Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
1998-06-02
2001-01-16
Reamer, James H. (Department: 1614)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S656000, C530S415000, C530S417000, C514S023000, C424S647000, C071S028000, C071S024000, C071S059000
Reexamination Certificate
active
06174442
ABSTRACT:
This invention relates to an adsorbent for phosphate from aqueous medium, for example from aqueous solutions. It is particularly suitable as an adsorbent for inorganic phosphate and phosphate bonded to foodstuffs, especially as a preparation for oral application for the prophylaxis and treatment of hyperphosphataemia conditions.
In patients with chronic renal insufficiency, a pathologically increased serum phosphate level occurs due to the decrease in the glomular filtration rate. The secondary hyperparathyroidism which sets in therewith must be considered as one of the causes of the occurrence of renal osteopathy. Attempts are normally made to maintain the phosphate balance in equilibrium by dialysis or by the administration of oral phosphate adsorbers which suppress the resorption of foodstuff phosphates in the gastrointestinal tract, or by the combination of both methods, but with the current state of the art this is either not efficient enough, is not economic, or is burdened with side effects.
Thus, in addition to dialysis encephalopathy syndrome, the aluminium(III) salts which are used as oral phosphate adsorbers cause renal osteopathy and microcytic anaemia. When calcium salts are used, hypercalcaemia frequently occurs, in combination with calcification of the vessels and internal organs and gastrointestinal complaints (Dialysis Journal 37, 1-40 (1991)).
In addition, the use of adsorption materials modified with polynuclear metal oxide hydroxides has been proposed in DE 42 39 442 A1, but the use of the water-soluble iron dextrans and dextrins described therein has the disadvantage that they are resorbable. Complexes which release only a little iron can be produced by the use of crosslinked polysaccharide carriers. The disadvantages of these complexes, which are based on alpha-iron hydroxides, are firstly the high cost of the crosslinked polysaccharide carriers which have to be used, and secondly their phosphate adsorption capacity, which is in need of improvement.
The object of the present invention is therefore to provide adsorbents for phosphate from aqueous medium, particularly from an aqueous solution. In particular, the adsorbents should be suitable for inorganic phosphate and phosphate bonded to foodstuffs from body fluids, chyme and foodstuffs, they should exhibit an improved phosphate adsorption capacity and they should be capable of being produced simply and economically.
It has been shown that this object can be achieved by the adsorbents for phosphate from aqueous medium, to which the present invention firstly relates, which contain polynuclear beta-iron hydroxide stabilised by carbohydrates and/or by humic acid. These adsorbents are particularly suitable for the adsorption of phosphates from aqueous solutions, for example for the adsorption of inorganic phosphates and phosphates bonded to foodstuffs.
Within the scope of the present invention, it has been shown that polynuclear beta-iron hydroxide has a superior phosphate adsorption capacity. However, since polynuclear beta-iron hydroxide ages with a change in structure, it could not hitherto be used for this purpose. It has been found within the scope of this invention that stabilisation can be effected by suitable compounds, particularly carbohydrates and humic acid. Without being tied to any one theory, it is assumed from this that no complex formation occurs with the carbohydrates, however.
The present invention further relates to the process for producing the polynuclear beta-iron hydroxide stabilised by carbohydrates and/or by humic acid, which can be used as an adsorbent or in adsorbents for inorganic phosphate and phosphate bonded to foodstuffs. In the process according to the invention, an aqueous solution of a base is mixed with an aqueous solution of an iron(III) salt containing chloride ions with the formation of a suspension of brown beta-iron hydroxide with a pH higher than 3, for example 3 to 10. The suspension is subsequently allowed to stagnate. In practice, the suspension can be allowed to stand, for example for 1 to 5 hours. It may be stirred briefly now and again during this stage, for example it may be stirred briefly (for example for 10 minutes) at intervals of 10 minutes. The beta-iron hydroxide obtained is washed with water. This can be effected, for example, by decantation, filtration and/or centrifuging. Washing is carried out until interfering anions, for example chloride ions, are removed. A moist product is obtained which is not dried. The moist product is slurried in water. The amount of water is not critical. The procedure employed is preferably such that the iron content of the suspension obtained (calculated as Fe) is up to 6 percent by weight, most preferably 2 to 6 percent by weight.
Sodium carbonate or sodium bicarbonate in aqueous solution may, for example, be used as an alkali metal carbonate or alkali metal bicarbonate solution.
Water-soluble salts of inorganic of organic acids may, for example, be used as the iron(III) salt. Iron(III) chloride is preferred.
The preparation of &bgr;-iron hydroxide (akaganeite) is known in principle in the prior art and is described, for example, in the literature reference by U. Schwertmann and R. M. Cornell, “Iron Oxides in the Laboratory”, VCH Verlagsgesellschaft mbH, 1991, pages 95-100. For economic reasons, it may be necessary for the industrial production of the adsorption agent containing &bgr;-iron hydroxide to precipitate the iron quantitatively at higher pH values. As is described on page 100 of the aforementioned literature reference, ferrihydrite is then also precipitated at the same time. Mixtures of &bgr;-iron hydroxide and ferrihydrite such as these can also be used as adsorption agents according to the present invention and the present invention therefore relates to them also.
One or more carbohydrates and/or humic acid are added to the suspension obtained as above. Water-soluble compounds are preferably used. The carbohydrates and/or humic acid may be added in solid form, wherein they can dissolve in the water which is present. However, it is also possible to add aqueous solutions of carbohydrates.
The amount of carbohydrates or humic acid is preferably selected so that at least 0.5 g carbohydrate or humic acid are added per g of iron (calculated as Fe). The maximum iron content should be 40 percent by weight. The maximum content of carbohydrates and/or humic acid is not subject to any limit, and is primarily determined on economic grounds.
Soluble carbohydrates can be used in particular as carbohydrates, such as various sugars, e.g. agarose, dextran, dextrin, dextran derivatives, cellulose and cellulose derivatives, saccharose, maltose, lactose or mannitol.
The adsorption materials comprising insoluble stabilised polynuclear beta-iron hydroxide which are prepared according to the invention have the advantage that in addition to a high phosphate binding capacity they release little iron and are inexpensive to produce.
It may be advantageous and preferable to add one or more calcium salts to the adsorbents according to the invention. Examples of suitable calcium salts include salts of inorganic or organic acids, particularly calcium acetate. The phosphate binding capacity is increased by the addition of the calcium salt, particularly at higher pH values. Adsorbents such as these, which are provided with calcium salts, can be used particularly advantageously at pH values higher than 5, since the full phosphate binding capacity is retained even then.
It has been shown that an addition of from 400 mg to 2 g, for example about 1 g, of a calcium salt, particularly calcium acetate, per g iron, is particularly advantageous.
The adsorbents according to the invention can be formulated for oral application, for example. They can be formulated as such or together with customary drug additives, such as customary carriers or auxiliary materials. Encapsulation may be effected, for example, wherein customary media which are used in the pharmaceutical sector are used as encapsulating media. It is also possible to provide the adsorbents,
Geisser Peter
Philipp Erik
Pillsbury Madison & Sutro LLP
Reamer James H.
Vifor (International) AG
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