Research Article

Screening, preparation, and characterization of aceclofenac cocrystals Sushma Verma1,2*, Arun Nanda3, S.P. Basu1

ABSTRACT

Aim: The aim of the present investigation was to prepare cocrystals of a poorly soluble biopharmaceutical classification system Class - II drug, aceclofenac after screening to enhance its solubility and in turn the bioavailability. Materials and Methods: The screening of the cocrystal formers was done by calculating the solubility parameters using Hoftyzer and Van Krevelen solubility parameters and slurry crystallization technique using seven cocrystal formers. Cocrystals of the drug were prepared using solvent evaporation technique using the selected cocrystal formers, that is, Gallic acid and nicotinamide in the stoichiometric ratio of 1:1. Characterization of the prepared cocrystals was done using differential scanning calorimetry, Fourier-transform infrared studies, X-ray diffraction, and scanning electron microscopic techniques. Conclusion: All the four characterization techniques confirmed the formation of cocrystals of the drug thereby establishing cocrystallization as the method for improving the physiochemical properties of an active pharmaceutical ingredient. KEY WORDS: Aceclofenac, Cocrystals, Hoftyzer, Slurry crystallization technique, Van Krevelen solubility parameters

INTRODUCTION nonsteroidal anti-inflammatory drug of the phenylacetic acid group, possessing remarkable anti-inflammatory, Cocrystallization has gained immense attention in the analgesic, and antipyretic properties. It is used to treat last decade as a means of tailoring the physicochemical pain, inflammation, rheumatoid arthritis, osteoarthritis, properties, such as solubility and dissolution of and inflammatory disease of the joints. Being a BCS biopharmaceutical classification system (BCS) Class Class - II drug, it exhibits very slight solubility in water, - II drugs. It is the method of producing multicomponent poor flow properties and compression characteristics. crystals in which the individual neutral molecules, It shows an elimination half-life of 4 h, volume of that is, the active pharmaceutical ingredient and the distribution 25 L and 50% oral bioavailability.[3] pharmaceutically acceptable molecules, known as the Cocrystal formers are pharmacologically inactive pharmaceutical cocrystal former are held together in material, safe and generally with improved stoichiometric ratios by freely reversible, non-covalent physicochemical properties.[4] They can be screened using interactions hydrogen bonds.[1] Cocrystals which a number of approaches such as supramolecular synthon are generally solid at ambient temperature have the approach using Cambridge database structure, hydrogen ability to partially design the crystal architecture using bonding between the drug and the coformer, Hansen established crystal engineering principles including the solubility parameters, and virtual cocrystal screening design of supramolecular synthons, and conduction of methods. Here, we have used solubility parameters using screening studies to evaluate stoichiometric variations Hoftyzer and Van Krevelen solubility parameters and in cocrystal composition.[2] slurry crystallization technique as the screening methods for the screening of cocrystal conformers.[5] Aceclofenac (2-[(2, 6-dichlorophenyl) amine] phenylacetoxyacetic acid) is an orally effective MATERIALS AND METHODS

Access this article online Materials Aceclofenac was generously gifted from Suraksha Website: jprsolutions.info ISSN: 0975-7619 Pharma, Hyderabad, India. Nicotinamide was

1Pharmacy Institute, NIET, Plot 19, KP-II Greater Noida, Uttar Pradesh, India, 2Faculty of Pharmacy, Dr. A.P.J. Abdul Kalam Technical University, Lucknow, Uttar Pradesh, India, 3Department of Pharmaceutical Sciences, Maharshi Dayanand University, Rohtak, Haryana, India

*Corresponding author: Sushma Verma, Pharmacy Institute, NIET, Greater Noida, Uttar Pradesh – 201306, India. Phone: +91-9350953160. E-mail: [email protected]

Received on: 17-08-2018; Revised on: 24-09-2018; Accepted on: 11-10-2018

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procured from Sigma Aldrich, India. Gallic acid, Where, t1 and t2 are carrier and drug, respectively. tartaric acid, and vanillic acid were supplied by CDH Materials with ∆δ ≤ 7MPa0.5 are miscible, while Chemicals, New Delhi. Urea, citric acid, and maleic systems with ∆δ ≥ 7MPa0.5 are immiscible. acid were purchased from Qualigens Fine Chemicals Pvt., Ltd., Mumbai, Maharashtra. Screening of Cocrystals Cocrystal screening of aceclofenac was conducted Selection of Suitable Drug Molecule and Cocrystal with seven cocrystal formers: Gallic acid, citric acid, Formers maleic acid, nicotinamide, D-tartaric acid, urea, and Suitable drug molecule and cocrystal formers were vanillic acid. A total of 14 combinations of host and selected on the basis of Hoftyzer and Van Krevelen a guest at a 1:1 and 1:2 molar ratios were dissolved solubility parameters. Hansen proposed that the in dimethyl sulfoxide (DMSO). Each DMSO solution total force of the various interactions can be divided containing a host and a guest mixture (4 mg) was into partial solubility parameters, that is, dispersion dispensed to 0.6-mL glass vials with screw caps [6] (δd), polar (δp), and hydrogen bonding (δh). The and then lyophilized at −20°C to get a dried mass. total solubility parameter (δt), also called the three- Cocrystallization was performed using different dimensional solubility parameter, can be defined as solvents covering a broad range of functional groups. follows: Each crystallization solvent was dispensed to the vials; the slurries were stored for 3 days at ambient 22205. δtd=+()δδδph+ temperature with slow shaking at 100 rpm. After observation under optical microscopy, the solids in These partial solubility parameters, that is, δ , δ , the vials were collected and subjected to subsequent d p analysis by powder X-ray diffraction (XRD).[10] and δh can be calculated using the combined group contribution methods of Van Krevelen–Hoftyzer and Preparation of Cocrystals Fedors,[7,8] as follows: Cocrystals of aceclofenac were prepared with nicotinamide [11] F and Gallic acid by a solvent evaporation technique. ∑i di δd = • Accurately weighed drug and coformer, 354 mg of V aceclofenac and 188 mg of Gallic acid (1:1 molar ∑i i ratio) were dissolved in ethanol and left for slow 05. evaporation. After 5 days the fine crystals were F 2 ()∑i pi obtained, which were collected into a tight container δ p = Vi and stored in desiccators. ∑i • Accurately weighed drug and coformers, 354 mg 05. of aceclofenac and 122 mg of nicotinamide (1:1   Eh molar ratio) were dissolved in ethanol. They were  ∑i i  δh = left for slow evaporation. The fine crystals were  V   ∑i i  obtained after 5 days, which were collected into a tight container and stored in desiccators. Where i is the structural group within the molecule, Fourier-transform Infrared (FT-IR) Studies Fdi is the group contribution to the dispersion forces,

Fpi is the group contribution to the polar forces, Fhi FT-IR spectra were obtained for the pure drug, is the group contribution to the hydrogen bonding coformer, and cocrystals. The spectra were recorded energy, and Vi is the group contribution to the molar in a PerkinElmer FT-IR spectrophotometer. Potassium volume. Van Krevelen and Hoftyzer have determined bromide pellet method was employed and background the miscibility of two compounds using the ∆δ ̅ factor, spectrum was collected under identical conditions. which can be calculated as follows: Each spectrum was derived from 16 single average scans collected in the range of 400–4000 cm−1 at the 2 2 20 ∆δ =[(-δδ)+(-δδ)+(-δδ)].5 −1 dd21 pp22hh1 spectral resolution of 2 cm .

Differential Scanning Calorimetry Krevelen et al. then suggested that good miscibility will be achieved if ∆δ ≤ 5MPa0.5. Recently, Greenhalgh Differential scanning calorimeter (DSC) was et al.[9] used the difference in total solubility parameter performed using DSC-60 (Shimadzu, Tokyo, Japan) calorimeter to study the thermal behavior of drug between the drug and the carriers ∆δt as a tool to predict miscibility: alone, a mixture of drug and coformer and the prepared cocrystals. The instrument comprised of calorimeter ∆=δδ−δ (DSC 60), flow controller (60), thermal analyzer tt21t (TA 60), and operating software (TA 60). The samples

82 Drug Invention Today | Vol 11 • Issue 1 • 2019 Sushma Verma et al. were heated in hermetically sealed aluminum pans F ∑i di 0.5 under nitrogen flow (30 ml/min) at a scanning rate of δd ==21.754MPa V 5°C/min from 24 ± 1°C to 250°C. Empty aluminum ∑i i pan was used as a reference. 05. 2 Fp ()∑i i 0.5 XRD δ p = = 54. MPa V The XRD patterns of pure drug and the prepared ∑i i 05. cocrystals were recorded using Philips X-ray  E  ∑i diffractometer (Model: PW1710) with a copper target.  hi  0.5 δh = = 9M.0 Pa The conditions were: Voltage −30 kV; current −30 mA;  V   ∑i i  and scanning speed −1/min; temperature of acquisition: Room temperature; detector: Scintillation counter 2 2 2 0.5 0.5 detector; and sample holder: Non-rotating holder. δt= (δd +δp + δh ) = 24.153MPa Screening of Cocrystals Scanning Electron Microscopy The slurry crystallization technique was used for the The surface characteristics of the pure drug and cocrystal screening method. Cocrystal screening of a prepared crystals were studied by scanning electron poorly soluble BCS Class II drug was carried with seven microscope (SEM) (JEOL, JSM 50A, Tokyo, Japan) cocrystal formers in the stoichiometric ratios of 1:1 and at 1600×. The samples were mounted on double- 1:2. A total of fourteen combinations were screened. Of sided adhesive tape that has previously been secured these all showed cocrystal formation except D-tartaric on copper stubs and then analyzed. The accelerating acid. This was confirmed by powder XRD patterns voltage was 20 kV. and melting points that differed from their related solid forms, including the starting material of their respective RESULTS AND DISCUSSION host and guest. In this research article, we have only elaborated the characterization of two cocrystals, first Selection of Suitable Cocrystal Formers is aceclofenac and Gallic acid cocrystals and second is aceclofenac and nicotinamide cocrystal. The Hansen solubility parameters for aceclofenac and the seven conformers, that is, Gallic acid, citric FT-IR Studies acid, maleic acid, nicotinamide, D-tartaric acid, The FT-IR spectra of aceclofenac, the two cocrystal urea, and vanillic acid were calculated using the formers, that is, Gallic acid and nicotinamide and the group contribution method following the combined two formed cocrystals of their respective combination models of Fedors and Van Krevelen–Hoftyzer.[12] in the stoichiometric ratio of 1:1 was analyzed and The solubility parameters for the drug aceclofenac represented in Figures 1-4. In the FT-IR spectrum are given below as an example in Table 1. The values of the pure drug aceclofenac, the peak at 850.51 can were calculated for each drug/conformer system. On be assigned to C-Cl stretching whereas the peaks at calculation of solubility parameters, it was found that 1718.59 and 3319.49 can be assigned to C=O and O-H all the cocrystal formers except for D-tartaric acid stretching of the carboxylic acid functional group. In the FT-IR spectrum of the cocrystals of aceclofenac showed a value of ∆δ ≤ 7MPa0.5, showing miscibility. and nicotinamide, the peak of C-Cl stretching has been shifted to 862.18 whereas the peak for the C=O and O-H stretching of the carboxylic acid functional group has been shifted to 1712.79 and 3290.79, respectively, when compared with the pure drug. The peak at 1681.93 can be attributed C=O stretching in the spectrum for

Table 1: Calculation of HSPs and molar volume for Aceclofenac in according to the Hoftyzer–Van Krevelen method

1/2 3/2 −1 1/2 3/2 −1 3 Structural group Frequency Fdi (J cm mol ) Fpi2 (J cm mol ) Ehi (J /mol) Molar volume (cm /mol) Phenylene 2 1270 110 0 52.4 Cl‑ 2 450 550 400 24.0 ‑NH‑ 1 160 210 3100 4.5

‑CH2‑ 2 270 0 0 16.1 ‑CO‑ 1 290 770 2000 10.8 ‑O‑ 1 100 400 3000 3.8 ‑COOH 1 530 420 10,000 28.5 ∑=5060 ∑=16,02,600 ∑=18,900 ∑=232.6

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Figure 1: FTIR spectrum of pure drug Aceclofenac

Figure 2: FTIR spectrum of cocrystal former Nicotinamide

Figure 3: FTIR spectrum of crystal of aceclofenac and nicotinamide

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Figure 4: FTIR spectrum of Aceclofenac Gallic acid cocrystals

Figure 7: Differential scanning calorimeter of coformer Figure 5: Differential scanning calorimeter of pure nicotinamide aceclofenac

Figure 8: Differential scanning calorimeter curve of cocrystals of aceclofenac and Gallic acid

Figure 6: Differential scanning calorimeter curve of shift of wavelength only to lower numbers confirms conformer Gallic acid that a proton transfer did not occur. Hence, confirming the formation of the cocrystals. the pure drug which has been shifted to 1747.92 in the cocrystal spectra. The decrease in frequencies implies Differential Scanning Calorimetry that the functional groups have participated in strong The obtained DSC curves for the drug, the two hydrogen bond formation. Furthermore, the significant cocrystal formers and the two formed cocrystals were

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Figure 9: Differential scanning calorimeter curve of cocrystals of aceclofenac and nicotinamide Figure 13: SEM of cocrystals of aceclofenac and Gallic acid

Figure 10: Graph of pure drug aceclofenac

Figure 11: X-ray diffraction graph of aceclofenac, Gallic Figure 14: SEM of cocrystals of aceclofenac and Nicotinamide acid cocrystals (1:1) former Gallic acid and Nicotinamide are shown in Figures 10-12. The XRD scan of pure aceclofenac drug showed intense peaks of crystallinity whereas the XRD pattern of the prepared crystals exhibited a reduction in both number and intensity of peaks compared to plain aceclofenac indicating the decrease in crystallinity or partial amorphization of the drug.

Figure 12: X-ray diffraction graph of aceclofenac Scanning Electron Microscopy nicotinamide cocrystals The scanning electron micro-graphs of the prepared co-crystals of the drug Aceclofenac and co-crystal analyzed and represented in Figure 5-9. In the case of former Gallic acid is shown in Figure 13, while the the pure drug aceclofenac, a sharp peak was obtained SEM for Aceclofenac and Nicotinamide is shown in at 156.14°C. The two cocrystal formers, nicotinamide, Figure 14. The pure aceclofenac was characterized and Gallic acid showed sharp peaks at 134.33°C and by crystals of bigger size and regular shape with an 279.13°C, respectively. The cocrystal of aceclofenac and apparently smooth surface. In contrary to that the nicotinamide in the stoichiometric ratio of 1:1 showed cocrystals of aceclofenac Gallic acid and aceclofenac a peak at 99.92°C which is different from the drug nicotinamide show a crystalline structure which is as well as the cocrystal former and points toward the quite obvious in the scanning electron micrographs.[3] formation of a new cocrystal. Similarly, the cocrystal of aceclofenac in the ratio of 1:1 showed a peak at 77.67°C CONCLUSION again confirming the formation of a cocrystal.[13] The present study showed a simple and successful XRD method for the formation of cocrystals of the poorly The XRD scan of the pure drug Aceclofenac and the soluble drug aceclofenac by simple solvent evaporation prepared co-crystals of Aceclofenac and the cocrystal method which is a promising tool for improving the

86 Drug Invention Today | Vol 11 • Issue 1 • 2019 Sushma Verma et al. physiochemical properties of the drug. The formation Pharmacol 2010;62:1547-59. of cocrystal formation was preceded by screening of 2. Brittain HG. Cocrystal systems of pharmaceutical interest: 2010. Cryst Growth Des 2012;12:1046-54. the cocrystal conformers by calculating the solubility 3. Usha AN, Mutalik S, Reddy MS, Ranjith AK, Kushtagi P, parameters using Hoftyzer and Van Krevelen solubility Udupa N, et al. Preparation and, in vitro, preclinical and parameters and slurry crystallization technique. Of clinical studies of aceclofenac spherical agglomerates. Eur J the seven cocrystal formers tested all showed positive Pharm Biopharm 2008;70:674-83. 4. Blagden N, de Matas M, Gavan PT, York P. Crystal engineering results except for tartaric acid. Here, the characterization of active pharmaceutical ingredients to improve solubility and by DSC, FT-IR, X-RD, and SEM techniques was dissolution rates. Adv Drug Deliv Rev 2007;59:617-30. done for only two cocrystals, that is, aceclofenac with 5. Kumar S, Nanda A. Pharmaceutical cocrystals: An overview. Gallic acid and nicotinamide. The characterization Indian J Pharm Sci 2016;2016:637. 6. Hansen C. Hansen Solubility Parameters: A User’s Handbook. supported the formation of cocrystallization. Therefore, Boca: CRC Press; 2007. p. 10. it can be concluded that cocrystallization is once again 7. Fedors R. A method for estimating both the solubility parameters established as a technique for improving the solubility and molar volumes of liquids. Polym Eng Sci 1974;14:147-54. rd and in turn the bioavailability of the poorly soluble drug 8. Van Krevelen DW. Properties of Polymers. 3 ed. Amsterdam: Elsevier Scientific Publication; 1990. p. 212. which can be supported further by the animal study. 9. Greenhalgh DJ, Williams AC, Timmins P, York P. Solubility parameters as predictors of miscibility in solid dispersions. ACKNOWLEDGMENT J Pharm Sci 1999;88:1182-90. 10. Noriyuki T, Koji S, Takano R, Yoshiki H, Katsuhide T. Co The authors wholeheartedly thank the management of crystal screening of stalone and metastalone using slurry crystallization. Cryst Growth Des 2008;8:3032-7. Noida Institute of Engineering and Technology, Pharmacy 11. Gao Y, Zu H, Zhang J. Enhanced dissolution and stability of Institute, Greater Noida, for providing the necessary adefovir dipivoxil by cocrystal formation. J Pharm Pharmacol facilities for carrying out this research work. We are also 2011;63:483-90. thankful to Centre for Nanoscience and Nanotechnology, 12. Mohammad MA, Alhalaweh A, Velaga SP. Hansen solubility parameter as a tool to predict cocrystal formation. Int J Pharm Jamia Milia Islamia, New Delhi, for carrying out XRD 2011;407:63-71. and scanning electron microscopy studies. Our heartfelt 13. Zhou Z, Chan HM, Sung HH, Tong HH, Zheng Y. is also due to Diya Labs Mumbai for supporting in the Identification of new cocrystal systems with stoichiometric Differential Scanning Calorimetry studies. diversity of salicylic acid using thermal methods. Pharm Res 2016;33:1030-9. REFERENCES

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