Improving the Solubility and Bioavailability of Apixaban via Apixaban

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Improving the Solubility and Bioavailability of Apixaban via Apixaban−Oxalic Acid Cocrystal Yong Chen,†,§ Long Li,§ Jia Yao,§ Yu-Yu Ma,§ Jia-Mei Chen,*,‡ and Tong-Bu Lu*,†,‡ †

MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, China ‡ School of Pharmaceutical Sciences, Sun Yat-Sen University, Guangzhou 510006, China § HEC Pharmaceutical Co., Ltd., Dongguan 523871, China S Supporting Information *

ABSTRACT: Apixaban (apx), with a trade name of Eliquis, is a highly selective and efficacious inhibitor of blood coagulation factor Xa. Apixaban has poor solubility in water (0.028 mg/mL at 24 °C) and a relatively low oral bioavailability (about 50% for a single 10 mg dose). The purpose of this study is to improve the solubility and consequently the oral bioavailability of apixaban via a cocrystal. A cocrystal of apixaban with oxalic acid (apx-oxaH2O, 4:3:0.5) was successfully obtained and characterized. The structure of the cocrystal was determined by single-crystal X-ray diffraction. The solubility of the cocrystal in 0.1 M HCl (pH 1.0) and phosphate buffer of pH 6.8 was evaluated, and the results show the solubility values of the cocrystal are approximately 2.2 and 2.1 times as large as those of apixaban form N-1 (the marketed product), respectively. The pharmacokinetics in beagle dogs was also investigated, and the mean AUC0−24h of the cocrystal is approximately 2.7 times as large as that of apixaban form N-1, indicating that both solubility and bioavailability of apixaban can be improved via a cocrystal.

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efficacious inhibitor for blood coagulation factor Xa.32,33 It is a new oral inhibitor of blood coagulation drug for the prevention of venous thromboembolism (VTE) after hip or knee replacement surgery.34,35 apx shows polymorphism, and a number of hydrates and solvates have also been identified, while only form N-1 is consistently produced as the marketed product.32 Form N-1 is a thermodynamically stable anhydrous form, which has poor solubility in water (0.028 mg/mL at 24 °C) and relative low oral bioavailability (about 50% for a single 10 mg dose).36 When the single dose is increased to more than 25 mg, oral bioavailability even decreases due to its poor solubility.37 Therefore, the development of new formulations of apx could be of interest and important for increasing its solubility and consequently improving its bioavailability. There are no ionizable moieties in the molecular structure of apx, thus increasing the solubility of apx via salt formation could be impossible. However, cocrystal formation is possible, as it contains amide groups which can act as hydrogen bonding sites to interact with coformers (Scheme 1). apx contains three amide groups, and the apx molecules are linked together through a N−H···O intermolecular hydrogen bond to form a one-dimensional chain in the structure of form N-1 (Scheme 1),32 and it may form hydrogen bonds with

INTRODUCTION In the pharmaceutical industry, one of the crucial parts for the drug development process is to optimize the performance of drug products by the preformulation research, the heart of which is the screening and selection of crystalline solids.1−3 In general, the forms of crystalline solids are either single components or multicomponents. There are many approaches to change the forms of crystalline solids forming for improving the physicochemical properties of active pharmaceutical ingredients (APIs), including hydrates, solvates, salts, and cocrystals.4 Though some of the hydrates have been selected and developed as marketed drugs, most of them exhibit low thermal stability.5,6 A solvate often suffers from its instability and potential toxicity.7,8 Salt formation is a well-established approach to generate new solid forms for improving the physicochemical properties of APIs,9 while the primary limitation is that APIs should contain ionizable moieties. Cocrystals, the stoichiometric multicomponent crystals, have been recently attracting much attention.10 Cocrystal formation could be used to modify the physicochemical properties of APIs,4 such as improving the aqueous solubility,11−21 intrinsic dissolution,22−25 stability,26−29 bioavailability,4,10,30,31 etc. Moreover, cocrystals of APIs with pharmaceutically acceptable molecules do not suffer from the limitations of the abovementioned multicomponent crystalline solids. Apixaban (apx), with a trade name of Eliquis and marketed by Bristol-Myers Squibb, is a highly potent, selective, and © 2016 American Chemical Society

Received: February 18, 2016 Revised: March 30, 2016 Published: March 31, 2016 2923

DOI: 10.1021/acs.cgd.6b00266 Cryst. Growth Des. 2016, 16, 2923−2930

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Scheme 1. Chemical Structures of apx (left) and the Intrachain Hydrogen Bonds in Form N-1 (right)

H, 5.00; N, 13.30%. IR data (KBr, cm−1): 3455, 3441, 2994, 1762, 1686, 1619, 1514, 1439, 1403, 1378, 1302, 1244, 1168, 1145, 1017, 1002, 826, 760, 703, 585. Single-Crystal X-ray Diffraction. Single-crystal X-ray diffraction data for the apx-oxa cocrystal were collected on an Agilent Technologies Gemini A Ultra system with graphite monochromated Cu Kα radiation (λ = 1.54178 Å). Cell refinement and data reduction were applied using the program of CrysAlis PRO. The structure was solved by the direct methods using the SHELX-97 program38 and refined by the full-matrix least-squares method on F2. All nonhydrogen atoms were refined anisotropically. The hydrogen atoms were placed in calculated positions with fixed isotropic thermal parameters and included in the structure factor calculations in the final stage of full-matrix least-squares refinement. Crystallographic data and details of refinements are listed in Table 2, and the hydrogen bonding distances and angles are given in Table 3.

carboxylic and hydroxyl groups. Thus, a series of coformers containing carboxylic and hydroxyl groups were used to interact with apx (Table 1), and a cocrystal of apx with oxalic acid was Table 1. Coformer Library Used in Cocrystal Screening S/N

cofomer

1 2 3 4 5 6 7 8 9 10

oxalic acid malonic acid succinic acid maleic acid adipic acid glycolic acid salicylic acid 4-hydroxybenzoic acid L-malic acid L-tartaric acid

Table 2. Crystallographic Data for apx-oxa Cocrystal apx-oxa

successfully obtained. The cocrystal was characterized by singlecrystal and powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and dynamic vapor sorption. The powder dissolution, intrinsic dissolution, and pharmacokinetics were also investigated.

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formula formula weight temperature (K) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z D (g·cm−3) F(000) range of indices Rint R [I > 2σ(I)]a wR2 [all data]b GOF

EXPERIMENTAL SECTION

Materials and General Methods. Apixaban (>99%, form N-1) was provided by HEC pharmaceutical Co., Ltd. 2,2,2-Trifluoroethanol and anhydrous oxalic acid (99%) were purchased from Aladdin Industrial Corporation. Methanol and acetonitrile of high-performance liquid chromatography (HPLC) grade were purchased from Merck, Darmstadt, China. All the other reagents were analytical grade and commercially available. Elemental analyses (EA) were carried out by an Elementar Vario EL elemental analyzer. The infrared spectra were recorded in the 4000−400 cm−1 region using KBr pellets and a Thermo Nicolet AVATAR 330. Thermogravimetric analyses (TGA) was recorded on a TA Instruments Q500 instrument and alumina crucibles in a nitrogen atmosphere, with a heating rate of 10 °C/min. Differential scanning calorimetry (DSC) was recorded on a TA Instruments Q 2000 instrument and aluminum sample pans in a nitrogen atmosphere, with a heating rate of 10 °C/min. Powder X-ray diffraction (PXRD) patterns were obtained on a PANalytical Empyrean with Cu Kα radiation (45 kV, 40 mA). Apixaban−Oxalic Acid Cocrystal Hydrate (apx-oxa-H2O, 4:3:0.5). A mixture of apx (459 mg, 100 mmol) and anhydrous oxalic acid (67.5 mg, 75 mmol) in 2,2,2-trifluoroethanol (5 mL) was stirred at room temperature for 12 h. Then, 10 mL of ethyl acetate was added dropwise and precipitate was formed. The precipitate was filtered off and dried under vacuum at 60 °C for 12 h. Yield: 90% based on apx. The filtrate was left to evaporate slowly at room temperature in a sealed glass desiccator containing P2O5. After 1 week, block-shaped crystals of apx-oxa cocrystal were obtained. Anal. Calcd for C106H107N20O28.5: C, 60.14; H, 5.09; N, 13.23%. Found: C, 60.33;

C106H107N20O28.5 2117.12 150 triclinic P1̅ 11.8196(8) 13.6930(8) 17.1999(8) 102.601(4) 90.662(5) 112.100(6) 2503.5(3) 2 1.404 1111 −11, 13; −16, 11; −18, 20 0.0788 0.0585 0.1518 1.018

a R1 = ∑||Fo| − |Fc||/∑|Fo|. bwR2 = [∑[w(Fo2 − Fc2)2]/∑w(Fo2)2]1/2, w = 1/[σ2(Fo)2 + (aP)2 + bP], where P = [(Fo2) + 2Fc2]/3.

Powder Dissolution Experiments. For powder dissolution studies of apx form N-1, dihydrate form H2-2, and apx-oxa cocrystal, the solids were dried under vacuum (except H2-2) and milled to powder, and sieved using standard mesh sieves to provide samples with approximate particle size ranges of 65−125 μm. In a typical experiment, 50 mL of medium (0.1 M HCl and phosphate buffered saline (PBS) of pH 6.8) was added to a flask containing excess sample and the resulting mixture was stirred at 37 ± 0.5 °C and 100 rpm. Aliquots were withdrawn from the flask at regular intervals and replaced with fresh solvent in the same volume. Each aliquot was 2924

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Chromatographic separation of the analytes was based on an Agilent 1260 series HPLC system (Agilent Technologies, USA). A Waters XBridge C18 column (30 × 2.1 mm, 3.5 μm) was used. A binary mobile phase composed of 0.1% (v/v) acetic acid and 2 mM ammonium formate in water (eluent A) and methanol (eluent B) pumped at a total flow rate of 0.4 mL/min was used for separation of apixaban. The gradient elution program started with 10% B and increased linearly to 90% B in 3 min, and kept at 90% B for 1 min, and then returned to the initial composition in 1 min and held for 2 min for re-equilibrium. The column temperature was set at 40 °C, and the injection volume was 2 μL. MS/MS analysis was performed on an API 4000 triplestage quadrupole (3Q) tandem mass spectrometer (Applied Biosystems/MDS Sciex, Toronto, Canada) equipped with a TurboIonspray electrospray ionization (ESI) source. The ESI source was operated in the positive ion mode. MS/MS experiments were performed in the MRM acquisition mode with 460.1→199.0 for apx and 260.1→116.3 for propranolol (IS). Dynamic Vapor Sorption (DVS). DVS study was performed on a DVS intrinsic instrument (Surface Measurement Systems, U.K.). All samples were initially dried for several hours under a stream of nitrogen to establish the equilibrium dry mass under 25 °C. Then, the relative humidity (RH) was increased in 5% RH steps from 0% to 95% RH. Finally, the RH was decreased in a similar fashion for the desorption phase. The temperature was maintained at a constant of 25 ± 0.1 °C. The sorption/desorption isotherms were calculated from the equilibrium mass values.

Table 3. Hydrogen Bond Distances and Angles for apx-oxa Cocrystala D−H···A

d(D···A) (Å)

∠(DHA) (deg)

O(10)−H(10C)···O(5) O(11)−H(11A)···O(1) O(14)−H(14)···O(6) N(10)−H(10A)···O(3)#1 N(5)−H(5C)···O(8)#2 N(10)−H(10B)···O(4)#3 N(5)−H(5D)···O(7)#4 O(15)−H(15A)···O(5)#5 O(15)−H(15B)···O(2)

2.694(3) 2.585(3) 2.710(3) 2.876(3) 3.008(3) 3.105(3) 2.897(3) 2.645(12) 2.983(13)

150.8 150.9 146.3 170(3) 130(3) 126(2) 175(4) 136.2 160.9

a Symmetry codes: #1, x + 1, y, z − 1; #2, x − 1, y − 1, z + 1; #3, x + 1, y + 1, z − 1; #4, x − 1, y, z + 1; #5, −x + 1, −y, −z + 1.

immediately filtered through a 0.22 μm nylon filter, properly diluted, and then assayed by HPLC at 280 nm. Concentrations of apx in 0.1 M HCl (pH 1.0) and 0.02 M phosphate buffered saline (PBS) of pH 6.8 were determined by HPLC with a diode array detector (Aglient 1260) at 280 nm. The analysis column was an Aglient ZOBARX RX-C8 column (250 × 4.6 mm, 5 μm). The method employed a linear gradient elution with the potassium dihydrogen phosphate buffer solution (pH 3.8): acetonitrile (9:1, eluent A) and acetonitrile (eluent B), at the flow rate of 1.0 mL/min. The gradient elution program started with 25% B, and increased linearly to 39% B in 8 min, and further increased linearly to 67% B in 7 min and held for 2 min, and then returned to the initial composition (25% B) in 1 min and held for 7 min for re-equilibrium. All the experiments were repeated twice and averaged against a qualified reference standard. Intrinsic Dissolution Measurements. The intrinsic dissolution rate (IDR) experiments of solid materials were carried out on a ZRS8G Dissolution Tester (Tianjin TIANDA TIANFA-pharmaceutical testing instrument manufacturer). Approximately 120 mg of each solid was compressed in a hydraulic press at 2 t for 30 s in a die of 12 mm diameter disk. The disk was coated using paraffin wax, leaving only the surface under investigation free for dissolution. Then, the disk was dipped into 900 mL of 0.02 M phosphate buffered saline (PBS, pH 6.8) at 37 °C, with the paddle rotating at 100 rpm. At each time interval, 2 mL of the dissolution medium was withdrawn and replaced by an equal volume of fresh medium to maintain a constant volume. After filtration through a 0.22 μm nylon filter, solutions were properly diluted, and then assayed by HPLC at 280 nm. The analysis method and column are the same to powder dissolution experiments. Pharmacokinetics in Beagle Dogs Plasma. Male beagle dogs for in vivo pharmacokinetics study were provided by the animal research center of HEC Pharmaceutical Co., Ltd. All the animal experiments were carried out in accordance with institutional guidelines in compliance with regulations formulated by HEC Pharmaceutical Co., Ltd. The experimental protocol was approved by the Institutional Animal Care and Use Committee of HEC Pharmaceutical Co., Ltd. Pharmacokinetics was evaluated in six male beagle dogs (average weight 13 kg). Free apx (form N-1) and the apx-oxa cocrystal were encapsuled and orally administered at 1 mg/kg (the equivalent amount of free apx for cocrystal) to beagle dogs, respectively. Blood samples were collected from the right or left small saphenous vein in the hindlegs, using a heparinized injector, at the following time intervals: 0.25, 1, 2, 4, 6, 8, and 24 h after oral dosing, respectively. Because of the financial budget, crossover experiments were not performed. The blood was centrifuged (10 min, 6000 rpm), and the plasma samples were then stored at −70 °C until analysis. 30 μL of plasma was mixed with 100 μL of acetonitrile containing 100 ng/mL of propranolol (used as the internal standard (IS)) and was vortexed for 5 min. After centrifugation (5 min, 6000 rpm), 80 μL of supernatant was mixed with 70 μL of a methanol/water mixture (1:1) and was then injected for LC-MS/MS analysis.

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RESULTS AND DISCUSSION Crystal Structure. The structure of the apx-oxa cocrystal belongs to the triclinic, P1̅ space group. The asymmetric unit contains two apx, one and a half oxalic acid, and one-fourth water molecules. After the formation of the cocrystal, two apx molecules are linked together through two N5−H5D···O7 (2.897(3) Å) and N10−H10A···O3 (2.876(3) Å) intermolecular hydrogen bonds to form a dimer, and the dimers are alternately connected by oxalic acid molecules through O11− H11A···O1 (2.585(3) Å) and O10−H10C···O5 (2.694(3) Å) hydrogen bonds to generate a one-dimensional (1D) chain (Figure 1a). The 1D chains are further connected via interchain hydrogen bonds (N10−H10B···O4, 3.105(3) Å; N5−H5C··· O8, 3.008(3) Å) to generate a two-dimensional (2D) sheet (Figure 1b). The two adjacent sheets are connected by oxalic acid through O14−H14···O6 (2.710(3) Å) interlayer hydrogen bonds to form a 2D bilayer (Figure 1c), and the bilayers are further linked by water molecules through O15−H15A···O5 (2.645(12) Å) and O15−H15B···O2 (2.983(13) Å) hydrogen bonds to form a three-dimensional (3D) structure (Figure 1c). PXRD and Thermal Analyses. PXRD was used to check the crystalline phase purity of the apx-oxa cocrystal. The result shows that the pattern of the cocrystal is different from that of either API or the coformer (Figure S1, Supporting Information), indicating the formation of a new crystalline phase. In addition, all the peaks displayed in the measured pattern of the apx-oxa cocrystal closely match those in the simulated pattern generated from single-crystal diffraction data (Figure S1, Supporting Information), demonstrating the formation of pure crystalline phase of the apx-oxa cocrystal. The DSC and TGA curves of the apx-oxa cocrystal are shown in Figure 2. From Figure 2, it can be found that the water molecules in the cocrystal were lost first, and then the oxalic acid molecules were decomposed in the temperature range of 150−200 °C, with a weight loss of 12.6% (calcd 12.7%). After the loss of oxalic acid, an exothermic peak at 237 °C was observed in the DSC curve, corresponding to the melting of form N-1 (the melting point for form N-1 is 237 2925

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Figure 1. (a) 1D chain, (b) 2D sheet, and (c) 3D structure with double layers for apx-oxa cocrystal.

°C), indicating that the cocrystal transformed to form N-1 after the loss of oxalic acid. The variable-temperature (VT)-PXRD patterns for the apx-oxa cocrystal confirms that the conversion from apx-oxa cocrystal to form N-1 started around 180 °C and completed over 200 °C (Figure 3).

IR Spectroscopy. The FTIR spectra for apx, oxalic acid, and the apx-oxa cocrystal are shown in Figure S2 (Supporting Information), in which apx shows the CO stretching absorption peaks of the primary amide and lactam at 1594, 1630, and 1682 cm−1, respectively, as well as N−H stretching absorption peaks of the primary amide at 3310 and 3483 cm−1, 2926

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Figure 2. DSC and TGA curves for apx-oxa cocrystal.

Figure 4. Powder dissolution profiles for form N-1, form H2-2, and apx-oxa cocrystal in 0.1 M HCl (a), and 0.02 M phosphate buffer of pH 6.8 (b) at 37 °C within 48 h.

0.02 M PBS, respectively. The apx-oxa cocrystal reached its maximum solubility (Smax) within 1 h and then decreased slowly over time. This type of profile is a product of the “spring and parachute effect”, which has been exhibited by many pharmaceutical cocrystals recently.11,39−41 The supersaturated solution of apx was formed at the initial stage of dissolution and then remained for several hours (Figure 4), and such a behavior is especially favorable for pharmaceutical applications.42 After 24 h, the concentrations of apx reached a plateau, which fully overlaps with the plateau of the dihydrate form H2-2 (Figure 4). After the dissolution experiments, the undissolved solids were filtered and dried under a vacuum, and the results of PXRD analysis indicated that most of the cocrystal transformed to the dihydrate form H2-232 (Figure S3a, Supporting Information), while apx form N-1 did not transform to form H2-2 after the dissolution experiments (Figure S3b, Supporting Information), probably due the existence of strong intermolecular hydrogen bonding interactions within the chain of apx form N-1. It is assumed that the intrinsic dissolution rate (IDR) has a better correlation with in vivo drug dissolution dynamics than solubility.43,44 In order to get quantitative information on the dissolution rates, IDR experiments for form N-1 and the apxoxa cocrystal were performed in 0.02 M phosphate buffer of pH 6.8, and the profiles of IDR results within 60 min are shown in Figure 5. The calculated R2 for form N-1 (0.996) shows excellent linearity over the entire time interval, while R2 for the apx-oxa cocrystal is relatively low (0.982), which can be

Figure 3. Variable-temperature PXRD patterns for apx-oxa cocrystal.

respectively (Figure S2b, Supporting Information). The spectrum of oxalic acid displays the carboxylic CO and O− H stretches at 1694 and 3427 cm−1, respectively (Figure S2a). The spectrum of the apx-oxa cocrystal shows the O−H stretch of oxalic acid and the N−H stretch of apx at 3441 and 3455 cm−1 (Figure S2c, Supporting Information), as well as the C O stretches of the primary amide and lactam at 1619, 1686, and 1762 cm−1, respectively (Figure S2c, Supporting Information). Shifts of CO stretching frequency of the primary amide and lactam and N−H stretching frequency of the primary amide indicate the change of hydrogen bonding interactions on these functional groups in the apx-oxa cocrystal. Powder Dissolution and IDR Studies. Apparent solubility and dissolution rate of APIs are important in the pharmaceutical industry, as higher apparent solubility may result in higher solubility-limited bioavailability. Powder dissolution profiles for apx form N-1, dihydrate form H2-2, and the apx-oxa cocrystal in 0.1 M HCl and 0.02 M phosphate buffered saline (PBS) of pH 6.8 are shown in Figure 4. From Figure 4, it can be found that both the dissolution rate and the solubility value of the cocrystal are larger than those of form N1 and form H2-2, indicating that the solubility of apx can be improved after the formation of cocrystal. The maximum solubility values of the apx-oxa cocrystal are approximately 2.2 and 2.1 times as large as those of form N-1 in 0.1 M HCl and 2927

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Figure 6. Mean plasma concentrations versus time profiles of apx following oral administration of free apx (black square) and apx-oxa cocrystal (red circle) in male beagle dogs. Each point represents the mean ± SD (n = 3).

Figure 5. IDR profiles for form N-1 and apx-oxa cocrystal in 0.02 M phosphate buffer of pH 6.8 at 37 °C.

ascribed to the disproportionation of apx-oxa in 0.02 M phosphate buffer of pH 6.8. The IDR curve for the apx-oxa cocrystal is a result of two processes, namely, the dissolution accompanied by disproportionation, thus it does not show a perfect linearity. From the result of the IDR experiments, it can be found that the apx-oxa cocrystal shows a faster dissolution rate than form N-1, which coincides with the result of the powder dissolution experiments. Those results mean that this new cocrystal form is probably a potential crystalline solid for the development of new formulations of apx. The undissolved solids after the IDR experiments were also analyzed by PXRD. The results indicated that form N-1 remained its crystal form, while part of the apx-oxa cocrystal converted to dihydrate form H2-2 (Figure S4, Supporting Information). Pharmacokinetics in Beagle Dogs Plasma. The results of the above powder dissolution and intrinsic dissolution experiments show that the solubility value and IDR of apx were increased after the formation of the apx-oxa cocrystal. To see if the oral bioavailability of apx can be also improved after the formation of the apx-oxa cocrystal, pharmacokinetics in male beagle dogs was performed (Table S1, Supporting Information). The plasma concentration−time profiles of free apx and the apx-oxa cocrystal are shown in Figure 6, and the mean pharmacokinetic parameters are summarized in Table 4. The higher CV% and SD values for the group of dogs receiving cocrystal and the lower CV% and SD values for the group of dogs receiving pure apx drug may be the result of individual differences. From Table 4, it can be found that the pharmacokinetic parameters of the cocrystal are statistically different from those of free apx. The plasma concentration of the cocrystal is higher than that of the free API at most times. The AUC0−24h and Cmax values of the cocrystal are approximately 2.7 times as large as those of free apx. Moreover, the mean Tmax (2.33 h) of the apxoxa cocrystal is close to that of free apx (2 h). The above results of in vivo pharmacokinetic studies coincide with the results of in vitro powder dissolution and IDR experiments, demonstrating that the oral bioavailability of apx can be indeed improved via the formation of an apx-oxa cocrystal, which originates from the increased solubility and IDR of the apx-oxa cocrystal. Dynamic Vapor Sorption (DVS). Although both in vitro solubility and in vivo pharmacokinetics of apx are effectively enhanced by the formation of the apx-oxa cocrystal, the

Table 4. Mean Pharmacokinetic Parameters of Free apx and apx-oxa Cocrystal in Male Beagle Dogs

a

parameter

apx form N-1

apx-oxa

AUC0−24h (h*ng/mL)a AUC0−24h (h*μM)a Cmax (ng/mL) Cmax (μM) Tmax (h)

3500 ± 528 7.6 ± 1.2 439 ± 116 1.0 ± 0.3 2±0

9720 ± 3210 21.2 ± 7 1220 ± 540 2.7 ± 1.2 2.33 ± 1.53

Each value represents the mean ± SD (n = 3).

enhanced hydrophilic property of the cocrystal may also give rise to the concerns of solid state physical stability. Thus, the advantage of increased solubility and bioavailability that the cocrystal provides must be considered relative to this potential stability disadvantage. Consequently, a DVS study was performed to investigate the physical stability of the apx-oxa cocrystal (Figure 7). Form N-1 is nonhygroscopic as it adsorbs less than 0.1% of water even at 95% RH, while the apx-oxa cocrystal has a relatively high hygroscopicity as it uptakes 1.2% of water on the surface at 95% RH. Maybe the enhanced

Figure 7. DVS isotherm plots for form N-1 and apx-oxa cocrystal at 25 °C. 2928

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Notes

hydrophilic property of the cocrystal is one reason for its relatively high hygroscopicity. However, the water sorption range (∼1.2%) of the apx-oxa cocrystal is generally acceptable in the pharmaceutical industry under good quality control. In addition, both sorption−desorption curves are closed, suggesting that there are no solid state transformation under the experimental conditions, which were further confirmed by PXRD detection (Figure 8).

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by NSFC (Nos. 21331007 and 21571194), NSF of Guangdong Province (No. S2012030006240), and Pearl River S&T Nova Program of Guangzhou for J.-M.C. (No. 2013J2200054).

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Figure 8. PXRD patterns for apx-oxa cocrystal before and after DVS study.

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CONCLUSIONS We tried using a crystal engineering approach to improve the solubility and bioavailability of a poorly soluble drug, apixaban. An apx-oxa cocrystal was successfully obtained, and its structure, solubility, IDR, and pharmacokinetics in beagle dogs were investigated. After the formation of the cocrystal, both the solubility and the pharmacokinetics of apixaban are improved. The solubility values of the cocrystal in 0.1 M HCl and phosphate buffer of pH 6.8 are approximately 2.2 and 2.1 times as large as those of apixaban form N-1, while the mean AUC0−24h of the cocrystal in beagle dogs is approximately 2.7 times as large as that of free apixaban. The DVS study indicates that the solid state stability of this new cocrystal form is acceptable in the pharmaceutical industry. This study suggests that the apx-oxa cocrystal with higher solubility and bioavailability is a potential crystalline solid for the development of a new formulation of apixaban.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b00266. Mean pharmacokinetic parameters, PXRD patterns, and FTIR spectra (PDF) Accession Codes

CCDC 1444463 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*Fax: +86-20-84112921. E-mail: [email protected] (T.-B.L.). *Fax: +86-20-84112921. E-mail: [email protected] (J.-M.C.). 2929

DOI: 10.1021/acs.cgd.6b00266 Cryst. Growth Des. 2016, 16, 2923−2930

Crystal Growth & Design

Article

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DOI: 10.1021/acs.cgd.6b00266 Cryst. Growth Des. 2016, 16, 2923−2930