of a temperature ot between about V'C and about δ'C As 3cα herein, the term "freeze' ' or "freezer conditions" mean the maintenance of a te iir-i rure of below about 0°C, particularly between about O'C and a out -20°C, As i ed herein, the term "particulate-frrr" means a solution that is stf rile, suitable for bolus injection, mil avcnous infucion, or subetusnenus administration, and meets ibr paniculate matter test rlescπbc in U.S. Phamiacopia. pagr 181 (, (23 M cd,, 1995). -.pecificallv, a solution is particn tc-frte it the average number of particles having a diameter of greater than 1U μm in the solution docs not exceed 6000 per uniiaincr and the average num er of pailicles having a diametsr of grrwir.i than 25 am in the solution rioe . net exceed 600 per con ι,u ucr. 3.2 FIGURES , Figure 1. Fowderx-ray diffi action pattern of crystalline amifostme prepared HS dcscnbed by U.S. P;.ic-.nt Ho. 5,591,731. Figure 2. Powder x-ray diffraction uiiem of an amorphous ami usύne dosage 5 form (ifthc present invention wherein niootina ide is used as a stabilizer (8:1 amifostine to nicoύnamklfi weight ratio). This diffraction pattern contains dearly discemablc peaks where 20 is approximately equal to the following- 7.9, 13.0, 16.1, 27.4 and 32.8. Fiuute 3. Powder x-ray diffraction pattern of nicutinamide. Figure <i Comparison of the powder x-ray diffraction patterns of (A) 10 crystalline amifostinr i eparcd. aa described by U.S . Patent No. 5,591 ,731 ; and (B) that of Mn amorphous amifostine usage form of the present invention wherein nic tinamide is used as a stabilizer (8:1 amifostine to meotinamide weight ratio). 4. TIET AILED DESCRIPTION OF THE INVENTION 15 Prior to the present invention, the available pharmaceutically useful dnsagc form ot aaiorpin-us amifostine (Amorphous Amifostine I) was thermally unstable, and would, for example, typically yield about ό weight percent degradation product (Lo,, 2 |(3- anιιnoρropyl)amiιn>]cthanc thiol) when ke.pt aL 25 "C for one month Bec use of its i-:mperaturc lnεtability, Amorphous Amifostine 1 was typically shipped and sloi ed at low 21) temperatures (generally 8 * C, ej., about 5 = i'C) in ordw in prevent itc degradation Now. the present invention provides a osajr. fuπn of amorphous amifostine (Amorphous Λmitoεtine II) that i_ unexpectedly more therm ally-stable than Amorplums Amifostine 1. 1 he present iπvt.1 ition can be applied to other aminoalkyl dihydrogen pliusphorothiates, and thus provides a more stable dosagr. forms of these ami_.oall.yl 25 dihydrogen phosphorothioates. Aminoalkyl dihydrogen phosphoιothioatc3 suitable for u_t. in he re5r.ni invention include, but are nut limited to, S 2-(3-aminupropylamιno)eflιyl dihydrogen pbn phuiothioatc (amifo.tine), S- -(3-mcthyl-jntnopropylaminυ)cthyl dihydrogen phosphoro ihioate CV7R-36i.y), S-2-(3-eΛhyl<un.nopropylam ιo)ethyl dihydrogen ρho:?horothloate, S-?-(3-_iπιiιιop-θpylaroιi-o)-2-me.hy lpι opyl dihydrogen 30 ptinsphorothioate, S-2-(2-amiiu.ethyl-inino)-2-ethyl di " hydrϋ^eιι phosphorothioate, S-?-(4- aπiiniibutylamino. 2-elhyl dihydrogen phosphorothioate, S-?-Ci-aminopcotvlamino)-2-ftthyl dihydrogcu phosphorothioate, S-2-(r.-.ιininθhcxγlanιmo ' )-2-elhyl dih.drogcn phosphorothtnate, S-2-(2-mcthylarmnoelhylHmmoV2-ethγl dιhydrogfiι phosphorothioate, S-2-(3-methylaminopni [ iylaminol-2 ethyl dihyrfmvcn phosphorothioate, l-prnpanuhto.- 3-[[3 ' (mcthylamιno)propyl]H.πιiιo dihvdrocen phosphnthioi tc) ( R-li l327) and ιl> free thiol fnmi (YYR-151326), and the disulfidc [2-l(amιnoproρyl)ai-imιι]e_haut_uol] N,N - dιth-θidι-2,l-ettnιιcdiyl)bi3-1.3 propanexlwmine) (WR-3327&) . In a prcfeπcd embodiment of the invention, the .mmoal yl dihydrogen phn phurϋttuoatc is amifostine In particular, the present invention provides a phdi ι naceutical dosage form of amorphous amifostme suitable for in. (-institution and parenteral administration to a patient that can be conveniently shipped, stored and handled at room temperature and refrigerated temperatures with less pmduct degradation than A ni plums Amifostine 1. The dosage fin ms of this invention (e g . Auu.φhous Amifostine ΪI) thus provide a solution to a long felt nr-tai the invention allows relatively low cost amifostine o.^e forms to be more easily shipped in, Λiid more easily stored in, hospitals and clinics whir-h lack temperature controlled εtorage anil maintenance capabilities required for Amorphous Amife-sliπe.1 The present invention is bdse in pan upon the unexpr. ted discovery that partieiftør amount, nf uertain compounds when mixe with arrutoεtme can be u e to produce amorphous do. Λ§C forms with reduced rates of ύc . mposition These certain are herein referred to <__ "stabilizers." Without limited bv theory, it is belie ed that ih.se stabilizers form van m Waals or a similar weak ιπrι_πuulecular interactions with thr <n-iifi._t.ne. sulfur atom These ιn.e.<_U-θns may prevent the aetiv.uinn (q.p.. protonation) of tne sulfur atom. Thwc stabilizers may alvi inhibit the interaction of water with, and prevent nucleophihc attack upon, the amifo-tine phosphorous atom. Because the pre.se.nce uf some stabilizers have been umnd to interfere with the measurement ot the amifostinr ι mvtcnt of dosage torm sample-;, the stabilitv ot o dosage fc.rπi comprising α stabilizer is preferably determined by measuring ihr formation ot amlfnςnne degiαdation or decomposition pmducts as a function of tem erature -.nd time uch products ιnι hi e, but are not limited to, 2^( r_mop_op>l)ammo]ethane thu.) (the primary degradation prodiu ι uf amifostine) and phosphoro πci It baa also been dl.eov p _ p <l ut the stability ol the dojag forms uf amorphous rtimfostino dependent upon the reeze drying r c ss u e for its *r <u ation, and that the simple uUMng of amitostine and a k h! ? docs not necessarily yirlil Λ more stable dosage fnrπi Even more unexpected is thr ri rovciy that, contrary lo trie teacninϋ uf the prior art, doςage forms of amorphous amifostine lo prising dilterent amount, of water may be thermally-stable. Consequently, thi. invention ι. directed to thr.i mally-stable dosage foπn of amifostme In particular, it is directed to a dθ3θge form that rxlύbits lcao than 5 weigln percent degradation when maintained at 4 ( . S C for one week, said rϊght percent baεed upon tutal weight of amifostinr.; preferably lesε thai.4 weight percent degradation whm maintaine at 40''C tor one we.e.k, _>aid weight percent based upon total weight of amifostine; and 11 iore prctcrubly less than 3 weight percent degrada rinn when maintained at 40° C for one week said weight percent based upon total weight, of amifα-tine. In another embodiment, the dosage form of this invention exhibits less than 5 weight percent dr.j j .adatioπ when maintained aL 25 C C for one month, εaid weight percent based upon total weight of amifostine; preferably less than 4 weight percent degradation when mnii itained at 2b "C for one nι< mfh, said weig t percent h - ed upon total weight of amifostine; more preferably less than 3 weight percent degradation when maintained at 25 U < for one monOi, said weight percent basr-l upon total weight of ami fasti r.e; and most preferably less than 2 Wr.iphl peicent degradation when maintained at 25°C for onr month, said weight percent based upon tolyl weight ot amifostine. In a furilier embodiment, the dosage fuuu of this invention exhrbit.. less than i weight percent degradaliun when maintained at 5 Λ C for about two years, said weight perc ui hased upon total u'eight if amifostine; prclerably le s than 2 weight percent degradation v,he_ι maintained at 5°C for it .out two years, eaid weigl percent baaed upon total weight of amifiistinc, and more preferably less than 1 weight percent nsgradation when maintained at ^C for ahoul two ycara, said weight pen cat based upon total weight uf amifublioe In A - further embodiment, this inveπtiun is directed to a Thermally-stable dosage form comprising substantially amorphous amifostinr P ι efcrably, the thermally-stable dosage form comprises amifo_ιiτικ that is at least SW. amoφhou. by weight. More preferably, the thcmidlly-stablc docage form compiiscs amitostine that is at lr_ι t %% amorphous by wriwlit. This invention is also riirw.ted to a thermal ly-stable osa e form comp ine ? mnrphuus amifostme In -mother embodiment, this invention is directed to athcmιally-s(__l_lc, subs'.antir.'ly amorphous dosage form comprising amifo.imr. Preferably, the thermally-stable osage - I I - foπn is at least amorphous by weight. ou-. preferably, the ιhemι?lly-_.table dθ3αge fui is at least 0% amorphous by weight. This invention is also directed to an amorphous thermally- stable o ge form comprising amifostine, Another embodiment of this invent inn provides α thermally-stable dusage form that 5 contains an amount o f water between about 0 and about 20 weight percent, pre.fr.. ably between obout U and about 15 weight percent, and more preferably between about 0 and about 6 weight percent. The pnssem invention is further dire ed to thcrmally-etable do.πgή form of amifostine which cnmpri_.es one or more stabilizer, and optionally one or more excipients, 10 Preferably, the molar ratio of stabilizer to orrufostine Is between about 0.05 and about 5.0, more i efcrably between about 0 1 and about 1.0, and most preferably between about <J.-_ and about 0.5 v. night percent. Aε above, (lit; thermally-stable dosage form which comprises one or more stabilizer^ and optionally one or more wu-ipicnts may also contain vui amount of water between ahnui 0 15 and about 20 weight percent, preferably between about 0 and about 15 weight percent, and more preferably between about 0.5 and about <i weight percent, Each of tht dosage forms of the invention can br. pioduccd as an elegant cal r. product (e.g., dissolves in lev. than 60 seconds). This invention is further diita.tcd to a process of alun * Λ thermally- stable dosage _.t) form of aruinp ous amifostine. In thi. process, amifostine may be combined with one or more stabilizers and/or one or more excipients. A made clear below, this method encompasses all means by which amitostine. water, bt.1l1ili7.ers, and excipients may he. combined. For example, amifostine and a stabilizer may be combined in any order prior to, during, formed in situ, or after lyophili/Λtion of bulk amifostine. Br<vtι_se several different 25 εtabilizers m j be used to prepare the dosπge form of this invention, each may be combined with amifostinr together or separately in any ordn m iug ts preparation. It has been found, however, that an especially economical and ctlicient means of creating a thermally-stable d sage form of amorphous ait.ifo.iiuf. (eg,. Amorphous Amifostine 11) involvec the formation of a single solution comprising hulk, dinifostinc, a i stabili/ci , and optionally an «xcipi .nt. According to the present invention, vials arc loaded with a sterile filtered solution comprising n mifostinc and optionally a stabiliz er aud o. excipient. A particular advantaiie of tni- prncessei is that the solvent used to form ihc -VI- solution may he pure water, instead of the ethanoi'water mixuuc required tor the production of stenle crystalline ami ostine composition... This invention, however, encompasses the use of other solvents, mid in particular aqueous solvents having pHs of br.i v.-een about 3 and about 11, more preferably between about 6 and abom 9, and most preferably between 5 about 7 and about 8. Bull; amifo_ιϊne is known to be moic stable in basic solution .. Risley, J.M. and Van Etiwi, R.L., Biochem. Ph-.ima_.ol 35:1^3-1455 (1986). After being filled with the amifostine. solution, the vials are loaded iuto a fτr,c7_c-drycr which is then evacuated. The freeze-dri may be pre chilled. The vials are kept ar a temperature and pressurr, sufficient to remove a significant portion of the solvent. 0 Typically, and as is well known to those skilled in the art, the temperature of the vials is increased near the end of the freeze-drying i-yele to cnaure that the desired amount of . ulvcnt is removed. The novel drying process drscribed in detail below, however, has been found to foπn cake products lliAthavc consistencies an stabilities previously thought not to be possible for non-cryo lline dosage forms. Furthermore, the rying process of this 5 invention helps ensure that if the dosage foi < i . of this invention (e.g., Amor hous Amifostine II) is to c ntain a stabilizer, the mavirnuin stabilizing effect of that stabilizer i. obtained. Although the following fieezc drying conditions ju c not meant to be limiting, it has been found tha Amorphous; Amifosilne II is most easily formed when the breeze drying, w ft lyopbiltzation, process comprises the following steps: freezing the amifostine solution during a fre zing cycle, to form, a frozen mixture; evacuating; (vacuum) the lyoplulization chamber; and drying the fro/ m mixture during a primary drying cycle which comp ises at least our primary drying stage. The process may further comprise further drying using Λ secondary drying cycle comprising at lf.«t one aeoondary drying Mage, and'or a desiccating 5 means uuch as th use of dcsiccants, a de.ύr.ator, desiccating stoppers, and the like. Upon completion of the lyophilization, an inert gas such as nitroecn is preferably added to the vials containing the lyophihzed dosage torm. It is preferred that the frt-exing cycle last from between about 1 hour and about 1.. hours, more preferably from between abuut 2 hours and about 10 boors, and mo.t preferabh 0 between about 5 hours and absut g boms. It is preferred that irmpαaturc of thy nee^e dryf.i during the f.r_s7,in£ cycle be maintainrxl at an average of between about -70°C and about -10 n C._ uioic preferably between about -65 υ C and about -3ύ"C, and most preferably between about -55 ° and about lU^C. Near the end, or upon completion, of the freezing cycle, the ireβ_.e drier is evalu ted such that the frozen mixtures are re osed to a pressure (vacuum) sufficient to remove the solvent (whii.-h may exist in a liquid and/nr solid phase) at the average temperature of the primary drying cycle. When the solvent is water, i cferrcd pressures are less than the vapor i assure of water at the particular drying cycle temperature. Such vapor ressur s are provided by the CP.C Handbook nf Chemistry and physics, pagr H-1 8 (64* ed; 1983- .9R4). The freeze iicr may instead be evacuated uμoti or following commencement of the primary drying cycle, h is dining this cycle that mo_ι ϋftlic water or solvent in the. frozen mixluif. is removed. This cycle is characterized by an average pressure, average temperature and duration, but may contain one or more stage;, each of which is characterized by an a «ι age pressure, average temp™ attire and duration. Typical ly, bowevcr, it is preferred that the primary drying cycle cnmpii.e onl one stage that lasts from between about ϋ hours and about 100 hour3, more preferably from between about lo hours and -ihout S6 hours, and most prr.fr.i bly between about 24 hours and about 72 hours, It is preferred that temperature ol the freeze di π during the primary drying .ycle be maintained at an average oflietwccti about -45 * C and >l.out 10°C. more preferably heLweeti iout -35 V C and about 0 * C\ and most preferably between about -30°C and about -10°C. The primary drying cycle is optionally followed by a secoπdwy drying cycle, during which residual water or solvent is removed. Tbis cycle is characterized by an aveuge pressure, average temperature and duration, but -> contain one or more εtages, eMi.h of which is characterized by wi average pressure, average iπupcraturc and duration. Ty ically, however, it is preferred that the secondary drying cyclr t.omprisconly one stage th. t lasLs fiuin between about 0-5 hours nml about 8 hours, more prefnJily from between about 2 hours and about 36 hours, and most preferably between about 6 hours and ..bout 24 hours. It is preferred lhaL temperature of the freeze dryr.i during the secondary drying i-yi.lc be maintained at an averagr of between about 25 "C and about 40 ft C. more preferably between about -li'C and about 40 C C, and most preferably b iwe . about O ' and about 35°C Instead of a secondl drying cycle, or in addition thereto , an optional desiccating ean ^ may be used to further dry the dosage torms. ' Desiccating means include, but arc not limited to, the use of dcsiccants, desiceatois, desiccating stoppers, and the like. For example, an elegant cake product has V.c.ι found to form if vial, a e initially loaded into a freeze drier kepi at a temperature of betwwu about -20"C and about l_5 Λ C, after which the freeze drier shelf temperaiuie is decreased to between a out -70 U C and about -30"< over a period of time that allows unifuj m reezing of the amifostine./ Kiabiliz.er solution. The freeze drying chamber is then evacuated to cause lemoval ot the εolvent. It is preferred that the pressure be maintained Λ t between about 10 μm ¥ g to about 500 μm Hg, more preferably bei ween about 75 μm Hg and about 200 μm Hg if the solvent is water. Typically, atter <ihs pressure is allowed to equilibrate the. temperature of the chambr.ι- is inrrea.sed to a temperature of belu,r.ι.n about -ii"C to about 91 β C for atune sufficient to remove most of the solvent, As described in moie detail below, it has been found that a suitable cake product is best formed by exposing thr. vials to a yαnety of different i r.ι nperaturC- and pressure- ; ver periods of time ranging from minutes to days. Completion ot the lyophili^tion process yields a stablr, amifostine dosage foπn comprising . uiorphoiis amifostine that is suitable for reconstitution into a particulats-free solution suitable for paientcral administered to a p.iticnt. It is preferred, hov, rv<_r, that the fiee__c-dryin£ obamber be fillrd with an inert gas such as nitrogen, argon or xenon prior to the idlin of the vial* tt has bwπ found that this facilitates the .i-diihty of the dosage form. The v ' w can then be stored and shipped at a temperature that depend, upon the desired shelf lifr. of the dos ge torm. A particularly suitable temperature is bei ecn about 0 U C to about 2 "C, most prclerably about 4 ft C It has been lound that by varying the tem erature, time and number of drying cycle_, products with different stabilities and w-al .i contents can be obtained, <dl of which are encompassed by thr present invention Karl Fiςher titration. for example, may be uv . to determine water content According to the pr mt invention, any amount of siabϋiz.cτ may be combined with amifostine iust so long as that amount rs sufficient to increase ihr ihcm.al stability ot the lyophihzed product. It is preferred, however, that between ahoπ. O.Oj mol to about >X> mol of stPhili/et be used per 1.<J mol pure bulk crystalline amifostine tnb>dι ate (hW = 2 ι .S g'mnl) This amount is more prrfr.i ably between about 0.1 mol tn about 1.0 -13- mol. and most preferably I tween about 0.2 mol to about 0.5 mol bulk crvstalline ami fustint tπhydrate. As those billed in the art will recognize., however, the exact antoum of stabili/ci- added depends upon a variety of factors, including the chemiι-.l and pharmaceutical characteristic, of the stabilizer w.rl the purity and water content of the bulk amitostine. The latter is particularly noteworthy, as hulk aiif.fos.uic is available In crystalline forms, and in varying degrees ot hydration. Bulk amifostine haa been described as a cry llinc form having from one to three water molecules per molecule., but may also exist in other n ms. Bulk amifostine may be made by the process diεclosed in TJ ,8 Patent No.3,S92,S24, which is heieby incorporated by reference, Stabilizers of the present invention are compounds or mixtures of compounds that arc pi lAiniaccuticαlly acceptable and when combined with amifostine do noi facilitate its degradation in uluύon yet enhance its stability when stored as a solid at room temperature. Suitable compound* iu lude amides and amines such as, but die not limited to, nicotinamide, derivatives nf πicut aπύdc, mcctinic acidj derivatives of nicotinio acid, and a variety of natural find synthetic amino acids and amino acid derivativ. rs including, but not limited to, glycine, alanme, valine, leucine, ixoleucinc, phenylalarune, tryptophan. and a∑paragine. Preferred stabilij.r.ιs arc nicotinamide, derivative, of nicotinamide, nicotimc acid, and derivatives of nicotinic acid When nicotinamide is used as a si hiliier, it is prcterably used in an amifostine to nicotinamide weight ratio of between about 2-l and about 12:1. mote preferably between about 4:1 and about 10.1. A most preferred weight ratio is about 8:1 (amifostinr in nicotinamide). It has been found that in order to obtain on elegant cake upon lyophilization Ot a MTuin...tine/stabili2er colution ; the concentration of bulk amifostine should be between about 1 mg mL to about 2UU mg ml, more preferably between about 50 nig'mL in about 150 mg/mL, and mo3t preferably between nhnut 75 mg mL to about 125 mg'ml The preferred of stabilizer (s) may be determined horn the preferred a ifostine-to- stabilizcr molar ratios provided above. A3 those εkilled in the mi will quickly recog ze, the solubility ot the desired stabiliv n(s), readily determined from the lit .raiuie, may also [ ay e. role in determining desire/1 coneeutiations. It is important to note that when used in combination with certain lyophiliλation methiit , -.umc stabihtero and concentrations of tjbilizers car. yield crystalline or pn"-ιi.ιlk -lo- crystalline, rather than purely amoφhous, products. For example, when nicotinamide is used as a stabilizer in a weight ratio of 4:1 (amifostine to nicotinamide) under lyophilization conditions encompassed by this invention, a crystalline dosage form can sometimes result. Further, a dosage form with crystalline or partially crystalline stabilizer(s) and/or excipient(s) can also result. The present invention is concerned, however, with amorphous dosage forms or dosage forms containing amorphous amifostine. As mentioned above, lyophilization of the bulk amifostine may optionally occur in the absence of a stabilizer. If it is done in the absence of a stabilizer, the stabilizer may be added following lyophilization. Similarly, excipients may be added to the dosage forms of the present invention either before, during, or after sterilization and lyophilization of the bulk amifostine. Excipients found useful for this purpose, often in combination, include, but are not limited to, sodium chloride, citric acid, tartaric acid, gelatin, polyvinylpyτrolidone (PVP), dietylenetriamine-pentaacetic acid (DTP A), ethylenediamine- tetraacetic acid (EDTA), sodium deoxycholate, sodium taurocholate, and carbohydrates such as, but not limited to, dextrose, sucrose, sorbitol, inositol, dextran, mannitol, and carboxymethyl cellulose sodium salt, although mannitol is not preferred. A specific preferred excipient is PVP, which is commercially available in a variety of different viscosity-average molecular weights. Polyvinylpyrrolidone having a viscosity- average molecular weight of 30 (PVP30) is a specific preferred excipient. When PVP is used as an excipient, it is preferably used in an amifostine to PVP weight ratio of between about 2:1 and about 50:1, more preferably between about 5:1 and about 15:1. A most prefeiτed weight ratio is about 10:1 (amifostine to PVP). In addition to the excipients mentioned herein, others known to those skilled in the art can be used. It is preferred that the excipient not be a source of free phosphate, however, as this has been reported to facilitate the degradation of amifostine. See, e.g., Zadeii, J. M., et al.. Pharm. Res. 8(10):S172 (1991). Whatever excipient is incorporated into the present formulations, mat excipient must be sterile when added, or sterilized during the same process that sterilizes the amifostine. An embodiment of the present invention includes a sterilization step. Sterilization may be affected, for example, by sterile filtering a solution, e.g.. through a 0.2 μm pore size filter. Other methods of sterilizing known to those skilled in the an may also be employed. Suitable sterile and non-sterile excipients arc commercially available from: EM Industries, Inc., Hawthorne, NY.; J.T Baker, Inc., Hayward, CA; Spectrum Quality Products, Inc., Gardcna CA; Fisher Scientific International, Inc., Hampton NH; Aldrich Chemical Co., Inc., Milwaukee \VΪ; Abbott Laboratories, Inc., North Chicago 1L; Baxter Healthcare Corporation, Deerfield IL; and Amresco, Inc., Cleveland OH. The dosage form of the invention may be provided in single dose container forms by aseptically filling suitable containers with the sterile solution to a prescribed amifostine content as described above, or in multiple dose containers. It is intended that these filled containers will allow rapid dissolution of the solid composition upon reconstitution with appropriate sterile diluents in situ, giving an appropriate sterile solution of desired amifostine concentration for administration. As used herein, the term "suitable containers" means a container capable of maintaining a sterile environment, such as a vial, capable of delivering a vacuum dried product hermetically sealed by a stopper means. Additionally, suitable containers implies appropriateness of size, considering the volume of solution to be held upon reconstitution of the vacuum dried composition; and appropriateness of container material, generally Type I glass. The stopper means employed, £ ., sterile rubber closures or an equivalent, should be understood to be that which provides the aforementioned seal, but which also allows entry for the purpose of introduction of diluent, e.g., sterile Water for Injection, USP, Normal Saline, USP, or 5% Dextrose in Water, USP, for the reconstitution of the desired amifostine solution. These and other aspects of the suitability of containers for pharmaceutical products such as those of the invention are well known to those skilled in the practice of pharmaceutical arts, The stenle, thermally-stable pharmaceutical compositions (dosage forms) of the present invention are suitable for parenteral administration, for example, intravenous, intramuscular, intracavitary, intrathecal, and subcutaneous injections. These dosage forms have enhanced temperature stability over the prior dosage forms of amoφhous amifost e, have good physical appearance, and are efficacious in the prevention and treatment of radiation damage and chemotherapy damage. 5. EXAMPLES The following examples arc intended to be illustrative of the present invention and should not be construed, in any way, to be a limitation thereof. 5.1. EXAMPLE J STABLE AMORPHOUS AMIFOSTINE DOSAGE FORM COMPRISING NICOTINAMIDE An aqueous solution of 100 mg/mL amifostine and 12.5 mg/mL nicotinamide (Aldrich) is sterile filtered at 25 °C through a 0.2 μm filter, and then divided into 5 mL aliquots, each of which is transferred to 10 mL vials. Lyophilization stoppers are placed on the vials and the samples are loaded onto the freeze-dryer shelf maintained at 5 "C. The shelf temperature is decreased to -45 °C over 60 minutes, at which temperature it is kept for about 3 hours. The freeze-dryer condenser is then turned on and chamber is evacuated to about 100 μm Hg. After the chamber vacuum has equilibrated, the shelf temperature is ramped to -25 °C over 60 minutes while the vacuum is held constant. The shelf temperature is held at -25 ώ C for about 48 hours. The shelf temperature is then ramped to -10°C over 60 minutes, and then maintained at -10°C for 24 hours. Finally, the shelf temperature is ramped to about 35 "C over 60 minutes and then kept at that temperature for about 24 hours. At this point, the chamber is filled with nitrogen to a pressure of about 650 mm Hg and the vials are mechanically stoppered. This procedure results in thermally-stable, vacuum-dried single dose vials containing approximately 500 mg of amifostine (anhydrous basis) and 62.5 mg nicotinamide stabilizer as an elegant cake. Dosage forms prepared according to this procedure were placed on stability tests, and yielded the results provided in Table 1 below. 5.2. EXAMPLE 2 STABLE AMORPHOUS AMIFOSTINE DOSAGE FORM COMPRISING NICOTINAMIDE AND PVP An aqueous solution of 100 mg/mL amifostine, 12.5 mg/mL nicotinamide (Aldrich), and 10 mg/mL polyvinylpyrrolidone 30 (PVP30: BASF Aktiengesellschaft, Fe chemie, 0- 6700 Ludwigsbafen, Germany) is sterile filtered at 25 °C through a 0.2 μm filter, and then divided into 5 L aliquots, each of which is transferred to 10 mL vials. Lyophilization stoppers are placed on the vials and the samples are loaded onto the freeze-dryer shelf maintained at 5 D C, The shelf temperature is decreased to -45 X over 60 minutes, at which temperature it is kept for about 3 hours. The freeze-dryer condenser is then turned on and chamber is evacuated to about 100 μm Hg. After the chamber vacuum has equilibrated, the shelf temperature is ramped to -25 β C over 60 minutes while the vacuum is held constant. The shelf temperature is held at -25 °C for about 12 hours. The shelf temperature is then ramped to -10°C over 60 minutes, and then maintained at -10 6 C for 12 hours. Finally, the shelf temperature is ramped to about 35 β C over 60 minutes and then kept at that temperature for about 6 hours. At this point, the chamber is filled with nitrogen to a pressure of about 650 mm Hg and the vials are mechanically stoppered. This procedure results in thermally-stable, vacuum-dried single dose vials containing approximately 500 mg of amifostine (anhydrous basis), 62.5 mg nicotinamide and 50 mg PNP30 as an elegant cake. Dosage forms prepared according to this procedure were placed on stability tests, and yielded the results provided in Table 4 below. 5.3. EXAMPLE 3 DETERMINATION OF CRYSTALLINTTY The crystallinity of the dosage forms of this invention may be determined by powder x-ray diffraction as described, for example, in Remington's Pharmaceutical Sciences, 18 th ed. page. 173; The United States Pharmacopeia, 23 ,<J ed. (1995) pages 1843-1844. Figure 2 shows a typical powder x-ray diffraction spectrum of a dosage form of amoφhous amifostine prepared according to the method of Example 1 which was measured with a Geiger-Mϋller detector using nickel-filtered Cu K radiation. This diffraction pattern contains the broad baseline characteristic of amoφhous material. The peaks at 2Θ ~ 14.8, 25.6, and 26.3 are attributed to nicotinamide and/or noise. This assignment is clear from Figure 3, which shows the x-ray powder diffraction pattern of crystalline nicotinamide. Figure 4 shows the difference between the x-ray diffraction patterns of crystalline amifostine prepared as described by U.S. Patent No. 5,591,731 and that of an amoφhous amifostine dosage form of the present invention wherein nicotinamide is used as a stabilizer (8:1 amifostine to nicotinamide weight ratio). 10- 5.4. EXAMPLE 4 PREFERRED MANNER OF CONDUCTING STABILITY TEST OF STABLE AMORPHOUS AMIFOSTINE DOSAGE FORMS The stability of sterile amoφhous amifostine dosage forms obtained as described in Example 1 was tested at 5°C and 25*C Samples were stored in sealed, nitrogen-filled 10 mL tubing vials. Results of these tests may be correlated to stability at other temperatures by conventional methods. See, e.g., L. Lachman, et al. The Theory and Practice of Industrial Pharmacy pages 766-67 (1986), for a general discussion of stability prediction. From the results of the tests conducted here, decomposition of a dosage foπn kept at 25 °C for one month is generally equal to about one-half the decomposition of the same dosage form kept a °C for two years. At the end of each testing period, the amoφhous amifostine in the vials was tested for water content, thiol content, and/or amifostine content. In some cases, the water content was determined by Karl Fischer titration. Because amifostine may undergo hydrolysis under stress to produce 2-((3-aminopropyl)amino] ethane thiol ("WR-1065") and phosphoric acid, determination of the amount of this thiol gives an indication of the stability of the amifostine. Measurement of the amount of amifostine, however, is not preferred, as it has been found that stabilizers such as nicotinamide interfere with assays that determine the amount of amifostine in a sample. Consequently, it is preferred that the decomposition of a sample be determined by analysis of decomposition products, and WR-1065 in particular. Analysis of thiol content was conducted by high pressure liquid chromatography (HPLC) using the following procedure: 1, Preparation of Standards and Samples Weight and volumes may be adjusted provided the final concentrations remain the same. Store solutions under refrigeration and or in a refrigerated autosampler immediately after preparation. Shelf-life: 24 hours. 1.1 Preparation of Amifostine Standard Solution Accurately weigh approximately 30.0 mg of amifostine standarded into a 10-mL volumetric flask. Dissolve in 5 mL of water and dilute to volume with methanol. 1.2 Preparation of 2 (3-amino pronvDaminol ethancthiol. dihvdrochloride f WR-1065) Standard Solution Accurately weigh approximately 7 mg of WR-1065 standard into a 100-mL volumetric flask. Dissolve and dilute to volume with mobile phase. 1.3 Preparation of Amifostine (Drug Substance, for Amifostine Content Accurately weigh approximately 30.0 mg of amifostine into a 10-mL volumetric flask. Dissolve in 5 mL of water and dilute to volume with methanol. 1.4 Preparation of Amifostine (Drug Substance) for Related Substances Accurately weigh approximately 150.0 mg of amifostine into a 10-mL volumetric flask. Dissolve and dilute to volume with water. 1.5 Preparation of Amifostine for Injection Dissolve contents of one drug product vial with about 9 mL water. Quantitatively transfer sample to 50 L volumetric flask and dilute to volume with water. Transfer 6 mL of this solution to a 25-mL volumetric flask, add 6.5 mL of water and dilute to volume with methanol. 2. Svstem Suitability (Using Standard Solutions) Amifostine (Use Standard Solution 1.1) % RSD of 6 Replicate Injection of Amifostine ≤2% Tailing Factor ≤2 Theoretical Plates ≥ 1,000 WR-1065 (Use Standard Solution 1.2) % RSD of 6 Injections ≤4 Tailing Factor ≤2 Theoretical Plates 27,000 3. Equipment and Materials (As Stated Below or Equivalent) Equipment: HPLC System with UV Detector. Materials: Amifostine Standard; WR-1065 Standard; Concentrated Phosphoric Acid (H 3 PO,) (HPLC Grade); Methanol (MeOH) (HPLC Grade); Purified Water (16 meg-ohm or greater); and 1-Octanesulfonic Acid, Sodium Salt (OSA) (HPLC Grade). HPLC Chromatrographic Conditions Column Specifications: Packing Material- Bcckman Ultraspherc ODS (USP LI) Dimensions: 4.6 x 250 mm Particle Size: 5μm Mobile Phase: Methanol/Aqueous Phosphoric Acid, pH 2.5, 5 mM OSA (50/50) 1. Dissolve 0.54 g OSA in 500 mL of water, adjust with phosphoric acid to pH 2.5. 2. Dilute to 1000 L with methanol. 3. Filter and degas the mobile phase. Detection: 220 nm Absorbance Flow Rate: 1.0 mL/min Injection Volume: lOμL Column Temperature: Ambient Sample Temperature: 4°C 4. Procedure Inject sample and standard solutions, record retention time of the amifostine peak (approximately 4 minutes). Retention time of the standard amifostine peak and the sample preparation peak should agree within 10% to confirm identification of amifostine in the sample. 5. Calculations The calculations used to determine the degree of sample decomposition are the same as those described in U.S. Patent No. 5,591,731, which is hereby incoφorated by reference. 5.5. EXAMPLE 5 STABILITY RESULTS OFAMORPHOUS AMIFOSTINE II Typical results obtained by testing dosage forms of the invention using the method described in Example 4 are summarized below. The dosage form for which data is provided in Table 1 was made by the process described in Example I. As examination of this data makes clear, the stability of the dosage forms of the present invention is suφrisingly independent of their moisture content. TABLE 1 * Temperatures approximately accurate to -t 3 C C. n.d. = not determined. It has been observed that the stability of the dosage forms of this invention can be varied by changing the length of the drying steps, described in Example 1. For example, when vials prepared according to Example 1 are kept at -25 °C for 12 hours, then maintained at -10°C for 12 hours and finally kept at 35°C for 6 hours, samples are produced that show the stability results provided in Table 2. TABLE 2 Temperatures approximately accurate to £ 3°C. n.d. = not determined. The above results clearly indicate the enhanced thermal-stability of the amifostine dosage foπn produced by the method described herein. The enhanced stability is evident from the low weight percent of thiol formation, which indicates very little decomposition of the amifostine to form 2-[(3-aminopropyl)amino] ethane thiol (WR-1065). The exceptional and unexpected thermal stability of the dosage forms of this invention is also apparent from Table 3, which provides stability measurements of conventional dosage forms of amifostine (Amoφhous Amifostine I), dosage forms of this invention (Amoφhous Amifostine II), and the crystalline dosage form of U.S. Patent No. 5,424,471 ("Crystalline Ethyol®"). It is clear that the dosage form of the present invention possesses stability heretofore only exhibited by crystalline dosage forms. TABLE 3 b Comprising nicotinamide as a stabilizer in a 8:1 ratio (amifostine to nicotinamide). ς Comprising nicotinamide as a stabilizer in a 8:1 ratio (amifostine to nicotinamide). d Comprising nicotinamide as a stabilizer in a 8: 1 ratio (amifostine to nicotinamide). c Dosage form produced by the methods of this invention comprising nicotinamide as a stabilizer in a 4:1 ratio (amifostine to nicotinamide) (a mixture of crystalline and amoφhous). f Duration of 20 days. ; Temperatures approximately accurate to ± 3°C. n.d. = not determined. Further, as can be seen from Table 3, variations in drying cycle can affect thermal- stability. For example, Amoφhous Amifostine I was prepared using the prior method discussed above, while the embodiments of Amoφhous Amifostine II were prepared using different drying cycles. Using the superscripts of Table 3, Amoφhous Amifostine II was prepared using the drying cycle of Example 1, and Amoφhous Amifostme IF was prepared using the drying cycle described above that provided the results in Table II. Amoφhous Amifostine II s * and Amoφhous Amifostine IF were both prepared using the following drying cycle: freezing for about 3 hours at a temperature of about -45 °C; primary drying for about 60 hours at a temperature of about -25 °C; and secondary diying for about 24 hours at about -10°C, and then for about 6 hours at about 0°C. Dosage forms comprising amifostine, nicotinamide, and an excipient also exhibit suφrising stability. For example, dosage forms prepared according to the method of Example 2, wherein the excipient is PVP30, provide the stability data shown in Table 4. TABLE 4 Temperatures approximately accurate to ± 3 ' n.d. = not determined. Amifostine compositions of the invention that simply comprise amifostine and an excipient provide the stability data shown in Table 5. These compositions were prepared using the lyophilization cycle described in Example 2. TABLE 5 : Temperatures approximately accurate to ± 3 β C. * Comprising PVP30 in a ratio of 10:1 (amifostine to PVP30). b Comprising sucrose in a ratio of 10:1 (amifostine to sucrose). e Comprising low viscosity carboxymethyl cellulose sodium salt (CMC) in a ratio of 40: 1 (amifostine to CMC). d Comprising dextran in a ratio of 10: 1 (amifostine to dextran). n.d. = not determined. From these results, it is clear that the amoφhous amifostine of the invention can be combined with a wide variety of excipients to yield themially stable amoφhous amifostine compositions. It should be apparent to one of ordinary skill that other embodiments not specifically disclosed nonetheless fall within the scope and spirit of the present invention. Hence, the descriptions herein should not be taken as limiting the invention in any way, except as stated in the following claims.

Claims: THE CLAIMS What is claimed is: 1. A dosage foπn of amifostine which comprises thermally-stable, sterile, amoφhous amifostine which is suitable for reconstitution with a pharmaceutically acceptable vehicle into an injectable particulate-free drug product for parenteral administration to a subject. 2. A dosage form of amifostine suitable for reconstitution with a pharmaceutically acceptable vehicle into an injectable particulate-free drug product for parenteral administration to a subject which comprises thermally-stable, sterile, amoφhou≤ amifostine. 3. A thermally-stable, amoφhous, sterile dosage form comprising amifostine. 4. A thermally-stable amoφhous dosage form comprising sterile amifostine suitable for reconstitution with a pharmaceutically acceptable vehicle into an injectable particulate-free drug product for parenteral administration to a subject. 5. The dosage foπn of claim 1 further comprising a stabilizer. 6. The dosage form of claim 5 wherein the stabilizer is substantially amoφhous. 7. The amoφhous dosage form of claim 5 wherein the stabilizer is an amide or an amino acid. 8. The dosage form of claim 7 wherein the amide or amino acid is selected from the group consisting of nicotinamide, derivatives of nicotinamide, nicotinic acid, derivatives of nicotinic acid, glycine, alaninc, valine, leucinc, isoleucine, phenylalanine, tryptophan, asparagine, and mixtures thereof. 9. The dosage form of claim 5 wherein the molar ratio of stabilizer to amifostine is between about 0.05 and about 5.0. 10. The dosage form of claim 9 wherein the molar ratio of stabilizer to amifostine is between about 0.1 and about 1.0. 11. The dosage form of claim 10 wherein the molar ratio of stabilizer to amifostine is between about 0.2 and about 0.5. 12. The dosage form of claims 1 or 5 further comprising an excipient. 13. The dosage form of claim 12 wherein the excipient is selected from the group consisting of sodium chloride, citric acid, tartaric acid, gelatin, polyvinylpyrrolidone, dietylenetriamine-pentaacctic acid, ethylenediamine-tetraacetic acid, sodium deoxycholatc, sodium taurocholate, dextrose, sucrose, sorbitol, inositol, dextran, mannitol, carboxymethyl cellulose sodium salt, and mixtures thereof. 14. The dosage form of claim 1, 5 or 12, said dosage form having a water content of between about 0 weight percent and about 20 weight percent. 15. The dosage form of claim 14, said dosage form having a water content of between about 0 weight percent and about 15 weight percent. 16. The dosage foπn of claim 15, said dosage form having a water content of between about 0.5 weight percent and about 6 weight percent. 17. The dosage foπn of claims 1 wherein said dosage form forms less than about 5 weight percent of 2-[(3-aminopropyl)amino]ethane thiol when sealed in a vial and maintained at a temperature of about 40 °C for about one week, said weight percent based upon total weight of amifostine. 18. The dosage form of claim 17 wherein said dosage form forms less than about 4 weight percent of 2-[(3-aminopropyl)amino]ethane thiol when sealed in a vial and maintained at a temperature of about 40 °C for about one week, said weight percent based upon total weight of amifostine. 19- The dosage form of claim 18 wherein said dosage form forms less than about 3 weight percent of 2-[(3-aminopropyl)amiπo]ethane thiol when sealed in an inert gas filled vial and maintained at a temperature of about 40°C for about one week, said weight percent based upon total weight of amifostine. 20. The dosage form of claims 1 wherein said dosage form forms less than about 5 weight percent of 2-[(3-aminopropyl)amino]ethane thiol when sealed in a vial and maintained at a temperature of about 25°C for about one month, said weight percent based upon total weight of amifostine. 21. The dosage form of claim 20 wherein said dosage form forms less than about 4 weight percent of 2-[(3-aminopropyl)amino]ethane thiol when sealed in a vial and maintained at a temperature of about 25 °C for about one month, said weight percent based upon total weight of amifostine. 22. The dosage form of claim 21 wherein said dosage form forms less than about 3 weight percent of 2-[(3-aminoproρyl)amino]ethane thiol when sealed in a vial and maintained at a temperature of about 25 °C for about one month, said weight percent based upon total weight of amifostine. 23. The dosage form of claim 22 wherein said dosage form forms less than about 2 weight percent of 2-[(3-aminopropyl)amino]elhane thiol when sealed in a vial and maintained at a temperature of about 25 °C for about one month, said weight percent based upon total weight of amifostine. 24. The dosage form of claim 1 wherein said dosage form forms less than about 3 weight percent of 2-[(3-aminoρropyl)amino]cthane thiol when sealed in a vial and maintained at a temperature of about 5 °C for about two years, said weight percent based upon total weight of amifostine. 25. The dosage form of claim 24 wherein said dosage form forms less than about 2 weight percent of 2-[(3-aminopropyl)am_noJethane thiol when scaled in a vial and maintained at a temperature of about 5°C for about two years, said weight percent based upon total weight of amifostine. 26. The dosage form of claim 25 wherein said dosage form forms less than about 1 weight percent of 2-[(3~aminopropyl)amino] ethane thiol when sealed in a vial and maintained at a temperature of about 5 °C for about two years, said weight percent based upon total weight of amifostine. 27. A room temperature stable dosage form of amifostine comprising sterile, amoφhous amifostine which is suitable for reconstitution with a pharmaceutically acceptable vehicle into an injectable particulate-free drug product for parenteral administration to a subject. 28. A room temperature stable amoφhous dosage form comprising sterile, amoφhous amifostine which is suitable for reconstitution with a pharmaceutically acceptable vehicle into an injectable particulate-free drug product for parenteral administration to a subject. 29. A refrigerated stable dosage form comprising sterile, amoφhous amifostine, wherein said dosage form forms less than about 3 weight percent of 2-[(3- aminopropyl)amino]ethane thiol when sealed in a vial and maintained at a temperature of about 5°C for about two years, said weight percent based upon total weight of amifostine. 30. A dosage form of amifostine consisting essentially of thermally-stable, sterile, amoφhous amifostine. 31. A dosage form of amifostine consisting of thermally-stable, sterile, amoφhous amifostine. 32- A thermally-stable dosage form comprising sterile amoφhous amifostine and nicotinamide in an amifostine to nicotinamide weight ratio of between about 4:1 and about 10:1. 33. The dosage form of claim 32 wherein the amifostine to nicotinamide weight ratio is about 8:1. 34. The dosage form of claim 27 or 29 further comprising a stabilizer. 35. The dosage form of claim 27 or 29 further comprising an excipient. 36. The dosage form of claim 27 or 29, said dosage form having a water content of between about 0 weight percent and about 20 weight percent. 37. A dosage form of claim 1, 2, 3, 27, 28 or 28, wherein said dosage form is substantially amoφhous. 38. A dosage form of claim 1, 2, 3, 27, 28 or 28, wherein said dosage form is at least about 80% amoφhous by weight. 39. A dosage form of claim 1, 2, 3, 27, 28 or 2S, wherein said dosage form is at least about 90% amoφhous by weight. 40. A process for the preparation of a thermally-stable dosage form of amoφhous amifostine comprising lyophilizing a sterile aqueous solution of amifostine wherein said lyophilization comprises: a freezing cycle having a first average temperature of between about -70 C C and about -10 β C and lasting for a first period of time of between about 1 hour and about 15 hours; and a primary drying cycle having a second average temperature of between about -45 °C and about 10 α C and lasting for a second period of time of between about 8 hours and about 100 hours. 41. The process of claim 40 wherein the aqueous solution is substantially free of alcohol. 42. The process of claim 40 wherein the aqueous solution has a pH of between about 6 and about 9. 43. The process of claim 40 further comprising dissolving a stabilizer in the aqueous solution prior to lyophilization. 44. The process of claim 40 further comprising dissolving an excipient in the aqueous solution prior to lyophilization. 45. The process of claim 40 further comprising mixing the product formed upon lyophilization with a stabilizer. 46. The process of claim 40 further comprising mixing the product formed upon lyophilization with an excipient. 47. The process of claim 43 or 45 wherein the stabilizer is an amide, amino acid, or pharmaceutically acceptable base. 48. The process of claim 47 wherein the amide or amino acid is selected from the group consisting of nicotinamide, derivatives of nicotinamide, nicotinic acid, derivatives of nicotinic acid, glycine, alanine, valine, leucine, isoleucine, phenylalanine, tryptophan, asparagine. and mixtures thereof. 49. The process of claim 47 wherein the molar ratio of stabilizer to bulk amifostine is between about 0.05 and about 5.0. 50. The process of claim 49 wherein the molar ratio of stabilizer to bulk amifostine is between about 0, 1 and about 1.0. 51. The process of claim 50 wherein the molar ratio of stabilizer to bulk amifostine is between about 0.2 and about 0.5. 52. The process of claim 40 wherein the first average temperature is between about -65 C C and about -30 β C. 53. The process of claim 52 wherein the first average temperature is between about -55 °C and about -40 ς C. 54. The process of claim 40 wherein the first time is between about 2 hours and about 10 hours. 55. The process of claim 54 wherein the first time is between about 5 hours and about 8 hours. 56. The process of claim 40 wherein the second average temperature is between about -35 °C and about 0°C. 57. The process of claim 56 wherein the second average temperature is between about -30°C and about -10°C. 58. The process of claim 40 wherein the second time is between about 16 hours and about 86 hours. 59. The process of claim 58 wherein the second lime is between about 24 hours and about 72 hours. 60. The process of claim 40 wherein lyophilizing the solution further comprises a secondary drying step having a third average temperature of between about -25 °C and about 40°C and a third average time of between about 0.5 hours and about 48 hours. 61. The process of claim 60 v/herein the third average temperature is between about -15 6 C and about 40°C. 62. The process of claim 61 wherein the third average temperature is between about O'C and about 35 °C. 63. The process of claim 60 wherein the third time is between about 2 hours and about 36 hours. 64. The process of claim 63 wherein the third time is between about 6 hours and about 24 hours. 65. The process of claim 40 further comprising stoppering the vials with desiccating stoppers after lyophilizing the solution. 66. The process of claim 40 wherein the aqueous solution is lyophihzed under conditions such that the dosage form of amifostine has a water content of between about 0 weight percent and about 20 weight percent. 67. The process of claim 66 wherein the aqueous solution is lyophihzed under conditions such that the dosage foπn of amifostine has a water content of between about 0 weight percent and about 15 weight percent. 68. The process of claim 67 wherein the aqueous solution is lyophihzed under conditions such that the dosage form of amifostine has a water content of between about 0.5 weight percent and about 6 weight percent. 69- A thermally-stable dosage form of amoφhous amifostine fomied by the process of claim 40.

Inventors: STOGNIEW MARTIN, ZADEI JAVAD M, STOGNIEW, MARTIN, ZADEI, JAVAD, M.
Applicants: MEDIMMUNE ONCOLOGY INC, MEDIMMUNE ONCOLOGY, INC.
Application year: 2000
Main classification: A61K47
IPC codes: A61K9, A61K31, A61K47, A61P7, A61P13, A61P31, A61P35, A61P39, A61P43