Particle Production of Steroid Drugs Using Supercritical Fluid Processing

Micronization and Polymorphic Conversion of Tolbutamide and Barbital by Rapid Expansion of Supercritical Solutions

Rapid expansion of supercritical solutions (RESS) was applied to tolbutamide and barbital. The solubility in supercritical CO2 was determined to estimate the extraction efficiency roughly by a simple method and accurately by a direct spectrophotometric technique. The latter revealed that the solubility of tolbutamide was a function of applied pressure and temperature and was proportional to the pressure. No significant difference in solubility between polymorphic Forms I and II of tolbutamide was detected. Tolbutamide and barbital particles produced by the RESS were characterized by size distribution measurement, polymorph identification and morphological evaluation. Significant size reduction to micron or sub-micron level with narrow size distribution was achieved, while conventional mechanical grinding had only slight effect. The particle size was greatly affected by both extraction and expansion conditions. The lower the extraction temperature was, the smaller was the mean particle size. Higher extraction pressure resulted in smaller mean particle size when compared at the same extraction temperature. The mean particle size was reduced by lowering the spray nozzle temperature, by lowering the expansion chamber temperature, by increasing the CO2 amount per spray, and by increasing the exhaust gas flow rate. The RESS processing realized the polymorphic conversion as well. As for tolbutamide, three polymorphs (Forms I, II, and IV) out of four could be produced by changing the extraction conditions, and in the case of barbital, one polymorph (Form II) out of three was produced consistently.

The formation of fluorinated tetraphenylporphyrin nanoparticles via rapid expansion processes: RESS vs RESOLV

Organic nanoparticles of a fluorinated tetraphenylporphyrin (TBTPP) were produced by rapid expansion of supercritical CO(2) solutions into both air (RESS) and an aqueous receiving solution containing a stabilizing agent (RESOLV). The effect of processing conditions on both particle size and form was investigated. The size of the porphyrin nanoparticles produced via RESS increased in a well-behaved manner from 40 to 80 nm as the preexpansion temperature increased from 40 to 100 degrees C, independent of porphyrin concentration, degree of saturation, and preexpansion pressure. RESOLV of TBTPP + CO(2) solutions was investigated both for minimizing particle growth in the free jet and for the prevention of particle agglomeration. Anionic, nonionic, and polymeric stabilizing agents for the aqueous receiving solution were considered. Expansion into a 0.05 wt % SDS solution produced nanorods 50-100 nm in diameter with an aspect ratio of 3-5. RESOLV in a 0.025 wt % Pluronic F68 solution produced well-dispersed, individual, spherical nanoparticles averaging 23 +/- 10 to 32 +/- 10 nm in diameter, independent of the rapid expansion processing conditions selected. Furthermore, the resulting nanoparticle suspensions were stable, with particle sizes remaining unchanged after several months. However, some particle agglomeration occurred at higher (i.e., 1 wt % TBTPP in CO(2)) concentrations. Contact-angle measurements on solid TBTPP compacts with the tested receiving solutions indicate that a moderate wetting agent such as Pluronic F68 is most effective for preserving the size and form of the porphyrin nanoparticles produced by RESOLV. Finally, the fact that nanoparticles are produced from RESS of TBTPP, in contrast with other organics for which microparticles are produced, can be explained in terms of the high melting point of TBTPP (388 degrees C), which results in a solid-state diffusion coefficient of TBTPP low enough so that particle coalescence is significantly reduced in the free jet.

Preparation of uniform prednisolone microcrystals by a controlled microprecipitation method

Prednisolone (PDL) microcrystals were successfully prepared by a controlled microprecipitation method. The characterization of PDL microcrystals by SEM and PSD indicated that the hexagonal and tetragonal PDL microcrystals with an average particle size of 1.60 and 1.46 microm could be prepared under a stirring speed of 10,000 rpm at 14 and 4 degrees C, respectively. The morphology and the particle size of PDL could be well controlled, from 1.60 to 6.12 microm for hexagonal microcrystals and 1.46 to 3.90 microm for tetragonal ones, by altering the operating parameters such as temperature, stirring speed and stabilizers. The XRD, TGA-DSC, FT-IR and physical stability studies demonstrated that the as-prepared hexagonal and tetragonal PDL microcrystals with the same pseudopolymorphic form were much more stable in water than the commercial micronized PDL with another crystal form. The dissolution tests showed that the hexagonal and tetragonal PDL microcrystals exhibited significantly enhanced dissolution property when compared to commercial micronized PDL.

Formation and characterization of porous indomethacin-PVP coprecipitates prepared using solvent-free supercritical fluid processing

Supercritical carbon dioxide (sc-CO2) was used to prepare coprecipitates of indomethacin (IM) and poly(vinylpyrrolidone) (PVP) with the aim to improve the dissolution rate of IM. The coprecipitates of IM and PVP at various proportions were prepared using a stirred batch reactor containing sc-CO2 as a gas saturated solution (i.e., the compressible CO2 is dissolved in the molten compound). Temperatures between 40 and 90 degrees C and pressure of 150 or 200 bar were employed. The coprecipitates prepared at 75 degrees C and 150 bar were characterized using differential scanning calorimetry (DSC), powder X-ray diffraction (PXD), scanning electron microscopy (SEM), and dissolution testing. The results suggested that IM was totally amorphous at PVP weight fraction of 0.80 and above (indeed, as a molecular composite in which the drug molecules interact with the polymer backbone). As the PVP weight fraction decreased, IM displayed an increasing amount of crystalline material. The SEM photographs of coprecipitates showed a foamed and porous structure. The dissolution rate of IM was increased by incorporation of PVP. IM and PVP at various weight fractions exhibited comparatively higher dissolution rates than that of crystalline IM alone. The sc-CO2 based process produced a solvent free, completely amorphous porous IM solid dispersion with a rapid dissolution rate.

Polymeric Nanoparticles from Rapid Expansion of Supercritical Fluid Solution

In this concept paper we highlight applications of supercritical fluid technology in particle formation and production, especially some recent advances in the rapid expansion of supercritical solutions (RESS) processing technique. We also highlight the simple but significant modification to the traditional RESS by using a liquid solvent or solution at the receiving end of the supercritical solution expansion, or the rapid expansion of a supercritical solution into a liquid solvent (RESOLV), and applications of the technique to the preparation of nanoparticles. In particular, successes and challenges in the use of RESOLV for nanoscale (<100 nm) polymeric particles and the subsequent protection of the suspended nanoparticles from agglomeration are discussed.

Micronization of Phenylbutazone by Rapid Expansion of Supercritical CO2 Solution

Rapid expansion of supercritical solutions (RESS) technique was applied for the preparation of phenylbutazone fine particles. The operating temperature and pressure affected the yield of the drug fine particles, which was evaluated by dissolving the sprayed product of drug into ethanol. Effect of pre- and post-expansion conditions on the particle size distribution of phenylbutazone was investigated and the smallest sample (mean particle size: 1.59 microm) was obtained when the RESS method was operated at a pressure of 26 MPa combined with a temperature of 32 degrees C. Physicochemical properties of the fine particles were investigated by powder X-ray diffraction and differential scanning calorimetry. It was found that the phenylbutazone fine particles obtained were meta-stable beta form under the experimental conditions tested, suggesting polymorphic transformation during the RESS process.

Phospholipid-stabilized nanoparticles of cyclosporine A by rapid expansion from supercritical to aqueous solution

The purpose of this research was to form stable suspensions of submicron particles of cyclosporine A, a water-insoluble drug, by rapid expansion from supercritical to aqueous solution (RESAS). A solution of cyclosporine A in CO2 was expanded into an aqueous solution containing phospholipid vesicles mixed with nonionic surfactants to provide stabilization against particle growth resulting from collisions in the expanding jet. The products were evaluated by measuring drug loading with high performance liquid chromatography (HPLC), particle sizing by dynamic light scattering (DLS), and particle morphology by transmission electron microscopy (TEM) and x-ray diffraction. The ability of the surfactant molecules to orient at the surface of the particles and provide steric stabilization could be manipulated by changing process variables including temperature and suspension concentration. Suspensions with high payloads (up to 54 mg/mL) could be achieved with a mean diameter of 500 nm and particle size distribution ranging from 40 to 920 nm. This size range is several hundred nanometers smaller than that produced by RESAS for particles stabilized by Tween 80 alone. The high drug payloads (approximately 10 times greater than the equilibrium solubility), the small particle sizes, and the long-term stability make this process attractive for development.

Preparation of cyclosporine A nanoparticles by evaporative precipitation into aqueous solution

Amorphous nanoparticle suspensions of a poorly water-soluble drug, cyclosporine A, are produced by a new process, evaporative precipitation into aqueous solution (EPAS). The rapid evaporation of a heated organic solution of the drug, which is atomized into an aqueous solution, results in fast nucleation leading to nanoparticles suspensions. Hydrophilic stabilizers, introduced in the organic or aqueous phases, limit particle growth and inhibit crystallization for drug concentrations as high as 35 mg/ml, and drug/surfactant ratios up to 1.0. The suspensions may be used in parenteral formulations to enhance bioavailability or may be dried to produce oral dosage forms with the potential for high dissolution rates due to the low crystallinity, small particle size and hydrophilic stabilizer that enhances wetting.

Spectroscopy of polymer/drug formulations processed with supercritical fluids: in situ ATR-IR and Raman study of impregnation of ibuprofen into PVP

In situ ATR (attenuated total reflectance)-IR spectroscopy has been used to study poly(vinylpyrrolidone) (PVP) films subjected to a solution of ibuprofen in supercritical CO2. The process of impregnation of ibuprofen into PVP has been monitored in situ. It has been shown that the supercritical fluid impregnation process results in ibuprofen being molecularly dispersed in a polymer matrix with ibuprofen molecules interacting with the C=O group of PVP. Raman spectra of ibuprofen impregnated into PVP from supercritical fluid solution have also been measured and compared with the Raman spectra of crystalline ibuprofen. ATR-IR spectroscopy has also revealed specific interactions between the C=O groups of PVP and CO2. Impregnation of ibuprofen into PVP makes the C=O groups of PVP less available for interactions with CO2. It has also been demonstrated that the presence of ibuprofen in PVP also affects sorption of water into PVP.

Encapsulation of lysozyme in a biodegradable polymer by precipitation with a vapor-over-liquid antisolvent

Lysozyme was encapsulated in biodegradable polymer microspheres which were precipitated from an organic solution by spraying the solution into carbon dioxide. The polymer, either poly(l-lactide) (l-PLA) or poly(DL-lactide-co-glycolide) (PGLA), in dichloromethane solution with suspended lysozyme was sprayed into a CO2 vapor phase through a capillary nozzle to form droplets which solidified after falling into a CO2 liquid phase. By delaying precipitation in the vapor phase, the primary particles became sufficiently large, from 5 to 70 microm, such that they could encapsulate the lysozyme. At an optimal temperature of -20 degrees C, the polymer solution mixed rapidly with CO2, and the precipitated primary particles were sufficiently hard such that agglomeration was markedly reduced compared with higher temperatures. More uniform particles were formed by flowing CO2 at high velocity in a coaxial nozzle to mix the droplets at the CO2 vapor-liquid interface. This process offers a means to produce encapsulated proteins in poly(DL-lactide-co-glycolide) microspheres without earlier limitations of massive polymer agglomeration and limited protein solubility in organic solvents.