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Title:
PREPARATION OF SEVELAMER WITH REDUCED CONTENT OF ALLYLAMINE
Document Type and Number:
WIPO Patent Application WO/2013/087238
Kind Code:
A1
Abstract:
The invention relates to a process of making polyallylamine with a reduced content of residual allylamine and, consequently, to the use of such product in making epichlorohydrin- crosslinked polyallylamine (a sevelamer polymer) of pharmaceutical quality.

Inventors:
LUTEN JORDY (NL)
Application Number:
PCT/EP2012/066473
Publication Date:
June 20, 2013
Filing Date:
August 24, 2012
Export Citation:
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Assignee:
SYNTHON BV (NL)
LUTEN JORDY (NL)
International Classes:
C08F6/00; A61K31/785; C08F8/00; C08F26/02; C08G73/02; C08J3/24; G01N1/00
Domestic Patent References:
WO2011099038A22011-08-18
WO2008062437A22008-05-29
WO2008005217A22008-01-10
WO2010041274A22010-04-15
WO2001018072A12001-03-15
Foreign References:
US6395849B12002-05-28
US20090155368A12009-06-18
US20050239901A12005-10-27
US5496545A1996-03-05
EP0716606A11996-06-19
EP0831857A21998-04-01
EP1133989A22001-09-19
EP1676581A22006-07-05
US5667775A1997-09-16
JPS63286405A1988-11-24
Attorney, Agent or Firm:
STERREN-MOL VAN DER, Josephine E.M. (GN Nijmegen, NL)
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Claims:
CLAIMS

1. A process of making a high-molecular-weight polyallylamine having a content of residual allylamine of less than 500 ppm, preferably less than 100 ppm and most preferably less than 50 ppm, comprising subjecting an aqueous solution of a high- molecular-weight polyallylamine having a content of more than 500 ppm of residual allylamine, said solution having a pH of between 8.0-13.0, preferably between 8.5-11.0 and most preferably between 9.0-10.0, and a concentration of about 5-50 weight %, preferably between 10-40 weight % of the polyallylamine, to a partial evaporation of volatiles at a temperature of between 40 and 80°C and a pressure of between 0.1-10 mbar.

2. The process according to claim 1 , wherein the evaporation is performed by a distillation of the solution, advantageously by a fractional distillation using a distillation column.

3. The process according to claims 1-2, wherein the amount of volatiles removed by the distillation is 20-75% of the original volume.

4. The process according to claims 1-3, wherein the average evaporation speed

corresponds to removal of 5-25% of the original volume per hour.

5. The process according to claims 1-4, wherein the starting polyallylamine has a content of residual allylamine less than 30,000 ppm.

6. The process according to claims 1-5, wherein the content of allylamine in the

distillation residue is monitored by an analytical method.

7. The process according to claims 1-6, wherein the high-molecular-weight

polyallylamine of a content of 500-30,000 ppm of residual allylamine is obtained by subjecting a high-molecular-weight polyallylamine having a content higher than 30,000 ppm to a pre -purification step.

8. A process of making a sevelamer hydrochloride polymer comprising less than 1 ppm of physiologically extractable residual allylamine, said process comprising crosslinking the polyallylamine having a residual allylamine content of less than 500 ppm, preferably less than 100 ppm, and most preferably less than 50 ppm, with

epichlorohydrin in water at alkaline pH, and washing the obtained sevelamer hydrochloride with water.

9. A process of making a sevelamer carbonate polymer comprising less than 1 ppm of physiologically extractable residual allylamine, said process comprising crosslinking the polyallylamine having a residual allylamine content of less than 500 ppm, preferably less than 100 ppm, and most preferably less than 50 ppm, with

epichlorohydrin in water at alkaline pH, treating the product with a carbonate buffer and washing the obtained sevelamer carbonate with water.

10. The process according to claims 8-9, wherein the polyallylamine having the residual allylamine content of less than 500 ppm, preferably less than 100 ppm and most preferably less than 50 ppm, is obtained by the process of claims 1-7.

11. The process according to claims 8-10, further comprising a step of subjecting the

sevelamer to a process of determination of the content of the physiologically extractable residual allylamine by an analytical method.

12. A process for the determination of the physiologically extractable residual

allylamine in sevelamer and/or a salt of sevelamer, such as sevelamer hydrochloride or sevelamer carbonate, comprising:

a] treating, under agitation, a sample comprising sevelamer with an aqueous buffer of pH higher than 5.0, preferably between 5.0 and 9.0, at 37°C;

b] optionally, separating the solid substrate from the liquid phase, preferably at ambient temperature; and c] subjecting the liquid phase to a determination of the content of allylamine by a suitable analytical method.

13. The process for determination of claim 12 in which the sample comprising sevelamer of step a] is extracted for a time period ranging from 10 to 40 hours, preferably from 20 to 30 hours and most preferably of 24 hours.

14. A sevelamer polymer, preferably sevelamer carbonate, comprising less than 1 ppm of physiologically extractable residual allylamine.

15. A pharmaceutical composition for oral administration of sevelamer comprising the sevelamer polymer according to claim 14.

16. Use of a high-molecular-weight polyallylamine having a residual allylamine content of less than 500 ppm, preferably less than 100 ppm and most preferably less than 50 ppm in a process for making a sevelamer polymer, preferably sevelamer carbonate, having a content of less than 1 ppm of physiologically extractable residual allylamine.

Description:
PREPARATION OF SEVELAMER WITH REDUCED CONTENT OF

ALLYLAMINE

BACKGROUND OF THE INVENTION

Sevelamer is a non-absorbed phosphate binding polymer used in the treatment for the control of serum phosphorus in patients with Chronic Kidney Disease (CKD). It is a polymer of poly(allylamine) crosslinked with epichlorohydrin. Its chemical structure is as follows:

= number of primary amine groups (a + b = 9) number of crosslinking groups (c = 1)

= large number to indicate extended polymer network

The compound contains multiple amines that become partially protonated in the intestine and interact with phosphate ions through ionic and hydrogen bonding. By binding phosphate in the gastrointestinal tract facilitating phosphorus excretion in feces, sevelamer lowers the plasma phosphorus concentration.

Sevelamer may form acid addition salts, in which a part of the amine groups has been neutralized by an acid ion. In existing medicinal products, sevelamer is marketed as sevelamer carbonate (Renvela®) or sevelamer hydrochloride (Renagel®).

Process of preparing a polyallylamine crosslinked with epichlorohydrin has been disclosed in several patent documents, e.g. in US 5,496,545, EP 0716606, EP 0831857, EP 1133989 and EP 1676581. In essence, the process of making sevelamer comprises two steps:

a] In the first step, polyallylamine hydrochloride of relatively high molecular weight (around 15 000 Da ) is prepared by polymerization of allylamine in concentrated HC1 using a suitable initiator of polymerization such as azobis(amidinopropane) dihydrochloride.

b] The polyallylamine polymer reacts with epichlorohydrin in alkalinized water. The formed gel is solidified in isopropanol, washed and dried to form the final product as a granular solid.

As the sevelamer product has to comply with requirements of pharmaceutical quality, it must be essentially free from residual allylamine, which is a toxic compound. As the allylamine may be quite firmly bound in the network of the sevelamer molecule (the whole sevelamer particle must be regarded as a single molecule), it is of utmost need to use polyallylamine with a reduced content of residual allylamine.

US 5667775 discloses a process for reducing the allylamine content in poly(allylamine hydrochloride) by precipitation in methanol and repeated washing of the poly(allylamine hydrochloride) with methanol. The purification is not efficient as the polymer is produced in a granulated mass in which the allylamine is easily entrapped. Consequently, the amount of methanol necessary to purify 1 kg of poly(allylamine hydrochloride) in the first step is around 80 kg, which is undesirable in respect of cost of goods, environment, etc.

WO 01/18072 discloses a process in which the produced polyallylamine hydrochloride is neutralized, at least partly, in water to form a polyallylamine base solution and the counter ions are removed preferably by electrodialysis and ultrafiltration yielding a polyallylamine solution with reduced salt content. Such product is, after optional concentration, crosslinked with epichlorohydrin. The content of residual allylamine should also be decreased within the removal of salt ions by the above procedures. However, while the above process has been shown as efficient with respect to removal of inorganic salts, no effectivity in removal of allylamine has been demonstrated in the document.

JP 63-286405 describes a process for purifying poly(allylamine hydrochloride) containing 9.93% unreacted allylamine by using electrodialysis using ion-exchanging membranes and 1% sodium chloride aqueous solution at 16- 17V for 1.5h to give a product containing 0.3% monomers.

While the prior art documents deal with several processes of how to decrease the content of the undesired allylamine in a process of making sevelamer, an improvement in the art is still desirable. In particular, it is desired to have a simple and efficient process for reducing the amount of allylamine in the starting polyallylamine to an acceptable low level, which would lead to minimal need of purification of the final sevelamer polymer.

SUMMARY OF THE INVENTION

The present invention relates to a process of making polyallylamine with a reduced content of residual allylamine and, consequently, to use such product in making

epichlorohydrin-crosslinked polyallylamine (a sevelamer polymer) of pharmaceutical quality.

In a first main aspect, the invention provides a process of making a high-molecular- weight polyallylamine having a content of residual allylamine of less than 500 ppm, preferably less than 100 ppm, and most preferably less than 50 ppm, comprising subjecting an aqueous solution of a high-molecular-weight polyallylamine comprising more than 500 ppm of residual allylamine, said solution having a pH of between 8.0 and 13.0, preferably between 8.5 and 11.0, and most preferably between 9.0 and 10.0, and a concentration of about 5-50 weight %, preferably between 10-40 weight % of the polyallylamine, to a partial evaporation of volatiles at a temperature of between 40 and 80°C and a pressure of between 0.1-10 mbar (10-1000 Pa). Advantageously, the evaporation is performed by a distillation of the solution, advantageously by a fractional distillation using a distillation column.

Advantageously, the amount of volatiles removed by the evaporation is 20-75% of the original volume.

Advantageously, the average evaporation speed corresponds to removal of 5-25% of the original volume per hour.

Advantageously, the starting polyallylamine has a content of residual allylamine less than 30,000 ppm.

In a particular aspect, the starting polyallylamine having a content of residual allylamine higher than 30,000 ppm is subjected to a pre-purification to obtain a

polyallylamine having a content of residual allylamine between 500-30,000 ppm and the obtained product is subjected to the above process.

In a particular aspect, the evaporation process is monitored by measuring the content of residual amount of allylamine in the distillation residue and is terminated after the desired concentration of the allylamine is obtained.

In a second main aspect the invention provides a process of making a sevelamer polymer, preferably sevelamer carbonate polymer, comprising less than 1 ppm of physiologically extractable residual allylamine, said process comprising crosslinking the polyallylamine having the residual allylamine content of less than 500 ppm, preferably less than 100 ppm, and most preferably less than 50 ppm, with epichlorohydrin in water at alkaline pH, optionally treating the product with a carbonate buffer and washing the obtained sevelamer hydrochloride or sevelamer carbonate with water.

In a particular aspect, the polyallylamine having the residual allylamine content of less than 500 ppm, preferably less than 100 ppm, and most preferably less than 50 ppm, is obtained by the above purification process. In a third main aspect, the invention provides a process for the determination of the physiologically extractable residual allylamine in sevelamer and/or a salt of sevelamer, such as sevelamer hydrochloride or sevelamer carbonate, comprising:

a] Treating, under agitation, a sample comprising sevelamer with an aqueous buffer of pH higher than 5.0, preferably between 5.0 and 9.0, at 37°C;

b] Optionally, separating the solid substrate from the liquid phase, preferably at ambient temperature; and

c] Subjecting the liquid phase to a determination of the content of allylamine by a suitable analytical method.

In a particular aspect, the sample comprising sevelamer of step a] is extracted for a time period ranging from 10 to 40 hours, preferably from 20 to 30 hours and most preferably of 24 hours.

The sevelamer polymer, preferably sevelamer carbonate, comprising less than 1 ppm of physiologically extractable residual allylamine, as well as pharmaceutical compositions comprising it, represent a fourth main aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is focused to a sevelamer polymer, particularly to a sevelamer carbonate polymer, comprising less than 1 ppm of physiologically extractable residual allylamine. The objective of the invention is to provide a process of separating a high- molecular- weight polyallylamine from residual allylamine to obtain a high-molecular- weight polyallylamine having a content of less than 500 ppm, preferably less than 100 ppm, and most preferably less than 50 ppm, of residual allylamine. Another objective of the invention is the use of such high-molecular-weight allylamine with the reduced amount of residual allylamine in a process for making a sevelamer polymer, preferably sevelamer carbonate, having less than 1 ppm of physiologically extractable allylamine.

Polyallylamine is a cationic polymer comprising ionizable amino groups.

Consequently, at least part of these groups may be neutralized by an acid ion, such as a chloride ion, to form a "salt" of the polyallylamine. The term "polyallylamine", as used throughout the invention, relies also to such salts of polyallylamine, typically to

polyallylamine hydrochloride.

Within the present invention, the polyallylamine (and/or a salt thereof) is a high- molecular- weight polyallylamine. The "high-molecular-weight polyallylamine" within the invention typically has an average molecular weight greater than about 10.000 and more preferably greater than about 15.000. Preferably the high-molecular-weight polyallylamine polymer used in the invention typically has an average molecular weight less than 100.000.

Polyallylamine hydrochloride polymer, the product of polymerization of allylamine hydrochloride, is the preferred polyallylamine polymer.

The "content" of residual allylamine, as used throughout this invention, is the relative mass amount of allylamine in respect to:

• The total mass of the polyallylamine polymer, which comprises, if relevant, also the mass of the polyallylamine salt; and/or

• The total mass of sevelamer or a sevelamer salt polymer.

Polyallylamine polymers are commercially available in various molecular weights, including the high-molecular- weight polyallylamine as defined above. This one is typically available in the form of an aqueous solution of a polyallylamine hydrochloride, i.e. having at least a part of the amino-groups saturated by a chloride anion. The polyallylamine hydrochloride can be typically prepared by a polymerization of allylamine hydrochloride in the presence of an azo-type radical initiator by methods known in the art. Concentration, nature and amount of the radical initiator, pH and temperature of polymerization affect the molecular weight of the resulting polymer. The high-molecular-weight polyallylamine may be obtained by a proper selection of these variables.

The high-molecular-weight polyallylamine hydrochloride is typically obtained in the form of an aqueous solution after the polymerization. An isolated form of polyallylamine hydrochloride may be obtained, e.g., by treatment of the solution with methanol, wherein the polymer precipitates. For purpose of further use in making sevelamer polymer, i.e. for purpose of the subsequent crosslinking reaction with epichlorohydrin, it is, however, not necessary to isolate the polyallylamine from the aqueous solution. Instead, the original acidic solution of polyallylamine hydrochloride may be neutralized to an alkaline pH and said alkaline solution may be subjected to the reaction with epichlorohydrin.

In a polymerization process known in the art, the aqueous solution of high-molecular- weight polyallylamine hydrochloride obtained after the polymerization reaction typically comprises 1-5% (10000-50000 ppm) of residual allylamine. Known purification processes focused to a further removal of the residual allylamine often do not lead to a proper result. For instance, as shown above, a process of JP 63-286405 based on electrodialysis using ion- exchanging membranes and 1 % sodium chloride aqueous solution gives a product containing 0.3% (30000 ppm) of residual allylamine. The use of polyallylamine of such quality, however, requires, after subjecting it to a crosslinking reaction with epichlorohydrin, a further purification of the crosslinked product (the sevelamer polymer), wherein such purification has a low degree of efficacy due to the gel-like nature of the sevelamer capable to a relatively firm adsorption of the allylamine within the polymer network.

Now it was found that sevelamer polymer having an extraordinary low amount of residual allylamine may be prepared by a simple process without need of a specific purification step for the removal of residual allylamine from the crude sevelamer polymer. The key step in the overall inventive process is a step of making the high-molecular-weight allylamine polymer with a low content of residual allylamine; the amount of allylamine is so low that, within the ordinary crosslinking and subsequent separation processes, the sevelamer polymer product may be obtained with a pharmaceutically acceptable level of residual allylamine. In particular, the process of the present invention may provide a sevelamer hydrochloride or carbonate polymer comprising less than 1 ppm of physiologically extractable residual allylamine. The "physiologically extractable residual allylamine" as used within this invention is that portion of the total amount of residual allylamine actually present in the sevelamer polymer, which is removable from the polymer under physiological conditions, i.e. by an extraction with a buffer of physiological pH, which typically is a buffer of pH between 5.0 and 9.0, preferably about 6.5, at 37°C (which corresponds to the temperature of human body). The determination of physiologically extractable residual allylamine shows how much of the toxic allylamine may interact with human body fluid and thus affect the safety of the taken sevelamer medicine. It thus represents an important parameter in the quality control of both the sevelamer active substance and the

pharmaceutical compositions comprising it.

In a first aspect of the present invention, an aqueous solution of high-molecular- weight polyallylamine comprising more than 500 ppm of residual allylamine, said solution having a pH of between 8.0 and 13.0, preferably between 8.5 and 11.0 and most preferably between 9.0 and 10.0, and a concentration of about 5-50 weight %, preferably between 10-40 weight % of the polyallylamine, is subjected to a partial evaporation of volatiles at a temperature of between 40-80°C and a pressure of between 0.1-10 mbar (10-1000 Pa).

The "aqueous solution" of the polyallylamine is substantially free from any other solvent except water. The "temperature" of the evaporation is the temperature of the polyallylamine - comprising solution.

In general, the starting aqueous solution of high-molecular-weight polyallylamine comprising more than 500 ppm of residual allylamine is the solution obtained by a conventional polymerization process, the conditions of which were adjusted to produce polyallylamine of a molecular weight between 10.000 and 100.000. Typically, the initial acidic pH of the solution after the polymerization is further adjusted to a pH range of between 8.0 and 13.0, preferably between 8.5 and 11.0 and most preferably between 9.0 and 10.0, by ordinary processes; in addition, residual salt ions may be also removed, at least partly, by a dialysis or similar methods. Typically, such solution after polymerization comprises from 1 to 5 weight % of residual allylamine. In an advantageous embodiment, the starting high- molecular- weight polyallylamine comprises less than 3% (30000 ppm) and preferably less than 2% (20.000 ppm) of residual allylamine; under this condition a single partial evaporation process of the present invention is sufficient to yield the polyallylamine of the desired quality. At higher concentrations of residual allylamine, the partial evaporation process has to be often repeated; thus, any suitable pre-treatment of the polyallylamine solution leading to a reduction of the content of residual allylamine to the range of between 500 and 30000 ppm, may be performed instead.

The desired concentration of the polyallylamine solution prior to the evaporation step is within the range of about 5-50 weight %, preferably between 10-40 weight %. If the solution after the polymerization is not within these ranges, the volume may be adjusted by methods known per se.

The step of partial evaporation of volatiles from the aqueous solution of a high- molecular- weight polyallylamine may be performed, e.g., as a simple evaporation, e.g. on a rotary vacuum evaporator. Advantageously however, the evaporation is performed by means of a batch distillation with condensing and receiving the evaporated volatiles. The distillation may be a simple distillation or, advantageously, a fractional distillation (a rectification) where a part of the evaporated and condensed liquid has been returned back to the pot. For such purpose, a suitable distillation column may be used.

Advantageously, the amount of volatiles removed by the evaporation corresponds to 20-75% of the original volume of the solvent. In some embodiments, the amount of volatiles removed may exceed 75%. The advantageous speed of evaporation typically corresponds to a removal of 5-25% of the original volume per hour.

In an advantageous embodiment, the course and effectivity of the evaporation process may be monitored by measuring the content of the residual amount of allylamine in the distillation residue. Any suitable method, for instance a GC method or an HPLC method, may be employed. Accordingly, the evaporation process is terminated after the desired concentration of the allylamine in the distillation residue is obtained.

The so obtained polyallylamine having a residual allylamine content of less than 500 ppm, preferably less than 100 ppm, and most preferably less than 50 ppm is obtained mainly in the form of a free base. Typically, less than 10% of the amino-groups are protonated and bound to an acid anion. According to a further aspect of the present invention, it is used for making sevelamer polymer, typically sevelamer hydrochloride or carbonate, comprising less than 1 ppm of physiologically extractable residual allylamine. In essence, said process of making sevelamer polymer comprises a step of crosslinking the polyallylamine having a residual allylamine content of less than 500 ppm, preferably less than 100 ppm, and most preferably less than 50 ppm, with epichlorohydrin in water at alkaline pH, optionally followed by treating the product with a carbonate buffer and washing the obtained sevelamer hydrochloride or sevelamer carbonate with water. The crosslinking reaction with epichlorohydrin is typically performed with the distillation residue obtained in the above process of removal of the residual allylamine. The distillation residue is typically adjusted by water or by a water-miscible solvent, e.g. by acetonitrile, to a concentration of between 10-40 weight %, preferably of between 15-30%, of polyallylamine. No adjustment of pH is generally required.

The conditions of the reaction with epichlorohydrin are well known in the art.

Epichlorohydrin is preferably used in an amount of about 5-15% w/w of polyallylamine.

The sevelamer hydrochloride resulting from the crosslinking reaction is allowed to cure and form a gel. Typically, curing takes about 16-36, about 18-30, or about 16-18 hours. The gel is preferably washed, preferably with a water-miscible solvent, followed by water, to obtain wet sevelamer hydrochloride. The preferred water-miscible solvent comprises an alcohol, such as methanol, isopropanol, or a combination thereof.

The sevelamer hydrochloride may then undergo an anion exchange reaction with an aqueous solution of a carbonate, typically with an alkali or alkaline earth metal carbonate to form sevelamer carbonate. Preferably, the carbonate is ammonium carbonate, sodium carbonate, or potassium carbonate. The concentration of the carbonate solution used is preferably about 0.5-2.0 M. The contact time of the wet product with the carbonate solution is preferably at least 2 hours; in some embodiments, a repeated contacting with fresh carbonate solutions may be performed. The sevelamer carbonate is then washed with water, and separated by filtration or centrifugation.

Alternately, the sevelamer hydrochloride may be converted to sevelamer carbonate by an anion exchange reaction with carbon dioxide at alkaline pH.

Advantageously, the sevelamer carbonate is dried, preferably in an air tray dryer or a fluidized bed dryer. Preferably, the drying temperature is about 40-100°C. The material can be optionally milled after drying. Preferably, the sevelamer carbonate is milled to achieve an average particle size of less than 100 microns.

Sevelamer carbonate obtained according to the process of the present invention preferably has a chloride content of less than about 2% w/w, preferably less than about 1 % w/w, most preferably than about 0.5% w/w. Preferably the pH is about 8.0- 11.0 in a 1% solution. LOD (Loss on Drying) of sevelamer carbonate obtained according to the above processes is preferably not more than (NMT) 7% w/w, preferably below 5% w/w.

Preferably, the obtained sevelamer carbonate has a phosphate binding capacity of about 5.0-7.0 mmol/g.

Similarly, optionally, sevelamer hydrochloride may be prepared using the technique of processing and drying described above.

In a particular aspect, the present invention provides sevelamer hydrochloride and/or carbonate having a content of physiologically extractable residual allylamine (as explained above) of less than 1 ppm. Such extraordinary low amount of residual allylamine is obtained by crosslinking a polyallylamine, preferably high-molecular- weight polyallylamine, which comprises less than 500 ppm, preferably less than 100 ppm, and most preferably less than 50 ppm of residual allylamine, and which is typically obtained by the above process of the present invention, followed by isolation procedures disclosed above.

A confirmation of the actual content of the physiologically extractable residual allylamine may be done by measuring it by a suitable analytical method. However, no such method has been reported in the prior art.

A suitable process for the determination of the physiologically extractable residual allylamine in sevelamer and/or a salt of sevelamer, such as sevelamer hydrochloride or sevelamer carbonate, comprises: a] Treating, under agitation, a sample comprising sevelamer with an aqueous buffer of pH higher than 5.0, preferably between 5.0 and 9.0, at 37°C;

b] Optionally, separating the solid substrate from the liquid phase, preferably at ambient temperature; and

c] Subjecting the liquid phase to a determination of the content of allylamine by a suitable analytical method.

Sub a]

Typically, a sample of sevelamer and/or a salt of sevelamer is stirred in a milligram amount (typically 5 to 100 mg) in a flask comprising several milliliters (typically 1-10 ml) of the buffer at 37 °C for a suitable time. The extraction time typically ranges from 10 to 40 hours, preferably from 20 to 30 hours and most preferably is 24 hours. The buffer is advantageously a borate buffer, preferably of a concentration of between 1 to 50 mM, most preferably between 5 and 25 mM. As allylamine is a volatile product, the extraction is advantageously performed in a closed vial.

Sub b]

The separation step provides a liquid sample comprising the extracted residual allylamine, which is not contaminated by the solid. Typically, the liquid phase may be separated by filtration or centrifugation, and may be optionally diluted by water to a desired volume. Alternately, the separation may be only partial, i.e. the solid is allowed to sediment either spontaneously or in a centrifuge and a sample of the supernatant is taken for analysis.

Sub c]

The liquid extract can be analyzed by any appropriate analytical method developed in the art for separation and quantification of allylamine, or of aliphatic amines or amino acids. Typically, a chromatographic method, such as high performance liquid chromatography (HPLC) may be used. Advantageously, the allylamine in the sample may be subjected to a derivatization to provide a derivative with better detectability, e.g. by increased absorbance, or by fluorescence. Thus, in a particular aspect, the process of the present invention also comprises a step of treating the liquid sample comprising allylamine with a derivatization agent. For HPLC purposes, a suitable derivatization agent may be, e.g., 6-Aminoquinolyl-N- hydroxysuccinimidyl carbonate (AccQ-Tag™, Waters), fluorenylmethylchloroformate (FMOC), dimethylamino-naphthalensulphonyl chloride (Dansyl-Cl), phenylisothiocyanate (PITC), ortho-phthaldialdehyde, etc.

In general, an HPLC method after a derivatization of allylamine in the sample prepared by the above process is the most useful method for determining the content of the allylamine. Proper stationary and mobile phase may be determined by experimentation; in general, chromatographic columns and mobile phases useful for analyses of amino acids and their derivatives may be used.

Other useful methods to separate, identify and quantify allylamine may be ion chromatography, gas chromatography or capillary electrophoresis.

Advantageously, the useful analytical method should have a limit of detection of 0.1 ppm or lower.

In an advantageous way, the processes of determination of the content of the physiologically extractable residual allylamine according to the present invention may be used for the analysis of a sample of sevelamer hydrochloride or carbonate for use in pharmaceutical applications. The sample of the sevelamer hydrochloride or carbonate may be a sample of the active substance per se or a sample or the final pharmaceutical composition comprising sevelamer hydrochloride or carbonate, for instance a tablet or a powder for oral suspension. The invention will be further described with reference to the following non-limiting examples.

Example 1 Process for making sevelamer carbonate

A 25% w/w solution of poly(allylamine).HCl, containing 1.5% of allylamine, was prepared. The pH was adjusted with NaOH to pH 10 and the solution was divided equally into four flasks in such a way that each flask contained 5 g of polyallylamine. Each flask was subjected to evaporation at a certain temperature and pressure (see table below) for 2 hours.

Content of allylamine in flasks 1-3 was about 20 ppm.

The mass loss due to evaporation of water was compensated by adding water to obtain a 25% solution and epichlorohydrin (0.5 ml) was added to each flask. The solutions were stirred for 30 minutes (gel point) and then cured for 18 hr. The gel was cut into particles and washed with carbonate buffer (70 ml, 1.0 M, pH 9.5), followed by washing three times with water (70 ml) and then with isopropanol (120 ml). The resulting white material was dried overnight at 40 C under vacuum and milled.

The content of physiologically extractable residual allylamine in the respective samples 1-4, determined by HPLC, was as follows: Reactor Allylamine content

1 0.87 ppm

2 0.20 ppm

3 0.17 ppm

4 1.50 ppm

Example 2 Process for analyzing sevelamer carbonate

Extraction process for the drug substance

30 mg of sevelamer carbonate was weighed into a safe-lock tube of 2 mL and 1.5 mL of 10 mM boric acid was added. The tube was vortexed until all powder was released from the bottom of the tube. The tube was placed in a thermostated mechanical shaker for 24 hours at 37°C at 1400 rpm. Subsequently, the tube was centrifuged for 10 minutes at 14,650 rpm.

Extraction process for 800 mg tablet

800 mg sevelamer carbonate tablet was transferred into a ball mill and grinded until fine powder was obtained (30 hrs for 30 seconds). 42.5 mg of the powder was transferred into a safe-lock tube of 2 mL and 1.5 mL of 10 mM boric acid was added. The tube was vortexed until all powder was released from the bottom of the tube. The tube was placed in a thermostated mechanical shaker for 24 hours at 37°C at 1400 rpm. Subsequently, the tube was centrifuged for 10 minutes at 14,650 rpm.

Derivatization

Three milligram of commercially available AccQ-Tag reagent (6-aminoquinolyl-N- hydroxysuccinimidyl carbamate) is dissolved in 1 mL acetonitrile and completely dissolved by agitation and mildly heating. An appropriate amount of the extract from the extraction process step (by preference \0 μL· oτ 30 μL· (the latter when there are low amounts of allylamine present)) is mixed with 70 μL· of AccQ-tag Ultra Borate buffer in an appropriate vial. To this mixture 20 μL· of the dissolved AccQ-Tag reagent is added, mixed immediately and then placed for 5 minutes at 55 °C. The derivatized extract is ready for HPLC analysis.

Analysis

Analysis of the derivatized sample was performed by UPLC method on an AccQ-Tag Ultra column (2.1 xlOO mm, dp 1.7 μιη) using conditions as prescribed by the manufacturer of the column for analysis of derivatized amino acids.

The invention having been described it will be obvious that the same may be varied in many ways and all such modifications are contemplated as being within the scope of the invention as defined by the following claims.