AU782143B2 - Crystals of the sodium salt of pravastatin - Google Patents

Description

WO 01/10813 PCT/IB00/01103 1 CRYSTALS OF THE SODIUM SALT OF PRAVASTATIN The present invention relates to a crystalline form of the sodium salt of pravastatin, which is known by the chemical name l-naphthaleneheptanoid acid, 1,2,6,7,8,8ahexahydro-P5,, 6-trihydroxy-2-methyl-8- (2-methyl-loxobutoxy)-, mono sodium salt, which is useful as a pharmaceutical substance. The present invention further relates to the method for its preparation and isolation, to a pharmaceutical formulation containing the sodium salt of pravastatin in the crystalline form and a pharmaceutically acceptable carrier, and to the pharmaceutical method of treatment.

Lovastatin, pravastatin, simvastatin, mevastatin, atorvastatin, fluvastatin and cervastatin and derivatives and analogs thereof are known as HMG-CoA reductase inhibitors and are used as antihypercholesterolemic agents. The majority of them are produced by fermentation using microorganisms of different species identified as species belonging to Aspergillus, Monascus, Nocardia, Amycolatopsis, Mucor or Penicillium genus, some are obtained by treating the fermentation products using the methods of chemical synthesis (simvastatin) or they are the products of total chemical synthesis (fluvastatin, atorvastatin and cervastatin).

Processes for the preparation of the sodium salt of pravastatin in a solid form known from the prior art comprise, for example, the step of lyophilisation. After lyophilisation only the solvent is removed but impurities remain together with the sodium salt of pravastatin.

Apart from the aforementioned, lyophilisation is not very economical in large-scale production operations. During precipitation due to nonselectivity of the process, CONFIRMnON cm7 WO 01/10813 PCT/IBOO/01103 2 impuricies precipitate together with the desired substance. Compared to the both aforementioned processes for the preparation of pharmaceutical substances in the solid form, crystallization is the only selective process wherein the molecules of the desired substance are selectively incorporated into the crystal matrix.

Possibility of inclusion of impurities into the crystal is minimal because only small size molecules are able to incorporate into intermolecular space inside a crystal (related impurities, which are usually within the desired substance size range may only be incorporated into this space with great difficulty), incorporation of other molecules into the crystal matrix is not favoured thermodynamically.

The advantage of substances in the crystal structures over those in amorphous structures is that their physical as well as chemical parameters are better defined and they are more stable. The latter is of particular importance for the substances which in their nature are unstable and sensitive to different ambient influences, such as light, pH, atmosphere and temperature.

Pravastatin sodium is particularly sensitive to these negacive influences.

It has been known that thus far the sodium salt of pravastatin may only be present in an amorphous form. The Merck Index 1996 describes the sodium salt of pravastatin as an amorohous substance.

Methods for the preparation of the sodium salt of pravastatin described in many patents, for example US Pat. No. 44,537,859, US Pat. No. 4,448,979, US Pat. No.

4,410,629 and US Pat. No. 4,346,227, afford only the preparation of an amorphous form. In the methods disclosed, after separation on the chromatographic 19/05 '05 THU 11:18 FAX 61 3 9288 1567 FREEHILLS PATENT TRADE PATENT OFFICE 1(I016 004649280 3 columns, the fractions obtained comprising the sodium salt of pravastatin are lyophilized and the sodium salt in a solid amorphous form is obtained.

The WO-A-98/45410 discloses that after the sodium salt of pravastatin is purified using reverse-phase chromatography, alleged crystals may be obtained by precipitation in the ethanol/ethyl acetate mixture; however, the experiments we have carried out suggest that this combination of the solvents affords the preparation of pravastatin in the amorphous form and not in the crystalline form.

The present invention relates to a sodium salt of pravastatin which is improved in purity and stability compared to the salts described in the prior art mentioned above.

10 The present invention further relates to a process for the preparation of such a sodium salt of pravastatin.

In a first aspect, the present invention provides the sodium salt of pravastatin in a crystalline form. Furthermore, the present invention also provides the sodium salt of pravastatin in a specific crystalline form, wherein the crystals in an X-ray diffraction measurement produce a signal substantially in accordance with that illustrated in the diffractogram shown in Figure 2.

In a further aspect, the present invention provides a crystalline sodium salt of pravastatin having an X-ray diffraction pattern comprising characteristic strongest peaks at 16.3 0.2; 17.4 0.2 and 20.0 0.2 degrees measured at reflection angle 2 Theta.

In a further aspect, the present invention provides a crystalline sodium salt of pravastatin having an X-ray diffraction pattern comprising characteristic peaks at 4.0 0.2; 10.2 0.2; 16.3 0.2; 17.4 0.2 and 20.0 0.2 degrees measured at reflection angle 2 Theta.

In a further aspect, the present invention provides a process for the preparation of the sodium salt of pravastatin in a crystalline form comprising the steps COMS ID No: SBMI-01254151 Received by IP Australia: Time 10:25 Date 2005-05-19 WO 01/10813 PCT/IB00/01103 4 of: dissolution of the sodium salt of pravastatin in a lower aliphatic alcohol; addition of ethyl acetate to the alcoholic solution of the sodium salt of pravastatin; cooling of said alcohol/ethyl acetate mixture; and crystallization.

According to a third aspect of the present invention, there is further provided a pharmaceutical formulation containing the sodium salt of pravastatin in the aforementioned crystalline forms.

The crystalline sodium salt of pravastatin according to the present invention is particularly suitable for the preparation of pharmaceutical products for the treatment of hypercholesterolemia and hyperlipidemia.

In the following, drawings will be briefly described.

Figure 1: Figure 2: Diffractogram of a conventional amorphous sodium salt of pravastatin which is commercially available, scanned on the X-ray powder diffractometer within 2 to 420 20 range with a 0.0250 20 step and an integration time of 1 second/step.

Diffractogram of crystals of the sodium salt of pravastatin prepared according to Example 2 of the present invention, which are scanned on the X-ray powder diffractometer within 2 to 480 20 range with a 0.0350 20 step and an integration time of 1 second/step.

WO 01/10813 PCT/IB00/01103 5 Figure 3: Image of the amorphous sodium salt of pravastatin used for the X-ray diffraction measurement shown in Fig. 1, which is obtained under the microscope under 400-fold magnification.

Figure 4: Image of crystals of the sodium salt of pravastatin prepared according to Example 2 of the present invention, obtained under the microscope under 400-fold magnification.

X-ray diffraction measurements were carried out with a X-ray powder diffractometer (Phillips PW 1710) using a Cu-K, (20 mA, 40 kV, X 1.5406 A) light source. For microscopic observations, an OLYMPUS BX 50F microscope with a CCD Sonny DXC-950-P camera was used with 400-fold magnification.

In the following, the present invention will be illustrated in more detail by the description of preferred embodiments.

In our research work we have surprisingly found that by suitable selection of the solvents and adequate order of their use the sodium salt of pravastatin in a form having an improved crystallinity, relative to the conventional solid form, can be prepared. Thus, in contrast to the white appearance of the pravastatin sodium solid described in the WO-A-98/45410, it is possible according to the present invention to achieve crystals exhibiting a colorless or pale yellow appearance, which clearly indicates the improved crystallinity and, thus, the clearly crystalline form of the sodium salt of pravastatin provided by the present invention.

WO 01/10813 PCT/IBOO/01103 6 Other physical properties of the crystals of the pravastatin sodium of the present invention further indicate the improved crystallinity obtained. Firstly, the crystals according to the present invention can be preferably obtained in the form of needles, sometimes in the form of radiating clusters. Such crystal shape can be readily observed under the microscope, for example when the observation is carried out under 400-fold magnification (see Fig. By contrast, conventionally available amorphous pravastatin sodium appear in the shape of granular particles (see Fig. 3).

Secondly, the melting point of the pravastatin sodium crystals according to the present invention is preferably between 170 and 174 0 C, more preferably between 172 and 174 0 C. This melting point range achieved in the present invention is very small for such a complicated chemical structure and confirms the high crystallinity of the pravastatin sodium crystals obtained.

Thirdly, a further characteristic feature of the crystalline pravastatin sodium according to the present invention is that the signal obtained in an X-ray diffraction measurement (Cu-Ka, 20) have sharp and distinct peaks. In particular, the shape of the X-ray diffraction peaks of pravastatin sodium according to the present invention are defined by a small half-value width, which confirms a high degree of crystallinity. The term "half-value width" means the value of the of one peak a7 the half height or magnitude of the respective peak. Accordingly, the signals obtained by these measurements comprise distinct peaks (28) having a half-value width preferably below 20, more preferably below and most preferably below WO 01/10813 PCT/IB00/01103 7 Exemplary crystals of pravastatin sodium prepared according the present invention produce a diffractogram in an X-ray diffraction measurement that is shown in Figure 2. Due to its particularly improved crystallinity and, thus, purity and stability, such pravastatin sodium crystals which, in an X-ray diffraction measurement produce a signal sufficiently comparable to that, preferably essentially as that illustrated in the diffractogram shown in Figure 2, constitute preferred embodiments of the present invention. Unit cells of this crystal could not be determined because of its size and high background at the angles 200 20. Comparison of the recorded diffractogram with the reference from the PDF and CSD databases (PDF "Powder Diffraction File issued by "International Center for Diffraction Data", 12 Campus Boulevard, Newtown Square, PA 19073-3273 USA; CSD "Cambridge Structural Database System" issued by "Cambridge Crystallographic Data Centre", 12 Union Road, Cambridge CB2 1EZ, the United Kingdom) has shown that the crystals of the sodium salt of pravastatin according to the present invention are really a novel and thus only known crystalline form of the sodium salt of pravastatin.

For comparison, a diffractogram of amorphous pravastatin sodium which is commercially available is shown in Figure 1.

The process for the preparation of crystals according to the present invention as described above comprises the following steps: Providing a solution containing pravastatin and sodium cations in a lower aliphatic alcohol. This is suitably carried out by dissolution of an solid and/or amorphous sodium salt of pravastatin in a lower aliphatic alcohol having preferably 1 to 4 carbon atoms. More WO 01/10813 PCT/IB00/01103 8 preferably, the alcohol used for the dissolution of pravastatin sodium is ethanol or methanol. The best crystallization results have been achieved when preparing a solution of pravastatin sodium in methanol.

Addition of ethyl acetate into the alcoholic solution, preferably while the alcoholic solution obtained in step is stirred continually. The addition of ethyl acetate into the alcoholic solution of pravastatin sodium is preferably carried out slowly, while the addition may be continuously or stepwise.

Cooling of the resulting alcohol/ethyl acetate mixture.

Crystallization.

In step from the cooled mixture crystals of the sodium salt of pravastatin, which preferably have a colorless or pale yellow appearance and are in the form of needles or radiating clusters, are formed.

Additionally, the crystals obtained by this process may preferably be filtered, ethyl acetate washed and dried.

The crystallization is carried out advantageously if the initial concentration of the sodium salt of pravastatin in the aliphatic alcohol used for the dissolution -is preferably between 0.03 and 0.3 g/ml, more preferably between 0.05 and 0.2 g/ml, particularly about 0.1 g/ml, and if the volume of added ethyl acetate in step does preferably not exceed the 15-fold volume, more preferably the 10-fold volume of the starting solution of the sodium salt of pravastatin in the aliphatic alcohol.

WO 01/10813 PCT/IB00/01103 9 Furthermore, to achieve a higher crystallization rate, the preferred temperature of crystallization is below 0 C, more preferably below 10 0 C, particularly about 8 0

C.

For enforcing further crystallization, it is preferred to carry out the process according to the invention with additional steps of: Further adding ethyl acetate to the mixture of step This is done after an appropriate period of a first crystallization stage where crystallization occurs.

then, crystallization of pravastatin sodium is continued while cooling.

With such an additional crystallization stage the yield of crystalline pravastatine sodium can be increased, normally by 5 to 10 The volume of ethyl acetate additionally added to the cooled mixture in step is preferably in the range of from 25 to 75 by volume, more preferably from 40 to by volume based on the volume of ethyl acetate added in step Furthermore, the crystals are preferably formed within a total crystallization time of 3 to 20 hours. More preferably, the total crystallization time is between 4 and 12 hours, particularly about 4 hours.

The present invention also relates to pharmaceutical formulations containing the sodium salt of pravastatin in the form of crystals. The pharmaceutical formulation is present in the form which is suitable for oral and parenteral administration, respectively, and is useful for the treatment of hypercholesterolemia and WO 01/10813 PCT/IB00/01103 10 hyperlipidemia. The pharmaceutical formulation of the present invention is available in the form of tablets, capsules, granules and suppositories as well as in the form of suspensions.

The pharmaceutical formulation of this invention may comprise, in addition to the sodium salt of pravastatin, one or more fillers, such as microcrystalline cellulose, lactose, sugars, starches, modified starch, mannitol, sorbitol and other polyols, dextrin, dextran and maltodextrin, calcium carbonate, calcium phosphate and/or hydrogen phosphate, sulphate, one or more binders, such as lactose, starches, modified starch, dextrin, dextran and maltodextrin, microcrystalline cellulose, sugars, polyethylene glycols, hydroxypropyl cellulose, hydroxypropyl methylcellulose, ethylcellulose, hydroxyethyl cellulose, methylcellulose, carboxymethyl cellulose, gelatin, acacia gum, tragacanth, polyvinylpyrrolidone, magnesium aluminium silicate, one or more disintegrating agents such as croscarmellose sodium, cross-linked polyvinylpyrrolidone, cross-linked carboxymethyl starch, starches and microcrystalline cellulose, magnesium aluminium silicate, polyacrylin potassium, one or more different glidants such as magnesium stearate, calcium stearate, zinc stearate, calcium behenate, sodium stearyl fumarate, talc, magnesium trisilicate, stearic acid, palmitic acid, carnauba wax, silicon dioxide, one or more buffering agents such as sodium or potassium citrate, sodium phosphate, dibasic sodium phosphate, calcium carbonate, hydrogen phosphate, phosphate, sulphate, sodium or magnesium carbonate, sodium ascorbinate, benzoate, sodium or potassium hydrogen carbonate, lauryl sulphate, or mixtures of such buffering agents.

00455,316 11 If required any, the formulation may also comprise surfactants and other conventional components for solid, pharmaceutical formulations such as coloring agents, lakes, aromas and adsorbents. As surfactants the following may be used: ionic surfactants, such sodium lauryl sulphate or non-ionic surfactants such as different poloxamers (polyoxyethylene and polyoxypropylene copolymers), natural or synthesized lecithins, esters of sorbitan and fatty acids (such as Span®, manufactured by Atlas Chemie), esters of polyoxyethylenesorbitan and fatty acids (such as Tween®, manufactured by Atlas Chemie), polyoxyethylated hydrogenated castor oil (such as Cremophor®, manufactured by BASF), polyoxyethylene stearates (such as Brij®, manufactured by Atlas Chemie), dimethylpolysiloxane or any combination of the above mentioned surfactants.

If the solid pharmaceutical formulation is in the form of coated tablets, the coating may be prepared from at least one film-former such as hydroxypropyl methylcellulose, hydroxypropyl cellulose, at least from one plasticizer such as polyethylene glycols, dibutyl sebacate, triethyl citrate, and other pharmaceutical auxiliary substances conventional for film coatings, such as pigments, fillers and others.

The pharmaceutical formulation can be prepared by conventional formulation methods known to those skilled in the art.

20 Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment, or any form of suggestion, that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

25 As used herein, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude other additives, components, integers or steps.

The present invention is illustrated but by no means limited by the following examples.

WO01/10813 PCT/IB00/01103 12 Example 1 The sodium salt of pravastatin (1 g) was dissolved in methanol (10 ml) and while stirring ethyl acetate was added. The resulting clear yellow solution was cooled to 8 0 C and allowed to stand overnight. Formed radiating clusters of thin, long needle-like crystals were filtered, washed with ethyl acetate (20 ml) and dried.

Yield: 0.87 g of pale yellow crystals, melting point 172 174 0

C.

Example 2 The sodium salt of pravastatin (2 g) was dissolved in methanol (20 ml) and while stirring ethyl acetate (80 ml) was added. The clear, slightly yellow solution was cooled to 8 0 C and allowed to stand for 4 hours. Formed radiating clusters of thin, long needle-like crystals were filtered, washed with ethyl acetate (20 ml) and dried.

Yield: 1.53 g of colorless crystals, melting point 172 174 0

C.

Example 3 The sodium salt of pravastatin (2 g) was dissolved in methanol (20 ml) and while stirring ethyl acetate (150 ml) was added. The resulting clear, slightly yellow solution was cooled to 8°C and allowed to stand for 4 hours. Formed radiating clusters of thin, long needlelike crystals were filtered, washed with ethyl acetate ml) and dried. Yield: 1.66 g of colorless crystals, melting point 172 174°C.

Example 4 The sodium salt of pravastatin (2 g) was dissolved in mcr.hanoL (20 ml) and while stirring ethyl acetate WO01/10813 PCT/IB00/01103 13 (170 ml) was added. The resulting clear, slightly yellow solution was cooled to 8 0 C and allowed to stand for 4 hours. Formed radiating clusters of thin, long needlelike crystals were filtered, washed with ethyl acetate (20 ml) and dried. Yield: 1.75 g of colorless crystals, melting point 172 174°C.

Example The sodium salt of pravastatin (2 g) was dissolved in methanol (12 ml) and while stirring ethyl acetate (100 ml) was added. The resulting clear, slightly yellow solution was cooled to 8 0 C and allowed to stand for 1 hour. After that further ethyl acetate (60 ml) was added, so the pravastatin still dissolved in the solution was forced to crystallize. After 2 hours at 8°C the formed radiating clusters of thin, long needle-like crystals were filtered, washed with ethyl acetate (20 ml) and dried. Yield: 1.85 g of colorless crystals, melting point 172 174 0

C.

Claims (21)

1. A crystalline sodium salt of pravastatin having an X-ray diffraction patter substantially in accordance with that shown in Figure 2.

2. A crystalline sodium salt of pravastatin having an X-ray diffraction pattern comprising characteristic strongest peaks at 16.3 0.2; 17.4 0.2 and 20.0 0.2 degrees measured at reflection angle 2 Theta.

3. A crystalline sodium salt of pravastatin having an X-ray diffraction pattern comprising characteristic peaks at 4.0 0.2; 10.2 0.2; 16.3 0.2; 17.4 0.2 and 20.0 0.2 degrees measured at reflection angle 2 Theta. 10 4. A crystalline sodium salt of pravastatin according to claim 2 or 3, wherein the peak at 16.3 is resolved into characteristic peaks at 16.5 0.2 and 16.3 0.2 degrees measured at a reflection angle 2 Theta.

5. A crystalline sodium salt of pravastatin according to any one of claims 2 to 4, wherein the peak at 17.4 is resolved into characteristic peaks at 17.1 02 and 17.4 0.2 15 degrees measured at reflection angle 2 Theta.

6. A crystalline sodium salt of pravastatin according to any one of claims 2 to additionally comprising characteristic peaks in an X-ray diffraction pattern at 4.5 t 0.2; 6.3 0.2; 7.3 0.2 and 11.8 0.2 degrees measured at reflection angle 2 Theta.

7. A crystalline sodium salt of pravastatin according to any one of claims 3 to 6, wherein any of the peaks identified in any one of the claims 7 to 11 which are separated on an X-ray diffraction pattern by less than 2 degrees measured at reflection angle 2 Theta, appear on an X-ray diffraction pattem as single broadened peak.

8. The sodium salt of pravastatin according to any one of claims 1 to 7, wherein the crystals exhibit a colourless or pale yellow appearance.

9. The sodium salt of pravastatin according to any one of claims 1 to 8, wherein the crystals clearly appear in the form of needles or radiating clusters. COMS ID No: SBMI-01254151 Received by IP Australia: Time 10:25 Date 2005-05-19 19/05 '05 THU 11:18 FAX 61 3 9288 1567 FREEHILLS PATENT TRADE PATENT OFFICE 004640280 A sodium salt of pravastatin according to any one of claims 1 to 9, having a melting point in the range of from 170 0 C to 174 0 C.

11. A sodium salt of pravastatin according to any one of claims 1 to 10, wherein the crystals in an X-ray diffraction measurement produce distinct peaks having a half-value width below 2 degrees measured at reflection angle 2 Theta.

12. A process for the preparation of the sodium salt of pravastatin in a crystalline form, comprising the steps of. providing a solution containing pravastatin and sodium cations in a lower aliphatic alcohol; adding ethyl acetate to said alcoholic solution; cooling of said alcohol/ethyl acetate mixture; and crystallizing said sodium salt of pravastatin.

13. A process according to claim 12 additionally comprising, after a first crystallization stage, the steps of: 15 adding further ethyl acetate to the alcohol/ethyl acetate mixture; and further crystallizing the sodium salt of pravastatin.

14. A process according to claim 12 or 13, wherein the lower aliphatic alcohol is ethanol or methanol. S: 15. A process according to claim 14, wherein the lower aliphatic alcohol is methanol. S 20 16. A process according to any one of claims 12 to 15, wherein the addition of ethyl acetate is performed while the alcoholic solution of the sodium salt of pravastatin is stirred continually. 17: A process according to any one of claims 12 or 16, wherein the concentration of the sodium salt of pravastatin in the alcoholic solution of step is between 0.03 and 0.3 g/ml.

18. A process according to any one of claims 12 to 17, wherein the volume of added ethyl acetate in step does not exceed the 15-fold volume of the initial alcoholic solution of the sodium salt of pravastatin. J 018 COMS ID No: SBMI-01254151 Received by IP Australia: Time 10:25 Date 2005-05-19 19/05 '05 THU 11:19 FAX 61 3 9288 1567 FREEHILLS PATENT TRADE PATENT OFFICE 1&019 004649280 16

19. The process according to claim 13, wherein the volume of further added ethyl acetate in step is in the range of from 25 to 75% by volume based on the volume of ethyl acetate added In step A process according to claim 13, wherein the alcohol/ethyl acetate mixture Is cooled to a temperature below

21. A process according to any one of claims 12 to 20, wherein the total crystallization time is between 3 and 20 hours.

22. A process according to any one of claims 12 to 21, wherein the formed crystals are filtered, ethyl acetate washed and dried. 0 10 23. A pharmaceutical formulation containing the sodium salt of pravastatin in a crystalline form as defined in any one of claims 1 to 11.

24. A pharmaceutical formulation according to claim 23 comprising the sodium salt of pravastatin in a crystalline form; the crystals being in the form of needles or radiating clusters having a melting point of from 170°C to 174 0 C and an X-ray diffraction pattern 15 substantially in accordance with that shown in Figure 2.

25. A method of treating hypercholesterolemia and hyperlipidemia comprising administering to a person in need of such treatment, a hypercholesterolemia and hyperlipidemia treating effective amount of a crystalline sodium salt of pravastatin as defined in any one of claims 1 to 11.

26. Use of a crystalline sodium salt of pravastatin according to any one of claims 1 to 11 for the preparation of a medicament.

27. A crystalline sodium salt of pravastatin according to claim 1 substantially as hereinbefore described with reference to the examples.

28. A process according to claim 12 substantially as hereinbefore. described with reference to the examples. COMS ID No: SBMI-01254151 Received by IP Australia: Time 10:25 Date 2005-05-19 19/05 '05 THIT 11:19 FAX 61 3 9288 1367 19/0 '05T~u 1:19FAX 1 3 288 567FREEHILLS PATENT TRADE 4*-4 PATENT OFFICE d02 4020 004849280 Dated: 17 May 2005 Freehills Patent Trade Mark Attorneys Patent Attorneys for the Applicantls: LEK Pharmaceuticals n JC. COMS ID No: SBMI-01 254151 Received by IP Australia: Time 10:25 Date 2005-05-19