Impact of Crystal Habit on Biopharmaceutical Performance of

Subscriber access provided by MONASH UNIVERSITY

Article

Impact of Crystal Habit on Biopharmaceutical Performance of Celecoxib Sameer R Modi, Ajay K Dantuluri, Vibha Puri, Yogesh B Pawar, Prajwal Nandekar, Abhay T. Sangamwar, Sathyanarayana R Perumalla, Changquan C. Sun, and Arvind K. Bansal Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/cg400140a • Publication Date (Web): 21 May 2013 Downloaded from http://pubs.acs.org on May 22, 2013

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Crystal Growth & Design is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design

Impact of Crystal Habit on Biopharmaceutical Performance of Celecoxib Sameer R. Modi a, Ajay K. R. Dantuluri a, Vibha Puri a, Yogesh B. Pawar a, Prajwal Nandekar b, Abhay T. Sangamwar b, Sathyanarayana R. Perumalla c, Changquan Calvin Sun c, and Arvind K. Bansal a* a

Department of Pharmaceutics, National Institute of Pharmaceutical Education and Research

(NIPER), SAS Nagar, Punjab 160062, India b

Department of Pharmacoinformatics, National Institute of Pharmaceutical Education and

Research (NIPER), SAS Nagar, Punjab 160062, India c

Department of Pharmaceutics, College of Pharmacy, University of Minnesota, 308 Harvard

Street S.E., Minneapolis, Minnesota 55455-0343, USA

*CORRESPONDING AUTHOR’S AFFILIATION Department of Pharmaceutics National Institute of Pharmaceutical Education and Research (NIPER) Sector 67, SAS Nagar, Punjab 160 062, INDIA Tel: +91-172-2214682-86. Fax: +91-172-2214692. E- mail: [email protected]

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 29

ABSTRACT. Poor biopharmaceutical performance of Biopharmaceutical Classification System (BCS) class II drug molecules is a major hurdle in the design and development of pharmaceutical formulations. Anisotropic surface chemistry of different facets in crystalline material affects physicochemical properties, such as wettability, of drugs. In present investigation, a moleculecentered approach is presented towards crystal habit modification of celecoxib (CEL) and its effect on oral bioavailability. Two crystal habits of CEL, acicular crystal habit (CEL-A) and plate shaped crystal habit (CEL-P), were obtained by recrystallization from toluene at 25 °C and 60 °C, respectively. Compared to CEL-A, CEL-P exhibited significantly faster dissolution kinetics in aqueous media and significantly higher Cmax and shorter Tmax in an oral bioavailability study. The significant enhancement in dissolution and biopharmaceutical performance of CEL-P was attributed to its more abundant hydrophilic surfaces than CEL-A. This conclusion was supported by wettability and surface free energy determination from contact angle measurements, and surface chemistry determination by X-ray photoelectron spectroscopy (XPS), crystal structure modeling, and crystal face indexation. KEYWORDS. Celecoxib, crystal habits, Wettability, Solubility, Anisotropic surface chemistry, Face indexation, Oral bioavailability


2

Page 3 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. INTRODUCTION Variability in biopharmaceutical performance of active pharmaceutical ingredients (APIs), can affect their bioavailability, safety, and efficacy.1,

2

Solid form of a chemical

compound is usually defined in terms of their internal structure. The ability of a compound to pack into different crystal lattice arrangements is termed ‘polymorphism’. On the other hand, the external appearance of crystal is termed as ‘crystal habit’. Both polymorphs and crystal habits of an API can have considerable influence on physicochemical properties and, therefore, product performance.3-5 Solvent of crystallization, degree of supersaturation, temperature, rate of change of temperature, additives, and stirring rate can all influence the outcome of crystallization in terms of both polymorphism6 and crystal habits.7-13 Crystallization variables that affect growth, either promotion or inhibition, of different crystal facets subsequently affect the crystal habit.7, 11, 14 Studies have shown differential surface energetics, wetting behavior, and dissolution kinetics between individual crystalline facets.15-21 Since the surface properties of crystal facets are directly related to the localized chemical functionality22, a clear understanding of differential pharmaceutical performance of crystal habits relies on an understanding of the molecular arrangement on the surface of pharmaceutical solids. It has been shown that variations in pharmaceutical processes involving interfaces, such as dissolution, of bulk crystalline materials can be attributed to anisotropic surface chemistry of the crystals.19,

23, 24

This is because that

particle wetting, governed by powder surface energetics, is a prerequisite for interfacial phenomena.19, 21, 23-31 However, the impact of crystal habits on biopharmaceutical properties of an API remains poorly understood.


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 29

The goal of this work was to systematically investigate how crystal habit can impact biopharmaceutical properties of celecoxib (CEL). Two crystal habits of CEL were obtained by controlled crystallization32 and evaluated for their surface molecular environment and in vivo biopharmaceutical performance. The differences in biopharmaceutical performance were correlated to the anisotropic surface properties of CEL crystals. Surface energetics of both crystal habits were characterized using sessile drop contact angle technique. Surface chemistry was determined using X-ray photoelectron spectroscopy (XPS) and MOLCAD® software in an attempt to rationalize the observed differences in surface energetics. The findings were confirmed by crystal face indexation experiments. 2. EXPERIMENTAL SECTION 2.1. Materials The room temperature stable Form III of CEL, chemically designated as 4-[5-(4-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl] benzenesulphonamide (assay value > 99%), was received as a gift from Zydus Cadila Healthcare Ltd. (Ahmadabad, India). Toluene (Merck, India), ethylene glycol (EG, Merck, India) and diiodomethane (DIM, Sigma–Aldrich, Steinheim, Germany) were of > 99.0% purity. The solvents used were of high-performance liquid chromatography (HPLC) grade. All other chemicals used were of analytical grade. 2.2. High-Performance Liquid Chromatography (HPLC) All the samples from solubility and oral bioavailability experiments were analyzed for drug content using a validated HPLC method with minor modifications.33, 34 The HPLC system (Shimadzu Corporation, Kyoto, Japan) included a system 210 controller (SCL-10A), a pump (LC-10AT), a degasser (DGU-14A), an autosampler (SIL-10AD), a column oven (CTO-10AS)


4

Page 5 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and a UV detector (SPD-10AP) with Class-VP (Release 6.10) software. The analytical column ®

®

used was LiChrospher 100 RP-18e (250 mm x 4.6 mm, 5 μm), attached with a LiChroCART

100 RP-18e guard column (4mm x 4 mm, 5 μm) (Merck, Darmstadt, Germany). The mobile phase, acetonitrile (ACN): phosphate buffer (pH 3, 10 mmol) (55:45 v/v), was pumped in isocratic mode at a flow rate of 1.0 mL/min at ambient temperature. Indomethacin was used as internal standard for all plasma samples to nullify any processing errors during extraction. The injection volume was 40 µL. The PDA detector was set at a wavelength of 252 nm. 2.3. Solubility studies The equilibrium solubility of ‘as received’ CEL in toluene at different temperatures (28, 32, 36 and 40 °C) were determined by adding an excess amount of the drug in 20 mL of toluene in 25 mL screw capped glass vials. These vials were then shaken mechanically in a shaker water bath (Julabo Labortechnik GmbH, Seelbach, Germany), at 100 rpm maintained at required temperature (± 0.2 ºC). Samples were withdrawn after 1, 2, 4, 8, 16, 24, 36, 48 and 72 h, filtered using 0.22 µm nylon filters, and analyzed by HPLC after appropriate dilution. The equilibrium solubility values at different temperatures were analyzed by the means of a van’t Hoff plot, which was used to determine the equilibrium solubility at a different temperature, from which the degree of supersaturation during crystallization experiments was calculated. 2.4. Crystallization experiments Different CEL crystal habits were generated by controlling the degree of supersaturation and crystallization temperature. Accurately weighed amount (about 200 mg) of drug was dissolved in 10 mL of toluene by heating to 72 ºC. The hot drug solution was immediately filtered into a glass beaker using 0.22 µm nylon filters and cooled to a predetermined


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 29

temperature, 25 ºC or 60 ºC, to achieve a desired degree of supersaturation of 190% and 102%, respectively. The crystals were collected after 72 h by filtration and dried under vacuum at room temperature sieved, through British sieve size (BSS) No. 50 and retained on BSS No. 72, before all further experiments. 2.5. Characterization of crystallized solid forms 2.5.1. Optical and polarized light microscopy Crystals of CEL were observed at a magnification of 500X, under optical and polarized light microscope (Leica Microsystems Wetzlar GmbH, Wetzlar, Germany) with and without silicon oil. The birefringence pattern was viewed under cross polarizer. Aspect ratio was determined using a pre-calibrated stage micrometer. For both crystal habits, the distribution of particle size, taken as the length along the longest axis of individual crystal, was plotted using 100 particles. D90, i.e., length corresponding to 90% of cumulative undersize particles, was determined from the size distribution plot. 2.5.2. Scanning electron microscopy (SEM) SEM photographs of the crystals were captured using scanning electron microscope (S3400, Hitachi Ltd., Tokyo, Japan) operated at an excitation voltage of 25 kV. Samples were prepared by laying particles on to a double-sided adhesive tape pasted over sample stubs and sputter coated with gold using ion sputter (E-1010, Hitachi Ltd., Tokyo, Japan), before analysis. 2.5.3. Thermogravimetric analysis (TGA) Presence of solvent or any degradation during heating was examined using Mettler Toledo 851e TGA/SDTA (Mettler Toledo, Switzerland) operating with Stare software (version Solaris 2.5.1). Accurately weighed (5-10 mg) samples were loaded in alumina crucibles and


6

Page 7 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


heated at a rate of 20 ºC/min over a temperature range of 35 to 200 ºC, under nitrogen purge (50 mL/min), to determine loss in weight. 2.5.4. Hot stage microscopy (HSM) HSM was carried out to observe thermal transitions using Leica DMLP polarized microscope (Leica Microsystems Wetzlar GmbH, Wetzlar, Germany) equipped with Linkam LTS 350 hot stage. Photomicrographs were captured using JVS color video camera and analyzed using Linksys32 software. Samples were mounted in silicon oil and heated from 35 to 200 ºC, at a heating rate of 20 ºC /min. 2.5.5. X-Ray powder diffraction (XRPD) XRPD patterns of samples were recorded at room temperature on Bruker’s D8 Advance X-ray diffractometer (Karlsruhe, Germany) using Cu-Kα radiation (λ = 1.54 Ǻ) at 35 kV, 30 mA passing through a nickel filter. Data was collected in a continuous scan mode with a step size of 0.01o and dwell time of 1 s over an angular range of 3° to 40° 2θ. Accurately weighed amount of powder (about 300 mg) was loaded in a 25 mm poly-methyl methacrylate (PMMA) holder and gently pressed by a clean glass slide to ensure coplanarity of the powder surface with the surface of the holder. Obtained diffractograms were analyzed with DIFFRACplus EVA (version 9.0) diffraction software. 2.5.6. Differential scanning calorimetry (DSC) Conventional DSC experiments were conducted to determine melting point and heat of fusion using DSC Q2000 (TA Instruments, Delware, USA) equipped with a refrigerated cooling system and operating with Universal Analysis 2000 software (version 4.5A). The sample cell was purged with dry nitrogen at a flow rate of 50 mL/min. Accurately weighed samples (3–5mg)


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 29

in aluminum crimped pans were scanned at a heating rate of 20 ºC/min over a temperature range of 35-200 ºC. The DSC instrument was pre-calibrated for temperature and heat flow using high purity indium. All measurements were performed in triplicate. 2.5.7. Specific surface area Specific surface area was determined using nitrogen gas sorption (SMART SORB 91 Surface Area analyzer; Smart Instruments, Mumbai, India). The instrument was calibrated by injecting a known quantity of nitrogen. The measured parameters were then used to calculate the surface area of the sample by employing the adsorption theories of Brunauer, Emmett and Teller (BET). The weighed samples (5 g) were degassed to remove moisture. Samples were dipped in liquid nitrogen and the quantity of the adsorbed gas was measured using a thermal conductivity detector. The obtained data were integrated using an electronic circuit in terms of counts. The reported values were average of three measurements. 2.5.8. Solubility study Solubility of CEL crystals was determined (n=3) in double distilled water and in pH 12 phosphate buffer. Accurately weighed sample (about 20 mg) was added to 20 mL of medium in a tightly capped vial. The vial is placed in a shaker water bath (Julabo Labortechnik GmbH, Seelbach, Germany) maintained at 100 rpm and 37 ± 0.5 °C. Samples were withdrawn at appropriate intervals (up to 72 h), filtered through 0.22 µm nylon filter and analyzed for drug content using HPLC. Residual solids were analyzed by XRPD for phase identification. 2.5.9. Contact angle measurement Sessile drop contact angle is most commonly measured on surface of compacted disc. However, compaction of the material can alter the particle morphology and surface free energy.


8

Page 9 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Alternatively, contact angle may be measured on a powder layer adhered to an inert support.35, 36 The later method was adopted in the present work as it allows the study of ‘as is’ powder properties. Advancing and receding contact angles made by double distilled water, pH 12 phosphate buffer, EG and DIM with powder samples were measured using sessile drop method on a Drop Shape Analyzer (FTA 1000, First Ten Angstrom, Virginia, USA). Powder samples were mounted on double sided adhesive tape adhered to a glass slide. Excess powder was removed by tapping and a drop of liquid medium was dispensed on them. From a captured video, contact angle was calculated as a function of time by fitting mathematical expression to the shape of the drop and then calculating the slope of the tangent to the drop at the liquid-solid-vapor interface line. All measurements were performed under ambient conditions of 25 ± 2 °C and 55 ± 5% RH, with the reported values being an average of six measurements. 2.5.10. X-Ray photoelectron spectroscopy (XPS) X-Ray photoelectron spectra were recorded using an ESCA-3000 (VG Scientific Ltd, England) with a 9 channeltron CLAM4 analyzer under a vacuum better than 1 x 10-8 Torr, using Mg-Kα radiation (1253.6 eV) and a constant pass energy of 50 eV. Binding energy range was from 0 to 1100 eV for regions of C 1s, N 1s, O 1s, F 1s, and S 2p with average peak binding energy of 286.0, 400.9, 533.0, 688.7, and 170.2 eV, respectively. All spectra were corrected for baseline and fitted using Gaussian function. Fitting was performed using PeakFit

®

(V.4.12,

SeaSolve Software, Inc., MA, USA). Similar curve fitting treatments were given for both the crystal habits. Surface atomic concentration was determined from integrated peak intensities and the corresponding relative sensitivity factor.


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 29

2.5.11. Molecular modelling Molecular lipophilic surface potential (MLSP) analysis of CEL was carried out using the MOLCAD program implemented in the SYBYL7.1 molecular modelling package. The Gasteiger-Hückel charges were assigned to the atoms of CEL structure and surfaces were generated and visualized. The color ramp for the MLSP ranges from deep blue color, representing lower lipophilic potential (LP), to the deep red color, representing higher LP. This analysis can provide LP surrounding each atom or group of atoms and the 3D spatial features of the molecular interactions in crystal. Molecular arrangement on different crystal facets of CEL form III was visualized using Mercury (version 2.3, Cambridge Crystallographic Data Centre, Cambridge, UK). 2.5.12. Face indexation A crystal was placed onto the tip of a 0.1 mm diameter glass capillary and mounted on a Bruker Smart Apex 2 diffractometer (Karlsruhe, Germany) with CCD area detector for determining unit cell parameters and orientation matrices at -100 °C. Cell constants were determined from reflections harvested from three sets of 12 frames. These initial sets of frames were oriented such that orthogonal wedges of reciprocal space were surveyed. This produced initial orientation matrices determined from 89 and 104 reflections for CEL-A and CEL-P respectively. The data collection was carried out using Mo-Kα radiation having λ = 0.71073 Å (graphite monochromator) with a frame time of 30 seconds and a detector distance of 6 cm. A series of images were taken with a video microscope as the crystal is rotated through 360° about the ψ axis. Miller’s indices of various facets of the crystal were identified using T-tool, the faceindexing plug-in of APEX 2.


10

Page 11 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2.5.13. Oral bioavailability study All animal experiments were performed in accordance with the Committee for Purpose of Control and Supervision on Experiments on Animals (CPCSEA) guidelines and the experimental protocols were approved by the Institutional Animals Ethics Committee (IAEC/12/40). Male Sprague–Dawley rats ranging from 250 ± 25 g, were kept on fasting for 12 h before the experiment and were allowed free access to water before and during the experiment. Both CEL crystal habits were administered at a dose of 5 mg/kg of rat body weight via an oral gavage. The powder was filled in wide bore, bulb tipped gastric gavage of sufficient length, to allow intra-gastric administration. The gavage was attached to a syringe, filled with 1.0 mL double distilled water, and the dose was delivered with the aid of a jet of water, which drained the sample along with it. Blood samples were collected from retro-orbital plexus after 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 24, and 48 h in heparinzed microcentrifuge tubes.

Plasma was separated

immediately by centrifugation at 15000 rpm for 10 min at 4 °C and stored at -80 °C until processed and analyzed. Plasma samples were extracted with acetonitrile and quantified using a validated HPLC method. Various pharmacokinetic parameters were calculated from the mean plasma CEL concentration–time profiles using the Thermo Kinetica software (V5.0, Thermo Fischer Scientific, USA). Statistical significance for pharmacokinetic parameters was compared using the paired t-test assuming equal variances. The test was considered to be statistically significant, if p < 0.05.


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 29

3. RESULTS 3.1. Solubility studies Equilibrium solubility of “as received” CEL in toluene, at different temperatures, is captured in table 1. The data was used to generate van’t Hoff plot, which allowed extrapolation of solubility to different temperatures for determining degree of supersaturation during recrystallization experiments. Table 1. Equilibrium solubility of CEL in toluene Equilibrium Solubility (mg/mL) 28 °C

32 °C

36 °C

40 °C

11.56 ± 0.22 12.70 ± 0.16 13.88 ± 0.36 14.97 ± 0.20

3.2. Crystallization experiments The degree of supersaturation was varied by controlling solution concentration and temperature of crystallization. Polarized light microscopic images (Figure 1a, 1b) and SEM photographs (Figure 1c, 1d) revealed that acicular crystals (CEL-A) were obtained from toluene when saturated solution of CEL was cooled and allowed to crystallize at 25 °C (degree of supersaturation was 190%). On the other hand, plate shaped crystals (CEL-P) were generated when solvent was evaporated at 60 °C (degree of supersaturation was 102%). The aspect ratio for CEL-A was 12-20 while that for CEL-P was 4–8. Both CEL-A and CEL-P were confirmed to be anhydrous by HSM and TGA. Further, gas chromatography and Karl Fischer analysis confirmed the absence of residual solvent and water respectively in these samples (< 0.02%).


12

Page 13 of 29

Figure 1. Polarized microscopic and SEM images of (a, c) CEL-A and (b, d) CEL-P respectively

XRPD patterns of both CEL-A and CEL-P showed characteristic diffraction peaks at 2θ values of 5.37°, 10.72°, 16.11°, 19.72° and 21.52° corresponding to CEL form III. The observed variation in relative peak intensity (Figure 2) can be ascribed to preferred orientation of the crystals during XRPD analysis.

200000

Lin(Counts) (Counts) Lin Lin (Counts)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CEL-P

100000

CEL-A 0

3

10

20

30

40

2-Theta 2-Theta scale Scale

Figure 2. Overlay of XRPD scans of CEL crystal habits


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 29

DSC heating curves (Figure 3) of CEL-A and CEL-P showed melting point of 160.75 ± 1.00 °C and 161.09 ± 1.22 °C with melting enthalpy of 90.92 ± 1.76 J/g and 91.63 ± 1.50 J/g respectively (Table 2).

Table 2. DSC results for CEL crystal habits Crystal habit

Melting point (οC)

Heat of fusion (J/g)

CEL-A

160.75 ± 1.00

90.92 ± 1.76

CEL-P

161.09 ± 1.22

91.63 ± 1.50

Figure 3. Overlay of DSC heating curves of CEL crystal habits

Further, the D90 value and specific surface area of two sieved crystal habits were comparable (Table 3).


14

Page 15 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 3. Particle size distribution and specific surface area of CEL crystal habits Crystal

D90

Specific surface area (m2/g)

habits

(µm)

(n = 3)

CEL-A

252.8

0.92 ± 0.04

CEL-P

248.2

0.85 ± 0.02

3.3. Solubility study The dissolution profiles of CEL-A and CEL-P, in double distilled water and pH 12 phosphate buffer, are presented in Figure 4. The CEL-P dissolves much faster than CEL-A in both media. The solution concentration of CEL-A is considerably lower than that of CEL-P up to 24 h (p < 0.05) in both media. However, at 48 and 72 h, the difference in concentration is statistically insignificant (p > 0.05) in both media. Table 4 summarizes the solubility values at 2 h, 4 h, and 12 h (S2, S4 and S12), respectively. There were no polymorphic transformations observed at the end of experiment in both cases.

(a)

(b)

Figure 4. Solution concentration - time profiles of CEL crystal habits in (a) double distilled water and (b) pH 12 phosphate buffer


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 29

Table 4. Solution concentration at different time points for two CEL crystal habits Crystal habits

Water (µg/mL) S2

S4

pH 12 buffer (µg/mL) S12

S2

S4

S12

CEL-A

0.8 ± 0.2 1.8 ± 0.2 2.8 ± 0.1 166.6 ± 7.4

227.1 ± 16.5 365.7 ± 11.8

CEL-P

2.7 ± 0.2 3.4 ± 0.1 3.8 ± 0.1 283.6 ± 16.9 345.3 ± 11.6 396.7 ± 7.1

3.4. Contact angle and wettability Wetting behavior of

pharmaceutical

solids

was

assessed

by contact

angle

measurements.35, 37 The advancing and receding contact angle of drop of different probe liquids, deposited on powder surface, was determined and also characterized for loop of hysteresis (Table 5). The advancing contact angles, using double distilled water, were 102.0° ± 0.7° and 91.5° ± 1.3° for CEL-A and CEL-P, respectively (p < 0.05). When using pH 12 phosphate buffer as the probe liquid, advancing contact angle of CEL-A and CEL-P were 94.5° ± 1.2° and 85.3° ± 1.8°, respectively (p < 0.05). Further, with EG, CEL-A and CEL-P showed a contact angle of 72.1° ± 0.8° and 66.4° ± 2.2°, respectively (p < 0.05). Hence, CEL-P has a higher wetting tendency with both polar and semipolar media. When the nonpolar DIM was used as the probe liquid, CEL-A and CEL-P showed an initial contact angle of 20.8° ± 2.0° and 27.8° ± 0.6°, respectively (p < 0.05). Hence, CEL-A has a higher wetting tendency in nonpolar medium. The loop of hysteresis (θHys) was determined by subtracting receding contact angle from advancing contact angle for each probe liquid. Most liquid-solid interactions exhibit hysteresis


16

Page 17 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


because of differences in behavior of liquid, advancing over surface or receding from it. Hysteresis is indicative of surface roughness and / or heterogeneity. Both CEL-A and CEL-P showed similar hysteresis values (

Impact of Crystal Habit on Biopharmaceutical Performance of

Recommend Documents