Characterization and Solubility Studies of Pharmaceutical Cocrystals

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CHARACTERIZATION AND SOLUBILITY STUDIES OF PHARMACEUTICAL COCRYSTALS OF EPROSARTAN MESYLATE Jaswanth S Bhandaru, Narender Malothu, and Raghu Rao Akkinepally Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/cg501532k • Publication Date (Web): 12 Feb 2015 Downloaded from http://pubs.acs.org on February 13, 2015

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Crystal Growth & Design

COVER PAGE

CHARACTERIZATION AND SOLUBILITY STUDIES OF PHARMACEUTICAL COCRYSTALS OF EPROSARTAN MESYLATE Jaswanth S. Bhandaru, Narender Malothu and Raghuram R. Akkinepally* Medicinal Chemistry Division, University College of Pharmaceutical Sciences Kakatiya University, Warangal, India -506 009 [email protected] Abstract Eprosartan mesylate (EM), an angiotensin II antagonist, used as an antihypertensive drug. It’s poor (13%) bioavailability, is limited by its solubility rather than metabolism (hepatic CYP450). The hydrogen bond interactions between EM and pharmaceutical coformers involving carboxylic–carboxylic or carboxylic–amino interactions have been considered as the basis for the formation of cocrystals. Liquid-assisted grinding method was successfully employed. These cocrystals were characterized basing on their unique thermal [differential scanning calorimetry (DSC)] and spectroscopic [Fourier transform infrared spectroscopy (FTIR)] profiles. They were confirmed by Powder X- ray diffraction (PXRD) studies and characteristic vibrational modes in Raman spectra. The cocrystals prepared using succinic, p-amino benzoic and salicylic acids exhibited markedly high solubility (30-60 fold) compared to the pure drug (EM). Their in-vitro dissolution studies also showed impressive dissolution profiles (50%) suggesting that they are in favor of increasing the oral bioavailability of EM.

Corresponding Address Prof. Raghuram Rao Akkinepally Head, Department of Medicinal Chemistry University College of Pharmaceutical Sciences Kakatiya University, Warangal – 506 009 Phone: +918790432456 E-Mail: [email protected] 1 ACS Paragon Plus Environment


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CHARACTERIZATION AND SOLUBILITY STUDIES OF PHARMACEUTICAL COCRYSTALS OF EPROSARTAN MESYLATE Jaswanth S. Bhandaru, Narender Malothu. and Raghuram R. Akkinepally* Medicinal Chemistry Division, University College of Pharmaceutical Sciences Kakatiya University, Warangal, India -506 009 [email protected] Abstract Eprosartan mesylate (EM) is an angiotensin II antagonist used as an antihypertensive drug. It’s poor (13%) bioavailability, is limited by its solubility rather than metabolism (hepatic CYP450). The hydrogen bond interactions between EM and pharmaceutical coformers involving carboxylic–carboxylic or carboxylic–amino interactions have been considered as the basis for the formation of cocrystals. Liquid-assisted grinding method was successfully employed. These cocrystals were characterized basing on their unique thermal [differential scanning calorimetry (DSC)] and spectroscopic [Fourier transform infrared spectroscopy (FTIR)] profiles. They were further confirmed by Powder X- ray diffraction (PXRD) studies and characteristic vibrational modes in Raman spectra. The cocrystals prepared using succinic, p-amino benzoic acid (PABA) and salicylic acid exhibited markedly high solubility (30-60 fold) compared to the pure EM. Further they were evaluated for their in-vitro dissolution studies where all the prepared co-cryatals showed markedly high dissolution profiles (50%) which suggests that they are in favor of increasing the oral bioavailability of EM.

Key words: Crystal form, bioavailability, drug solubility, dissolution, physicochemical property.

2 ACS Paragon Plus Environment

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INTRODUCTION The process of conventional drug product development fosters several empirical practices that often end up in compromised product quality and patient safety. The drug development practices in the pharmaceutical industries gained prominence in developing new drug entities with improved efficiency which are in line with the regulatory frame work1. Physico-chemical properties of an active pharmaceutical ingredient (API), the actual substance that is primarily responsible for the pharmacological activity of a pharmaceutical formulation, are the key parameters in developing an acceptable dosage form in order to deliver it to the end user, the patient. Solubility is among the key physicochemical properties for pharmaceutical product design which affects the drug efficacy. Its role in development and formulation efforts, and also the pharmacokinetics, such as the release, transport and the degree of absorption, need not be overemphasized. Drug molecules with limited aqueous solubility are becoming increasingly common resulting in their slow dissolution in biological fluids, less systemic exposure and consequently decreased efficacy in patients2. As aqueous solubility of a drug influences its bioavailability, a lot of efforts are currently being invested for poorly soluble drugs. It is pertinent to mention here that around 70% of currently used drugs, specially the newer ones, suffer from poor aqueous solubility issues. Therefore solubility enhancement techniques are intensely investigated; of which pharmaceutical cocrystallization has been gaining prominence because of its versatility. In recent years cocrystal formation has emerged as a viable strategy towards improving the solubility and bioavailability of poorly soluble drugs. They can be constructed through several types of interactions, mainly non-covalent ones, such as hydrogen bonding, pi-stacking and Van der Waals forces3. Cocrystals consist of two or more solid components (at ambient conditions), Cocrystal is essentially a multicomponent solid form of an API with a GRAS (Generally Regarded as Safe) partner molecule4. The coformer solubility correlates with the solubility of the cocrystals but it is unpredictable and unobvious5. This trend is consistent with the observation that solubility of cocrystals to parent drug increases with the solubility ratio of the coformer to drug for several APIs. Pharmaceutical cocrystallization 3 ACS Paragon Plus Environment


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is

a

reliable

method

to

modify

physico-chemical

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properties

of

drugs

such

as

bioavailability, dissolution rate, stability, solubility, hygroscopisity, and compressibility without

alternating

their

pharmacological

action.

Other

techniques

for

improving

dissolution rate include micronisation to produce increased surface area for dissolution6, the use of salt forms with enhanced dissolution profiles7, solubilisation of drugs in cosolvents8 and micellar solutions9 complexation with cyclodextrins10 and the use of lipidic systems for the delivery of lipophilic drugs11. The successful delivery of any active pharmaceutical ingredient (API) to patients requires the ability to manufacture effective drug products. Much work has been done to improve the physical properties of the API’s, since the efficacy and efficiency of the API or drug molecule is often strongly related to them12. Cocrystallisation provides an alternative to traditional methods of creating targeted soluble molecules and has potential to assist the industry in creating new drugs with increased stability, speed and more efficiency13. Several workers outlined the suitability and potential of this technique in enhancing solubility or dissolution rate of poorly soluble drugs14, 15. If molecules are built by connecting atoms with covalent bonds, solid-state supermolecules

(crystals)

are

built

by

connecting

molecules

with

intermolecular

interactions thus a cocrystal is being formed16. This definition is sometimes extended to specify that the components be solid in their pure forms at ambient conditions17. However, it has been argued that this separation based on ambient phase is arbitrary18. A more inclusive definition is that cocrystals consist of two or more components that form a

unique

crystalline

structure

having

unique

properties19.

Unlike

salt

formation;

cocrystallisation does not rely on ionisation of the API and the counter ion to make a solid. Cocrystals are multiple component systems where intermolecular interactions (including hydrogen bonds, Van der Waals, and π-π interactions) and favourable geometries lead to a self-assembled supramolecular network. A pharmaceutical cocrystal contains an API and a coformer molecule(s) which form a unique crystalline structure having unique properties and interact by hydrogen bonding or by other non-covalent bonds.


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Chemically EM is (E)-2-butyl-1-(p carboxy benzyl)-α-2 thienylmethylimidazole-5acrylic acid. Eprosartan (mesylate) is a competitive angiotensin II type 1 (AT1) receptor antagonist used for the treatment of high blood pressure with IC50 values of EM are in the range as shown 1.4–3.9 nM and also the elimination half-life is 5-7 hr20. EM is structurally distinct from other noncompetitive angiotensin receptor blockers (ARBs) in that it does not contain moieties such as biphenyl and tetrazole which are responsible for blockade of angiotensin II receptors on both sympathetic nerve terminals and blood vessels21.

Figure 1: Structures of Eprosartan Mesylate and Coformers

The present work was oriented towards improving solubility of EM by preparing cocrystals using liquid-assisted grinding technique (LAG) with the help of coformers such as succinic acid, p-aminobenzoic acid and salicylic acid22. The improvement in solubility is confirmed by characterizing prepared cocrystals by using several techniques such as Fourier transformation-infrared spectroscopy (FTIR), X-ray powder diffraction analysis (XPRD), DSC and dissolution test.



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EXPERMENTAL SECTION MATERIALS AND METHODS EM was a gift sample from Glochem Laboratories, Vishakhapatnam, Andhra Pradesh, India, p-aminobenzoic acid, salycilic acid and succinic acid (99%) were purchased from SD Fine Chemicals, Mumbai, India. Ethanol (AR) was purchased from Himedia, Mumbai, India. Preparation of cocrystals Cocrystals were prepared using LAG technique. API and coformer in molar ratios of 1:1 were ground manually in a mortar and pestle at room temperature for 1 hour with slow addition of small volume of ethanol drop wise. Resulted mass was dried further and evaporated at room temperature. Cocrystals with succinic acid (EM-SUC), salicylic acid (EM-SAL), and p-aminobenzoic acid (EM-PABA) were obtained as dry mass. They were characterized further. Differential Scanning Calorimetric (DSC) Studies DSC analysis is a thermoanalytical technique used to identify the difference in the amount of heat required to increase the temperature of a sample and reference as a function of temperature. The DSC Analysis of the samples was performed on a DSC 4000 Perkin Elmer instrument incorporating a refrigerated cooling system. Samples (3−5 mg) were crimped in non-hermetic aluminium pans and scanned from 30 to 300 °C at a heating rate of 10 °C/ min under a continuously purged dry nitrogen atmosphere. Powder X-ray Diffraction (PXRD) Studies The synthesized cocrystals were commonly analyzed using X-ray powder diffractometry (PXRD) as the primary technique. It reveals the information about the crystal structure, chemical composition, and physical properties of the material and also helps in structural characterization. PXRD detects changes in the crystal lattice and is therefore a powerful tool for studying polymorphism, pharmaceutical salts, and cocrystalline phases. PXRD data were recorded on a sample stage Spinner PW3064. The samples were exposed to nickel filtrate Cukœ radiations (40 KV, 30 mA) and were scanned from 10° to 40° , 2Ɵ at a step size of 0.045° and step time of 0.5 s.


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Fourier Transform Infrared (FT-IR) Studies FT-IR spectra of pure API, coformers and selected cocrystals were recorded individually by a spectrum RXI, BRUKER FTIR spectrophotometer using with potassium bromide (KBr) pellet method [Scans were recorded in the range of 400-4000 cm-1 at spectral resolution of 4 cm-1]. Raman Spectroscopic Studies Raman spectra of the samples were obtained using Lab Ram (HORIBA) instrument. The laser power at the sample was approximately 30 mW. A 50× objective lens was used, giving a laser spot diameter (footprint) of 2 µm at the sample. Spectra were obtained for a 10s exposure of the AN_USB detector in the region 4000-50 cm-1 using the extended scanning mode of the instrument. Solubility Studies The saturation solubility studies of EM and its cocrystals were determined using a 24hour shake flask method (used previously for many compounds). In this study an excess quantity of drug was placed in vials containing 10 mL of water. This was agitated using mechanical shaker for 24 hrs at room temperature. The solution was filtered and the amount of drug dissolved was analyzed spectrophotometrically at 235 nm23. Intrinsic Dissolution Studies Intrinsic dissolution measures the rate of dissolution of a pure drug substance from a constant surface area, which is independent of formulation effects and measures the intrinsic properties of the drug as a function of dissolution media, e.g. pH, ionic strength and

counter-ions.

The intrinsic dissolution rate is

a good

indicator for in-vivo

performance of APIs. The dissolution rate studies were conducted in 900 mL of buffer (pH=7.4) at 50 rpm maintained at 37 ± 0.5°C in a dissolution apparatus [Electrolab Dissolution Tester (USP), TDT-06L] using the paddle method. 100 mg of drug or its equivalent amount of cocrystals were added to dissolution medium (7.4 pH buffer) and the samples were withdrawn at appropriate time intervals for four hours. The volume of dissolution medium was adjusted to 900 mL by replacing it with fresh medium. The samples were immediately filtered through 0.40 µm membrane filter, suitably diluted and analyzed spectrophotometrically at 235 nm.



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RESULTS AND DISCUSSION Carboxylic acid is one of the important functional group in crystal engineering. Carboxylic acid can act as both hydrogen bond donor as well as acceptor thus can form a complementary unit with themselves. Two types of associations were observed, dimers and catemers. The ability of carboxylic acids and aromatic nitrogen to form reliable carboxylic

acid-aromatic

nitrogen

supramolecular

heterosynthon

has

been

already

established. The possible carboxylic-carboxylic interactions with the EM and coformers were shown in Figure 2.

a

b

c

Figure 2 a) Hydrogen bond interactions of EM-SAL b) Hydrogen bond interaction of EM–PABA c) Hydrogen bond interactions of EM- SUC Characterization DSC Studies From the DSC thermograms it was observed that the thermograms of the cocrystals were different in pattern and intensity as compared to EM and coformers which indicates their interaction. This shift in the melting point is due to the change in crystal lattice of the EM in presence of coformer, forming a relatively different crystal lattice in cocrystals. DSC, thermoanalysis gave characteristic and comparable results for the APIs and the synthesized cocrystals as shown in Figures 3, 4 and 5. The DSC data of the pure EM revealed single sharp endotherm at 250.20°C, pure PABA showed peak at 198.76 °C and EM-PABA (cocrystals of PABA with EM) showed peak at 149.35 °C, pure salicylic acid showed peak at 172.76 °C and EM-SAL (cocrystals of salicylic acid with EM) showed peak at 134.20°C, pure succinic acid showed peak at 140.39 °C and EM-SUC (cocrystals of succinic acid with EM) showed peak at 166.29 °C indicating the formation of cocrystals and not simple physical mixtures. The cocrystals described here 8 ACS Paragon Plus Environment

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showed reduced melting temperatures from that of EM, suggesting that the cohesive energy of cocrystals EM-PABA, EM-SAL and EM-SUC is decreased from that of pure EM form.

Fig.3: a) DSC thermogram of cocrystal of EM-PABA. b) DSC thermogram of pure PABA c) DSC thermogram of pure EM

Fig.4: a) DSC thermogram of prepared cocrystal of EM–SAL b) DSC thermogram of salicylic acid c) DSC thermogram of Pure EM



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Fig.5: a) DSC thermogram of cocrystal of EM-SUC . b) DSC thermogram of pure succinic acid c) DSC thermogram of pure EM

Powder X-ray Diffraction Studies (PXRD) Powder XRD is useful method for fast identification of new crystalline phase in solid state. A different pattern for the cocrystal from those of the individual components confirms the formation of a new phase. The PXRD pattern of EM and it’s cocrystals have been depicted in Figures 6, 7 and 8, respectively. The PXRD pattern of the pure EM exhibited characteristic diffraction lines to 2θ values at 14.54, 18.46, 19.96, 20.59, 20.96, 22.35, 24.44, 29.08, 30.52, 31.21, 32.86 and 34.26. The EM-PABA showed several different characteristic interference peaks different from that of EM and PABA with 2θ values at 10.63, 12.58, 13.97, 15.32, 20.22, 21.11, 21.90, 22.72, 24.48, 25.42, 28.93 and 31.18. The EM-SUC also showed new characteristic inference peaks to 2θ values at 10.07, 12.67, 13.66, 15.54, 16.85, 1.21, 27.94, 28.88, 32.26 and 33.06 and EM-SAL showed peaks at 12.69, 13.68, 17.29, 18.53, 21.60 which are different and new from that of the EM and coformers used which confirms the purity of the new solid phases formed. The new characteristic diffraction peaks and the absence of the characteristic peaks of the pure and coformers confirms the formation of new solid phases.


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a

bb

cc

2 Theta/degree

Fig. 6: a) Powder –X-ray pattern of Eprosartan mesylate b) Powder –X-ray pattern of PABA c) Powder –X-ray pattern of EM-PABA

a

b

b

cc

2 Theta/degree

Fig. 7: a) Powder –X-ray pattern of Eprosartan mesylate b) Powder –X-ray pattern of Succinic acid c) Powder –X-ray pattern of EM-SUC



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a

b

c

2 Theta/degree

Fig. 8: a) Powder –X-ray pattern of Eprosartan mesylate b) Powder –X-ray pattern of Salicylic acid c) Powder –X-ray pattern of EM-SAL

Fourier Transform Infrared (FT-IR) Studies FT-IR is an excellent technique to give an insight into the kind of interactions occurring between API and coformer. The FT-IR spectra of EM and their respective cocrystals are presented in Figure 9, FT-IR spectroscopy is widely used to study the chemical and physical structure changes in the molecular structure of a substance. EM has a OH stretch bands at 3202 cm-1, C=O stretch for vinylic carboxylic acid ( conjugated with vinyl double bonds ) at 1713.59 cm-1, C=O stretch for aromatic carboxylic acid ( conjugated with phenyl ring ) at 1691.21 cm-1 and O-H bending at 1445.35 cm-1. The EM- PABA has a NH stretch bands at 3460. 54 cm-1 and 3335.7 cm-1, and O-H stretch is shifted from 3202 cm-1 to 3104 cm-1, C=O ( vinylic carboxylic acid ) stretch at 1713.47 cm-1, C=O ( aromatic carboxylic acid ) stretch was also shifted to lower frequency from 1691.21 cm-1 to 1660.21 cm-1 and O-H bending shifted from 1445.35 cm-1 to 1416.99 cm-1 respectively, which shows the formation of hydrogen bond between the carboxylic groups of PABA and EM. Similarly EM- SUC shows decrease in the frequency of OH stretch bands from 3202 cm-1 to 3103.7 cm-1, O-H bending from 1445.35 cm-1 to 1417 cm-1, C=O ( vinylic carboxylic acid ) stretch at 1713.30 cm-1, C=O (aromatic carboxylic acid) stretch from 1691.21 cm-1 to 1654.74 cm-1, and for EM-salicylic acid also shows decrease in the


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OH stretch band from 3202 cm-1 to 3105.41 cm-1, C=O (aromatic carboxylic acid) stretch from 1691.27 cm-1 1689.47 cm-1 and O-H bending from 1445 cm-1 to 1415 cm-1. There is a shift in the FT-IR frequency of functional groups present in the cocrystals compared to that of drug, showing presence of new bond formation. Shift into lower frequency of OH stretch, C=O stretch and O-H bending confirms

the presence of COOH- COOH

hydrogen bond interaction between EM and coformers used. Thus form the above discussions it can be confirmed that cocrystals might have formed using coformers such as succinic, salicylic and PABA.

Figure 9: a) FT-IR spectra of pure EM b) FT-IR spectra of cocrystal of EM-PABA c) FT-IR spectra of cocrystal of EM-SUC d) FT-IR spectra of cocrystal of EM- SAL



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Table 1: Relevant bands of EM, EM-PABA, EM-SUC & EM-SAL in FT-IR spectrum

O-H (str) C-H (Ar) C=O (Vinyl-COOH) C=O (Ar- COOH) C=C (Vinyl) C=C (Ar) O-H (VinylCOOH) bending O-H (ArCOOH) bending C-O str (VinylCOOH) C-O str (ArCOOH)

EM 3202.57 2876.21

EM-PABA 3104 2873.84

EM-SUC 3103.71 2873.94

EM-SAL 3105.41 2875.91

1713.59

1713.41

1713.5

-

1691.21

1660.21

1654.74

1689.47

1640.33 1610.09

1599.68 1580

1612 -

1620 -

1484.21

1416.99

1417.79

1415.76

1445.32

1288.55

1293.5

1309.18

1280.23

1212

1211.08

1199.48

1213.68

1157.43

1155.7

1159.65

Raman Spectroscopy Studies It is known that Raman spectroscopy is a very useful tool for characterisation of cocrystals24. The molecular interactions between p-aminobenzoic acid, salicylic acid, succinic acid and EM were examined by raman spectroscopy. The raman spectrum for pure EM has strong bands at 1650 cm-1, 1322 cm-1 and a medium intensity peak at 3200 cm-1 corresponding to (C=O) stretching, (C-O) stretching and (O-H) respectively. Also, the bands at, 1066 cm-1 and 754 cm-1, corresponding to the, C-H bending, C=O stretch (COOH), and CH wagging, respectively. In the cocrystal EM-PABA the band at 1650 cm-1 was shifted to 1630 cm-1, the band at 3200 cm-1 disappears and the peak at 1322 cm-1 appears as a very weak broad band; these observations indicate that the carboxylic group is participating in hydrogen bonding. During the cocrystallization of the succinic acid with EM, the band at 1632 cm-1 appears at 1645 cm-1 as a broad peak and the peak at 1322 cm-1 has disappeared in the cocrystal and a week band at 1298 cm-1 and also disappearance of the C-H bending and O-H stretch indicate that the 14 ACS Paragon Plus Environment

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carboxylic group is participating in hydrogen bond formation. The same in the case of the cocrystals prepared using salicylic acid, the shift in the C=O stretch from 1632 cm-1 to 1620 cm-1 and disappearance of the C-0 stretch and O-H stretch indicates the formation of hydrogen bonding between the carboxylic groups (Figure 10 & Table II). The results from raman spectra show that there existed carboxylic groups interactions between the EM and coformers used. Hence it can be suggested that the cocrystals of EM were formed with the above coformers by carboxylic – carboxylic interactions.

Fig. 10: a) Raman spectra of pure EM b) Raman spectra of EM -PABA c) Raman spectra of EM-SUC d) Raman Spectra of EM-SAL

Table 2: Relevant bands of EM, EM-PABA, EM-SUC & EM-SAC of raman spectroscopy EM (cm-1)

EM-PABA (cm-1)

EM- SUC (cm-1)

EM- SAL (cm-1)

C=O Stretching

1632

1630

1642

1620

C-O Stretching

1322

-

1298

-

O-H Stretching

1383

-

1438

-

C-H bending

1066

1032

-

984

Functional Group



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C-O Stretching

754

(COOH)

Page 16 of 21

750

762

748

Solubility Studies: The saturation solubility studies of the pure drug and the prepared cocrystals were performed in aqueous medium by subjecting the samples to shaking on a mechanical shaker

for

24

hr

at

room

temperature

and the samples

were

analyzed by

UV

spectrophotometer at 235 nm. Table 3 and Figure 11 depicts that the pure EM showed only 0.034 mg/ mL concentration, whereas EM-SUC showed a concentration of 2.08 mg/ mL, EM-PABA showed 1.084 mg/ mL and EM-SAL showed a concentration of 0.193 mg/ mL. The results suggested that the solubility of cocrystals prepared using succinic acid showed markedly high solubility in aqueous medium i.e., around 60 fold increase in the solubility than the pure API (EM). The phase conversion studies of EM cocrystals were also conducted in line with the solubility studies. The solids obtained after equilibrium time were collected, dried and subjected to XRPD studies (Figure 12). It was found that there is an excellent peak to peak match for the cocrystals after solubility in aqueous medium which indicates that the solids are stable even after 24 hrs solubility. Table 3: Solubility results of Eprosartan Mesylate and prepared cocrystals Solubility S.No

Samples

1

Eprosartan Mesylate

0.034

2

EM-SUC

2.08

3

EM-PABA

1.084

4

EM-SAL

0.193

(mg/ mL)


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2.5 Concentration (mg/ mL)

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Solubility… 2 1.5 1 0.5 0 Eprosartan EM- SUC EM-PABA Mesylate Samples

EM-SAL

Figure 11: Bar diagram showing the enhanced solubility of prepared cocrystals (EMPABA, EM- SAL & EM – SUC)

Figure 12: i) PXRD of EM cocrystals with PABA ii) PXRD of EM cocrystals with Salicylic acid iii) PXRD of EM cocrystals with Succinic acid. Excellent peak to peak match indicated that the cocrystals are stable and no phase conversion took place within 24 hrs solubility in aqueous medium. Intrinsic Dissolution Studies: The in-vitro dissolution studies were performed for 4 hrs in buffer (pH=7.4). As shown in the figure 12 the release profile of EM-PABA showed an initial release of 40% for the first 30 min and 102 % release after 4 hr, EM-SUC showed 41.5% release for the first 30 min and 108% release after 4 hr and EM-SAL showed 55% release after 30 17 ACS Paragon Plus Environment


min and 92% release after 4 hr, whereas EM showed 30% release after 30 min and only 50% release after 4 hr. The above result demonstrates that the dissolution rate of the prepared cocrystals is much greater than that of the pure API which shows the increase in the solubility of the EM using cocrystallization.

120 100 % Drug Release

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EM

80

40

EMPABA EM-SUC

20

EM-SAL

60

0 0

20 40 60 80 100 120 140 160 180 200 220 240 TIME (min)

Figure 12: In-vitro dissolution profile of pure EM and Prepared cocrystals CONCLUSION There are various techniques available which can either be used alone or in combination to enhance the solubility of a drug. To further enhance the solubility of EM, its cocrystals were prepared with coformers such as succinic acid, salicylic acid and PABA. Three novel cocrystals of EM with coformers were prepared using LAG technique and fully characterized by DSC, PXRD, FT-IR and raman spectroscopic studies. It is evident from these findings that primary intermolecular interactions are based on hydrogen bonding between carboxylic groups. The findings of this study will help us in advanced EM cocrystal screening and synthesis. Formation of new crystalline phase was indicated by DSC thermograms which exhibited a single sharp melting endotherm at a position different from that of EM and coformers. Presence of broad desolvation endotherm before the true melting indicated the formation of solvated cocrystals. The PXRD studies revealed different crystalline identity of these cocrystals from the API and coformers


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used. Raman and FTIR spectroscopic studies showed that the cocrystal of EM

was

formed by the carboxylic-carboxylic interactions with the coformers used. Equilibrium solubility studies of the prepared cocrystals and EM were performed in water for 24 hrs. The phase transformation studies also revealed the stability of EM cocrystals in aqueous medium. The EM-SUC showed high solubility than the other two cocrystals with 2.08 mg/ mL which indicates that succinc acid is the preferred coformer for the preparation of cocrystals of EM and the intrinsic dissolution studies performed in buffer (pH=7.5) also showed an markedly increased dissolution profile of prepared cocrystals than EM thus the cocrystallization method which clearly indicates increased bioavailability of the drug. ACKNOWLEDGEMENTS Authors are thankful to Ms. Glochem Pharmaceutical Ltd., Vishakhapatnam, A.P., India for providing drug (EM) as a gift sample and to Dr R. S. Varma, Sanative Therapeutics (Pvt) Limited, Hyderabad for financial support. We thank Dr S. V. Manorama, Principal Scientist, Nanomateials Department, IICT, Hyderabad, for recording Raman spectra and Dr Shayeda for recording DSC thermograms. We are thankful to Prof. YM Rao of Vaagdevi College of Pharmacy, Hanamkonda and Prof. KVR Murthy of Andhra University, Visakhapatnam (AP) for helpful suggestions. We thank the Principal, University College of Pharmaceutical Sciences, Kakatiya University, Warangal, for providing necessary facilities. REFERENCES 1. Hamad, M. L.; Bowman, K.; Smith, N.; Sheng, X.; Morris, K. S. Chem. Eng. Sci. 2001, 65, 5625-5638. 2. Jagadeesh, N. B.; Nangia, A. Cryst. Growth Des. 2011, 11, 2662-2679. 3. Nate, S.; Ann, N. Cryst. Growth Des. 2009, 9, 2950-2967. 4. Blagden, N.; de Matas, M.; Gavan, P.; York, P. Adv Drug Del Rev. 2007, 59, 617630. 5. Shan, N.; Perry, M. L.; Weyna, D. R.; Zaworotko, M. J., Expert Opin. Drug Metab. & Toxicol. 2014, 10, 1255-1271. 6. Chaumeil, J. C. Methods Find. Exp. Clin. Pharmacol. 1998, 20, 211–215.



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TABLE OF CONTENTS USE ONLY Graphical Abstract ENHANCED SOLUBILITY STUDIES OF EPROSARTAN MESYLATE BY COCRYSTALLIZATION AND THEIR CHARACTERIZATION USING DSC AND SPECTROSCOPIC METHODS Jaswanth S. Bhandaru, Narender Malothu and Raghuram R. Akkinepally

The cocrystals of EM using different coformers (salicylic acid, p- aminobenzoic acid & succinic acid) were prepared using liquid assisted grinding technique and fully characterized. They enhanced aqueous solubility of the drug to a tune of 30-60 times.


Characterization and Solubility Studies of Pharmaceutical Cocrystals

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