WO2003002120A1 - Polymorphic forms of 6-[4-(1-cyclohexyl-1h-tetrazol-5-yl)butoxy]-3, 4-dihydro-2(1h)-quinolinone - Google Patents

Abstract

Polymorphs Form B, Form C, and amorphous of 6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone, commonly known as cilostazol, have been identified. These polymorphs may be formed in pure form, in combination with each other, in combination with other polymorphs of cilostazol, or together with other pharmaceutical agents. Processes for preparing these polymorphs, and combinations of these polymorphs, as well as methods of use and unit dosages of these polymorphic forms, and their combinations, are described.

Description

POLYMORPHIC FORMS OF 6-[4-(l-CYCLOHEXYL-lH-TETRAZOL-5-YL) BUTOXY]-3,4-DIHYDRO-2(lH)-QUINOLINONE

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to compositions and methods of preparing novel forms of the free base of 6-[4-(l-cyclohexyl-lH-tetrazol-5-yl)butoxy]-3,4-dihydro-2(lH)- quinolinone (hereinafter referred to by its generic name "cilostazol"). More particularly, novel crystalline forms of cilostazol, in the form of polymorphs B, C, and amorphous are disclosed. Most particularly, such forms of cilostazol, individually and in combinations thereof, with and without polymorphic Form A, are useful in pharmaceutical formulations and methods for using such polymorphs and formulations thereof. 2. Description of Related Art

The compound 6-[4-(l-cyclohexyl- lH-tetr azol-5-yl)butoxy]-3,4-dihydro-2(lH)- quinolinone is generally known as the pharmaceutically active compound cilostazol.

Cilostazol has been known to have a singular crystalline form (Form A), which is a free base and used as an active pharmaceutical ingredient (API) for use in the preparation of drug products.

Cilostazol has the following chemical structure:

Cilostazol, and several of its metabolites, are known inhibitors of phosphodiesterase and, more particularly, phosphodiesterase III. As a phosphodiesterase inhibitor (type LU), cilostazol suppresses platelet aggregation and also acts as a direct arterial vasodilator, h addition to its reported vasodilator and antiplatelet effects, cilostazol has been proposed to have beneficial effects on plasma lipoproteins, increasing

/ plasma high density lipoprotein cholesterol and apolipoprotein (See e.g., Dawson et al., Circulation 98: 678-686 [1998]; Elam et al., Arterioscler Thromb. Vase. Biol. 18: 1942- 1947[1998]; Drag Evaluation Monographs, vol. 99, Micromedex Inc.). Additionally, cilostazol has been reported as useful for the treatment of sexual dysfunction in United States Patent No. 6,187,790 to Cutler. Cilostazol free base is the API in the pharmaceutical drug product marketed under the trademark PLETAL® (Otsuka America Pharmaceutical, Inc., Rockville, Maryland; and Pharmacia Company, Kalamazoo, Michigan).

Methods of preparation of cilostazol are set forth by Nishi et al. (Chem. Pharm. Bull. 31: 1151[1983], and United States Patent No. 4,277,479, the disclosure of both references are hereby incorporated by reference, and its pharmacology, metabolism, mechanism of action and clinical evaluations are described in Arzneimittel-Forsch. 35: 1117-1208 (1985).

Use of cilostazol in pharmaceutical formulations has been limited by its low aqueous solubility and low bioavailability, which impede its efficient therapeutic use. Therefore, it would be beneficial if pharmaceutical chemists could provide a more soluble and, thus, more bioavailable drug product. These forms could lead to lower doses of drug substance (per unit dose and per day) required to be administered to provide similar efficacy and, potentially, a better safety profile, to patients in need of treatment. To date, no such forms have been prepared.

Polymoφhic forms of the same drug substance or API, as administered by itself or formulated as a drug product (also known as the final or finished dosage form), are well known in the pharmaceutical art to affect, for example, the solubility, stability, flowability, fractability, and compressibility of drug substances and the safety and efficacy of drug products (see, e.g., Knapman, K Modern Drug Discoveries, March, 2000: 53). So critical are the potential effects of different polymoφhic forms in a single drug substance on the safety and efficacy of the respective drag products(s) that the United States Food and Drag Administration (FDA) requires each drag substance manufacturer, at least, to control its synthetic processes such that the percentages of the various respective polymoφhic forms, when present, must be controlled and consistent among batches and within the drug substance/product's specification as approved by the FDA. SUMMARY OF THE INVENTION

Form A is the material produced using the methods described in United States Patent No. 4,277,479 (hereinafter referred to as "the '479 patent"), and is clearly distinguishable from other polymoφhic forms of the present invention by X-ray powder diffraction and other methods of solid state characterization. Form A, the sole, previously lαiown form of cilostazol, as prepared by the procedures described in the '479 patent, has been found to have low aqueous solubility and low bioavailability. As such, Form A is not particularly well suited for commercial use in pharmaceutical formulations or for therapeutic use.

A novel crystalline form of cilostazol, Form B, which possesses distinct advantages over the previously known Form A of cilostazol has now been prepared and characterized. In accordance with the present invention, a newly discovered polymoφh, Form B of cilostazol, can be obtained in a pure form or in combination with other polymoφhic forms of cilostazol. Form B is stable, and can be prepared free from contamination by solvates such as water or organic solvents such as, for example, acetonitrile. As such, Form B is useful for the commercial preparation of pharmaceutical formulations such as tablets and capsules.

Another novel crystalline form of cilostazol, Form C, that has also been prepared and characterized, possesses distinct advantages over the previously known Form A of cilostazol, and is clearly distinguishable from other polymoφhic forms of the present invention by X-ray powder diffraction and other methods of solid-state characterization. In accordance with the present invention, Form C of cilostazol, can be obtained in a pure form or in combination with other polymoφhic forms of cilostazol. Form C is stable, and can be prepared free from contamination by solvates such as water or organic solvents such as, for example, acetonitrile. As such, Form C is also useful for the commercial preparation of pharmaceutical formulations such as tablets and capsules.

Another polymoφhic form, amoφhous cilostazol, has also been prepared and characterized. Such amoφhous is clearly distinguishable from Form A and other polymoφhic forms of cilostazol by X-ray powder diffraction and other solid-state methods of characterization. In accordance with the present invention, the newly discovered amoφhous cilostazol can be obtained in a pure form or in combination with other polymoφhic forms of cilostazol. Amoφhous cilostazol can also be prepared free from other polymoφhic forms of cilostazol and contamination by solvates such as water or organic solvents such as, for example, acetonitrile. As such, amoφhous cilostazol may be used for commercial pharmaceutical formulations such as tablets and capsules, but is preferably used as an intermediate for the preparation of other polymoφhic forms of cilostazol.

Accordingly, it is an object of the present invention to provide novel compositions pharmaceutical formulations, and methods of using the novel polymoφhic forms of the present invention, and combinations thereof. The present invention provides novel pure and combinations of polymoφhic forms of cilostazol, each of which are useful for providing more desirable solubility and improved bioavailability characteristics, particularly when administered in pharmaceutical dosage forms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an ORTEP drawing of the single crystal structure of Form A cilostazol;

FIG. 2 shows an ORTEP drawing of the single crystal structure of Form C cilostazol; FIG. 3 illustrates a Differential Scanning Calorimetry (DSC) thermogram for

Form A cilostazol;

FIG. 4 illustrates a DSC thermogram for Form B cilostazol;

FIG. 5 illustrates a DSC thermogram for Form C cilostazol;

FIG. 6 illustrates a DSC thermogram for the combination of Forms A and B cilostazol;

FIG. 7 illustrates a DSC thermogram for the combination of Forms B and C cilostazol;

FIG. 8 illustrates a DSC thermogram for the combination of Forms A, B and C cilostazol; FIG. 9 illustrates an X-ray powder diffraction (XRD) pattern for Form A cilostazol;

FIG. 10 illustrates an XRD pattern for Form B cilostazol; FIG. 11 illustrates an XRD pattern for Form C cilostazol;

FIG. 12 illustrates an XRD pattern comparing Form A cilostazol, Form B cilostazol and Form C cilostazol;

FIG. 13 illustrates an XRD pattern for amoφhous cilostazol; FIG. 14 illustrates an XRD pattern for the combination of Form A cilostazol

(minor) and Form B cilostazol (major);

FIG. 15 illustrates a Fourier Transform Infrared Spectroscopy (FTIR) spectrum for Form A cilostazol;

FIG. 16 illustrates a FTIR spectrum for Form B cilostazol; FIG. 17 illustrates a FTIR spectrum for Form C cilostazol;

FIG. 18 illustrates a FTIR spectrum overlaying Form A cilostazol, Form B cilostazol and Form C cilostazol;

FIG. 19 illustrates a FTIR spectrum for amoφhous cilostazol; and,

FIG. 20 illustrates a Fourier Transform Raman Spectroscopy (FT-Raman) spectrum for Form A cilostazol;

FIG. 21 illustrates a FT-Raman spectrum for Form B cilostazol;

FIG. 22 illustrates a FT-Raman spectrum for Form C cilostazol;

FIG. 23 illustrates a FT-Raman spectrum for Form A cilostazol, Form B cilostazol and Form C cilostazol; FIG. 24 illustrates a FT-Raman spectrum for amoφhous cilostazol;

FIG. 25 illustrates a HPLC chromatographic overlay comparing various combinations of crystalline polymoφhic forms of cilostazol;

FIG. 26 illustrates DSC thermograms of cilostazol Form A (a), Form B (b), and Form C (c); FIG. 27 depicts ORTEP representation of Form A (top left) and Form C (top right) and view of unit cells peφendicular to the c-axis (Form A, bottom left; Form C, bottom right); and

FIG. 28 illustrates free-Energy difference plots versus temperature for three anhydrous polymoφhs of cilostazol.

DETAILED DESCRIPTION OF THE INVENTION Preparation of Form A cilostazol, 6-[4-(l-cyclohexyl-lH-tetrazol-5-yl)butoxy]- 3,4-dihydro-2(lH)-quinolinone, is described in United States Patent No. 4,277,479, the disclosure of such patent is herein incoφorated by reference. The present invention is directed to polymoφhic Form B of cilostazol, Form C of cilostazol, amoφhous cilostazol, and combinations thereof, the preparation thereof, pharmaceutical formulations thereof, and the use of such polymoφhs, preferably in pharmaceutical formulations, for the therapeutic treatment of subjects in need of treatment. The polymoφhic forms of the present invention were characterized using differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Fourier Transform Raman Spectroscopy (FT-Raman) analysis as discussed below. Characterization with any of these methods reveals distinctive peaks for each particularly polymoφhic form, whether in a pure state or not. For example, pure Form B provides a distinct range of significant peaks when analyzed by XRD. These significant peaks will be present with XRD analysis for pure Form B as well as for samples containing Form B in combination with other polymoφhic forms of cilostazol.

As seen in FIGs. 1 and 2, as ORTEP drawings of the single crystal structures of Form A of cilostazol and Form C of cilostazol, respectively, show the different orientations of the two cilostazol molecules, thereby distinguishing these two forms of cilostazol. The ORTEP drawings are generated from the Oak Ridge Thermal Ellipsoid Program developed by Oak Ridge National Laboratory in Oak Ridge, Tennessee. X-ray single crystal structural analysis was not performed on Form B because of the microcrystalline nature of these samples, or amoφhous cilostazol because of the non- crystalline nature thereof. X-ray single crystal unit cell parameters for Form A of cilostazol and Form C of cilostazol are compared in Table 1, below:

Table 1

Characterization of Form A of cilostazol, Form B of cilostazol, and Form C of cilostazol was further completed using DSC thermograms, shown in FIGs. 3, 4, and 5, respectively, with DSC thermograms for combinations of Form A and Form B; Form B and Form C; and Forms A, B, and C are shown in FIGs. 6, 7, and 8 respectively. DSC data were generated using a Mettler-Toledo DSC 82 l^e (Columbus, Ohio) with a Julabo FT900 intercooler chiller (Julabo Company; Allentown, Pennsylvania). In general, samples were analyzed in a vented, sealed aluminum pan. Because the endothermic peak may vary depending upon the rate of heating and the calibration and precision of the instrument, with the amount of pealc variation dependent upon the heating rate used, all thermograms included herein were run under the same, consistent conditions: heating at 10°C per minute under a nitrogen purge at 40mL/minute.

As seen in FIG. 3, the DSC thermogram for Form A gives an endothermic peak at about 162°C (onset at about 160°C). The DSC thermogram shown in FIG. 4 shows an endothermic peak for Form B at about 139°C (onset at approximately

136°C). In FIG. 5, the DSC thermogram for Form C also shows an endothermic peak at about 149°C (onset at about 146°C).

The DSC thermogram in FIG. 6 shows several heat cycles of a cilostazol sample, with both Form A and Form B of cilostazol present in the third heat cycle. At the bottom of the thermogram, Form A of cilostazol appears during the first heating cycle at about 162°C. Typically, the maximum temperature used for the first heating cycle was from about 180°C to about 200°C and, more typically about 200°C. In this instance, after reaching a temperature of about 200°C, the cilostazol was then cooled to about 0°C, which is shown in the first cooling cycle of the DSC thermogram (immediately above the first heating cycle). Once the cilostazol sample reached approximately 0°C, it was immediately reheated to about 130°C, shown in the second heating cycle of the DSC thermogram. During this reheating of the cilostazol sample, the sample appears to pass through a glass transition at about 35°C (onset at about 32°C), with an exotherm occurring at about 104°C (onset at about 90°C). After this reheating, the sample was placed through a second cooling cycle (recooling) to about 0°C, and again reheated in a third heating cycle shown at the top of the DSC thermogram. During the third heating cycle, both Form B and Form A appear, with Form B appearing at about 138°C (onset at about 135°C) during this third heating cycle, and Form A appearing at approximately 161°C (onset at about 159°C).

FIG. 7 shows a DSC thermogram for the combination of Forms B and Form C in the third heating cycle. The DSC thermogram in FIG. 7 shows several heat cycles using Form A as the starting material. After reaching a temperature of about 200°C in the first heating cycle, the sample was then cooled to about 0°C. Once the cilostazol sample reached about 0°C, it was immediately reheated to about 100°C, and held at this temperature for about 5 minutes. During this reheating, the cilostazol sample passed through the glass transition temperature at about 35°C (onset at about 32°C), but was not permitted to completely proceed through the exotherm which typically starts at about 84°C by beginning the recooling stage once the temperature reached about 100°C and held for about 5 minutes. This step is critical for the formation of at least some Form C, which is necessary for preparing pure Form C as taught herein below. After this reheating the sample was placed through a second cooling cycle to approximately 0°C, and again reheated in a third heating cycle as shown at the top of the DSC thermogram. During the third heating cycle, both Form B and Form C are melted, with Form B melting at about 138°C (onset at about 135°C), and Form C melting at about 149°C (onset at about 147°C). The peaks show a Form B to Form C peak area ratio of approximately 4:3, respectively, with the relative amount of Form B and Form C ftirther variable on the heat of enthalpy of each polymoφhic form.

FIG. 8 illustrates a DSC thermogram for the combination of Form A, Form B and Form C having a second heating cycle with a maximum temperature of about 110°C with a holding time of about 30 minutes. The peaks in the third heating cycle show a Form A to Form B to Form C peak area ratio of approximately 8:2:1, respectively, with the relative amount of Form A, Form B and Form C ftirther variable on the heat of enthalpy of each polymoφhic form. This thermogram shows Form B and Form C having a lower melting point than Form A, indicating that the crystal packing forces for Forms B and C are not as great as Form A these data strongly suggest that Form B and Form C are more soluble than Form A of cilostazol.

In FIGs. 9, 10 and 11, the XRD patterns for Form A, Form B and Form C, respectively, are shown, with the three XRD patterns overlayed for comparison in FIG. 12. As seen in FIG. 12, the XRD patterns of Form A, Form B and Form C of cilostazol demonstrate three distinct crystalline forms of the cilostazol, evidencing pure Form B and pure Form C. Characterization of amoφhous cilostazol was also performed, as seen in the XRD pattern for amoφhous cilostazol in FIG. 13. XRD was performed using a Siemens D500 Diffractometer (Madison, Wisconsin). Samples were analyzed from 2-40° in 2Θ at 2.4 minute using CuKα (50k V, 30mA) radiation on a zero-background sample plate.

Tabulations of the peak positions from the X-ray powder patterns for Form A, Form B and Form C are listed in Tables 2, 3 and 4, respectively, below. It is well known by one of ordinary skill in the art that lot-to-lot variations of crystal shape and/or size, as well as variations among instruments and calibration of such instruments, can appear as preferred orientation in the X-ray powder diffraction patterns. This preferred orientation can be seen as variations in the relative intensities of the peaks, such variations in an amount of up to about 20%.

vs = very strong (>50%), s = strong (>20%), m = moderate (8-20%), w = weak (2-8%), vw = very weak (<2%) The XRD peaks shown in Table 2, demonstrated that the significant peaks of Form A (greater than 8%) are typically located at two-theta (2Θ) angles of about 9.4, 10.3, 12.9, 15.3, 15.8, 18.8, 19.4, 20.4, 20.8, 22.0, 23.5 and 31.7°. For Form B, the significant XRD peaks (shown in Table 3) are at two-theta (2Θ) angles of about 10.7, 14.2, 14.7, 15.8, 16.6, 17.9, 18.8, 20.4, 21.6, 22.4, 22.8, 23.5, 24.8, 25.9, 26.8, 29.7, 30.2, and 30.7°. For Form C, the significant XRD peaks (shown in Table 4) are at two- theta (2Θ) angles of about 8.6, 9.7, 10.1, 13.1, 16.7, 17.3, 19.4, 20.2, 23.7 and 25.7°.

The XRD pattern for the combination of a minor (approximately 10%) amount of Form A of cilostazol and a major (approximately 90%) amount of Form B of cilostazol is shown in Fig 14.

The FTIR spectrum for Form A, Form B and Form C, are shown in Figs. 15, 16, and 17, respectively and an overlay of the three spectra are shown in FIG. 18. The FTIR spectrum for amoφhous cilostazol is shown in FIG. 19. FTIR was performed using a Nicolet Nexus 670 FTIR spectrometer with a Micro-FTIR attachment (Silicon ATR). Analysis was generally performed on neat samples at 4 cm^"1 resolution, collecting 64 scans from 4000-650 cm^"1. The major bands of the FTIR spectra of Form A, Form B, and Form C are tabulated in Table 5, below:

Table 5 Major FTIR peaks of Form A, Form B, Form C and Amorphous Cilostazol (cm^"1)

The polymoφhic forms of cilostazol are further characterized in FIGs. 20, 21,22, and 24 for Form A, Form B, Form C, and amoφhous cilostazol respectively. FT-Raman was performed using a Nicolet Nexus 670 FTIR spectrometer with a FT-Raman attachment. Samples were generally analyzed neat at 8 cm^"1 resolution, collecting 100 scans from 3800-100 cm^"1 with a laser wattage of approximately IW. Major spectral bands of the FT-Raman for the Form A, Form B, Form C and amoφhous cilostazol are listed in Table 6, below:

Table 6 Major FT-Raman peaks of Form A, Form B, Form C (cm ¹) and Amorphous Cilostazol

The HPLC Chromatogram of Form A was overlayed with the chromatograms of a combination of polymoφhic Form B and Form C, and the chromatogram of a combination of polymoφhic Form A with Form B and Form C as shown in FIG. 25. This overlay demonstrates the purity and identity of each polymoφhic combination to be as the same compound in solution (i.e. , no degradation occurred in the thermal processing of the cilostazol) with a total amount of impurities of less than about 0.1 % in each polymoφhic combination.

Accordingly, the amoφhous, Form B, and Form C polymoφhic forms of cilostazol have been characterized as distinct from Form A, and from each other. X-ray single crystal structural analysis, DSC, XRD, FTIR, and/or FT-Raman confirm the existence of the novel Form B of cilostazol, Form C, and amoφhous cilostazol, and other various combinations of polymoφhic forms of the present invention.

In preparing amoφhous cilostazol, any polymoφhic form or combination of polymoφhs of cilostazol (preferably Form A) is used as a starting material. The starting material is heated sufficiently for melting. Typically, when the heating rate is held constant at about 10°C/minute Form A of cilostazol melts at a temperature at about 160°C. Thus, temperatures from about 170°C or greater (preferably up to about 200°C) are used to ensure complete melt of the cilostazol starting material. Excessive temperatures that may alter the chemical characteristics, (e.g., cause degradation) of the cilostazol molecules are not used. As such, representative melting temperatures range from about 170°C to about 200°C. Heating rates include any controllable heating process for complete melting of the cilostazol starting material. Representative static or variable heating rates include, for example, from about 5°C per minute, 10°C per minute, 15°C per minute, 50°C per minute, and other such rates. An inert atmosphere, such as for example, a nitrogen atmosphere or, preferably, nitrogen purge, should be used to reduce or eliminate potential oxidative reactions during the melting of the cilostazol.

The melted cilostazol is cooled from its molten state to about ambient temperature or below to provide amoφhous cilostazol. The cooling steps described herein were all run at a cooling rate at about 10°C/minute using the aforementioned Julabo FT900 intercooler chiller. The cilostazol sample should be maintained free of debris, such as dust and other foreign material and contaminates, and/or mechanical shock that would induce nucleation sites within the cilostazol sample. Rates of cooling are controlled to minimize thermal shock and performed in a manner to minimize contaminates and/or mechanical shock to the cilostazol which could induce nucleation sites which can induce crystallization. Typically, this will result in the formation Form A cilostazol. Representative cooling rates include, for example, from about 1°C per minute, 5°C per minute, 10°C per minute, 15°C per minute, 50°C per minute, and other such rates.

The identical steps of melting and cooling as described above are used for forming amoφhous cilostazol are used for preparing Form B and/or Form C of cilostazol. The samples are cooled for the formation of Form B and/or Form C, by reducing the temperature of the sample to about or below the glass transition temperature of cilostazol (about 32°C). Cooling such samples only to temperatures greater than about 32°C can provide such polymoφh formation, primarily Form B, but the resulting material typically is of significantly lower purity. Because this cooling step can significantly affect the purity of the polymoφh(s) formed in subsequent steps, the temperature of the melted cilostazol is cooled to a temperature of about 0°C or less, and more preferably to temperatures of from about 0°C to about -20°C. A preferred cooling rate is about 10°C/minute.

The next step, reheating of the cooled sample, is the step that controls the formation of Form B, Form C, and various combinations of the polymoφhic forms of cilostazol. Typically, three primary variables are responsible for such formation including: heating rate, maximum temperature (heating temperature), and holding time (collectively, the "heating variables"). One of ordinary skill in the art will recognize that the change of one heating variable will affect one or both of the other heating variables. It is important to note that maximum temperature refers to the heating temperature of the entire, respective sample, and hold time commences upon such entire sample reaching the desired heating temperature. For example, when the heating rate is held constant, an increase in the heating temperature will typically permit a reduction in the hold time while the same, desired polymoφh or combination of polymoφhs, is formed. Accordingly, the teachings herein are intended to demonstrate the preparation of the cilostazol polymoφhs of the present invention but, in no way, should be construed as limiting to the scope and breadth of the present invention.

Heating rates are controlled in a manner to systematically impart energy into the cilostazol sample. Representative heating rates include from about 1 °C per minute, 5°C per minute, 10°C per minute, 20°C per minute, 50°C per minute, and the like. However, it is best to maintain the heating rate constant at a rate of about 5°C to about 20°C per minute, and more preferably at about 10°C per minute.

For the preparation of Form B, when holding the heating rate constant, as temperatures are increased, the percent of Form B is generally increased compared to other polymoφhic forms as determined by the DSC methods taught herein. For example, when the cooled sample is heated to a temperature of 80°C, the sample primarily remains amoφhous cilostazol, generally, because the energy required to form crystalline polymoφhic cilostazol is insufficient, particularly when the heating hold time is negligible. Similarly, holding the heating rate constant and a hold time of about zero minutes, samples heated to about 90°C to about 105°C typically contain a combination of Form B and amoφhous cilostazol at varying percentages of each. However, some Form C and, potentially, Form A, may be crystallized using these heating temperatures when the heating rate is held constant as taught herein and, at a hold time of about zero minutes. As heating temperature is increased above 105°C, the purity of Form B is increased. For example, a temperature of about 120°C, hold time of about zero minutes, and heating rate of about 10°C/minute provides pure Form B (within detectable limits).

Temperatures above about 130°C will initiate melting of the resulting Form B polymoφh.

Alternately, when maintaining a constant heating rate of about 10°C/minute, lower temperatures can be employed using longer hold times. For example, with temperatures below about 105°C, hold times of about 5 minutes and greater will provide purities of Form B similar to purities obtained with heating temperatures greater than about 105°C with hold times of about zero minutes. Depending upon the heating variables used, more particularly, holding the heating rate constant, with a heating temperature of about 100°C, a hold time of about 5 minutes essentially eliminates amoφhous cilostazol. Under these conditions the resulting product is predominately Form B, with the remaining portion being predominately Form C.

Moreover, pure Form B can also be formed by using heating temperatures greater than about 100°C and, for small samples increased hold times. For examples when maintaining a constant heating rate of about 10°C per minute, a heating temperature of about 110°C and hold time of about 5 minutes also provides pure Form B. Other variations of the heating variables will also provide pure Form B providing the heating temperature does not exceed the melting point of Form B and the temperature is held for a time period sufficient to complete the formation of pure Form B of the present invention. As such, the scope of the present invention is not limited to these exemplifications.

After the heating step is completed and the desired polymoφhic form(s) are obtained, the resulting cilostazol is recooled. With regard to Form B, the cilostazol is actively recooled or allowed to passively recool, preferably at a controlled rate (preferably about 10°C/minute), to about ambient temperature.

Preferably, Form B is produced in a pure form (devoid of detectable amounts of other polymoφhic forms of cilostazol as determined by FTIR, FT-Raman and/or X-Ray powder diffraction, as appropriate), or in substantially pure form having negligible other amounts of detectable polymoφhic forms of cilostazol.

For the preparation of pure Form C of the present invention, the heating step for the preparation of Form B as described herein is used providing at least some Form C (as detected using DSC) is present in the sample. It is preferred to use a sample that has a higher rather than lower percentage of Form C. For example, the heating step for the preparation of Form B above wherein the heating rate is held constant, a heating temperature of about 100°C, and hold time of about 5 minutes provides a good starting material for the preparation of pure Form C.

Following such heating step, the sample is actively recooled, preferably in a controlled manner, to about ambient temperature or below. Preferred cooling temperatures are from about ambient temperature to about -80°C, and more preferred from about -10°C to about 10°C.

For the preparation of purer forms of Form C and, particularly, pure Form C, the recooled sample containing at least some Form C is reheated to a temperature which is greater than about the melting point of Form B (about 135°C to about 137°C) but below the melting point of Form C (about 147°C to about 149°C). The temperature typically is held for a period of time that is sufficiently long to ensure the complete melt of Form B.

Providing all Form B present is melted during this reheating step, pure Form C is formed during the final re-cooling step from the melted Form B, using the remaining, un-melted Form C as seed crystals for the resulting pure Form C. If the Form B crystals are not completely melted during the re-heating step, this resulting material will predominately comprise Form C with the unmelted portion of Form B remaining as Form B. As with all of the processes set forth herein, it is preferred to maintain the rate of heating constant at about 10°C/minute.

During the final recooling step, the cilostazol is actively recooled or allowed to passively recool, preferably at a controlled rate, to about ambient temperature. Preferably, Form C is produced in a pure form (devoid of detectable amounts of other polymoφhic forms of cilostazol as determined by FTIR, FT-Raman, and/or X-ray powder diffraction, as appropriate), or in substantially pure form having negligible amounts of other detectable polymoφhic forms of cilostazol.

The present invention also provides pharmaceutical formulations comprising pure Form B, pure Form C, or pure amoφhous cilostazol, either as the sole active ingredient or in combination with other active ingredients including, for example, other polymoφhic forms of cilostazol or other pharmaceutically active agents, at least one pharmaceutically acceptable carrier, diluent, and/or excipient. Combinations of more than one polymoφhic form of cilostazol are prepared via the described crystallization procedures or, for more precise combinations, via blending of pure or known polymoφhic ratios.

Preferred polymoφhic combinations include, for example, Form B with Form C, Form A, and/or amoφhous cilostazol; Form C with Form B, Form A, and/or amoφhous cilostazol, and amoφhous cilostazol with Form B, Form C and/or Form A of cilostazol.

Preferably, the novel crystalline forms of cilostazol, Form B and Form C, and amoφhous cilostazol, are in pure form. Pure form includes those samples of either Form B, Form C, or amoφhous cilostazol, individually, that do not possess detectable amounts of any additional form of cilostazol as evidenced by XRD, FTIR, and/or FT-Raman analysis.

For the most effective administration of the polymoφhic forms of the present invention, it is preferred to prepare a pharmaceutical formulation preferably in unit dose form, comprising one or more of the active ingredients of the present invention and one or more pharmaceutically acceptable carrier, diluent, or excipient.

As used herein, the term "active ingredient" refers to any of the embodiments set forth herein, particularly Form B, Form C, and amoφhous cilostazol, individually and in combination among polymoφhic forms of the present invention or other cilostazol polymoφhic forms. More preferably polymoφhic Form B and Form C of the present invention are used in pure form in the pharmaceutical formulations of the present invention.

Preferred pharmaceutical formulations may include, without being limited by the teachings as set forth herein, a solid dosage form, of Form B, Form C and/or amoφhous cilostazol, of the present invention in combination with at least one pharmaceutically acceptable excipient, diluted by an excipient or enclosed within such a carrier that can be in the form of a capsule, sachet, tablet, buccal, lozenge, paper, or other container. Additionally, such pharmaceutical formulation may include a liquid formulation prepared from Form B, Form C and/or amoφhous cilostazol API of the present invention in combination with at least one pharmaceutically acceptable excipient, diluted by an excipient or enclosed within an appropriate carrier. When the excipient serves as a diluent, it may be a solid, semi-solid, or liquid material which acts as a vehicle, carrier, or medium for the active ingredient(s). Thus, the formulations can be in the form of tablets, pills, powders, elixirs, suspensions, emulsions, solutions, syrups, capsules (such as, for example, soft and hard gelatin capsules), suppositories, sterile injectable solutions, and sterile packaged powders.

Examples of suitable excipients include, but are not limited to, starches, gum arabic, calcium silicate, microcrystalline cellulose, polyvinylpyrrolidone, cellulose, water, syrup, and methyl cellulose. The formulations can additionally include lubricating agents such as, for example, talc, magnesium stearate and mineral oil; wetting agents; emulsifying and suspending agents; preserving agents such as methyl- and propyl- hydroxybenzoates; sweetening agents; or flavoring agents. Polyols, buffers, and inert fillers may also be used. Examples of polyols include, but are not limited to: mannitol, sorbitol, xylitol, sucrose, maltose, glucose, lactose, dextrose, and the like. Suitable buffers encompass, but are not limited to, phosphate, citrate, tartrate, succinate, and the like. Other inert fillers which may be used encompass those which are known in the art and are useful in the manufacture of various dosage forms. If desired, the solid pharmaceutical compositions may include other components such as bulking agents and/or granulating agents, and the like. The compositions of the invention can be formulated so as to provide quick, sustained, controlled, or delayed release of the active ingredient after administration to the patient by employing procedures well known in the art. In certain embodiments of the present invention, the active ingredient(s) maybe made into the form of dosage units for oral administration. The active ingredient(s) may be mixed with a solid, pulverant carrier such as, for example, lactose, saccharose, sorbitol, mannitol, starch, amylopectin, cellulose derivatives or gelatin, as well as with an antifriction agent such as for example, magnesium stearate, calcium stearate, and polyethylene glycol waxes. The mixture is then pressed into tablets or filled into capsules. If coated tablets, capsules, or pulvules are desired, such tablets, capsules, or pulvules may be coated with a concentrated solution of sugar, which may contain gum arabic, gelatin, talc, titanium dioxide, or with a lacquer dissolved in the volatile organic solvent or mixture of solvents. To this coating, various dyes may be added in order to distinguish among tablets with different active compounds or with different amounts of the active compound present.

Soft gelatin capsules maybe prepared in which capsules contain a mixture of the active ingredient(s) and vegetable oil or non-aqueous, water miscible materials such as, for example, polyethylene glycol and the like. Hard gelatin capsules may contain granules or powder of the active ingredient in combination with a solid, pulverulent carrier, such as, for example, lactose, saccharose, sorbitol, mannitol, potato starch, corn starch, amylopectin, cellulose derivatives, or gelatin.

Tablets for oral use are typically prepared in the following manner, although other techniques may be employed. The solid substances are gently ground or sieved to a desired particle size, and a binding agent is homogenized and suspended in a suitable solvent. The active ingredient(s) and auxiliary agents are mixed with the binding agent solution. The resulting mixture is moistened to form a uniform suspension. The moistening typically causes the particles to aggregate slightly, and the resulting mass is gently pressed through a stainless steel sieve having a desired size. The layers of the mixture are then dried in controlled drying units for a pre-determined length of time to achieve a desired particle size and consistency. The granules of the dried mixture are gently sieved to remove any powder. To this mixture, disintegrating, anti-friction, and anti-adhesive agents are added. Finally, the mixture is pressed into tablets using a machine with the appropriate punches and dies to obtain the desired tablet size.

Liquid preparations for oral administration are prepared in the form of solutions, syrups, or suspensions with the latter two forms containing, for example, active ingredient(s), sugar, and a mixture of ethanol, water, glycerol, and propylene glycol. If desired, such liquid preparations contain coloring agents, flavoring agents, and saccharin. Thickening agents such as carboxymethylcellulose may also be used.

As such, the pharmaceutical formulations of the present invention are preferably prepared in a unit dosage form, each dosage unit containing from about 1 Omg to about 300mg, preferably from about 25mg to about 125mg and more preferably from about 40mg to about 11 Omg of the cilostazol active ingredient(s). Other pharmaceutically active agents can also be added to the pharmaceutical formulations of the present invention at therapeuticaUy effective dosages. In liquid form, unit doses contain from about 10 to about 300mg, preferably about 25mg to about 125mg and more preferably about 40mg to about 1 lOmg of such cilostazol active ingredient(s).

The term "unit dosage form" refers to physically discrete units suitable as unitary dosages for human subjects/patients or other mammals, each unit containing a predetermined quantity of active ingredient calculated to produce the desired therapeutic effect, in association with preferably, at least one pharmaceutically acceptable carrier, diluent, or excipient.

The invention also provides methods of treating a subject (e.g., mammal, particularly humans) comprising administering to a subject in need of such treatment a therapeuticaUy effective amount of at least one active ingredient, formulation thereof, or unit dose forms thereof, each as described herein. The active ingredient(s) are used to inhibit cellular phosphodiesterase, particularly phosphodiesterase HI. The primary use for such active ingredient(s) is for the reduction of intermittent claudication in such subjects, typically manifested by an increased walking distance. The cilostazol active ingredients of the present invention may also be used for the treatment of other disease states related to vasodilation including, for example, stroke and antiplatelet effects. Such active ingredients may also increase plasma high density lipoprotein cholesterol and apolipoprotein in subjects in need of such treatment as well as being used to treat sexual dysfunction.

As used herein, the term "treatment", or a derivative thereof, contemplates partial or complete inhibition of the stated disease state such as, for example, intermittent claudication, when an active ingredient of the present invention is administered prophylactically or following the onset of the disease state for which such active ingredient of the present invention is administered. For the puφoses of the present invention, "prophylaxis" refers to administration of the active ingredient(s) to a subject to protect the subject from any of the disorders set forth herein, as well as others.

The typical active daily dose of the cilostazol active ingredient(s) will depend on various factors such as, for example, the individual requirement of each patient, the route of administration, and the disease state. An attending physician may adjust the dosage rate based on these and other criteria if he or she so desires. A suitable daily dosage, typically administered b.i.d. in equally divided doses, is from about 50 mg to about 250 mg, preferably from about 80 mg to about 240 mg, and more preferably from about 100 mg to about 200 mg. A preferred range is from about 100 mg to about 200 mg total daily dose. It should be appreciated that daily doses other than those described above may be administered to a subject, as appreciated by an attending physician.

The following examples are for illustrative puφoses only and are not intended to limit the scope of the claimed inyention.

Example 1 Preparation of pure Form B of cilostazol A sample of approximately 5 mg of Form A of cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace. Under a nitrogen purge of 40 milliliters per minute, the sample was heated from a temperature of 30°C to approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled within the furnace to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 110°C, and held at 110°C for five minutes. After holding the cilostazol at 110°C for five minutes, the cilostazol was cooled to 0°C at a rate of 10°C per minute. The cilostazol was then reheated in an undisturbed state by DSC at a rate of 10°C per minute to a final temperature about 170°C, the sample showed an endothermic peak for Form B of cilostazol at approximately 138°C (onset observed at about 136°C) with a minor peak at 149°C which relates to Form C (onset observed at about 147°C).

Example 1A Preparation of pure Form B of cilostazol A sample of approximately 20 mg of Form A of cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace. Under a nitrogen purge of 40 milliliters per minute, the sample was heated from a temperature of 30°C to approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled within the furnace to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 110°C, and held at 110°C for five minutes. After holding the cilostazol at 110°C for five minutes, the cilostazol was cooled to 30°C at a rate of 10°C per minute. The sample was removed and analyzed by XRD, FTIR and FT-Raman which confirmed the sample as 100% Form B of cilostazol.

Example IB Transformation of pure Form B of cilostazol to Form A of cilostazol

The resultant sample of Example 1 A was disturbed with scratching, which caused the cilostazol sample to undergo a solid state phase transformation at approximately 119°C followed by an endotherm of melt at approximately 160°C (Form A) during heating by DSC from 30°C to approximately 200°C at 10°C per minute.

Example 2 Preparation of pure /essentially pure Form C of cilostazol

A sample of approximately 14 mg of Form A of cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace. Under a nitrogen purge of 40 milliliters per minute, the sample was heated from a temperature of 30°C to approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 100°C, and held at 100°C for five minutes. After holding the cilostazol at 100°C for five minutes, the cilostazol was cooled to 0°C at a rate of 10°C per minute. The cilostazol was then reheated at a rate of 10°C per minute to a temperature of 145°C and held at 145°C for 5 minutes, after which time the cilostazol was then recooled to 0°C at a rate of 10°C per minute. Upon reheating in an undisturbed state, by DSC, the sample showed single endothermic peak for Form C at about 149°C (onset of about 146°C).

Example 2A Preparation of pure Form C of cilostazol

A sample of approximately 22 mg of Form A cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace under a nitrogen purge of 40 milliliters per minute, the sample was reheated from a temperature of 30°C to approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 100°C, and held at 100°C for five minutes. After holding the cilostazol at 100°C for five minutes, the cilostazol was cooled to 0°C at a rate of 10°C per minute. The cilostazol was then reheated at a rate of 10°C per minute to a temperature of 145°C and held for five minutes, after which time the cilostazol was then recooled to 30°C at a rate of 10°C per minute. A single crystal was obtained from the DSC pan and analyzed by this technique.

The structure was found to have a different polymoφhic form than that of Form A or

Form B (identified in Example 1). The cilostazol sample displayed a unique XRD powder pattern, FTIR and FT-Raman spectra and was identified as 100% Form C of cilostazol.

Example 2B Transformation from Form C to Form A of cilostazol

When the sample is stressed and reheated (as detailed in Example 2A), the sample undergoes a solid state phase transformation at approximately 147°C followed by an endotherm of melt at about 160°C (Form A) during heating by DSC from 30°C to approximately 200°C at 10°C per minute. This disturbance of sample is believed to induce nucleation which preferentially causes Form A of cilostazol to form upon heating.

Example 3

Preparation of a combination of Form B of cilostazol and Form A of cilostazol (about 60:40)

A sample of approximately 7 mg of Form A cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace under a nitrogen purge of 40 milliliters per minute, the sample was heated from a temperature of 30°C to approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 130°C. The cilostazol was then cooled to 0°C at a rate of 10°C per minute.

The cilostazol was then reheated in an undisturbed state by DSC from 0°C to 200°C at 10°C per minute. Two endotherms of melt were observed at approximately

138°C (Form B) and 161°C (Form A) in aheat of enthalpy ratio of approximately 60:40, respectively, with the relative amount of Form B and Form A further variable on the heat of enthalpy of each polymoφhic form.

Example 4

Preparation of a combination of Form B of cilostazol and Form A of cilostazol (about 60:40)

A sample of approximately 6 mg of Form A cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace under a nitrogen purge of 40 milliliters per minute, the sample was heated from a temperature of 30°C to approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 120° and held for five minutes. After holding for five minutes, the cilostazol was cooled to 0°C at a rate of 10°C per minute.

The cilostazol was reheated in an undisturbed state by DSC from 0°C to 200°C at 10°C per minute. Two endotherms of melt were observed at approximately 138°C (Form B) (onset at about 135°C) and 161°C (Form A) (onset at about 159°C) in a heat of enthalpy ratio of approximately 60:40, respectively, with the relative amount of Form B and Form A further variable on the heat of enthalpy of each polymoφhic form. Example 5 Preparation of a combination of Form A of cilostazol, Form B of cilostazol and

Form C of cilostazol

A sample of approximately 5 mg of Form A cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace under a nitrogen purge of 40 milliliters per minute, the sample was heated from a temperature of 30°C to approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 110°C, and held at 110°C for 30 minutes. After holding the sample for 30 minutes at 110°C, the cilostazol was cooled to 0°C at a rate of 10°C per minute.

The cilostazol was reheated in an undisturbed state by DSC from 0°C to 200°C at 10°C per minute. Three endotherms of melt were observed at approximately 138°C (onset at about 136°C) (Form B), 149°C (onset at about 147°C) (Form C) and 161 °C (onset at about 159°C) (Form A) in a heat of enthalpy ratio of approximately 80:20:10, respectively, with the relative amount of Form B, Form C and Form A further variable on the heat of enthalpy of each polymoφliic form.

Example 6 Preparation of Form B: Form C (about 90:10)

A sample of approximately 7 mg of Form A of cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace. Under a nitrogen purge of 40 milliliters per minute, the sample was heated from atemperature of 30°C to a temperature of approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled within the furnace to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 130°C, and held at 130°C for five minutes. After holding the cilostazol at 130°C for the five minutes, the cilostazol was cooled to 0°C at a rate of 10°C per minute. The cilostazol was then reheated in an undisturbed state by DSC at a rate of 10°C per minute to a final temperature above 170°C. The sample showed an endothermic peak for Form B of cilostazol at approximately 138°C (onset at about 135°C) with a minor peak at 149°C (onset at about 147°C) which relates to Form C. The peaks show a Form B to Form C peak area ratio of approximately 90: 10, respectively, with the relative amount of Form B to Form C further variable on the heat of enthalpy of each polymoφhic form.

Example 7

Preparation of pure Form B of cilostazol

A sample of approximately 8 mg of Form A of cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace. Under a nitrogen purge of 40 milliliters per minute, the sample was heated from a temperature of 30°C to approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled within the furnace to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 120°C. The cilostazol was cooled to 0°C at a rate of 10°C per minute. The cilostazol was then reheated in an undisturbed state by DSC at a rate of 10°C per minute to a final temperature above 170°C. The sample showed an endothermic peak for Form B of cilostazol at approximately 139°C (onset at about 136°C) with a minor peak at 147°C (onset at about 149°C) which relates to Form C.

Example 8 Preparation of Form B: Form C cilostazol (about 66:34)

A sample of approximately 8 mg of Form A of cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace. Under a nitrogen purge of 40 milliliters per minute, the sample was heated from a temperature of 30°C to approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled within the furnace to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 110°C. The cilostazol was then cooled to 0°C at a rate of 10°C per minute. The cilostazol was then reheated in an undisturbed state by DSC at a rate of 10°C per minute to a final temperature above 170°C. The sample showed an endothermic peak for Form B of cilostazol at approximately 138°C (onset at about 135°) with a minor pealc at 149°C (onset at about 147°C) which relates to Form C. The peaks show a Form B to Form C peak area ratio of approximately 66:34, respectively, with the relative amount of Form B to Form C further variable on the heat of enthalpy of each polymoφhic form.

Example 9 Preparation of Form B: Form C cilostazol (about 92:8) A sample of approximately 7 mg of Form A of cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace. Under a nitrogen purge of 40 milliliters per minute, the sample was heated from a temperature of 30°C to a temperature of approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled within the furnace to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol again was heated from 0°C to 130°C, and held at 130°C for 30 minutes. After holding the cilostazol at 130°C for 30 minutes, the cilostazol was cooled to 0°C at a rate of 10°C per minute. The cilostazol was then reheated in an undisturbed state by DSC at a rate of 10°C per minute to a final temperature above 170°C. The sample showed an endothermic peak for Form B of cilostazol at approximately 139°C (with a minor peak at 149°C which relates to Form C. The peaks show a Form B to Form C peak area ratio of approximately 92:8, respectively, with the relative amount of Form B to Form C further variable on the heat of enthalpy of each polymoφhic form.

Example 10

Preparation of Form B: Form C cilostazol (about 87:13)

A sample of approximately 5 mg of Form A of cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace. Under a nitrogen purge of 40 milliliters per minute, the sample was heated from a temperature of 30°C to approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled within the furnace to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 100°C, and held at 100°C for five minutes. After holding the cilostazol for the five minutes, the cilostazol was cooled to 0°C at a rate of 10°C per minute. The cilostazol was then reheated in an undisturbed state by DSC at a rate of 10°C per minute to a final temperature above 170°C. The sample showed an endothermic peak for Form B of cilostazol at approximately 138°C (onset at about 135°C) with a minor peak at 149°C (onset at about 147°C which relates to Form C. The peaks show a Form B to Form C peak area ratio of approximately 87:13, respectively, with the relative amount ofFormB to Form C further variable on the heat of enthalpy of each polymoφhic form.

Example 11

Preparation of Form B: Form C cilostazol (about 83:17)

A sample of approximately 6 mg of Form A of cilostazol was placed in a vented, sealed aluminum holder and placed in a DSC furnace. Under a nitrogen purge of 40 milliliters per minute, the sample was heated from a temperature of 30°C to approximately 200°C (past the melting point of Form A) at a heating rate of 10°C per minute. The molten cilostazol was cooled within the furnace to approximately 0°C at a cooling rate of approximately 10°C per minute. The cooled cilostazol was reheated from 0°C to 120°C, and held at 120°C for 30 minutes. After holding the cilostazol at 120°C for 30 minutes, the cilostazol was cooled to 0°C at a rate of 10°C per minute. The cilostazol was then reheated in an undisturbed state by DSC at a rate of 10°C per minute to a final temperature above 170°C. The sample showed an endothermic peak for Form B of cilostazol at approximately 139°C (onset at about 136°C) with a minor peak at 149°C (onset at about 147°C which relates to Form C. The peaks show a Form B to Form C peak area ratio of approximately 83:17, respectively, with the relative amount of Form B to Form C further variable on the heat of enthalpy of each polymoφhic form.

Example 12 Hot Stage Microscopy

A sample of Form A of cilostazol was placed on a glass slide and inserted into a hot stage microscope furnace. Hot stage microscopy provides an analytical technique that allows for heat manipulation of the cilostazol sample while visual observing changes utilizing a microscope apparatus. Samples of Form A cilostazol were heated to approximately 170°C and held until visually melted, then cooled by removing the glass slide and placing it on a laboratory bench or other suitable place to cool in an area free of potential contamination. The sample was then heated under various conditions involving varying heating rate (HR), maximum temperature (70°C, 80°C, 90°C and 100°C) and hold times (T), XRD was performed on each sample to monitor the degree of crystallinity as well as crystalline forms present.

At 70°C: a heating rate 1 degree per minute held for 5 minutes resulted in amoφhous cilostazol; amoφhous with about 5% Form B (HR = 2, T = 5); amoφhous (HR = 5, T = 5); amoφhous with about 5% Form B (HR = 2, T = 5); amoφhous with about 20% Form B (HR = 2, T = 15); amoφhous with about 60% Form B (HR = 2, T =

30); and trace amount of amoφhous with about 95% Form B (HR = 2, T = 45).

At 80°C: about 100% Form B (HR = 1, T = 5); about 80% Form B with about

20% Form A (HR - 2, T = 5); about 100% Form B with trace amoφhous (HR = 5, T = 15); about 40% Form B with about 60% Form A (HR = 2, T = 2); about 20% Form B with about 80% Form A (HR = 2, T = 15); about 5% Form B with about 95% Form A

(HR - 2, T = 30); and about 100% Form A (HR = 2, T = 45).

At 90°C: about 100% Form A (HR = 1, T = 5); about 95% Form B and trace of Form A (HR = 2, T = 5); about 80% Form B (HR = 5, T = 5); about 95% Form B and trace Form A (HR = 2, T = 5); about 100% Form A (HR - 2, T = 15); about 100% Form A (HR = 2, T = 30); and about 100% Form A (HR = 2, T = 45).

At 100°C: Form A with trace of Form B (HR = 1, T = 5); about 100% Form A (HR = 2, T = 25); and about 50% Form A and about 50% Form B (HR = 5, T = 5).

Hot stage microscopy was performed to provide an indication of the trends of the solid state transformations of the cilostazol. If an alternative sample holder is used instead of glass (e.g., aluminum) the cooling process will need to be altered to avoid stress to the amoφhous sample which will create nucleation sites that cause Form A to preferentially form upon reheating.

Example 13

Differential Scanning Calorimetry (DSC). Initial discovery of cilostazol polymoφhism and investigation of temperature programs to prepare individual forms utilized a Mettler-Toledo DSC821^e differential scanning calorimeter. Data acquisition and manipulation was performed using the Mettler-Toledo STAR⁶ software using approximately 5-10 mg of sample heated at 10°C per minute under nitrogen in sealed vented aluminum pans. Heats of fusion and onset melting points for free-energy difference plots and calculation of theoretical solubility values utilized a PerkinElmer DSC4 with TA-PC thermal analysis software. Accurately weighed milligram amounts of material were heated at 20 °C per minute under nitrogen in sealed vented aluminum pans.

Both DSC systems utilize an indium metal reference standard analyzed on each analysis date at the same heating rate to confirm accurate temperature and heat-flow calibration constants.

Hot Stage and Optical Microscopy. Hot stage microscopy was performed using a Mettler-Toledo FP82HT Hot Stage with an FP90 Central Processor on aMeiji EMZ-TR microscope. Samples were analyzed using a glass slide to visually monitor the formation of the different phases of cilostazol. Powder X-ray Diffraction. The powder X-ray diffraction patterns were obtained using a Siemens D500 X-ray Diffractometer with Cu Kα radiation operating at 30 mA and 50 kV. Samples were analyzed on a quartz zero-background sample plate and scanned from 2 to 40° in 20 with data points taken every 0.05° at a scan rate of 2.4° per minute. Fourier Transform Infrared (FTIR) and FT-Raman Spectroscopy. FTIR spectra were obtained using a Nicolet Nexus 670 Inspect IR microscope with a micro- ATR attachment. FT-Raman spectra were obtained using a Nicolet Nexus 670 with a FT- Raman attachment, with samples placed in a diffuse reflectance sample holder. The Nicolet OMNIC software package was used for data acquisition and analysis of both types of spectroscopic data.

High Performance Liquid Chromatography (HPLC). HPLC analysis of cilostazol was performed to verify the absence of degradation products and integrity of the active pharmaceutical ingredient after the thermal transformation to the different polymoφhic forms. The analyses were performed using a Hewlett Packard HP 1100 chromatographic system with a variable wavelength diode-array UV detector and an Inertsil ODS-3 C18 reverse phase column (15 cm x 4.6 mm I.D., 3 μm, Metachem Technologies, Torrance, CA). The mobile phase consisted of a mixture of 50 mM potassium phosphate monobasic (pH 6.8) and acetonitrile (55 :45 v/v) at a flow rate of 1.0 mL per minute. Identification of cilostazol was achieved at a detection wavelength of 254 nm by comparison to the original cilostazol API using the Waters Millenium³² data acquisition software. Intrinsic Dissolution. Solubility rate of the different polymoφhs was studied by means of a USP intrinsic dissolution analysis. The dissolution studies were performed using a Van-Kel Vanderkamp 600 Six Spindle Dissolution tester equipped with Van-Kel USP intrinsic dissolution apparatus and a VK650 heater/circulator set at 37 °C. Cilostazol pellets were prepared using a laboratory press and intrinsic dissolution dies. Different sample weights and pressures were tested to optimize pellet formation and subsequently, the dissolution rate. A compression of approximately 100 mg of cilostazol at 4000 psi for one minute produced optimal results. FT-Raman analysis was utilized to demonstrate that no polymoφhic transition occurred under the high compression used during the formation of the pellets. Different dissolution media and die rotation speeds were evaluated to determine the most appropriate dissolution conditions. Initial intrinsic dissolution studies were carried out using 500 mL of 1% sodium lauryl sulfate as the medium, a die rotation speed of 200 φm, and a pull volume of 5 mL every 30 minutes up to six hours with one additional pull at 24 hours. An HP8452A diode array UV- visible spectrophotometer was used to determine the dissolution of the samples against a reference solution at a wavelength of 258 nm. Due to the poor solubility of the drag in aqueous media, more aggressive dissolution conditions were also tested. Ultimately, acetonitrile was also tested as the medium with a die rotation speed of 50 φm, and a pull volume of 5 mL every 2 minutes for up to 20 minutes. Single Crystal X-ray Crystallography. Single crystal X-ray crystallography was performed on a Nonius Kappa-CCD at 294 K with Mo Kα radiation operating at 32 mA and 55 kV. The data were analyzed and the structures determined and refined using the MolEN software system.

Scale-Up Thermal Procedures. Attempts to increase the scale of production of new polymoφhic forms were performed using a nitrogen purged programmable oven. The samples were placed in 32 mm aluminum pans and centered in the oven. Multiple heating programs with varying heat rates, hold temperatures, and hold times were initiated to produce the polymoφhic forms.

Example 14

The relative stability of Form B was investigated using hot stage microscopy. Samples from various hold times and temperatures were analyzed by means of X-ray powder diffraction, which evaluated the relative presence of the crystalline and amoφhous forms of cilostazol. During this study, as the heating rate, hold temperature and hold time increased, the proportion of Form A also increased. During hot stage microscopy, any outside physical stress applied to the sample after melt (such as probing) induced the spontaneous nucleation of the sample to Form A during the cold crystallization.

In studying the thermal preparation of Form B for additional testing, an experimental matrix was designed in which samples of Form A were melted in DSC pans and cooled to specific temperatures ranging from 80 to 130°C and held at that temperature for periods of time of up to thirty minutes. When analyzed by DSC these crystallized materials exhibited a variety of melting transitions for Forms A and B with some samples also exhibiting another melting transition of a third polymoφh (Form C) that melted between Forms A and B at about 146°C. Some of the materials crystallized from the melts of Form A resulted in thermal curves with single melting endotherms for Forms A, B, and C (Figure 26) dependent upon the specific cooling temperature and hold times used.

Based upon the experimental results, attempts were made to grow and isolate single crystals suitable for X-ray analysis of each form. Form A crystals were suitable needles and used "as is". Form B was found to exist only as tiny needles crystallized in microcrystalline clusters; therefore, single crystal structural analysis could not be performed. Suitable plate-like crystals of Form C were isolated from heat cycling with DSC. For example, cilostazol Form A was melted (at above 170 °C), then cooled to about 0 °C and reheated to about 100 °C and held for 5 minutes. This sample was then cooled to about 0 °C and reheated to about 145 °C and held for 5 minutes. This causes the Form B crystals to melt, leaving the Form C crystals to act as seeds for further crystallization. The sample was then cooled to ambient temperature to create the plate-like crystals of Form C. A comparison of the crystal structures and unit cells appears in Table A for the Form A and Form C crystals. Figure 27 shows the orientation differences in the two conformational polymoφhs. The polymoφhs exhibit a major twist of about 108° around the C12-C13-C14-C15 torsional angle creating distinct differences in the unit cell pacldng. Rietveld analysis using microcrystalline Form B material may yield stractural parameters and data on its crystalline state.

A wide variety of heat cycled DSC studies confirm that initiation and completion of crystallization of the various polymoφhic forms of cilostazol are time and temperature dependent. Typically, Form B crystallizes first. With continued heating, Form B converts to Form A. Crystallization from the melt is an exothermic process and monitoring the process with DSC determined when crystallization started and also when crystallization was complete. Some crystallized solids from cilostazol melts were polymoφhically pure Form B, which melts at about 136 °C with an apparent heat of fusion of 105.2 ± 3.9 J/g. Form A melts at about 159 °C with a heat of fusion of 127.7 ± 1.4 J/g. According to the heat of fusion rule, Forms A and B are monotropic, which means that crystalline Form A is physically more stable than Form B at all temperatures below its melting point. Conversely, Form B may spontaneously change to Form A, but not vice versa. Form C proved the most difficult to obtain for testing. On several occasions, polymoφhically pure Form C was crystallized and analyzed by DSC to show a melt at around 146 °C with a heat of fusion of about 115.7 ± 0.3 J/g. Because the heat of fusion of Form C is intermediate between Forms A and B, the heat of fusion rale suggests that each pair of cilostazol polymoφhs (A-B, A-C, and B-C) is monotropic. Using an approach described by Yu (See, Yu, "Inferring thermodynamic stability relationship of polymoφhs from melting data", J Pharm Sci 84:966-974 (1995); Yu et al., "Thermochemistry and conformational polymoφhism of a hexamoφhic crystal system", J Am Chem Soc 122:585-591 (2000)), and assuming that the difference in heat capacity for each polymoφhic pair is about zero, free energy difference plots versus temperature for cilostazol polymoφhs were calculated using equation 1 with heats of fusion and entropy values estimated from calorimetry data that are summarized in Table B.

ΔC7 (,A → A. B or C) = ΔH (.A → A. B.or C) T AS (,A → A, B or C) eq.l

Plots of the resulting free energy curves versus temperature, that is, the free energy differences between Forms, Forms A to B and Forms A to C according to Equation 1 are shown in Figure 28. In Figure 28, the solid bold line represents liquefied (melted) cilostazol. The free energy curve of liquefied cilostazol intersects the free energy difference plots at the melting point of each polymoφh. At temperatures below the melting points, the liquid free-energy curve is that of the super cooled melt. The free- energy difference plots for the cilostazol polymoφhic pairs indicate that Form B has the largest free energy difference to Form A at all temperatures below its melting point. Form A has the lowest free energy and the free energy of Form C is intermediate between Forms B and A. The free energy difference plots of the polymoφhs do not intersect below the melting points. Each pair of polymoφhs is monotropic and Form A is thermodynamically the most physically stable polymoφh. The free-energy difference plots apparently intersect at virtual transition temperatures (T_vt), well above their melting points. At a virtual transition temperature, two polymoφhs have the same free energy. Because the difference in their free energies is zero, the virtual transition temperature is the difference between their heats of fusion divided by the difference in their entropies. Calculated virtual transition temperatures appear above in Table B.

Grant and Higuchi and Grant and Gu have described in detail mathematical models to estimate polymoφh solubility. See, Grant et al., Solubility behavior of organic compounds. New York: John Wiley & Sons, pp 12-38 (2000); Gu et al., Estimating the relative stability of polymoφhs and hydrates from heats of solution and solubility data. J Phaπn Sci 90:1277-1287 (2001). Equations 2 and 3 for each of two polymoφhs when combined result in equation 4 that gives an expression for the ratio of their activities in solution.

G_! - G₀ - ΔG? eq.2

a

G_π - G₀ = ΔG° == ΔH_π - TΔS_U = RT In II eq.3

ΔG_I→π = ΔH?_→π - TΔS?_→π = eq.4

The ratio of the activities is proportional to ratios of their fugacity, vapor pressure, molality, and solubility as long as Henry's law is obeyed. Equation 4 was rearranged to

equation 5 and was used to calculate solubility ratios versus temperature where free energy differences were calculated using calorimetry data with equation 1 for each polymoφhic pair.

ΔG, a II _ ^mπ = e RT eq.5 a. m_τ

Table C lists calculated free energy differences from which solubility ratios were calculated at a variety of temperatures for three pairs of cilostazol polymoφhs. Form B should be at least four times more soluble than Form A, Form C two times more soluble than Form A, and Form B about two times more soluble than Form C in any ideal solvent.

Formulation 1

Hard gelatin 50 mg capsules are prepared using the following ingredients:

Quantity (mg/capsule)

active ingredient(s) 50 ethanedioate starch, dried 200 magnesium stearate 10

Total 260

The above ingredients are mixed and filled into hard gelatin Capsules in 260 mg quantities.

Formulation 2

A 100 mg tablet is prepared using the ingredients below:

Quantity (mg/tablet) active ingredient(s) 100 cellulose, microcrystalline 400 silicon dioxide, fumed 10 stearic acid 5

Total 515

The components are blended and compressed to form tablets each weighing 515 mg.

Formulation 3 Tablets each containing 50 mg of active ingredient are made as follows:

active ingredient 50 mg starch 45 mg microcrystalline cellulose 35 mg polyvinylpyrrolidone 4 mg

(as 10% solution in water) sodium carboxymethyl starch 4.5 mg magnesium stearate 0.5 mg talc l mg

Total 140 mg

The active ingredient, starch and cellulose are passed through aNo.45 mesh U.S. sieve and mixed thoroughly. The solution of polyvinylpyrrolidone is mixed with the resultant powders which are then passed through aNo. 14 mesh U.S. sieve. The granules so produced are dried at 50°C and passed through aNo. 18 mesh U.S. sieve. The sodium carboxymethyl starch, magnesium stearate and talc, previously passed tlirough a No.60 mesh U.S . sieve, are then added to the granules which, after mixing, are compressed on a tablet machine to yield tablets each weighing 140 mg.

Formulation 4 Capsules each containing 50 mg of medicament are made as follows:

active ingredient 50 mg starch 59 mg microcrystalline cellulose 59 mg magnesium stearate 2 mg

Total 170 g

The active ingredient, cellulose, starch and magnesium stearate are blended, passed through a No. 45 mesh U.S. sieve, and filled into hard gelatin capsules in 170 mg quantities. The examples and embodiments as set forth in the detailed description are for

illustrative puφoses only and do not limit the scope of the invention.

Claims

What is claimed is:

1. A composition comprising form C of cilostazol.

2. The composition of cilostazol of Claim 1 , characterized by having significant X-ray powder diffraction pattern peaks at 2Θ values of about 8.6, 9.7, 10.1, 13.1, 16.7, 17.3, 19.4, 20.2, 23.7 and 25.7°.

3. The composition of cilostazol of Claim 1, characterized by having a Fourier Transform Infrared spectrum with significant bands of about 3191, 3056, 2938, 2870,

1674, 1504,1430, 1398, 1243, 1187, 1154, 1126, 1036, 864, and 674 cm^-1.

4. The composition of cilostazol of Claim 2, characterized by having a Fourier Transform Infrared spectrum with significant bands of about 3191, 3056, 2938, 2870, 1674, 1504,1430, 1398, 1243, 1187, 1154, 1126, 1036, 864, and 674 cm^"1.

5. The composition of cilostazol of Claim 1, characterized by having a differential scanning calorimetry thermogram, when run at approximately 10°C per minute, containing at least one significant endotherm occurring in a temperature range of from about 146°C to about 151 °C.

6. The composition of cilostazol of Claim 2, characterized by having a differential scanning calorimetry thermogram, when run at approximately 10°C per minute, containing at least one significant endotherm occurring in a temperature range of from about 146°C to about 151 °C.

7. The composition of cilostazol of Claim 3, characterized by having a differential scanning calorimetry thermogram, when run at approximately 10°C per minute, containing at least one significant endotherm occurring in a temperature range of from about 146°C to about 151°C.

8. The composition of cilostazol of Claim 4, characterized by having a differential scanning calorimetry thermogram, when ran at approximately 10°C per minute, containing at least one significant endotherm occurring in a temperature range of from about 146°C to about 151°C. i

9. The composition of cilostazol of Claim 1 , characterized by having significant FT- Raman spectrum bands of about 3051, 2939, 2900, 2869, 1627, 1593, 1503, 1447, 1425, 1386, 1324, 1308, 1274, 1255, 1052, 1031, 1008, 873, 861, 817, 777, 740, 676, 592, 566, 535, 418, 379, and 276 cm^"1.

10. The composition of cilostazol of Claim 2, characterized by having significant FT- Raman spectrum bands of about 3051, 2939, 2900, 2869, 1627, 1593, 1503, 1447, 1425, 1386, 1324, 1308, 1274, 1255, 1052, 1031, 1008, 873, 861, 817, 777, 740, 676, 592, 566, 535, 418, 379, and 276 cm^"1.

11. The composition of cilostazol of Claim 3, characterized by having significant FT- Raman spectrum bands of about 3051, 2939, 2900, 2869, 1627, 1593, 1503, 1447, 1425, 1386, 1324, 1308, 1274, 1255, 1052, 1031, 1008, 873, 861, 817, 777, 740, 676, 592, 566, 535, 418, 379, and 276 cm^"1.

12. The composition of cilostazol of Claim 5, characterized by having significant FT- Raman spectrum bands of about 3051, 2939, 2900, 2869, 1627, 1593, 1503, 1447, 1425, 1386, 1324, 1308, 1274, 1255, 1052, 1031, 1008, 873, 861, 817, 777, 740, 676, 592, 566, 535, 418, 379, and 276 cm^"1.

13. The composition of cilostazol of claim 1 in pure form.

14. The composition of cilostazol of Claim 13, characterized by having an X-ray powder diffraction pattern similar to FIG. 10.

15. The composition of cilostazol of Claim 13, characterized by having a Fourier Transform Infrared spectrum similar to FIG. 16.

16. The composition of cilostazol of Claim 14, characterized by having a Fourier Transform Infrared spectrum similar to FIG. 16.

17. The composition of cilostazol of Claim 13, characterized by having a differential scanning calorimetry theπnogram, when run at approximately 10°C per minute, containing at least one significant endotherm occurring in a temperature range of from about 135°C to about 140°C.

18. The composition of cilostazol of Claim 14, characterized by having a differential scanning calorimetry thermogram, when ran at approximately 10°C per minute, containing at least one significant endotherm occurring in a temperature range of from about 135°C to about 140°C.

19. The composition of cilostazol of Claim 15, characterized by having a differential scanning calorimetry thermogram, when run at approximately 10°C per minute, containing at least one significant endotherm occurring in a temperature range of from about 135°C to about 140°C.

20. The composition of cilostazol of Claim 16, characterized by having a differential scanning calorimetry thermogram, when run at approximately 10°C per minute, containing at least one significant endotherm occurring in a temperature range of from about 135°C to about 140°C.

21. The composition of cilostazol of Claim 13, characterized by having a FT-Raman spectrum similar to FIG. 22.

22. The composition of cilostazol of Claim 14, characterized by having a FT-Raman spectrum similar to FIG. 22.

23. The composition of cilostazol of Claim 15, characterized by having a FT-Raman spectrum similar to FIG. 22.

24. The composition of cilostazol of Claim 16, characterized by having a FT-Raman spectrum similar to FIG. 22.

25. The composition of cilostazol of Claim 17, characterized by having a FT-Raman spectrum similar to FIG. 22.

26. The composition of cilostazol of Claim 18, characterized by having a FT-Raman spectrum similar to FIG. 22.

27. The composition of cilostazol of Claim 19, characterized by having a FT-Raman spectrum similar to FIG. 22.

28. The composition of cilostazol of Claim 20, characterized by having a FT-Raman spectrum similar to FIG. 22.

29. The composition of cilostazol of Claim 13, further characterized by having a single crystal structure represented by the ORTEP plot of FIG. 2.

30. The composition of cilostazol of Claim 14, further characterized by having a single crystal structure represented by the ORTEP plot of FIG. 2.

31. The composition of cilostazol of Claim 17, further characterized by having a single crystal structure represented by the ORTEP plot of FIG. 2.

32. The composition of cilostazol of Claim 21, further characterized by having a single crystal structure represented by the ORTEP plot of FIG. 2.

33. A process for preparing Form C of cilostazol, comprising the steps of: melting a cilostazol starting material; cooling the melted cilostazol; and, heating the cooled cilostazol sufficient to induce a cold crystallization of Form C of cilostazol.

34. The process of Claim 33, wherein the heating step is accomplished by: elevating the temperature of the cooled cilostazol to a temperature range from above the cold crystallization temperature to at less than aboutl30°C; and, holding said temperature for a period of time sufficient to induce the crystallization of said Form C.

35. The process of Claim 33, wherein the step of cooling the melted cilostazol comprises cooling to a temperature at or below about the glass transition temperature.

36. The process of Claim 34, wherein the step of cooling the melted cilostazol comprises cooling to a temperature at or below about the glass transition temperature.

37. The process of Claim 33, further comprising the step of: recooling the heated cilostazol.

38. A process for further purifying Form C of cilostazol, comprising the process of Claim 37 and further comprising the step of reheating the recooled cilostazol to a temperature of from about 138°C to about 147°C.

39. The process of Claim 38, further comprising the step of: re-recooling the reheated cilostazol.

40. A composition comprising form C of cilostazol prepared by the process as claimed in any one of claims 33 to 39.

41. A pharmaceutical formulation comprising Form C of cilostazol as an active ingredient. ,

42. The pharmaceutical formulation of Claim 41, comprising at least one pharmaceutically acceptable carrier, diluent, or excipient.

43. The pharmaceutical formulation of Claim 41 , wherein the Form C of cilostazol is the sole active ingredient.

44. The pharmaceutical formulation of Claim 41, further comprising at least one additional polymoφhic form of cilostazol.

45. The pharmaceutical formulation of Claim 44, further comprising Form A of cilostazol.

46. The pharmaceutical formulation of Claim 44, further comprising Form B of cilostazol.

47. The pharmaceutical formulation of Claim 44, further comprising Form A of cilostazol and Form B of cilostazol.

48. A method for inhibiting phosphodiesterase HI in mammals comprising administering to a mammal an effective amount of cilostazol as claimed in any one of claims 41 through 47.

49. A unit dosage form comprising the pharmaceutical formulation of any one of claims 41 through 47.

50. A method for inhibiting phosphodiesterase in mammals in need of treatment comprising administering to a mammal an effective amount of a unit dosage of the pharmaceutical formulation as claimed in any one of claims 41 through 47.

51. A method for inhibiting phosphodiesterase HI in mammals in need of treatment comprising administering to a mammal an effective amount of a unit dosage of the pharmaceutical formulation as claimed in any one of claims 41 through 47.

52. A method for inhibiting treating claudication in mammals in need of treatment comprising administering to a mammal an effective amount of a unit dosage of the pharmaceutical formulation as claimed in any one of claims 41 through 47.

53. A method for inhibiting for inducing vasodilution in mammals in need of treatment comprising administering to a mammal an effective amount of a unit dosage of the pharmaceutical formulation as claimed in any one of claims 41 through 47.

54. A method for inhibiting treating strokes in mammals in need of treatment comprising administering to a mammal an effective amount of a unit dosage of the pharmaceutical formulation as claimed in any one of claims 41 through 47.

55. A method for inhibiting platelet aggregation in mammals in need of treatment comprising administering to a mammal an effective amount of a unit dosage of the pharmaceutical formulation as claimed in any one of claims 41 through 47.

56. Form C of cilostazol.