the liposome - encapsulated amphotericin b ( amp b ) of the present invention may be prepared by a variety of methods . these methods involve the solubilization of the lipids in an appropriate solvent and the solubilization of amp b in an appropriate solvent . the amp b solution is then added to the lipid solution , and the solutions are distributed onto the bottom of a container . the solvent is then removed by evaporation , the lipid - amp b film is dispersed in a salt solution , and the liposomes allowed to form by shaking . it will be recognized by those with skill in the art who have the benefit of this disclosure that both the type of lipid and the proportion of that lipid in the liposome may be varied . applicants have experienced particular success with the phosphoglycerides dimyristoyl phosphatidylcholine ( dmpc ) and dimyristoyl phosphatidylglycerol dmpg ) in a 7 : 3 dmpc : dmpg molar ratio . this formulation is non - toxic to mammalian systems and is capable of encapsulating 100 % of the amphotericin b available in solution . combining these same lipids in a 9 : 1 dmpc : dmpg molar ratio reduces the encapsulation efficiency to 94 . 9 %. stable amphotericin b - containing liposomes have been prepared from the phosphoglycerides phosphatidylcholine ( pc ) and phosphatidylglycerol ( pg ) in a 9 : 1 pc : pg ratio . however , liposomes of this formulation were capable of incorporating only 91 . 8 % of the amphotericin b available in solution . as used throughout this specification , the term &# 34 ; sterol - free liposome &# 34 ; refers to liposomes comprised of lipid material of a type other than those lipids which may be considered &# 34 ; sterols &# 34 ;, for instance , the sterols ergosterol or cholesterol . other non - sterols , in particular , lipids selected from the phosphoglycerides and the sphingolipids , may be used in the amp b - containing liposomes of the present invention . selection of the appropriate lipids for liposome composition is governed by the factors of : ( 1 ) liposome stability , ( 2 ) encapsulation efficiency , and ( 3 ) non - toxicity to mammalian systems . it is expected that one of skill in the art who has the benefit of this disclosure could formulate liposomes according to the present invention which would optimize these factors from , for instance , the phosphoglycerides phosphatidylinositol and cardiolipin , the sphingolipids sphingomyelin and sphingosine , or any combination of these lipids with pc , pg , dmpc or dmpg . other phosphoglycerides and sphingolipids that might be useful include several types of liposomes are believed useful for encapsulating amphotericin b in accordance with the present invention , including stable plural lamellar vesicles and multilamellar liposomes . whenever &# 34 ; encapsulation &# 34 ; is used in this patent it is meant to include incorporation as well . the liposome - encapsulated amp b may then be administered to a mammal infected with a fungal infection . studies have indicated that the maximum dose of free amp b tolerated by mice is approximately 0 . 8 mg / kg of body weight and the ld 50 is about 1 . 2 mg / kg . when encapsulated in liposomes , doses of up to approximately 12 mg of amp b per kg body weight have been shown to result in no gross clinical evidence of toxicity . nor do such doses cause abnormalities in the serum creatine , blood urea nitrogen and serum glutamic pyruvic transaminase levels of the mice . histopathology revealed no sign cf kidney edema or nephrocalcinosis in mice receiving such doses . total doses as high as 28 mg / kg of amp b in liposomes have been given with no apparent acute side effect ; no ld 50 has been identified in the case of liposome - encapsulated amp b . comparable doses may be given to humans , again with no apparent toxicological symptoms . the present invention may be better understood by reference to the following examples . the liposome encapsulated amp b of the present invention may be prepared according to either of the following methods . the first method is described by lopez - berestein , g ., et al ., &# 34 ; treatment and prophylaxis of disseminated infection due to candida albicans in mice with liposome - encapsulated amphotericin b .&# 34 ; j . inf . dis ., vol . 147 ( 1983 ), pp . 939 - 945 , hereby incorporated by reference . briefly , the method of lopez - berestein , et al . involves the preparation of multilamellar vesicles as follows . the lipids dimyristoyl phosphatidylcholine ( dmpc ) and dimyristoyl phosphatidylglycerol ( dmpg ) were obtained from avanti polar lipids ( birmingham , ala . ), and desoxycholate - free amp b was obtained from dr . dan bonner ( squibb pharmaceuticals , new brunswick , n . j .). dmpc and dmpg were dissolved in chloroform in a molar ratio of 7 : 3 dmpc : dmpg . amp b was dissolved in methanol at a concentration of 40 μg / ml and the amp b solution added to the chloroform containing the dmpc and dmpg . this mixture was placed in a rotary evaporator ( rotavapor ®; brinkman instruments , westbury , n . y .) until all organic solvents were removed . normal saline was then added and the vesicles formed by gentle agitation . using this method , to prepare enough liposome - encapsulated amp b to make up a single dose for a 50 kg patient at a dose of 0 . 8 mg / kg body weight ( as discussed in example 4 ) requires the drying of at least 1 to 1 . 5 liters of the amp b - methanol solution . under controlled temperature and pressure conditions , approximately 3 to 4 hours are required to evaporate this volume of the amp b - methanol solution . the preferred method for formulation of liposome - encapsulated amp b in accordance with the present invention is as follows . the lipids dmpc and dmpg and amp b were obtained from the same sources as described above . the amp b is dissolved in chloroform in the presence of dmpc and dmpg in a 7 : 3 molar ratio . all other steps in the preparation of the liposome - encapsulated amp b were the same as described above . using this method , 640 μg of amp b was dissolved in 1 ml of chloroform ( containing 25 mg of the lipid mixture ), a significant increase over the 40 μg / ml which can be dissolved in methanol as in the method described above . consequently , a decreased volume of amp b solution is required with a concomitant decrease in the amount of time required to evaporate the solution . in vitro tests were conducted to determine the effect of free amp b , amp b encapsulated in nor - sterol - containing liposomes , ( l - amp b ), amp b encapsulated in cholesterol - containing liposomes ( l - amp b - c ) and amp b in ergosterol - containing liposomes ( l - amp b - e ). desoxycholate free amphotericin b was obtained from e . r . squibb & amp ; sons , inc . amp b was encapsulated in non - sterol containing liposomes by the method described by lopez - berestein , et al ., and summarized in example 1 , above . in order to obtain the different doses necessary , lipid concentration was held constant as the amp b concentration was decreased . the concentration of amp b within the liposome was determined by scanning in a uv absorption spectrophotometer ( gilford instrument laboratories , oberlin , ohio ) at 405 nm after the amp b was dissolved in methanol . cholesterol or ergosterol , obtained from avanti polar lipids ( birmingham , ala . ), was added to the chloroform dmpc : dmpg solution at a molar ratio of 7 : 3 : 4 ( dmpc : dmpg : sterol ). in vitro activity of free amp b , l - amp b , l - amp b - c and l - amp b - e was tested on the following yeast species , all clinical isolates obtained from the clinical microbiology laboratories at the university of texas m . d . anderson hospital and tumor institute at houston : candida albicans , c . tropicalis , c . parapsilosis , torulopsis glabrata and cryptococcus neoformans . the ynb tube dilution method described by shadomy , s ., et al ., &# 34 ; susceptibility testing with antifungal drugs .&# 34 ; in lennette , e . h ., et al . ( eds . ), manual of clinical microbiology , 3rd ed . ( washington , d . c ., american society for microbiology , 1980 ), pp . 647 - 653 , hereby incorporated by reference , was used to perform all tests . all tubes were subcultured ( 10 μl ) onto sabouraud - dextrose agar ( sda ) ( scott / randolph , houston , tex .) plates . minimal fungicidal concentrations ( mfc ) were determined after incubation for 18 hours . the mfc was defined as the lowest concentration of amp b that allowed no growth or growth of fewer than four colonies on the subculture plates . the results are presented in table 1 . these data indicate that the mfc of l - amp b was increased over that of amp b in only 8 of the 19 strains tested , and that only in 4 of those 8 strains was the increase significant . the mfc of l - amp b - c was increased over that of free amp b in 11 of the strains tested , and in 7 of those strains , this increase was significant . the mfc of l - amp b - e was higher than that of amp b in 18 of the 19 strains tested , and the increase was significant in all 18 of those strains . it can be seen that , in terms of the killing of these fungal strains , the efficacy of these compositions may be ranked in decreasing order , with amp b being most effective , then l - amp b , l - amp b - c and , finally l - amp b - e . this result was borne out by the killing curve of amp b , l - amp b , l - amp b - c and l - amp b - e shown in fig1 . this curve was constructed by incubation of c . albicans strain 336 for 18 hours at 35 ° c . for these tests , 0 . 1 ml was removed from all drug concentrations tested . ten - fold serial dilutions were made , and 0 . 1 ml of each dilution ( in duplicate ) was plated onto sda plates . colony counts were made after incubation for 48 hours using those dilution plates which grew between 30 and 300 colonies per plate . table 1__________________________________________________________________________mfc ( μg / amp b / ml ) results using avariety of yeast isolatesand liposome preparationorganisms strain amp b l - amp b l - amp b - c l - amp b - e__________________________________________________________________________candida albicans 306 1 . 6 1 . 6 3 & gt ; 25 *&# 34 ; 704 0 . 4 0 . 8 1 . 6 * & gt ; 25 *&# 34 ; 1091 0 . 8 0 . 8 1 . 6 & gt ; 25 *&# 34 ; 57 0 . 8 0 . 8 0 . 8 & gt ; 25 * candida tropicalis 251 3 6 12 * & gt ; 25 *&# 34 ; 2463 1 . 6 1 . 6 3 * 6 *&# 34 ; 1784 3 3 3 & gt ; 25 *&# 34 ; 1324 1 . 6 1 . 6 1 . 6 & gt ; 25 * candida parapsilosis 139 3 & gt ; 25 * & gt ; 25 * & gt ; 25 *&# 34 ; 1341 & gt ; 25 & gt ; 25 & gt ; 25 & gt ; 25 &# 34 ; 2300 3 3 3 & gt ; 25candida glabrata 684 3 25 * 25 * & gt ; 25 *&# 34 ; 1905 3 3 3 12 *&# 34 ; 2539 3 3 1 . 6 12 *&# 34 ; 1172 1 . 6 3 1 . 6 6 * candida neoformans 222 1 . 6 0 . 8 3 25 *&# 34 ; 843 0 . 8 12 * 12 * & gt ; 25 *&# 34 ; 881 1 . 6 12 * 12 * & gt ; 25 *&# 34 ; 595 0 . 4 0 . 8 1 . 6 6 * __________________________________________________________________________ * indicates mfc ≧ 4 fold difference compared to free amp b . as shown in fig1 the effect of sterols on growth inhibition was minimal at lower drug concentrations . the sterol - containing liposomes had a protective effect that prevented the killing of fungal cells at higher amp b concentrations ( greater than 1 . 0 μg / ml ). a 12 - fold higher concentration of l - amp - c was required to kill c . albicans 336 than either l - amp b or free amp b . l - amp b - e was even less effective in killing c . albicans 336 than l - amp b - c . as shown in fig1 concentrations of 50 μg of amphotericin b per ml were unable to kill the test organism when administered in ergosterol - containing liposomes . hale - stoner mice , 6 - 8 weeks old and weighing 20 - 25 g , were obtained from the university of texas science park ( bastrop , tex .). mice ( 10 per group ) were injected intravenously with candida albicans strain 336 . this strain was grown for 18 hours on sda plates at 37 ° c ., washed and resuspended in saline . the mice were injected in the tail vein with 0 . 2 ml of the suspension containing 7 × 10 5 colony - forming units . this concentration consistently caused a disseminated infection which , after 48 hours , primarily affected the kidney , liver , spleen and lungs . the mice were injected on the second day of infection with a single dose of amphotericin b . amp b was encapsulated in sterol - free and sterol - containing liposomes prepared by the method described in example 2 , above . amp b concentration was determined at 405 nm as described in example 2 . the effect of increasing concentrations of amp b in sterol - free liposomes on the survival of mice is shown in fig2 . in each liposome case shown in fig2 the liposomes contained 400 mg lipid / kg body weight . empty liposomes had no significant effect on mouse survival . at doses equivalent to the maximum amount of free amp b tolerated by mice ( 0 . 8 mg / kg body weight ), amp b in non - sterol containing liposomes was as effective as free amp b in prolonging the survival of infected mice . increasing the concentration of amp b in sterol - free liposomes resulted in a highly significant increase in survival time . on day 50 of the infection , 40 % of the animals that had received 2 mg amp b / kg were alive and 100 % of the animals that had received 4 mg / kg were alive . the effect of the lipid composition of the liposome on the survival of mice infected with c . albicans 336 was also evaluated . the results are shown in fig3 . each liposome case shown in fig3 used 1 . 6 mg amp b in 200 mg total lipid / kg . administration of free amp b improved survival time over the controls ( control 50 % survival , 5 days , free amp b 50 % survival , 10 days ). amp b encapsulated within liposomes ( all animals alive on day 60 ) significantly enhanced the survival time compared to that of free amp b ( p & lt ; 0 . 001 , generalized wilcoxon test ). however , in this study there was no significant difference between the survival time of mice treated with amp b in sterol - free liposomes as compared to the survival time of mice treated with amp b encapsulated in cholesterol - containing liposomes or ergosterol - containing liposomes . treatment of systemic fungal infections in cancer patients with liposome - encapsulated amphotericin b three cancer patients have been treated for systemic fungal infections with liposome - encapsulated amphotericin b ( amp b ). amp b was incorporated into multilamellar vesicles as described by lopez - berestein , et al ., supra ( see example 1 ). amp b content was determined by high performance liquid chromatography analysis as described by nilsson - ehle , i ., et al . &# 34 ; quantitation of amphotericin b with use of high - pressure liquid chromatograph .&# 34 ; j . infect . dis ., vol . 135 ( 1977 ), pp . 414 - 422 , hereby incorporated by reference . phospholipid content was quantified by determining the organic phosphorus in the preparation by the method of marinetti , g . v . &# 34 ; chromatographic separation , identification , and analysis of phosphatides .&# 34 ; j . lipid res ., vol . 3 ( 1962 ), pp . 1 - 20 , hereby incorporated by reference . the preparations were sterile as assessed by bacter and plate culture studies . in all three cases , liposome - encapsulated amp b was administered to the patients intravenously over 10 - 15 minutes . a 13 - year old female developed diffuse , poorly differentiated lymphocytic lymphoma a number of years ago . she achieved a complete remission following the administration of chemotherapy . five years later , she was hospitalized with fever , fatigue and general malaise and malignant lymphoid cells were identified in the bone marrow . she was treated with parenteral cyclophosphamide , vincristine and prednisolone . intrathecal cytosar , hydrocortisone and methotrexate were given prophylactically . after achieving complete remission , maintenance therapy was instituted with 6 - mercaptopurine and methotrexate for six months , after which all chemotherapy was stopped . during that hospitalization , she developed multiple infectious episodes including : typhlitis , escherichia coli and staphylococcus aureus septicemia , bacterial urinary tract infection and herpectic lesions of the skin . in the third month , therapy with amp b was initiated for persistent fever and c . albicans urinary tract infection . after 16 days , 5 - fluorocytosine ( 5fc ) was added because of persistent fever . no response was obtained and ketoconazole was administered . in the fifth month , the patient remained febrile . the liver was palpable 4 cm below the right costal margin . she also had cardiomegaly , tachycardia and an s 3 gallop . computerized tomography ( ct ) of the abdomen showed multiple areas of radiolucency in the liver consistent with fungal abscesses . an open liver biopsy showed infarcted parenchyma and necrotizing abscesses in the liver , due to fungi . no organisms could be cultured from the specimen , but it was morphologically consistent with aspergillus spp . due to persistence of fever , clinical deterioration and worsening of the liver lesions , hepatic artery infusion with amp b was started . the patient received a cumulative dose of more than 6 gm amp b over a seven - month period . throughout amp b therapy , fever and chills were observed . she continued to have a daily temperature of 38 . 5 ° c ., and remained severely ill , anorectic and malnourished . she had become jaundiced ( bilirubin 7 mg / dl ). on physical examination of the chest , bilateral basilary rales and a grade ii - iii apical ejection murmur were detected . the abdomen was distended and diffusely tender , the liver edge was 8 cm below the right costal margin . on chest x - ray examination , there were bilateral pleural effusions , patchy pulmonary infiltrates in both lung fields , and the cardiac silhouette was enlarged . computerized abdominal tomography showed increased hepatosplenomegaly with increased size of the radiolucencies already observed in the liver , and new lesions were detected in the spleen . laboratory findings at that time , and during treatment , are summarized in table 2 . anergy to skin test with recall antigens lymphopenia , an inverted t helper / t suppressor ratio ( okt4 / okt8 = 16 . 7 / 59 . 7 %), and absolute values of t helper of less than 2000 cells / mm 3 were observed throughout the course of her disease . table 2__________________________________________________________________________hematologic , hepatic and renal function studiesduring liposomal - amphotericin b therapy cumulative dose of white blood creatinine total alk . amphotericin b cells n / mm . sup . 3 / bun clearance bilirubin ldh sgot phosp . date ( mg ) segmented % mg / 100 ml cc / min mg / 100 ml mu / ml mu / ml mu / ml__________________________________________________________________________case 1before treatment baseline 8 . 8 / 9 37 44 7 . 0 256 123 253during treatment 484 4 . 5 / 29 14 61 0 . 8 134 60 350case 2before treatment baseline 0 . 1 / 0 35 106 2 . 4 222 82 320during treatment 189 0 . 1 / 0 21 96 0 . 8 183 18 159case 3before treatment baseline 19 . 6 / 88 5 36 0 . 8 277 125 304during treatment 551 17 . 5 / 72 10 67 0 . 5 193 49 298__________________________________________________________________________ liposomal amp b ( sterol - free ) was started at a dose of 0 . 4 mg / kg intravenously after all other medications were discontinued . no acute side - effects occurred after the first dose . subsequent therapy was 0 . 6 mg / kg for 2 doses , and 0 . 8 mg / kg thereafter . doses were given every 3 to 4 days for a total of 19 doses ( total amp b 484 mg , total lipid 20 gm ). no acute or chronic toxicity was observed during the 3 months of liposomal amp b treatment . four weeks after the initial treatment , marked improvement in her general status was reflected by disappearance of fever , increased appetite , improved strength , decreased abdominal pain and hepatomegaly as well as resolution of the lung infiltrates and cardiomegaly . a repeated open liver biopsy performed 4 months after the onset of liposomal amp b treatment disclosed only areas of fibrosis , and hemosiderosis . no fungal organisms were demonstrated . six months after discontinuation of treatment , the patient was in excellent general condition . a 22 - year old male with acute lymphocyte leukemia had achieved complete remission after induction chemotherapy . eleven months later , he was found to have recurrent leukemia in the bone marrow . after failing reinduction chemotherapy for four months , he was started on high dose cytosar ( 3 g / m 2 / daily × 12 ). he developed a lesion in the nasal turbinate which on biopsy and culture was found to be aspergillus terreus . he received a total of 2 . 4 gm amp b intravenously which was always associated with severe nausea , fever and chills . the nasal lesions worsened in spite of amp b therapy and new lung lesions appeared on chest x - ray examination which were compatible with typical &# 34 ; fungus balls .&# 34 ; at that time , a . terreus was cultured from a lung specimen , bronchial washings and the sputum , urine and stool . the patient developed progressive dypsnea , severe neutropenia , and markedly abnormal liver function tests ( table 2 ). anergy to skin tests was observed . he was given a total of 1 . 4 gm of amp b by aerosolization without improvement . subsequently , sterol - free liposomal amp b therapy was started at a dose of 0 . 4 mg / kg with no acute side - effects observed . doses were repeated at 3 - 4 day intervals . after the sixth dose , he was afebrile , the nasal lesions had improved and there was clearing of the lung infiltrates on chest x - ray examination improvement in liver function tests were observed ( table 2 ). a total of 5 doses of amp b in liposomes were administered ( total amp b 189 mg , total lipid 5 gm ). at that point , liposomal - amp b therapy was discontinued due to the presence of hallucinations which were later found to be related to the use of several neuroleptic drugs . two weeks later , the patient developed new lung infiltrates and clinical evidence of diffuse intravascular coagulation ( dic ), which was related to p . maltophilia septicemia . post mortem examination showed evidence of dic . this was evident by the presence of multiple thrombi in the lungs and kidneys . no fungal organisms were seen in the nose , liver or spleen . fibrosis was evident in both lungs . single microscropic foci containing a few fungal organisms were seen in one kidney and in one lung . p . maltophilia was cultured from the lung . a 22 - year old female was diagnosed of acute progranulocytic leukemia . she was treated with cytosar , daunorubicin , 6 - thioguanine , vincristine and prednisone . a bone marrow test conducted one month after initiation of therapy showed a complete remission . two months after initiation of therapy , she developed cavitary lung infiltrates and necrotizing retinitis . an open lung biopsy was done and the silver stain was positive for budding fungal hyphae . therapy with amp b and 5 fc was started . in the following month , she developed right upper quadrant abdominal pain and increased alkaline phosphatase . an abdominal ct scan in the following month showed multiple lesions in the liver and spleen . a liver biopsy showed yeast organisms which were consistent morphologically with candida . from then on , the patient followed a gradually deteriorating clinical course , requiring continued hospitalization . she was treated with a total of 4 grams of amp b during her 6 - month hospital stay . she was also treated with 5 fc , miconazole and rifampin . a repeated open liver biopsy conducted five months after the abdominal ct scan showed lesions consistent with candida microabscesses . throughout this period , the patient continued to spike fevers of 102 ° f . with rigors . at this point , the patient looked cachectic and had fever and rigors . an abdominal ct scan showed diffuse parenchymal lesions in the liver and spleen compatible with microabscesses . sterol - free liposomal - amp b therapy was started at a dose of 0 . 4 mg / kg for two doses and continued at 0 . 8 mg / kg every 72 hours , for a total of 500 mg of amp b . after two weeks of treatment , the patient showed marked improvement in her clinical condition as evidenced by an increased caloric intake which resulted in discontinuation of ivh . the results of hematologic , hepatic and renal function studies are given in table 2 . she also had decreased abdominal pain and decreased liver span on physical examination . after 3 weeks , she was discharged and therapy was continued as an outpatient . a repeated open liver biopsy done two months after the onset of liposomal amp b treatment showed no evidence of fungi . the patient continues in good general condition without evidence of chronic toxicity . comparison of minimal fungicidal concentration of amphotericin b encapsulated in different phospholipid compositions several different liposome compositions were tested , using generally the same procedure described in example 2 , to determine the effect of the phospholipids chosen on the minimal fungicidal concentration of amphotericin b when administered to mice infected with c . albicans . the compositions included one or more of the following : dmpc , dmpg , cholesterol ( chol ), ergosterol ( erg ), and stearylamine ( sa ). the results are shown in table 3 . table 3______________________________________effect of lipid composition on theminimal fungicidal concentration ( mfc ) of liposomal - amphotericin blipid mfc ( μg ofcomposition molar ratio amp b per ml ) ______________________________________amp b alone 1 . 6dmpc : dmpg 7 : 3 1 . 6dmpc alone 3 . 2dmpc : chol 9 : 1 3 . 2dmpc : erg 9 : 1 6 . 4dmpg alone 50dmpg : chol 9 : 1 50dmpg : erg 9 : 1 50dmpc : sa 7 : 3 12 . 5dmpc : sa : chol 9 : 1 25dmpc : sa : erg 9 : 1 25______________________________________ the above examples are presented for purposes of illustration only , and are not intended to be an exhaustive description of all embodiments of the present invention .
a method is disclosed for treatment of disseminated fungal infection in a mammal comprising the administration of a fungicidally effective amount of amphotericin b encapsulated in a substantially sterol - free liposome to the infected mammal . also provided is an agent for treatment of disseminated fungal infection in a mammal comprising amphotericin b encapsulated in a liposome which consists essentially of lipids other than sterols .