Abstract:
A method is disclosed for improving vascular access in a patient in need thereof by administering to the patient a therapeutically effective amount of at least one amine polymer. Cross-linked polyallylamine polymers are particularly efficacious.

Description:
RELATED APPLICATION(S)  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/284,445, filed on Apr. 18, 2001 and U.S. Provisional Application No. 60/285,031, filed Apr. 19, 2001. The entire teachings of the above application(s) are incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Sevelamer hydrochloride, commercially available as Renagel® (GelTex Pharmaceuticals, Inc., Waltham, Mass.) is a phosphate-binding gel that is used for clinical control of serum phosphate levels in patients on haemodialysis.  
         SUMMARY OF THE INVENTION  
         [0003]    The invention relates to a method for improving vascular access in patients with vascular shunts that includes administering to the patient a therapeutically effective amount of at least one amine polymer such as a cross-linked polyallylamine.  
           [0004]    The cross-linking avoids or minimizes absorption of the polymer in the patient. Such polyamines can include polyallylamine, polyvinylamine, and polybutenylamine.  
           [0005]    Preferred polymers employed in the invention comprise water-insoluble, non-absorbable, and optionally cross-linked polyamines as described herein. The polyamines of the invention can be amine or ammonium-containing aliphatic polymers. An aliphatic amine polymer, is a polymer which is manufactured by polymerizing an aliphatic amine monomer. In a preferred embodiment, the polymers are characterized by one or more monomeric units of Formula I:  
                         
 
           [0006]    and salts thereof, where n is a positive integer and x is 0 or an integer between 1 and about 4, preferably 1. In preferred embodiments, the polymer is cross-linked by means of a multifunctional cross-linking agent. In one embodiment, the polymer is sevelamer hydrochloride.  
           [0007]    Other features and advantages will be apparent from the following description of the preferred embodiments thereof and from the claims.  
         DETAILED DESCRIPTION OF THE INVENTION  
         [0008]    As described above, the preferred polymers employed in the invention comprise water-insoluble, non-absorbable, optionally cross-linked polyamines. Preferred polymers are aliphatic. Examples of preferred polymers include polyallylamine, polyvinylamine and polydiallylamine polymers. The polymers can be homopolymers or copolymers, as discussed below, and can be substituted or unsubstituted. These and other polymers which can be used in the claimed invention have been reported in U.S. Pat. Nos. 5,496,545, 5,667,775, 5,487,888, 5,607,669, 5,618,530, 5,624,963, 5,679,717, 5,703,188, 5,702,696 and 5,693,675, the contents of which are hereby incorporated herein by reference in their entireties. Polymers suitable for use in the invention are also reported in copending U.S. applications Ser. Nos. 08/659,264, 08/823,699, 08/835,857, 08/470,940, 08/826,197, 08/777,408, 08/927,247, 08/964,498, 08/964,536 and 09/359,226, the contents of which are incorporated herein by reference in their entireties.  
           [0009]    The polymer can be a homopolymer or a copolymer of one or more amine-containing monomers or a copolymer of one or more amine-containing monomers in combination with one or more non-amine containing monomers. Where copolymers are manufactured with the monomer of the above Formula I, the comonomers are preferably inert, and non-toxic. Examples of suitable non-amine-containing monomers include vinylalcohol, and vinylformamide. Examples of amine-containing monomers preferably include monomers having the Formula 1 above. Preferably, the monomers are aliphatic. Most preferably, the polymer is a homopolymer, such as a homopolyallylamine, homopolyvinylamine, homopolydiallylamine or polyethylenamine. The word “amine,” as used herein, includes primary, secondary and tertiary amines, as well as ammoniums such as trialkylammonium.  
           [0010]    Other preferred polymers include polymers characterized by one or more repeat units set forth below.  
                         
 
           [0011]    or copolymers thereof, wherein n is a positive integer, y and z are both integers of one or more (e.g., between about one and about 10) and each R, R 1 , R 2 , and R 3 , independently, is H or a substituted or unsubstituted alkyl group (e.g., having between 1 and 25 or between 1 and 5 carbon atoms, inclusive), alkylamino, (e.g., having between 1 and 5 carbons atoms, inclusive, such as ethylamino or poly(ethylamino)) or aryl (e.g., phenyl) group, and each X −  is an exchangeable negatively charged counterion.  
           [0012]    In one preferred polymer, at least one of R, R 1 , R 2 , or R 3  groups is a hydrogen atom. In a more preferred embodiment, each of these groups are hydrogen.  
           [0013]    In each case, the R groups can carry one or more substituents. Suitable substituents include therapeutic anionic groups, e.g., quaternary ammonium groups, or amine groups, e.g., primary, secondary or tertiary alkyl or aryl amines. Examples of other suitable substituents include hydroxy, alkoxy, carboxamide, sulfonamide, halogen, alkyl, aryl, hydrazine, guanadine, urea, poly(alkyleneimine), such as poly(ethyleneimine), and carboxylic acid esters.  
           [0014]    Preferably, the polymer is rendered water-insoluble by cross-linking. The cross-linking agent can be characterized by functional groups which react with the amino group of the monomer. Alternatively, the cross-linking group can be characterized by two or more vinyl groups which undergo free radical polymerization with the amine monomer.  
           [0015]    Examples of suitable cross-linking agents include diacrylates and dimethylacrylates (e.g. ethylene glycol diacrylate, propylene glycol diacrylate, butylene glycol diacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, butylene glycol dimethacrylate, polyethyleneglycol dimethacrylate and polyethyleneglycol diacrylate), methylene bisacrylamide, methylene bismethacrylamide, ethylene bisacrylamide, ethylene bismethacrylamide, ethylidene bisacrylamide, divinylbenzene, bisphenol A, dimethacrylate and bisphenol A diacrylate. The cross-linking agent can also include acryloyl chloride, epichlorohydrin, butanediol diglycidyl ether, ethanediol diglycidyl ether, succinyl dichloride, the diglycidal ether of bisphenol A, pyromellitic dianhydride, toluene diisocyanate, ethylene diamine and dimethyl succinate.  
           [0016]    A preferred cross-linking agent is epichlorohydrin because of its high availability and low cost. Epichlorohydrin is also advantageous because of its low molecular weight and hydrophilic nature, increasing the water-swellability and gel properties of the polyamine.  
           [0017]    The level of cross-linking makes the polymers insoluble and substantially resistant to absorption and degradation, thereby limiting the activity of the polymer to the gastrointestinal tract, and reducing potential side-effects in the patient. The compositions thus tend to be non-systemic in activity. Typically, the cross-linking agent is present in an amount from about 0.5-35% or about 0.5-25% (such as from about 2.5-20% or about 1-10%) by weight, based upon total weight of monomer plus cross-linking agent. The polymers can also be further derivatized; examples include alkylated amine polymers, as described, for example, in U.S. Pat. Nos. 5,679,717, 5,607,669 and 5,618,530, the teachings of which are incorporated herein by reference in their entireties. Preferred alkylating agents include hydrophobic groups (such as aliphatic hydrophobic groups) and/or quaternary ammonium- or amine-substituted alkyl groups.  
           [0018]    Non-cross-linked and cross-linked polyallylamine and polyvinylamine are generally known in the art and are commercially available. Methods for the manufacture of polyallylamine and polyvinylamine, and cross-linked derivatives thereof, are described in the above U.S. Patents. Harada et al. (U.S. Pat. Nos. 4,605,701 and 4,528,347), which are incorporated herein by reference in their entireties, also describe methods of manufacturing polyallylamine and cross-linked polyallylamine.  
           [0019]    As described above the polymer can be administered in the form of a salt. By “salt” it is meant that the nitrogen group in the repeat unit is protonated to create a positively charged nitrogen atom associated with a negatively charged counterion. A preferred polymer is a low salt, such as low chloride, form of polyallylamine where less than 40% of the amine groups are protonated.  
           [0020]    The cationic counterions can be selected to minimize adverse effects on the patient, as is more particularly described below. Examples of suitable counterions include organic ions, inorganic ions, or a combination thereof, such as halides (Cl −  and Br − ), CH 3 OSO 3   − , HSO 4   − , SO 4   2− , HCO 3   − , CO 3   − , acetate, lactate, succinate, propionate, oxalate, butyrate, ascorbate, citrate, dihydrogen citrate, tartrate, taurocholate, glycocholate, cholate, hydrogen citrate, maleate, benzoate, folate, an amino acid derivative, a nucleotide, a lipid, or a phospholipid. The counterions can be the same as, or different from, each other. For example, the polymer can contain two different types of counterions.  
           [0021]    The polymers according to the invention can be administered orally to a patient in a dosage of about 1 mg/kg/day to about 1 g/kg/day, preferably between about 10 mg/kg/day to about 200 mg/kg/day; the particular dosage will depend on the individual patient (e.g., the patient&#39;s weight). The polymer can be administrated either in hydrated or dehydrated form, and can be flavored or added to a food or drink, if desired to enhance patient acceptability.  
           [0022]    Additional active ingredients can be administered simultaneously or sequentially with the polymer. Where the ingredients are administered simultaneously, they can optionally be bound to the polymer, for example, by covalent bonding or by physically encapsulating the ingredient, on the exterior or interior of the polymeric particle. Covalent bonding can be accomplished by reacting the polymer and ingredient(s) with suitable cross-linking agents.  
           [0023]    Examples of suitable forms for administration (preferably oral administration) include pills, tablets, capsules, and powders (e.g., for sprinkling on food or incorporating into a drink). The pill, tablet, capsule, or powder can be coated with a substance capable of protecting the composition from disintegration in the esophagus but will allow disintegration as the composition in the stomach and mixing with food to pass into the patient&#39;s small intestine. The polymer can be administered alone or in combination with a pharmaceutically acceptable carrier substance, e.g., zinc salts, magnesium carbonate, lactose, or a phospholipid with which the polymer can form a micelle.  
           [0024]    The polymers of the invention can be used to improve vascular access in patients, preferably humans with shunts, except for those undergoing renal dialysis (ESRD), or as a prophylactic for example.  
       
    
    
     EXEMPLIFICATION  
       [0025]    A. Polymer Preparation  
       Example 1  
       [0026]    Poly(vinylamine)  
         [0027]    The first step involved the preparation of ethylidenebisacetamide. Acetamide (118 g), acetaldehyde (44.06 g), copper acetate (0.2 g), and water (300 mL) were placed in a 1 L three neck flask fitted with condenser, thermometer, and mechanically stirred. Concentrated HCl (34 mL) was added and the mixture was heated to 45-50° C. with stirring for 24 hours. The water was then removed in vacuo to leave a thick sludge which formed crystals on cooling to 5° C. Acetone (200 mL) was added and stirred for a few minutes, after which the solid was filtered off and discarded. The acetone was cooled to 0° C. and solid was filtered off. The solid was rinsed in 500 mL acetone and air dried 18 hours to yield 31.5 g of ethylidenebis-acetamide.  
         [0028]    The next step involved the preparation of vinylacetamide from ethylidenebisacetamide. Ethylidenebisacetamide (31.05 g), calcium carbonate (2 g) and filter agent, Celite® 541 (2 g) (available from Aldrich, Milwaukee, Wis.) were placed in a 500 mL three neck flask fitted with a thermometer, a mechanical stirrer, and a distilling head atop a Vigreaux column. The mixture was vacuum distilled at 24 mm Hg by heating the pot to 180-225° C. Only a single fraction was collected (10.8 g) which contained a large portion of acetamide in addition to the product (determined by NMR). This solid product was dissolved in isopropanol (30 mL) to form the crude vinylacetamide solution used for polymerization.  
         [0029]    Crude vinylacetamide solution (15 mL), divinylbenzene (1 g, technical grade, 55% pure, mixed isomers), and AIBN (0.3 g) were mixed and heated to reflux under a nitrogen atmosphere for 90 minutes, forming a solid precipitate. The solution was cooled, isopropanol (50 mL) was added, and the solid was collected by centrifugation. The solid was rinsed twice in isopropanol, once in water, and dried in a vacuum oven to yield 0.8 g of poly(vinylacetamide), which was used to prepare poly(vinylamine) as follows.  
         [0030]    Poly(vinylacetamide) (0.79 g) was placed in a 100 mL one neck flask containing water (25 mL) and conc. HCl (25 mL). The mixture was refluxed for 5 days, after which the solid was filtered off, rinsed once in water, twice in isopropanol, and dried in a vacuum oven to yield 0.77 g of product. Infrared spectroscopy indicated that a significant amount of the amide (1656 cm −1 ) remained and that not much amine (1606 cm −1 ) was formed. The product of this reaction (˜0.84 g) was suspended in NaOH (46 g) and water (46 g) and heated to boiling (˜140° C.). Due to foaming the temperature was reduced and maintained at ˜100° C. for 2 hours. Water (100 mL) was added and the solid collected by filtration. After rinsing once in water the solid was suspended in water (500 mL) and adjusted to pH 5 with acetic acid. The solid was again filtered off, rinsed with water, then isopropanol, and dried in a vacuum oven to yield 0.51 g of product. Infrared spectroscopy indicated that significant amine had been formed.  
       Example 2  
       [0031]    Poly(allylamine) Hydrochloride  
         [0032]    To a 2 liter, water-jacketed reaction kettle equipped with (1) a condenser topped with a nitrogen gas inlet, (2) a thermometer, and (3) a mechanical stirrer was added concentrated hydrochloric acid (360 mL). The acid was cooled to 5° C. using circulating water in the jacket of the reaction kettle (water temperature=0° C.). Allylamine (328.5 mL, 250 g) was added dropwise with stirring while maintaining the reaction temperature at 5-10° C. After addition was complete, the mixture was removed, placed in a 3 liter one-neck flask, and 206 g of liquid was removed by rotary vacuum evaporation at 60° C. Water (20 mL) was then added and the liquid was returned to the reaction kettle. Azobis(amidinopropane) dihydrochloride (0.5 g) was suspended in 11 mL of water was then added. The resulting reaction mixture was heated to 50° C. under a nitrogen atmosphere with stirring for 24 hours. Additional azobis(amidinopropane) dihydrochloride (5 mL) suspended in 11 mL of water was then added, after which heating and stirring were continued for an additional 44 hours.  
         [0033]    At the end of this period, distilled water (100 mL) was added to the reaction mixture and the liquid mixture allowed to cool with stirring. The mixture was then removed and placed in a 2 liter separatory funnel, after which it was added dropwise to a stirring solution of methanol (4 L), causing a solid to form. The solid was removed by filtration, re-suspended in methanol (4 L), stirred for 1 hour, and collected by filtration. The methanol rinse was then repeated one more time and the solid dried in a vacuum oven to afford 215.1 g of poly(allylamine) hydrochloride as a granular white solid.  
       Example 3  
       [0034]    Poly(allylamine) Hydrochloride Cross-linked with Epichlorohydrin  
         [0035]    To a 5 gallon vessel was added poly(allylamine) hydrochloride prepared as described in Example 2 (1 kg) and water (4 L). The mixture was stirred to dissolve the hydrochloride and the pH was adjusted by adding solid NaOH (284 g). The resulting solution was cooled to room temperature, after which epichlorohydrin cross-linking agent (50 mL) was added all at once with stirring. The resulting mixture was stirred gently until it gelled (about 35 minutes). The cross-linking reaction was allowed to proceed for an additional 18 hours at room temperature, after which the polymer gel was removed and placed in portions in a blender with a total of 10 L of water. Each portion was blended gently for about 3 minutes to form coarse particles which were then stirred for 1 hour and collected by filtration. The solid was rinsed three times by suspending it in water (10 L, 15 L, 20 L), stirring each suspension for 1 hour, and collecting the solid each time by filtration. The resulting solid was then rinsed once by suspending it in isopropanol (17 L), stirring the mixture for 1 hour, and then collecting the solid by filtration, after which the solid was dried in a vacuum oven at 50° C. for 18 hours to yield about 677 g of the cross-linked polymer as a granular, brittle, white solid.  
       Example 4  
       [0036]    Poly(allylamine) Hydrochloride Cross-linked with Butanediol Diglycidyl Ether  
         [0037]    To a 5 gallon plastic bucket was added poly(allylamine) hydrochloride prepared as described in Example 2 (500 g) and water (2 L). The mixture was stirred to dissolve the hydrochloride and the pH was adjusted to 10 by adding solid NaOH (134.6 g). The resulting solution was cooled to room temperature in the bucket, after which 1,4-butanediol diglycidyl ether cross-linking agent (65 mL) was added all at once with stirring. The resulting mixture was stirred gently until it gelled (about 6 minutes). The cross-linking reaction was allowed to proceed for an additional 18 hours at room temperature, after which the polymer gel was removed and dried in a vacuum oven at 75° C. for 24 hours. The dry solid was then ground and sieved to −30 mesh, after which it was suspended in 6 gallons of water and stirred for 1 hour. The solid was then filtered off and the rinse process repeated two more times. The resulting solid was then air dried for 48 hours, followed by drying in a vacuum oven at 50° C. for 24 hours to yield about 415 g of the cross-linked polymer as a white solid.  
       Example 5  
       [0038]    Poly(allylamine) Hydrochloride Cross-linked with Ethanediol Diglycidyl Ether  
         [0039]    To a 100 mL beaker was added poly(allylamine) hydrochloride prepared as described in Example 2 (10 g) and water (40 mL). The mixture was stirred to dissolve the hydrochloride and the pH was adjusted to 10 by adding solid NaOH. The resulting solution was cooled to room temperature in the beaker, after which 1,2-ethanediol diglycidyl ether cross-linking agent (2.0 mL) was added all at once with stirring. The resulting mixture was stirred gently until it gelled (about 4 minutes). The cross-linking reaction was allowed to proceed for an additional 18 hours at room temperature, after which the polymer gel was removed and blended in 500 mL of methanol. The solid was then filtered off and suspended in water (500 mL). After stirring for 1 hour, the solid was filtered off and the rinse process repeated. The resulting solid was rinsed twice in isopropanol (400 mL) and then dried in a vacuum oven at 50° C. for 24 hours to yield 8.7 g of the cross-linked polymer as a white solid.  
       Example 6  
       [0040]    Poly(allylamine) Hydrochloride Cross-linked with Dimethylsuccinate  
         [0041]    To a 500 mL round bottom flask was added poly(allylamine) hydrochloride prepared as described in Example 2 (10 g), methanol (100 mL), and triethylamine (10 mL). The mixture was stirred and dimethylsuccinate cross-linking agent (1 mL) was added. The solution was heated to reflux and the stirring discontinued after 30 minutes. After 18 hours, the solution was cooled to room temperature, and the solid filtered off and blended in 400 mL of isopropanol. The solid was then filtered off and suspended in water (1 L). After stirring for 1 hour, the solid was filtered off and the rinse process repeated two more times. The solid was then rinsed once in isopropanol (800 mL) and dried in a vacuum oven at 50° C. for 24 hours to yield 5.9 g of the cross-linked polymer as a white solid.  
       Example 7  
       [0042]    Poly(allyltrimethylammonium Chloride)  
         [0043]    To a 500 mL three-necked flask equipped with a magnetic stirrer, a thermometer, and a condenser topped with a nitrogen inlet, was added poly(allylamine) cross-linked with epichlorohydrin (5.0 g), methanol (300 mL), methyl iodide (20 mL), and sodium carbonate (50 g). The mixture was then cooled and water was added to total volume of 2 L. Concentrated hydrochloric acid was added until no further bubbling resulted and the remaining solid was filtered off. The solid was rinsed twice in 10% aqueous NaCl (1 L) by stirring for 1 hour followed by filtration to recover the solid. The solid was then rinsed three times by suspending it in water (2 L), stirring for 1 hour, and filtering to recover the solid. Finally, the solid was rinsed as above in methanol and dried in a vacuum over at 50° C. for 18 hours to yield 7.7 g of white granular solid.  
       Example 8  
       [0044]    Poly(vinylamine)  
         [0045]    Poly(vinylacetamide) (0.79 g) was placed in a 100 mL one neck flask containing water 25 mL and concentrated HCl 25 mL. The mixture was refluxed for 5 days, the solid was filtered off, rinsed once in water, twice in isopropanol, and dried in a vacuum oven to yield 0.77 g. The product of this reaction (˜0.84 g) was suspended in NaOH (46 g) and water (46 g) and heated to boiling (˜140° C.). Due to foaming, the temperature was reduced and maintained at ˜100° C. for 2 hours. Water (100 mL) was added and the solid collected by filtration. After rinsing once in water, the solid was suspended in water (500 mL) and adjusted to pH 5 with acetic acid. The solid was again filtered off, rinsed with water, then the isopropanol, and dried in a vacuum oven to yield 0.51 g.  
       Example 9  
       [0046]    Polyallylamine Cross-linked with Epichlorohydrin  
         [0047]    An aqueous solution of poly(allylamine hydrochloride) (500 lb of a 50.7% aqueous solution) was diluted with water (751 lb) and neutralized with aqueous sodium hydroxide (171 lb of a 50% aqueous solution). The solution was cooled to approximately 25° C., and acetonitrile (1340 lb) and epichlorohydrin (26.2 lb) were added. The solution was stirred vigorously for 21 hours. During this time, the reactor contents changed from two liquid phases to a slurry of particles in a liquid. The solid gel product was isolated by filtration. The gel was washed in an elutriation process with water (136,708 lb). The gel was isolated by filtration and rinsed with isopropanol. The gel was slurried with isopropanol (1269 lb) and isolated by filtration. The isopropanol/water wet gel was dried in a vacuum dryer at 60° C. The dried product was ground to pass through a 50 mesh screen to give a product suitable for pharmacologic use (166 lb, 73%).  
         [0048]    Clinical Trials  
         [0049]    Patients on hemodialysis were treated with Renagel® and showed reduced risk related to cardiovascular and vascular access hospitalization. 152 sevelamer hydrochloride treated Medicare patients on hemodialysis in a case-controlled study matching 152 randomly selected non-sevelamer hydrochloride treated Medicare patients from the same dialysis facilities and time period were evaluated. The main outcomes evaluated were the risk of all-cause first hospitalization and per-member per-month (PMPM) Medicare expenditures in the follow-up period. The 152 sevelamer hydrochloride Medicare patients were identified from a total of 195 sevelamer hydrochloride treated patients who were evaluated in a long-term safety and efficacy clinical trial [Chertow et al.,  Nephrol. Dial. Transplant,  14, 2907-2914, 1999]. The mean ending dose of sevelamer hydrochloride in this patient population was 5.3 g with average treatment time of 17 months. The average serum calcium-phosphorus product in the sevelamer hydrochloride treated group was 78 at baseline and 55 at the end of the trial. Baseline mean lipid parameters were total cholesterol 175 mg/dl, LDL-cholesterol 107 mg/dl, HDL-cholesterol 36 mg/dl and triglycerides 164 mg/dl. Final mean lipid parameters were total cholesterol 147 mg/dl, LDL cholesterol 75 mg/dl, HDL-cholesterol 42 mg/dl and triglycerides 153 mg/dl.  
         [0050]    In order to develop a case-controlled, matched population, the Medicare sevelamer hydrochloride treated patients were matched with randomly selected Medicare patients for age, gender, race, diabetic status, and geographic location. Age was matched within five years of the date of birth of the sevelamer hydrochloride treated patients, with specific matching of gender, race and diabetic status. Patients were randomly selected from the same geographic location and dialysis providers. Patient descriptive characteristics also included prior end-stage renal disease (ESRD) time and ten comorbid conditions obtained from prior Medicare Part A and Part B claims. Severity of disease was determined in the case-matched and sevelamer hydrochloride treated patients by determining the number of hospital days, history of wheelchair use, home oxygen therapy, IV chemotherapy, outpatient antibiotics, ambulance transportation, blood transfusions and vascular access and hematocrit levels during the six-month period prior to the start of the sevelamer hydrochloride study.  
         [0051]    Patient descriptive characteristics were compared by Chi-square and analysis of variance (ANOVA). A Cox regression model stratified on diabetic status was used to assess the risk of all-cause first hospitalization in the 17-month follow-up period. Four survival models were assessed with increasing degrees of adjustment for case mix. These included model M-1, with adjustments for age, gender and race only. Model M-2 was model M-1 plus co-morbidity. Model M-3 was M-2 plus prior ESRD time and total hospital days during the prior six months of the study; and model M-4 was M-3 plus severity of disease and hematocrit levels.  
         [0052]    The adjusted risk of first hospitalization was assessed with Cox regression analysis. The individual models with increasing adjustments for prior history of comorbidity, prior ESRD time and hospital days, as well as adjustments for several severities of disease measures and hematocrit levels are shown. Across all four models, the relative risk of hospitalization was 46-54% less in the sevelamer hydrochloride treated group, as compared to the case control group (significant at the p-value 0.03 level). A sub-group analysis for vascular access and cardiac hospitalization showed a 30-40% reduction in hospitalization in the sevelamer hydrochloride group, however this did not reach statistical significant difference and is most likely due to insufficient power.  
         [0053]    It should be understood, however, that the foregoing description of the invention is intended merely to be illustrative by way of example only and that other modifications, embodiments, and equivalents may be apparent to those skilled in the art without departing from its spirit.  
         [0054]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.