FIELD OF THE INVENTION
The present invention relates to amorphous form of carvedilol dihydrogen phosphate and process for the preparation of it.
BACKGROUND OF THE INVENTION
Carvedilol is chemically known as (±)-l-(9H-carbazol-4-yloxy)-3-[[2(2-methoxyphenoxy)ethyl]amino]-2-propanol having following structure (formula 1).

Carvedilol is disclosed in US patent No. 4 503 067. Carvedilol is a nonselective p-adrenergic blocking agent with #a1 blocking activity. It is used for treatment of hypertension, congestive heart failure and angina. Currently, carvedilol is synthesized as free base for incorporation in medication that is available commercially.
WO 2004/002419 discloses crystalline carvedilol phosphate salts such as carvedilol dihydrogen phosphate and its hemihydrate and dihydrate which are characterized by PXRD, FT-IR and FT-Raman spectroscopic methods.
WO 2005/051383 discloses various crystalline forms of carvedilol salts such as mandelate, lactate, maleate, sulfate, glutarate and benzoate.
One of the most important physical properties of a pharmaceutical compound is its solubility in aqueous solution, particularly the solubility in gastric juices of a patient. Other important properties relate to the ease of processing the form into pharmaceutical dosages, such as the tendency of a powdered or granulated form to flow and the surface properties that determine whether crystals of the form will adhere to each other when compacted into a tablet.
The discovery of new forms and solvates of a pharmaceutically useful compound provides a new opportunity to improve the performance characteristics of a
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pharmaceutical product. In light of the above, a need exists to develop different carvedilol forms which have greater aqueous solubility, chemical stability, sustained or prolonged drug or absorption levels.
SUMMARY OF THE INVENTION
The present invention provides an amorphous form of carvedilol dihydrogen phosphate. Further the present invention provides a process for the preparation of amorphous form of carvedilol dihydrogen phosphate that comprises of:
(a) preparing a solution of carvedilol base in a suitable solvent or mixture of solvents,
(b) adding ortho phosphoric acid to a solution of step (a),
(c) removing the solvent and
(d) recovering the solid
In another aspect the amorphous form of carvedilol dihydrogen phosphate of the present invention can also be prepared by another method which comprises of:
(a) preparing a solution of crystalline carvedilol dihydrogen phosphate in a suitable
solvent or mixture of solvents,
(b) removing the solvent and
(c) recovering the solid
DESCRIPTION OF THE DRAWINGS
Figure 1 is an X-ray powder diffraction pattern of amorphous form of carvedilol dihydrogen phosphate
Figure 2 is an FT-IR spectrum of amorphous form of carvedilol dihydrogen phosphate
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a novel amorphous form of carvedilol dihydrogen phosphate, which is characterized by having broad X-ray diffraction spectrum as shown in figure 1.
The FT-IR spectrum of amorphous form of carvedilol dihydrogen phosphate of the present invention exhibits the pattern of peaks as shown in figure 2.
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The present invention provides the amorphous form of carvedilol dihydrogen phosphate which is obtained by a process that comprises of:
(a) preparing a solution of carvedilol base in a suitable solvent or mixture of solvents,
(b) adding ortho phosphoric acid to a solution of step (a),
(c) removing the solvent and
(d) recovering the solid.
Generally, the aqueous or anhydrous ortho phosphoric acid is added to the solution of carvedilol base in a suitable solvent. The addition may be performed at a temperature 0-50 °C, preferably at 25-30 °C. The quantity of carvedilol base and ortho phosphoric acid may be equivalent or slightly molar excess.
In another aspect, amorphous form of carvedilol dihydrogen phosphate is obtained by using carvedilol dihydrogen phosphate which could be either in crystalline form or solvates or hydrates or anhydrous. The process comprises of:
(a) preparing a solution of crystalline carvedilol dihydrogen phosphate in a suitable
solvent or mixture of solvents,
(b) removing the solvent and
(c) recovering the solid.
The solution of crystalline carvedilol dihydrogen phosphate in a suitable solvent is generally stirred at a temperature of 0-50 °C, preferably at 25-30 °C before the removal of the solvent.
The term "suitable solvent" in either of the processes described above includes any solvent or mixture of solvents in which carvedilol is soluble, including, for example, lower alkanol, ketone, ester and chlorinated solvent.
Examples of lower alkanol include those primary, secondary and tertiary alcohols having one to six carbon atoms such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and t-butanol. Ketone include acetone, 2-butanone and 4-methyl pentanone. Ester include ethyl acetate and butyl acetate. Chlorinated solvent include chloroform,
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dichloromethane and dichloroethane. Mixtures of all of these solvents are also contemplated.
Removal of the solvent in either of the processes described above is accomplished by techniques which include distillation at atmospheric pressure, distillation under reduced pressure, evaporation, spray drying, freeze drying and agitation thin film evaporation. Moreover, the product obtained may be further dried to achieve the desired moisture values or desired residual solvent values.
The effective amount of amorphous form of carvedilol dihydrogen phosphate can be used to prepare pharmaceutical composition in association with one or more non toxic pharmaceutically acceptable carriers and/or diluents thereof, and if desired , other active ingredients, which may be administered orally, intravascularly, intraperitoneally, subcutaneously, intramuscularly or topically for the treatment of hypertension, congestive heart failure and angina in a mammal in need thereof.
The present invention is further illustrated by the following examples which are provided merely to be exemplary of the invention and are not intended to limit the scope of the invention.
EXPERIMENTAL
The powder X-ray diffraction spectrum is measured using Philips (PAN alytical X'pert pro) difractogram (copper anti cathode) and expressed in terms of inter planar distance d, Bragg's angle 2 theta, intensity and relative intensity (expressed as a percentage of the most intense peak). The scanning parameters included: measurment range: 3-40 degrees two theta; continuous scan.
The FTIR spectra were obtained using a Perkin-Elmer, Spectrum-100 instrument.
The thermogravimetric analysis (TGA) was done using Perkin Elmer Pyris 1 TGA
instrument.
Spray Dryer: Buchi mini spray dryer (Model B-191). The inlet temperature was set
between 50 to 55 °C. The outlet temperature was maintained between 30 to 37 °C. The
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flow rate of the solution was controlled to 500 ml to 600 ml/hour. The pumping pressure was maintained at 600 to 800 psi.
Example 1: Preparation of amorphous carvedilol dihydrogen phosphate using spray dryer
Carvedilol base (10 g) was taken in methanol (500 mL) and the solution was stirred at 25-30 °C for 15-20 minutes. To that ortho phosphoric acid (2.9 g, 88 % aqueous solution) was added and stirred further. The clear solution was subjected to spray drying to afford amorphous carvedilol dihydrogen phosphate. Yield: 5.0 g, M.P.: 62-63 °C. The moisture content of the product was 4.10%.
Example 2: Conversion of crystalline carvedilol dihydrogen phosphate into amorphous carvedilol dihydrogen phosphate
Crystalline carvedilol dihydrogen phosphate (10 g) was taken in methanol (750 mL) and the solution was stirred at 25-30 °C for 15-20 minutes to get clear solution. The clear solution was subjected to spray drying to afford amorphous carvedilol dihydrogen phosphate. Yield: 4.7 g.
Example 3: Preparation of amorphous carvedilol dihydrogen phosphate using anhydrous orthophosphoric acid
Carvedilol base (10 g) was taken in methanol (500 mL) and the solution was stirred at 25-30 °C for 15-20 minutes to get clear solution. To that anhydrous ortho phosphoric acid (2.9 g) was added and stirred further. The solution was subjected to spray drying to afford amorphous carvedilol dihydrogen phosphate. Yield: 5.2 g
Example 4: Preparation of amorphous carvedilol dihydrogen Phosphate using agitated thin film dryer
Carvedilol base (10 g) was taken in methanol (500 mL) and the solution was stirred at 25-30 °C for 15-20 minutes to get clear solution. To that ortho phosphoric acid (2.9 g, 88 % aqueous solution) was added and stirred further. The solution was feed to agitated thin film dryer to afford amorphous carvedilol dihydrogen phosphate. Yield: 5.0 g,
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We claim:
1. Amorphous carvedilol dihydrogen phosphate
2. The compound according to claim 1 having an X-ray diffraction pattern as shown in
figure 1.
3. A process for the preparation of compound of claim 1, which comprises of:

(a) preparing a solution of carvedilol base in a suitable solvent or mixture of
solvents,
(b) adding ortho phosphoric acid to a solution of step (a),
(c) removing the solvent and
(d) recovering the solid

4. A process according to claim 3 in which in step (a), the solvent is selected from lower
alkanol, ketone, ester and chlorinated solvent.
5. A process according to claim 4 wherein the lower alkanol includes methanol, ethanol,
n-propanol, isopropanol, n-butanol, isobutanol, t-butanol and mixtures thereof.
6. A process according to claim 4 wherein ketone includes acetone, 2-butanone and 4-
methyl pentanone.
7. A process according to claim 4 wherein ester includes ethyl acetate and butyl acetate.
8. A process according to claim 4 wherein chlorinated solvent includes chloroform,
dichloromethane and dichloroethane.
9. A process according to claim 3 wherein in step (c) the solvent is removed by spray
drying or agitation thin film drying.
10. A process for the preparation of compound of claim 1, which comprises of:

(a) preparing a solution of crystalline carvedilol dihydrogen phosphate in a
suitable solvent or mixture of solvents,
(b) removing the solvent and
(c) recovering the solid.
11. A process according to claim 10 in which in step (a), the solvent is selected from
lower alkanol, ketone, ester and chlorinated solvent.
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12. A process according to claim 11 wherein the lower alkanol includes methanol,
ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol and mixtures
thereof.
13. A process according to claim 11 wherein ketone includes acetone, 2-butanone and 4-
methyl pentanone.
14. A process according to claim 11 wherein ester includes ethyl acetate and butyl
acetate.
15. A process according to claim 11 wherein chlorinated solvent includes chloroform,
dichloromethane and dichloroethane.
16. A process according to claim 10 wherein in step (b) the solvent is removed by spray
drying or agitation thin film drying.
16.

Dated this 27th day of February 2007

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The present invention provides amorphous form of carvedilol dihydrogen phosphate and processes for the preparation of it.