NOVEL AMORPHOUS SOLID DISPERSIONS OF CANAGLIFLOZIN HEMIHYDRATE IN EUDRAGIT® E PO

NOVEL AMORPHOUS SOLID DISPERSIONS OF CANAGLIFLOZIN HEMIHYDRATE IN EUDRAGIT^® E PO

Ruchi Agrawal ^{1, * 2}, Nirav Patel ¹ and Mihir Raval ¹

Department of Pharmaceutical Sciences ¹, Saurashtra University, Rajkot - 360005, Gujarat, India.

Krupanidhi College of Pharmacy ², Carmelaram, Bengaluru - 560035, Karnataka, India.

ABSTRACT: The purpose of this research was to develop novel solid dispersions (SDs) of BCS class IV drug, canagliflozin hemihydrate (CFZ) using Eudragit^® E PO (EE PO) as a carrier, to enhance its solubility and dissolution rate. Solvent evaporation technique was used to prepare SDs. The SDs were evaluated for saturated solubility, in-vitro dissolution study, solid-state characterization using FTIR, DSC, XRD and SEM, and flow properties. The solubility of CFZ in SDs increased manifold as compared with pure CFZ.  Low values of angle of repose, Carr’s index, and Hausner ratio indicated good flow properties. The difference factor (f₁) and similarity factor (f₂) values suggested that dissolution profiles of the SDs were dissimilar to market product and the comparative dissolution curves revealed that SDs released CFZ faster than the marketed product. XRD patterns and DSC thermographs suggested that the SDs were present in an amorphous form, unlike pure crystalline CFZ. SEM studies showed CFZ has discrete crystalline particles whereas SD2 has diffuse, irregular asymmetrical structure. The SDs was superior to pure CFZ as they showed substantial improvement in solubility and dissolution rate along with good flow properties. Hence, the amorphous form of CFZ was successfully achieved by formulating it into SDs using EE PO as the carrier, which has conferred an increase in solubility and dissolution rate.

Amorphous, Canagliflozin, Dissolution rate, Eudragit^® E PO, Solid dispersion, Solubility enhancement

INTRODUCTION: Diabetes mellitus (DM) is a chronic and progressive disease which is characterized by impaired glucose utilization, and increased hepatic glucose and free fatty acid production. Epidemiological data reveals that the prevalence of diabetes in adults aged 18-99 years was estimated to be 8.4% in 2017 and predicted to rise to 9.9% in 2045 and is known to have important social, financial and developmental implications in the society ¹.

Diabetes is one of four priority non-communicable diseases (NCDs) targeted by world leaders in the 2011 Political Declaration on the Prevention and Control of NCDs ² and remains a thrust area for healthcare scientist to explore and make further inventions to develop cost-effective and patient compliant remedies for diabetic patients. In the year 2009, sodium glucose -2 transporters (SGLT2) inhibitors were developed as novel antidiabetic agents with independent insulin mechanism of action for reducing plasma glucose levels, to overcome the limitations of current antihyperglycemic agents (AHAs) ³. Canagliflozin (CFZ) ((1S)-1, 5- anhydro- 1- [3- [[5- (4- fluoro-phenyl)- 2- thienyl]- methyl]- 4-methylphenyl]-D-glucitol hemihydrate) is the first drug approved in this class of SGLT-2 inhibitors (also called as gliflozin class of drugs) ^{4, 5}. It is administered orally as a tablet in a dose of 100 or 300 mg once daily as an adjunct to diet and exercise for the treatment of type 2 diabetes mellitus(T2DM) ^{6, 7}. Based on low solubility and low permeability, canagliflozin is classified as a BCS 4 compound ⁸. Pharmacokinetic studies reveal that canagliflozin shows peak plasma concentrations within 1 to 2 h following oral administration, and steady-state levels are reached in 4 to 5 days; it has a bioavailability of 65% and is highly protein bound (99%), mainly to albumin. Following single oral doses, the terminal half-life was 10.6 and 13.1 h for canagliflozin 100 mg and 300 mg, respectively ^9-11. The FDA database of the patented product INVOKANA^® mentions that CFZ shows dose-dependent adverse effects. Some of them are related to reduced volume-related events such as hypotension, postural dizziness, while others include an increase in low-density lipoprotein cholesterol (LDL-C) and a small reduction in bone mineral density (BMD) ¹¹. Hence, the primary focus remains on exploring novel methods to enhance the bioavailability of CFZ and consequently, its dose reduction.

Solid dispersion (SD) technology has been explored by formulation scientists as one of the suitable approaches to formulate poorly water-soluble drugs to enhance their solubility and dissolution rate ^12-18. This technology was first introduced by Sekiguchi and Obi ^19, where they enhanced the solubility of poorly soluble sulfathiazole by using crystalline carriers like urea. Crystalline solid dispersions (SDs) have a major disadvantage of being thermodynamically unstable and hence being unable to release the drug quickly. The second generation solid dispersions were then introduced which used amorphous carriers like hydrophilic polymers leading to amorphous SDs as end product ²⁰. Due to its amorphous state, the drug-polymer SD possess a larger enthalpy, entropy and free energy than its the crystalline form of active pharmaceutical ingredient (API), which results in higher solubility of API ¹⁵. This may lead to significant improvement in bioavailability leading to dose-reduction possibilities. The objective of this research is to develop amorphous solid dispersions of novel antidiabetic drug CFZ, which is classified as BCS class IV drug for enhancing its aqueous solubility and dissolution rate.

In this study, Eudragit E^® PO (EE PO) was examined as a carrier for preparation of SDs with the purpose to enhance solubility and dissolution rate of CFZ. EE PO is a cationic copolymer, also known as poly(butyl methacrylate, (2-dimethylamino ethyl) methacrylate, methyl methacrylate) 1: 2: 1. It is popularly used as a film coating and taste masking agent for tablets and capsules ^21-23. Recently, it has been explored by formulation scientist as a carrier for preparation of solid dispersion to improve solubility and dissolution rate of API. Amorphous spray-dried solid dispersions of valsartan were prepared using EE PO as a carrier for enhancing its dissolution rate in a gastric environment ²⁴. Similarly, amorphous solid dispersions of curcumin - EE PO resulted in a significant increase in aqueous solubility of curcumin ²⁵.

MATERIALS AND METHODS:

Materials: The drug CFZ was generously donated by Cadila Health Care Limited, Sarkhej, Sanand, Gujarat, India. EE PO was donated by Cipla Limited, Vikhroli, Maharashtra, India. Sodium lauryl sulfate (SLS) was procured from Sigma-Aldrich, Bangalore, India; ethanol analytical grade (99.5%), methanol HPLC grade (99.9%), and acetonitrile HPLC grade (99.3%) were procured from SD Fine-Chem Limited, Bangalore, India. All the other chemicals and reagents were of analytical grade.

Preparation of CFZ- EE PO Solid Dispersions: Solid dispersions (SDs) of CFZ were prepared using EE PO as the carrier. The formulations containing drug and polymer in different ratios were prepared by using solvent evaporation method ¹⁵. Details on the composition of SDs are given in Table 1. Ethanolic solutions of CFZ and EE PO were prepared by dissolving the calculated amount of CFZ and EE PO in a predetermined volume of ethanol. The ethanolic solution of CFZ was added to an ethanolic solution of EE PO, and the resulting mixture was stirred using magnetic stirrer at 300 rpm for 10 min. The clear solution containing CFZ and EE PO was subjected to evaporation, overnight at room temperature. This was followed by vacuum drying at room temperature for 4 h for terminal drying. The powder mass obtained was pulverized using mortar and pestle, passed through a 710 µm sieve and retained on 250 μm sieve and finally stored in a desiccator until use. The method for preparation of SDs is also depicted in Fig. 1.

TABLE 1: FORMULATION CHART OF CANAGLIFLOZIN-EUDRAGIT^® E PO SOLID DISPERSIONS

FIG. 1: SCHEMATIC REPRESENTATION OF METHOD OF PREPARATION OF CANAGLIFLOZIN-EUDRAGIT^® E PO SOLID DISPERSIONS

Evaluation of CFZ- EE PO Solid Dispersions:

Determination of Saturated Solubility of CFZ and SDs: Solubility of CFZ and the SDs was determined in distilled water and 0.75% w/v solution of SLS at room temperature (RT) (25 ± 2 °C). For this purpose, excess of CFZ or SDs was added to vehicle and vortex mixed (SPINIX-Vortex Shaker) for 48 h at room temperature (25 ± 2 °C). The dispersion saturated with CFZ was centrifuged using microcentrifuge (Remi-RMI) at 3000 rpm for 30 min. The supernatant was decanted and filtered through a 0.22 µm syringe filter. The filtrate was then suitably diluted with methanol, and the concentration of CFZ was determined by measuring absorbance through UV-Visible spectroscopy (UV-1800, Shimadzu, Japan) at λ_max 290 nm. The procedure for solubility determination is summarised in Fig. 2.

FIG. 2: SCHEMATIC REPRESENTATION OF METHOD OF SOLUBILITY DETERMINATION OF CANAGLIFLOZIN IN PURE STATE AND IN SOLID DISPERSIONS

Solid State Characterisation: Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) was performed for pure CFZ, EE PO, physical mixture of CFZ and EE PO (1:1) (PM) and the SDs. X-ray powder diffraction (XRD) was carried out for CFZ, EE PO, and the SDs. Finally, surface morphology was studied and compared for CFZ and the best SD formulation.

Fourier-Transform Infrared Spectroscopy (FTIR): Fourier-transform infrared (FTIR) spectroscopy is powerful for identifying types of chemical bonds in a molecule by producing an infrared (IR) absorption spectrum that is similar to a molecular "fingerprint." The IR spectroscopy was performed using an FTIR spectrophotometer (Shimadzu Europe FTIR- 8400S) and software IR solutions 30. The spectra were generated by using the potassium bromide (KBr) pellet method. A little quantity of the previously dried sample was intimately mixed with dried KBr. The mixture was pressed using a die set for 2 min. The transparent sample-KBr pellet so obtained was put in the sample holder of FTIR and the spectrum recorded in the range of 4000-500 cm^-1 using a resolution of 4 cm^-1.

Differential Scanning Calorimetry (DSC): The DSC thermographs help to measure the heat flow associated with transitions in materials as a function of temperature and time. They provide information on physical and chemical changes that include endothermic/exothermic processes or changes in heat capacity ²⁶. Differential Scanning calorimeter (DSC 60, Shimadzu, Tokyo, Japan) was used to study the thermal behavior of the samples of CFZ, EE PO, PM, and SDs ¹⁸. The samples were subjected to the temperature range of 25°-200 ºC at a heating rate of 10 °C min^-1 under nitrogen atmosphere at a flow rate of 100 ml min^-1. Empty aluminum pan was used as a reference.

X-ray Diffraction (XRD): The X-ray diffraction study was carried out to characterize the physical form of CFZ in its pure state and samples of solid dispersion ¹⁸. The X-ray diffractometer (Rigaku SmartLab) recorded the XRD pattern using Cu Kα line at a voltage of 40k V and current 30mA. Samples were scanned using diffraction angles (2θ) between 4° to 40° at 0.01° sampling width at the scanning speed of 4° per min.

Field Emission Scanning Electron Microscopy (FESEM): The surface characteristics of pure CFZ and the best SD formulation were studied by field emission scanning electron microscopy (FESEM) (TESCAN-MIRA 3 LMH, Kohoutovice, Czech Republic). The samples were mounted onto the aluminum stage using double-sided carbon tape and sputter-coated, using an electron microscopy sputter coater equipped with a gold (Au) source. Samples were exposed to Au for 2.5 min and then examined using FESEM for morphological characterization.

In-vitro Dissolution Rate Studies: Comparative dissolution studies were performed between marketed product (MKT) (available as a film-coated tablet containing 100 mg CFZ) and different SD formulations. Before dissolution studies, each formulation of SD (equivalent to 100 mg CFZ) was filled in size “000” hard gelatine capsule. A sinker was attached to each capsule to prevent it from floating. The dissolution conditions were maintained as recommended in the FDA database for CFZ 27. USP dissolution apparatus II (paddle apparatus) was used, and the paddle speed was set at 75 rpm. The dissolution medium in each bowl consisted of 600 ml of freshly prepared 0.75% w/v solution of SLS in distilled water, which was maintained at 37 ± 0.5 °C. The dissolution conditions are summarised in Fig. 3.

FIG. 3: EXPERIMENTAL CONDITIONS FOR IN-VITRO DISSOLUTION STUDIES FOR MARKETED TABLET AND SOLID DISPERSION FILLED CAPSULES

Aliquots (2 ml) from the dissolution medium were withdrawn at different time intervals (5, 10, 15, 20, 30, 45 and 60 min). The withdrawn samples were replaced by equal volumes of dissolution medium to maintain the volume and sink conditions constant. The samples were filtered through a membrane filter (0.2 μm, Whatman), and drug concentration was analyzed via validated HPLC method 28. The HPLC (Agilent 1200 HPLC, Agilent Technologies, USA) conditions comprised use of C18 reversed phase column (250 mm × 4.6 mm, 5 μ); mixture of 0.1% orthophosphoric buffer and ACN in the ratio 55:45 (isocratic mode) as mobile phase and the injection volume of 10 μl with a flow rate of 1.1 ml/min. The elution was monitored at 290 nm, and the chromatographic data were acquired and processed with the Agilent Infinity Lab solutions software. All measurements were done in triplicate.

Difference Factor (f₁) and Similarity Factor (f₂): The dissolution profiles of MKT and SDs were compared by using a model-independent, the mathematical approach proposed by Moore and Flanner and recommended in guidelines for the industry for dissolution testing of immediate release solid oral dosage form ^{29, 30}. This approach involves calculating the difference factor (f₁) and the similarity factor (f₂) between two dissolution profiles and is given by equations (1) and (2) respectively ^{27, 29}.

Where ‘n’ is the sampling number, ‘T’ and ‘R’ is the percent dissolved of the test and product reference at each time point ‘t.’ Two dissolution profiles are similar if the value of f₁ is between 0 and 15, and value of f₂ is greater than 50.

Evaluation of Flow Properties: Flow properties of pure CFZ and the SDs were evaluated by measuring the angle of repose (θ), bulk density (ρ_b) and tapped density (ρ_t) and calculating Carr’s index (C) and Hausner ratio (H).

Angle of Repose: The angle of repose of pure CFZ and the SDs was determined by fixed funnel method ³¹. Height of the funnel was adjusted in such a way that the tip of the funnel just touches the apex of the heap of SD powder. The powder was allowed to flow through funnel freely onto the surface. The diameter of the powder cone was measured, and the angle of repose was calculated using equation (3), given below

Tan θ = h/r ..3

Where; h = height of the heap, r = radius of the heap

Bulk Density (ρb) and Tapped Density (ρ_t): Bulk density (ρ_b) and tapped density (ρ_t) were calculated by measuring bulk volume (V_b) and tapped volume (V_t) for the predetermined weight (W) of CFZ and SDs. The sample was introduced into a 10 ml cylinder in quantity sufficient to fill the cylinder to 10 ml mark. The initial volume was noted, and the cylinder was allowed to fall under its weight onto a hard surface from a height of 2.5 cm at 2 s intervals. The tapping was continued until no further change in volume was observed (minimum 500 taps). Bulk density and tapped density were calculated using equations 4 and 5, respectively ³¹.

ρ_b = W / _{Vb ....4}

ρ_t = W / _{Vt ....5}

Carr’s Compressibility Index (C): The Carr’s compressibility index (C) was calculated for CFZ and SDs using equation (6) shown below ³¹:

...6

Hausner ratio (H): Hausner ratio (H) is the ratio of tapped density to bulk density. It gave an insight into the flow characters of powder particles and was calculated for CFZ and the SDs using equation (7) as shown below ³¹:

H = ρ_t / ρ_{b ...7}

RESULTS:

Evaluation of CFZ- EE PO Solid Dispersions:

Determination of Saturated Solubility of CFZ and SDs: The values obtained by saturated solubility determination of CFZ and the SDs are shown in Table 2. Fig. 4A and 4B present the solubility results in distilled water and 0.75% solution of SLS, respectively. In distilled water, pure CFZ showed solubility of 0.104 ± 0.005 mg/ml, which increased nearly twice when formulated as SD1 (0.214 ± 0.005 mg/ml) and nearly 20 times when formulated as SD2 (2.084 ± 0.044 mg/ml). Further increase in the proportion of EE PO (SD3) showed decreased solubility of CFZ (0.058 ± 0.005 mg/ml). Similar results were obtained when the solubility was determined in 0.75% w/v solution of SLS. Pure CFZ showed solubility of 10.08 ± 0.51 mg/ml in 0.75% SLS solution, which increased marginally in SD1 (12.95 ± 0.198 mg/ml) but significantly in SD2 (20.79 ± 3.08 mg/ml). A higher proportion of EE PO in SD3 led to the lower solubility of CFZ (15.93 ± 2.09 mg/ml) than in SD2.

TABLE 2: SATURATED SOLUBILITY DETERMINATION OF CANAGLIFLOZIN AND CANAGLIFLOZIN-EUDRAGIT^® E PO SOLID DISPERSIONS IN DISTILLED WATER AND 0.75% SLS SOLUTION AT ROOM TEMPERATURE (25 ± 2 °C)

Solid State Characterisation:

Fourier-Transform Infrared Spectroscopy (FTIR): Fig. 5 depicts the IR spectra of CFZ, EE PO, PM and the SDs. The spectrum of CFZ showed bands: 3477 cm^-1, 3372 cm^-1, 2914 cm^-1, 1626 cm^-1, 1600 cm^-1, 1549 cm^-1, 1509 cm^-1, 1438 cm^-1, 1233 cm^-1, 1161 cm^-1, 1086 cm^-1, 1054 cm^-1, 1022 cm^-1 and 831 cm^-1. IR spectrum of EE PO showed characteristic bands at 2958 cm^-1, 1730 cm^-1, 1458 cm^-1 and 1149 cm^-1.

The PM retained characteristic peaks of CFZ (3275 cm^-1, 1626.05 cm^-1, 1600 cm^-1, 1556 cm^-1, 1509 cm^-1, 1232 cm^-1, 1151 cm^-1, 1087 cm^-1, 1057 cm^-1, and 819 cm^-1) and EE PO (2956 cm^-1, 1732 cm^-1, 1456 cm^-1 and 1151 cm^-1). The IR spectrum of SD1, SD2 and SD3 formulations displayed broadening of band at 3412.19 cm^-1, 3429.55 cm^-1 and 3433.41 cm^-1 respectively, while retaining other charac-teristic peaks of CFZ and EE PO.

FIG. 5: FTIR SPECTRA OF CANAGLIFLOZIN, EUDRAGIT^® E PO, CANAGLIFLOZIN-EUDRAGIT^® E PO PHYSICAL MIXTURE AND CANAGLIFLOZIN-EUDRAGIT^® E PO SOLID DISPERSIONS

Differential Scanning Calorimetry (DSC): The DSC curves obtained for pure CFZ, EE PO, PM, and SDs are displayed in figure 6. DSC curve for CFZ showed an endothermic peak at 98 °C. No distinct peaks were observed for the polymer EE PO. The PM retained the endothermic peak of CFZ while it disappeared completely in SD1 and SD2. SD3 showed a broad endothermic peak at 71.7 °C.

FIG. 6: DSC THERMOGRAPHS OF CANAGLIFLOZIN, EUDRAGIT^® E PO, CANAGLIFLOZIN-EUDRAGIT^® E PO PHYSICAL MIXTURE AND CANAGLIFLOZIN-EUDRAGIT^® E PO SOLID DISPERSIONS

X-ray Powder Diffraction (XRD): The XRD patterns CFZ, EE PO, and the SDs are shown in Fig. 7. The XRD scan of pure CFZ illustrates high-intensity sharp peaks at 4.75 ± 0.2°, 13.02 ± 0.2°, 16.2 ± 0.2°, 18.76 ± 0.2°, 19.09 ± 0.2°, and 20.24 ± 0.2° which are consistent with the canagliflozin hemihydrate intrinsic peaks at diffraction angles 4.36 ± 0.2°, 13.54 ± 0.2°, 16.00 ± 0.2°, 19.32 ± 0.2°, and 20.80 ± 0.2° as disclosed in the patent document U.S. Pat. No. 7,943,582B2 ³². No intrinsic peaks were observed in the case of EE PO, SD1, SD2, and SD3.

FIG. 7: XRD SPECTRUM OF A) CANAGLIFLOZIN, B) EUDRAGIT^® E PO, C) SD1, D) SD2, E) SD3

Field Emission Scanning Electron Microscopy (FESEM): FESEM micrographs of pure CFZ and SD2 are shown in Fig. 8A and 8B, respectively. Fig. 8A displays crystalline morphology of pure CFZ while Fig. 8B displays diffuse, irregular particles in SD2.

FIG. 9: COMPARATIVE DISSOLUTION PROFILES OF MARKETED TABLET AND CANAGLIFLOZIN-EUDRAGIT^® E PO SOLID DISPERSIONS

In-vitro Dissolution Study: The comparative in-vitro dissolution profiles of MKT and SDs are presented in Fig. 9. The dissolution curves reveal that at the end of 5 min, MKT, SD1, SD2 and SD3 exhibit % cumulative drug release (% CDR) of 24%, 38%, 50% and 49% CFZ respectively. The % CDR at the end of 15 min was found to be 60%, 55%, 80% and 70% for MKT, SD1, SD2, and SD3 respectively.

Difference Factor (f₁) and Similarity Factor (f₂): Each dissolution profile was paired with another and compared by calculating values of f₁ and f₂ factors which are summarised in Table 3. While comparing the dissolution profiles of MKT and SD1, the f₁ value was found to be below 15 (11.21), and the f₂ value was found to be above 50 (51.67). Relatively, higher values of f₁ and lower values of f₂ were obtained while comparing dissolution curves of MKT and SD2 (f₁=19.72, f₂ =39.69) and that of MKT and SD3 (f₁=17.5, f₂ =45.23). The f₁ value was found to be well below 15 (f₁=5.88) and f₂ value much above 50 (f₂ = 62.63), while comparing dissolution profiles of SD2 and SD3.

TABLE 3: DIFFERENCE FACTOR (F₁) AND SIMILARITY (F₂) FACTOR FOR COMPARING DISSOLUTION PROFILES OF MARKETED TABLET (MKT) AND SOLID DISPERSIONS (SDS)

Evaluation of Flow Properties: Flow properties of pure CFZ and SDs were evaluated in terms of bulk density (ρ_b), tapped density (ρ_t), Carr’s compressibility index (C), Hausner ratio (H) and angle of repose (θ), are displayed in Table 4. The SDs showed C value ranging from 19.83 ± 0.76 to 12.5 ± 0.55, which are much lower than C value of CFZ (37.6 ± 1.5). The H values for SDs (1.25 ± 0.01 to 1.14 ± 0.01) were also found to be lower than CFZ (1.59 ± 0.04). Similar observations were recorded for θ values, which were in the range of 30.15 ± 0.4° to 27.59 ± 0.37° for SDs and 37 ± 0.6° for CFZ.

TABLE 4: FLOW PROPERTY CHARACTERISATION OF CANAGLIFLOZIN AND CANAGLIFLOZIN-EUDRAGIT^® E PO SOLID DISPERSIONS

DISCUSSION: Canagliflozin is a poorly water-soluble (~ 0.558 mg/L at 25° C), BCS IV compound which is practically insoluble in aqueous media from pH 1.1 to pH 12.9 ^{4, 8, 11, 33}. The insolubility of CFZ in aqueous me­dia throughout the pH range makes buffers unsuitable as the dissolution medium.

In such cases, the addition of surfactants helps to obtain sink conditions, by enabling the drug release process at the solid-liquid interface and micelle solubilization in bulk ³⁴ and is recom­mended for performing in-vitro dissolution studies ^{35, 36}.

For CFZ, 0.75% w/v SLS solution in water is recommended as dissolution media ²⁷. Hence, the solubility determination of CFZ and the solid dispersions was done in distilled water as well as 0.75% SLS solution. The solubility studies indicate that solubility of CFZ in water and SLS solution, increases initially on increasing the proportion of EE PO in SD formulations, (solubility of SD2> SD1>CFZ). The solubility decreases when proportion of EE PO is raised further (as in SD3).

The initial increase in solubility might be attributed molecular dispersion of CFZ in an amorphous matrix of EE PO, which leads to the transformation of the crystalline state of CFZ to an amorphous or partially amorphous state. The amorphous state is a highly disordered and high- energy state which results in augmented solubility. Decreased solubility of CFZ upon increasing proportion EE PO (SD3) might be attributed to the formation of a viscous matrix, which decreases the drug diffusion across the thick polymeric matrix and hence decreased solubility. The results indicate that the highest increase in solubility is seen when CFZ and EE PO are present in a ratio of 1:2 (SD2).

The conversion of crystalline CFZ to amorphous form when formulated as SDs was established by solid-state characterization of CFZ and the SDs. The endothermic peak of CFZ at 98 °C observed in DSC corresponds to its melting point range (95 °C-105 °C) ^{37, 38}. The endothermic peak height and heat of fusion were reduced in PM and completely disappeared in solid dispersions SD1 and SD2. These findings suggest that the physical state of CFZ transformed from crystalline to amorphous in SD1 and SD2. A broad endothermic peak in case of SD3 indicates an interaction between the drug and the polymer. The small peaks at the beginning of all thermographs are supposed to be endothermic startup hooks, which appeared due to differences in the heat capacity of the sample and reference, and were therefore ignored.

The powder X-ray diffractometry patterns supported results obtained in DSC. XRD pattern of CFZ showed intrinsic peaks at the diffraction angles, showing a typical crystalline pattern, while, the XRD pattern of EE PO shows broad, amorphous peak characteristic of a polymer. The solid dispersions of CFZ and EE PO depicts XRD spectrum which is diffuse and represents low-frequency halo, characteristic of ‘amorphous halo’ ³¹. This confirmed the transformation of CFZ from crystalline form to amorphous form when formulated as solid dispersions. The absence of crystallinity contributes to the enhancement of dissolution of CFZ when formulated as SDs.

FESEM micrographs of SD2 show rough and diffuse structure of particles in contrast to FESEM micrograph of CFZ where particles appeared to be regular and crystalline. This morphological visualization further confirmed the presence of CFZ in the amorphous form in SD2.

IR spectra of CFZ, EE PO, PM, and SDs were studied to detect any complexation or chemical interaction between CFZ and EEPO. The IR spectrum of CFZ displayed characteristic peaks in confirmation with literature ³⁷. The band at 3477 cm^-1 indicates O-H stretch of water molecule (hemihydrate composition of CFZ), 3277 cm^-1 signifies O-H stretch of alcohol, several bands at 1626.05 cm^-1, 1600 cm^-1, 1556 cm^-1, 1509 cm^-1 relate to C=C stretch in aromatic ring, medium peak at 1431 cm^-1 is due to CH₂ bend, strong peak at 1087 cm^-1 indicates C-F stretch, several strong peaks from 1232 cm^-1, 1151 cm^-1, 1087 cm^-1, 1057 cm^-1 are due to dialkyl C-O-C  stretch; peak at 1232 cm^-1 may also be due to C-O stretch of alcohol, and peak at 819 cm^-1 is due to  aromatic C-H bend (para). EE PO shows peaks at 2956 cm^-1, 1732 cm^-1, 1456 cm^-1 and 1151 cm^-1, characteristic of C-H stretch of alkanes, C=O stretch of esters, CH2 bend of alkanes, C-C(O)-C stretch of esters. The IR spectra of a physical mixture retain the peak of the CFZ and EE PO, indicating that the drug and the polymer are compatible with each other. The formulations SD1, SD2 and SD3 show broadening of the band at 3400-3300 cm^-1 which suggests hydrogen bonding at hydroxyl groups. Other peaks and bands of CFZ and EE PO remain unchanged in all SD formulations.

The in-vitro dissolution studies reflect that highest dissolution is achieved by SD2 followed by SD3, SD1, and MKT, which is in confirmation with solubility order of SDs in dissolution medium (SD2>SD3>SD1>CFZ). The calculation of the difference factor and the similarity factor revealed that MKT and SD1 illustrated similar dissolution profiles (f₁<15 and f₂>50). SD2 and SD3 dissolution curves are dissimilar to MKT dissolution curve (f₁>15 and f₂ <50 for SD2- MKT and SD3-MKT) but similar to each other (f₁< 15 and f₂ >50 for SD2-SD3). The results also show that nearly 50% of the % CDR took place in the first 5 min by SD2 and SD3 as compared to 25% CDR by MKT.

Hence, there was a significant increase in dissolution rate when CFZ was formulated as SD2 and SD3. This may be attributed to the conversion of crystalline CFZ into an amorphous system when it is molecularly dispersed into amorphous carrier EE PO. This may be due to the lack of energy requirements during the dissolution process to break up the disordered amorphous structure unlike the organized crystalline state ¹⁵. The lower values of C, H, and θ for SDs than CFZ indicate that flow property of CFZ was improved when formulated as SDs. The value of C for SD2 in range of 11 - 15, H in range of 1.12 - 1.18 and θ value ~ 25° suggest good flow property of SD2, which makes it suitable to attain weight uniformity when filling in capsules³⁹.

CONCLUSION: Amorphous form of CFZ is successfully achieved by formulating it into SDs, which has conferred an increase in solubility and dissolution rate. SD2 shows the best performance in this regard as the further increase in the proportion of EE PO in SDs is detrimental to solubility and dissolution rate of CFZ. SD2 also exhibits good flow properties and is expected to show good performance in the uniform filling of the capsule. The CFZ- EE PO SDs are novel and fill the knowledge gap as they are not being investigated earlier.

ACKNOWLEDGEMENT: Authors express their sincere thanks to Shrideep Labs Pvt. Ltd., Bangalore for supporting this research work.

CONFLICT OF INTEREST: All the authors declare no conflict of interest.

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    How to cite this article:

    Agrawal R, Patel N and Raval M: Novel amorphous solid dispersions of canagliflozin hemihydrate in Eudragit® E PO. Int J Pharm Sci & Res 2019; 10(6): 2923-33. doi: 10.13040/IJPSR.0975-8232.10(6).2923-33.

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