Article pubs.acs.org/IECR
Preparation of Silybin/Poly(vinylpyrrolidone) Nanodrugs by Using the Aerosol Solvent Extraction System for Improving Drug Solubility Wei Teng,† Jiexin Wang,† Neil R. Foster,† Ning Wen,*,‡ and Jianjun Zhang*,† †
State Key Laboratory of Organic−Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China ‡ Department of Prosthodontics, Chinese PLA General Hospital, Beijing 100853, People’s Republic of China ABSTRACT: Silybin (SLB), a kind of antihepatotoxic polyphenolic substance, is currently available for a variety of acute and chronic liver diseases. However, its poor solubility and low bioavailability have strongly limited its therapeutic applications. In this work, we demonstrate a simple solution to address these issues by designing SLB/poly(vinylpyrrolidone) (PVP) nanodrugs via the aerosol solvent extraction system (ASES). In the ASES process, SLB and PVP are prepared via coprecipitation by using the dimethylformamide/dense gas CO2 solvent/antisolvent strategy. The size of the as-obtained SLB/PVP nanodrugs (denoted as NanoSLB) can be tuned from 100 to 300 nm. Compared with raw SLB, NanoSLB is of low crystallinity and hence shows drug solubility greatly enhanced by more than 8-fold. This work will broaden the applications of water-insoluble drugs in pharmaceutical treatments.
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INTRODUCTION Silybin (SLB) is an antihepatotoxic polyphenolic substance which has been widely used as a therapeutic agent for a variety of acute and chronic liver diseases.1−4 The administration of SLB in pharmaceutical treatments is often limited by poor solubility and bioavailability. To solve these problem, various approaches such as forming SLB nanosuspensions, incorporating SLB into polymer micelles or liposomes, and preparing SLB nanoparticles have been explored.5−7 SLB may be incorporated into liposomes with a good dissolution rate, but the drug loading efficiency would be low. Recently, the synthesis of nanodrugs has been a promising strategy for enhancing the dissolution rate and bioavailability of water-insoluble drugs owing to increased surface area available for dissolution as described by the Noyes−Whitney equation.8 However, the conventional strategies for producing nanodrugs, including grinding, spray drying, recrystallization from solution, and emulsion-solvent evaporation, are not suitable for many pharmaceutical applications because of the heat and mechanical stresses placed on the drug, which can alter the properties of the drugs.9−13 Otherwise, the process can also leave high levels of residual solvent, leading to the need for further purification. To date, the use of a green approach such as dense gas (DG) technology as an alternative has been favorable for pharmaceutical processing due to the ability to circumvent both the use of organic solvents and the need for additional complex postprocessing purification and separation stages.14−16 The DG antisolvent processes present significant advantages when compared with conventional techniques, as the particles are prepared with a smaller size and narrower size distributions.17−19 In this process, DG and organic solvent are used as the antisolvent and solvent, respectively, and can be used to recrystallize solid compounds that are insoluble in DG. As one of the DG antisolvent processes, the aerosol solvent extraction system (ASES) methodology has been used extensively for processing pharmaceuticals and biopolymers © 2014 American Chemical Society
and is capable of producing micrometer-sized/nanosized particles with low levels of residual solvent.20 Furthermore, in the ASES process the particle size and morphology can be easily modulated by the optimization of the processing parameters, such as the nozzle geometry and orientation, operating pressure and temperature, and solute concentration.21 Herein, we report the synthesis of SLB nanodrugs (denoted as NanoSLB) using the ASES technique. In the process, watersoluble and biocompatible poly(vinylpyrrolidone) (PVP), which is the most popular polymer excipient for oral, parenteral, and topical applications,21 was used to improve the dissolution rate and bioavailability of SLB. The various processing parameters of the ASES and weight ratios of SLB to PVP were investigated to study the effects on the particle morphology, dispersibility, and dissolution rate of SLB.
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EXPERIMENTAL SECTION Materials. Silybin (purity 98.6%) was supplied by Panjin Huacheng Pharmacrutical Co. Ltd. (Liaoning, China). Poly(vinylpyrrolidone) was provided by Beijing Hengye Zhongyuan Chemical Co. Ltd., with an average Mw of 10 000. N,NDimethylformamide (DMF; HPLC grade), which was used as the solvent, was purchased from Beijing Chemical Works. Carbon dioxide (industrial grade), which was provided by Beijing Ruyuan Ruquan Technology Co. Ltd., was used as an antisolvent in the precipitation experiments. All reagents and chemicals were used without further purification. Procedure and Apparatus. A schematic diagram of the ASES apparatus used for coprecipitation in this study is shown in Figure 1. The carbon dioxide used as the gas antisolvent was Received: Revised: Accepted: Published: 10519
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copper stub using double-sided conducting resin and sputter coated with gold. Particle Size Distribution. The particle size distribution of the samples was measured by a ζ potential analyzer (Zetasizer 3000HS, Malvern Instruments, United Kingdom). The turbid liquid, which was prepared using 2 mg of the sample dispersed into 5 mL of deionized water, was filtered by a 0.45 μm filter and then examined by the analyzer. Fourier Transform Infrared (FT-IR) Spectroscopy. FTIR spectra were recorded with a Nicolet model 8700 spectrometer (Nicolet Thermo Electron Instrument Corp., United States) in the range of 400−4000 cm−1. Samples for which the percentage in the mixing powder was 10% were diluted with KBr and pressed to obtain self-supporting disks. X-ray Diffraction (XRD) Studies. The X-ray diffraction analysis was done using an XRD-6000 diffractometer (Shimadzu Inc., Japan) to detect if there were any changes in the physical characteristics and crystallinity of the samples. Sample powder was placed in an aluminum sample holder, and the scanning speed was 5 deg/min from 5° to 90°. Differential Scanning Calorimetry (DSC) Studies. Thermal analysis of raw SLB, PVP, and the physical mixture of raw SLB and PVP at a weight ratio of 50:50 was performed on a Mettler DSC1/1100 SF differential scanning calorimeter. Dissolution Studies. The dissolution of raw SLB, MicroSLB, NanoSLB, and the physical mixture of raw SLB and PVP at a weight ratio of 50:50 in PBS buffer (150 mM, pH 7.4) at 37 °C was studied. In each experiment, 2.0 mg of the sample was mixed with 3 mL of the buffer solution and the mixture was extracted into a dialysis tube with an Mw cutoff of 3500. The dissolution medium was 50 mL of the buffer water, and a stirring rate of 100 rpm was used. Aliquots were withdrawn over certain time intervals, and the absorbance was measured at 288 nm using a UV spectrophotometer (Cary50).
Figure 1. Schematic diagram of the ASES apparatus: (A) CO2 cylinder, (B) syringe pump, (C) solution reservoir, (D) HPLC pump, (E) pressure transducer, (F) heater, (G) precipitation vessel, (H) filter, (I) water bath, (J) solvent trap.
supplied to the system by a syringe pump (B), which made the dense gas inside the chamber (G) reach a desired pressure, and the pressure transducer (E) monitored the pressure of the vessel. The precipitation chamber was submerged in a water bath (I) to hold the system at a constant temperature, and the temperature of the bath was controlled by a recirculation heater (F). The solutes, which were mixtures of PVP and SLB, were dissolved in an organic solvent (DMF) and contained in a beaker (C). After the system reached the steady state, the organic solution was delivered to the precipitation vessel using an HPLC pump (D), sprayed into the precipitation vessel via a nozzle, so both the organic solution and dense gas antisolvent were fed to the vessel concurrently. Once the flow of the solution to the vessel was stopped, at least 200 mL of dense gas was needed to wash the coprecipitate at the specified temperature and pressure for removing the residual organic solvent. The sample was collected on the 0.5 μm filter (H) at the bottom of the chamber. The dense gas with the organic solvent passed through a solvent trap, and then the residual solvent was collected. Next the system was depressurized, and the sample collected was taken for analysis. Particle Size and Morphology. The morphology of the raw SLB, MicroSLB, and NanoSLB was examined using a model JSM-6701 scanning electron microscopy (SEM) system (JEOL, Japan). A glass slide with the sample was fixed on a
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RESULTS AND DISCUSSION Micronized SLB (denoted as MicroSLB) was prepared by using the ASES process with an operating pressure and temperature of 298 K and 14 MPa and solute concentration of 20 mg/mL. Compared with raw SLB, which had an irregular shape with a wide size distribution around several micrometers (Figure 2a), MicroSLB reveals a spherical morphology and a size distribution in the range of 5−10 μm (Figure 2 b). Figure 2c shows a high-magnification SEM image of MicroSLB. Clearly, MicroSLB is composed of small drug nanoparticles, indicating that without the protection of excipient the drug nanoparticles would aggregate to form a microsphere in the ASES process. PVP is an attractive excipient for use in many types of pharmaceutical formulations. By coprecipitation with PVP, the solubility of water-insoluble drugs has been improved owing to
Figure 2. SEM images of raw SLB (a) and MicroSLB (b, c) processed by ASES (298 K, 14 MPa, 20 mg/mL). 10520
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Figure 3. Characterization of NanoSLB-A, NanoSLB-B, and NanoSLB-C prepared by the ASES (298 K, 14 MPa, 20 mg/mL). DLS analyses of NanoSLB-A (a), NanoSLB-B (b), and NanoSLB-C (c). SEM images of NanoSLB-A (d), NanoSLB-B (e), and NanoSLB-C (f). The nanodrugs were redispersed in deionized water at a concentration of 0.2 mg/mL for all testing.
To explore the effect of the operating parameters in the ASES process, three various operating conditions, a vapor-overliquid condition (298 K and 6.6 MPa), a subcritical liquid condition (298 K and 14 MPa), and a supercritical fluid condition (313 K and 16 MPa), were chosen for the preparation of NanoSLB by the ASES process. Figure 5 gives SEM images of NanoSLB at each of these conditions. However, there are no obvious changes in the particle size. NanoSLB ranges in size from 100 to 300 nm for all three samples. This result indicated that the various conditions of dense gas CO2 at vapor-over-liquid, subcritical liquid, and supercritical fluid conditions had a negligible effect on the size and morphology of the NanoSLB, suggesting that the dense gas CO2 at these three conditions of density had similar antisolvent capacities for coprecipitation of SLB and PVP in the ASES process. The characterizations of MicroSLB and NanoSLB were confirmed by FT-IR, XRD, and DSC. Figure 6 gives the FT-IR spectra of raw SLB, MicroSLB, PVP, and NanoSLB-A. The spectra of raw SLB and MicroSLB exhibit characteristic absorptions at 3455 and 3180 cm−1, which are attributed to the free hydroxyl group and hydroxyl group involved in intermolecular bonding, respectively.28 The characteristic absorption peaks of PVP appeared at 2950 and 1652 cm−1, and were assigned to the C−H stretching vibration and carbonyl group (CO), respectively.29 Moreover, the spectrum of NanoSLB-A presents the characteristic absorptions of both SLB and PVP, suggesting the formation of SLB/PVP nanocomplexes. Figure 7 compares the XRD patterns of the powder of raw SLB, MicroSLB, PVP, and NanoSLB-A. The raw SLB is highly crystallized with many sharp peaks in the XRD pattern. However, after the ASES process the MicroSLB and NanoSLB have no valuable diffraction peaks, with is due to the ASES process resulting in the formation of an amorphous state of SLB. XRD can detect the presence of crystalline material in powder to about 5% or less, indicating that after the ASES process more than 90% of crystalline SLB was transformed into the amorphous state in MicroSLB and NanoSLB. This amorphous transformation is probably due to the use of dense gas CO2 as the antisolvent effectively decreasing the
PVP preventing the aggregation and crystallization of the drug particles.22−27 Various weight ratios of SLB to PVP of 50:50, 30:70, and 10:90 were used in the ASES process to synthesize the SLB/PVP nanodrugs denoted as NanoSLB-A, NanoSLB-B, and NanoSLB-C, respectively. Parts a−c of Figure 3 show the sizes of NanoSLB by dynamic light scattering (DLS). Compared with MicroSLB, NanoSLB exhibits a smaller particle size with average diameters of 199, 180, and 175 nm for NanoSLB-A, NanoSLB-B, and NanoSLB-C, respectively. Parts d−f of Figure 3 show SEM images of NanoSLB indicating that it has a spherical shape with the particle size in the range of 100−300 nm, consistent with the DLS results. Moreover, as shown in the SEM images, the degree of agglomeration of the NanoSLB was reduced with an increasing of the PVP proportion. The DLS and SEM results confirmed that these PVP polymers effectively prevent growth and aggregation of SLB nanoparticles in the ASES process, leading to a significantly smaller and uniform particle size compare to those of MicroSLB, which had no PVP excipient in the process. Figure 4 presents a schematic illustration of NanoSLB formation. First, raw SLB and PVP were dissolved in DMF to
Figure 4. Schematic illustration showing the synthesis and redispersion in the aqueous phase of NanoSLB.
form a mixed solution. Subsequently, the ASES process using dense gas CO2 as the antisolvent resulted in NanoSLB containing hydrophilic chains of PVP. Moreover, these hydrophilic chains enable NanoSLB to redisperse in the aqueous phase and form a transparent solution. 10521
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Figure 5. SEM images of NanoSLB formed by the ASES process (50:50 weight ratio of SLB/PVP, 20 mg/mL): (a) 298 K, 6.6 MPa; (b) 298 K, 14 MPa; (c) 313 K, 16 MPa.
Figure 8. DSC thermogram of raw SLB, PVP, NanoSLB-A, and the physical mixture (50:50).
Figure 6. FT-IR spectra of raw SLB, MicroSLB, PVP, and NanoSLB-A.
physical mixture exhibits two endothermic peaks, including a broad peak of PVP ranging from 50 to 135 K and another peak of raw SLB at around 150 K. Compared with the physical mixture, NanoSLB-A shows that there is no endothermic peak of SLB observed in the curve, further confirming that coprecipitating SLB with PVP by the ASES process significantly influences the crystallinity of SLB, resulting in an amorphous state of SLB in the nanocomplexes.29 The content of SLB in NanoSLB was measured at 288 nm by using UV spectrophotometry. Drug loading efficiencies of 52%, 32%, and 13% were estimated for NanoSLB-A, NanoSLB-B, and NanoSLB-C, respectively, consistent with the original 50:50, 30:70, and 10:90 weight ratios of SLB/PVP. The loading efficiency results further confirmed that SLB was coprecipitated with PVP in the ASES process to form SLB/PVP nanocomplexes. Figure 9 compares the dissolution rates of raw SLB, MicroSLB, NanoSLB-A, NanoSLB-C, and the physical mixture of raw SLB and PVP at a weight ratio of 50:50. For the raw SLB and physical mixture, only 10% and 16% of SLB was dissolved during the 480 min incubation period, respectively. In contrast, the ASES process effectively reduced the crystallinity of SLB, leading to a higher dissolution rate at 28% for MicroSLB in the same period. Furthermore, dissolution rates of 72% and 83% were observed for NanoSLB-A and NanoSLB-C, respectively, indicating that the dissolution rate increased with an increase of the amount of PVP in the ASES. The results for the dissolution rates could prove that an amorphous structure, a smaller particle size (leading to a high surface area), and water-soluble polymer matrixes could improve the solubility of water-
Figure 7. XRD patterns of raw SLB, MicroSLB, PVP, and NanoSLB-A.
crystallinity of SLB during the precipitation process. Otherwise, on the basis of previous studies, PVP can effectively inhibit recrystallization of drug molecules in the coprecipitation or solvent evaporation process due to the hydrogen-bonding interaction between the drug and PVP and the entrapment effect of PVP.29−31 However, it has been recognized that the transformation from the crystalline state to the amorphous state may improve the bioavailability and dissolution rate of SLB.32 The DSC thermograms of raw SLB, PVP, NanoSLB-A, and the physical mixture of raw SLB and PVP at a weight ratio of 50:50 are shown in Figure 8. The curve of raw SLB shows an endothermic peak at 152 K. For PVP, a broad endothermic peak ranging from 50 to 135 K is observed, indicating that PVP contains water due to it is high hygroscopic property. The 10522
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(5) Wang, Y. C.; Zhang, L.; Wang, Q. W.; Zhang, D. R. Recent advances in the nanotechnology-based drug delivery of silybin. J. Biomed. Nanotechnol. 2014, 10 (4), 543. (6) Xiao, Y. Y.; Song, Y. M.; Chen, Z. P.; Ping, Q. N. The preparation of silybin−phospholipid complex and the study on its pharmacokinetics in rats. Int. J. Pharm. 2006, 307 (1), 77. (7) El-Samaligy, M. S.; Afifi, N. N.; Mahmoud, E. A. Increasing bioavailability of silymarin using a buccal liposomal delivery system: preparation and experimental design investigation. Int. J. Pharm. 2006, 308 (1), 140. (8) Young, T. J.; Johnston, K. P.; Mishima, K.; Tanaka, H. Encapsulation of lysozyme in a biodegradable polymer by precipitation with a vapor-over-liquid antisolvent. J. Pharm. Sci. 1999, 88 (6), 640. (9) Byers, J. E.; Peck, G. E. The effect of mill variables on a granulation milling process. Drug Dev. Ind. Pharm. 1990, 16 (11), 1761. (10) Rubinstein, M. H.; Gould, P. Particle size reduction in the ball mill. Drug Dev. Ind. Pharm. 1987, 13 (1), 81. (11) Broadhead, J.; Edmond, R. S. K.; Rhodes, C. T. The spray drying of pharmaceuticals. Drug Dev. Ind. Pharm. 1992, 18 (11−12), 1169. (12) Nes, E. The effect of a fine particle dispersion on heterogeneous recrystallization. Acta Metall. Sin. 1976, 24 (5), 391. (13) Langer, R.; Chasin, M. Biodegradable Polymers as Drug Delivery Systems. Marcel Dekker: New York, 1990. (14) York, P. Supercritical fluids ease drug delivery. Manuf. Chem. 2000, 71 (6), 26. (15) Charoenchaitrakool, M.; Dehghani, F.; Foster, N. R.; Chan, H. K. Micronization by rapid expansion of supercritical solutions to enhance the dissolution rates of poorly water-soluble pharmaceuticals. Ind. Eng. Chem. Res. 2000, 39 (12), 4794. (16) Domingo, C.; Berends, E.; Van Rosmalen, G. M. Precipitation of ultrafine organic crystals from the rapid expansion of supercritical solutions over a capillary and a frit nozzle. J. Supercrit. Fluids 1997, 10 (1), 39. (17) Debenedetti, P. G.; Tom, J. W.; Kwauk, X.; Yeo, S. D. Rapid expansion of supercritical solutions (RESS): fundamentals and applications. Fluid Phase Equilib. 1993, 82, 311. (18) Domingo, C.; Berends, E.; Van Rosmalen, G. M. Precipitation of ultrafine organic crystals from the rapid expansion of supercritical solutions over a capillary and a frit nozzle. J. Supercrit. Fluids 1997, 10 (1), 39. (19) Reverchon, E.; Della Porta, G.; Di Trolio, A.; Pace, S. Supercritical antisolvent precipitation of nanoparticles of superconductor precursors. Ind. Eng. Chem. Res. 1998, 37, 952. (20) Bleich, J.; Mü ller, B. W. Production of drug loaded microparticles by the use of supercritical gases with the aerosol solvent extraction system (ASES) process. J. Microencapsulation 1996, 13 (2), 131. (21) Meure, L. A.; Warwick, B.; Dehghani, F.; Regtop, L. H.; Foster, R. N. Increasing copper indomethacin solubility by coprecipitation with poly (vinylpyrrolidone) using the aerosol solvent extraction system. Ind. Eng. Chem. Res. 2004, 43 (4), 1103. (22) Tantishaiyakul, V.; Kaewnopparat, N.; Ingkatawornwong, S. Properties of solid dispersions of piroxicam in polyvinylpyrrolidone. Int. J. Pharm. 1999, 181 (2), 143. (23) Doherty, C.; York, P. Mechanisms of dissolution of frusemide/ PVP solid dispersions. Int. J. Pharm. 1987, 34 (3), 197. (24) Stupak, E. I.; Bates, T. R. Enhanced absorption and dissolution of reserpine from reserpine-poly(vinylpyrrolidinone) coprecipitates. J. Pharm. Sci. 1972, 61 (3), 400. (25) Badawi, A. A.; El-Sayed, A. A. Dissolution studies of povidonesulfathiazole coacervated systems. J. Pharm. Sci. 1980, 69 (5), 492. (26) Stupak, E. I.; Bates, T. R. Enhanced absorption of digitoxin from orally administered digitoxin-poly(vinylpyrrolidinone) coprecipitates. J. Pharm. Sci. 1973, 62 (11), 1806. (27) Kearney, A. S.; Gabriel, D. L.; Mehta, S. C.; Radebaugh, G. W. Effect of polyvinylpyrrolidone on the crystallinity and dissolution rate
Figure 9. Dissolution profile of raw SLB, MicroSLB, NanoSLB-A, NanoSLB-C, and the physical mixture (50:50).
insoluble drugs. Therefore, using the ASES process with a hydrophilic polymer as the excipient is an effective way to improve the solubility and bioavailability of water-insoluble drugs.
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CONCLUSIONS In this study, we have demonstrated the synthesis of SLB/PVP nanodrugs by the ASES process. It is evident that the chemical structure of the SLB was not changed in the ASES process, and after addition of PVP polymer as the excipient, small and lowcrystallinity NanoSLB was successfully achieved owing to PVP effectively preventing the growth and aggregation of drug nanoparticles. The NanoSLB exhibits an extremely excellent dissolution property and bioavailability, as well as a good dispersibility in the aqueous phase. Moreover, we believe that such a synthesis strategy is not limited to SLB; it can be adapted to a variety of poorly water-soluble drugs for therapeutic applications.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was financially supported by the National Science Foundation of China (Grant 51303009) and the National 863 Program of China (Grant 2013AA032201).
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REFERENCES
(1) Theodosiou, E.; Purchartova, K.; Stamatis, H.; Kolisis, F.; Kren, V. Bioavailability of silymarin flavonolignans: drug formulations and biotransformation. Phytochem. Rev. 2013, 13, 1. (2) Kvasnicka, F.; Biba, B.; Sevcik, R.; Voldrich, M.; Kratka, J. Analysis of the active components of silymarin. J. Chromatogr., A 2003, 990, 239. (3) Flora, K.; Hahn, M.; Rosen, H.; Banner, K. Milk thistle (Silybum marianum) for the therapy of liver disease. Am. J. Gastroenterol. 1998, 93, 139. (4) Kren, V.; Marhol, P.; Purchartova, K.; Gabrielova, E.; Modriansky, M. Biotransformation of silybin and its congeners. Curr. Drug Metab. 2013, 14 (10), 1009. 10523
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of solid dispersions of the antiinflammatory CI-987. Int. J. Pharm. 1994, 104 (2), 169. (28) Yao, W. W.; Bai, T. C.; Zhu, J. P.; Zhu, C. W.; Hu, J.; Zhang, H. L. Thermodynamic properties for the system of silybin and poly(ethylene glycol) 6000. Thermochim. Acta 2005, 437, 17. (29) Ma, Y.; Li, W. Z.; Gu, J. H. Preparation and evaluation of the solid dispersions of poorly soluble silybin. J. Chin. Pharm. Sci. 2011, 20, 604. (30) Wang, J. X.; Zhang, Z. B.; Le, Y.; Zhao, H.; Chen, J. F. A novel strategy to produce highly stable and transparent aqueous ‘nanosolutions’ of water-insoluble drug molecules. Nanotechnology 2011, 22, 305101. (31) Sethia, S.; Squillante, E. Solid dispersion of carbamazepine in PVP K30 by conventional solvent evaporation and supercritical methods. Int. J. Pharm. 2004, 272, 1. (32) Lindfors, L.; Skantze, P.; Skantze, U.; Westergren, J.; Olsson, U. Amorphous drug nanosuspensions. 3. Particle dissolution and crystal growth. Langmuir 2007, 23, 9866.
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