Formation and characterization of solid dispersions of piroxicam and polyvinylpyrrolidone using spray drying and precipitation with compressed antisolvent

Solid dispersions of a poorly water-soluble drug piroxicam in polyvinylpyrrolidone (PVP) were prepared by precipitation with compressed antisolvent (PCA) and spray drying techniques. Physicochemical properties of the products and drug-polymer interactions were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry, etc. Piroxicam was found amorphously dispersed in both solid dispersion systems with the drug to polymer weight ratio of 1:4. Spectra data indicated the formation of hydrogen bonding between the drug and the polymer. Both techniques evaluated in this work resulted in improved dissolution of piroxicam. By comparison, PCA-processed solid dispersions showed distinctly superior performance in that piroxicam dissolved completely within the first 5 min and the dissolution rate was at least 20 times faster than raw drug did within the first 15 min. PCA processing could provide an effective pharmaceutical formulation technology to improve the bioavailability of poorly water-soluble drug.     

Physical stabilisation of amorphous ketoconazole in solid dispersions with polyvinylpyrrolidone K25.

The glass forming properties of ketoconazole were investigated using differential scanning calorimetry (DSC), by quench cooling liquid ketoconazole from T(m)+10 to 273.1 K, followed by subsequent heating at 5 K/min to T(m)+10 K. It was shown that liquid ketoconazole forms a glass which did not recrystallise following reheating, indicating its stability; T(g) was found to be 317.5+/-0.3 K. However, the presence of a small amount of crystalline ketoconazole was able to convert the amorphous drug back to the crystalline state: the addition of only 4.1% (w/w) of crystalline material converted 77.1% of the glass back to the crystalline state, and this value increased as the amount of added crystals increased. PVP K25 was found to be highly effective in the prevention of such recrystallisation, but only if the amorphous drug was formulated in a solid dispersion, since physical mixing of amorphous ketoconazole with the polymer resulted in recrystallisation of the former compound. Storage of the solid dispersions for 30 days at 298.1 K (both 0 and 52% RH) in the presence or absence of crystals did not result in recrystallisation of the amorphous drug. Solid dispersions formed compatible blends as one single T(g) was observed, which gradually increased with increasing amounts of PVP K25, indicating the anti-plasticising property of the polymer. The values of T(g) followed the Gordon-Taylor equation, indicating no significant deviation from ideality and suggesting the absence of strong and specific drug-polymer interactions, which was further confirmed with 13C NMR and FT-IR. It can be concluded therefore that the physical mechanism of the protective effect is not caused by drug-polymer interactions but due to the polymer anti-plasticising effect, thereby increasing the viscosity of the binary system and decreasing the diffusion of drug molecules necessary to form a lattice.     

Characterization and solubility study of solid dispersions of flunarizine and polyvinylpyrrolidone

Flunarizine is a selective calcium entry blocker poorly water-soluble. In this report, the interactions of this drug with polyvinylpyrrolidone in solid dispersions, prepared according to the dissolution method using methanol as the solvent, have been investigated. For purposes of comparison physical mixtures were prepared by simple mixture and homogeneization of the two pulverized components. Combinations of flunarizine/polyvinylpyrrolidone of the following percentage proportions were prepared: 10/90, 20/80, 30/70, 40/60, 50/50, 60/40 and 80/20 (mean particle size of 0.175 mm). The physicochemical properties of solid dispersions were investigated with X-ray diffraction, infrared spectroscopy, differential scanning calorimetry and solubility in equilibrium. X-ray patterns and differential scanning calorimetry have shown that polyvinylpyrrolidone inhibits the crystallization of flunarizine when percentages drug/polymer are 10/90, 20/80 and 30/70. The infrared spectra suggest that there was no chemical interaction between flunarizine and polyvinylpyrrolidone. Equilibrium solubility studies showed that drug solubility was enhanced as the polymer content increased. In general, the solubility increase was greater in solid dispersions than in physical mixtures and the solubility in equilibrium for solid dispersions and physical mixtures at the same drug/polymer proportion showed significant differences (P < 0.05).     

Solid dispersions of dihydroartemisinin in polyvinylpyrrolidone

In the present study the physicochemical characteristics of dihydroartemisinin, polyvinylpyrrolidone and their solid dispersions were evaluated at various proportions of drug and polyvinylpyrrolidone. These properties were investigated with X-ray diffraction, fourier transform infrared spectrophotometry, differential scanning calorimetry, equilibrium solubility at twenty five and thirty seven degree centigrade. X-ray diffraction analysis detected that dihydroartemisinin became more amorphous as drug carrier ratio was enhanced in solid dispersions. Fourier transform infrared spectra suggested that there was a hydrogen bonding interaction between dihydroartemisinin and polyvinylpyrrolidone in all solid dispersions. These interactions reflected the changes in crystalline structures of dihydroartemisinin. The thermal behavior of dihydroartemisinin was unusual as it exhibited melting exotherm instead of endotherm. In solid dispersions containing varying contents of polyvinylpyrrolidone, enthalpy change and peak area were enhanced while melting onset temperature decreased with increase in polyvinylpyrrolidone proportion. This was attributed to a solid-state interaction. Equilibrium solubility of dihydroartemisinin increased sixty-fold due to induction of polyvinylpyrrolidone. When this solubility was compared among thirty-seven and twenty five degree centigrade in solid dispersions, it was up to seven times more at higher temperature. Physicochemical characteristics of solid dispersions containing drug carrier ratio of one: nine prepared in acetonitrile, ethanol, methanol and tetrahydrofuran showed differences which indicated that properties of medium i.e. dielectric constant, dipole moment and structure, influenced the amount of amorphousness and related properties of dihydroartemisinin.     

Solid state properties of pure UC-781 and solid dispersions with polyvinylpyrrolidone (PVP K30)

The purpose of this study was to elucidate the physical structure of solid dispersions of the antiviral agent UC-781 (N-[4-chloro-3-(3-methyl-2-butenyloxy)phenyl]-2-methyl-3-furancarbothioamide) with polyvinylpyrrolidone (PVP K30). Solid dispersions were prepared by coevaporating UC-781 with PVP K30 from dichloromethane. The physicochemical properties of the dispersions were evaluated in comparison with the physical mixtures by differential scanning calorimetry (DSC), X-ray powder diffraction, and FT-IR spectroscopy. We investigated the single crystal structure of pure UC-781. The data from single crystal analysis showed that UC-781 crystallized with orthorhombic symmetry in the space group Pcab. Its cell parameters were found to be; a = 8.1556(7) A,b = 17.658(2) A and c = 23.609(2) A; the unit cell was made up of eight molecules of UC-781. The molecules formed intermolecular hydrogen bonds between NH and thio groups, and were packed in a herringbone-like structure. The data from X-ray powder diffraction showed that crystalline UC-781 was changed into the amorphous state by co-evaporating it with PVP K30. From differential scanning calorimetry analysis, UC-781 peaks were observed in the DSC curves of all physical mixtures, while no peaks corresponding to the drug could be observed in the solid dispersions with the same drug composition up to the concentration of 50% w/w. The data from FT-IR spectroscopy showed the distortions and disappearance of some bands from the drug, while other bands were too broad or significantly less intense compared with the physical mixtures of the crystalline drug in PVP K30. Furthermore, the results from IR spectroscopy demonstrated that UC-781 interacted with PVP K30 in solid dispersions through intermolecular H-bonding.     

Physicochemical characterization and dissolution study of solid dispersions of Lovastatin with polyethylene glycol 4000 and polyvinylpyrrolidone K30

Solid dispersions in water-soluble carriers have attracted considerable interest as a means of improving the dissolution rate, and hence possibly bioavailability, of a range of hydrophobic drugs. The aim of the present study was to improve the solubility and dissolution rate of a poorly water-soluble drug, Lovastatin, by a solid dispersion technique. Solid dispersions were prepared by using polyethylene glycol 4000 (PEG 4000) and polyvinylpyrrolidone K30 (PVP K30) in different drug-to-carrier ratios. Dispersions with PEG 4000 were prepared by fusion-cooling and solvent evaporation, whereas dispersions containing PVP K30 were prepared by solvent evaporation technique. These new formulations were characterized in the liquid state by phase solubility studies and in the solid state by differential scanning calorimetry, X-ray powder diffraction, and FT-IR spectroscopy. The aqueous solubility of Lovastatin was favored by the presence of both polymers. The negative values of the Gibbs free energy and enthalpy of transfer explained the spontaneous transfer from pure water to the aqueous polymer environment. Solid-state characterization indicated Lovastatin was present as amorphous material and entrapped in polymer matrix. In contrast to the very slow dissolution rate of pure Lovastatin, the dispersion of the drug in the polymers considerably enhanced the dissolution rate. This can be attributed to improved wettability and dispersibility, as well as decrease of the crystalline and increase of the amorphous fraction of the drug. Solid dispersion prepared with PVP showed the highest improvement in wettability and dissolution rate of Lovastatin. Even physical mixture of Lovastatin prepared with both polymers also showed better dissolution profile than that of pure Lovastatin. Tablets containing solid dispersion prepared with PEG and PVP showed significant improvement in the release profile Lovastatin compared with tablets containing Lovastatin without PEG or PVP.     

Stability of extruded 17 beta-estradiol solid dispersions.

Recrystallization is one of the main problems concerning the stability of solid dispersions. Different analytical methods were applied showing that no recrystallization occurred after treating melt extruded solid dispersions with 17 beta-Estradiol as the model drug with heat or water vapor. A skillful choice of excipients--a combination of polymers and additives--could be the reason for improving the stability. The requirements of the USP 23 for Estradiol tablets of 75% dissolved drug after 60 min were fulfilled after storing the tablets for 6 months at 40 degrees C/75% RH. By observing the change in glass transition temperature, DSC analysis showed that the solid dispersions were stable against thermal stress. Isothermal microcalorimetry as well as moisture absorption gravimetry were methods to prove the stability of the solid dispersions against water vapor.     

Solid dispersions in pharmaceutical technology. Part I. Classification and methods to obtain solid dispersions

There are many methods to increase solubility of a substance. These include, inter alia, preparation of solid dispersions, i.e. eutectic mixtures, solid solutions, glassy solutions and suspensions. When compared to the individual constituents prior to dispersion formation solid dispersion components are better soluble in water. Therefore, solid solutions became one of the most promising ways to modify solubility, ensuring improved bioavailability and consequently therapeutic efficacy of a substance. In this part of the publication solid dispersions were classified and described in regard to their properties and preparation methods, i.e. melting method, melt evaporation and melt extrusion methods, lyophilisation technique, melt agglomeration process as well as SCF technology and electrospinning.     

Characteristics of rofecoxib-polyethylene glycol 4000 solid dispersions and tablets based on solid dispersions

The aim of this work was to report the properties of rofecoxib-PEG 4000 solid dispersions and tablets prepared using rofecoxib solid dispersions. Rofecoxib is a poorly water soluble nonsteroidal anti-inflammatory drug with a poor dissolution profile. This work investigated the possibility of developing rofecoxib tablets, allowing fast, reproducible, and complete rofecoxib dissolution, by using rofecoxib solid dispersion in polyethylene glycol (PEG) 4000. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the solid state of solid dispersions. The effect of PEG 4000 concentration on the dissolution rate of rofecoxib from its solid dispersions was investigated. The dissolution rate of rofecoxib from its solid dispersions increased with an increasing amount of PEG 4000. The extent of dissolution rate enhancement was estimated by calculating the mean dissolution time (MDT) values. The MDT of rofecoxib decreased significantly after preparing its solid dispersions with PEG 4000. The FTIR spectroscopic studies showed the stability of rofecoxib and absence of well-defined rofecoxib-PEG 4000 interaction. The DSC and XRD studies indicated the amorphous state of rofecoxib in solid dispersions of rofecoxib with PEG 4000. SEM pictures showed the formation of effective solid dispersions of rofecoxib with PEG 4000 since well-defined change in the surface nature of rofecoxib and solid dispersions were observed. Solid dispersions formulation with highest drug dissolution rate (rofecoxib: PEG 4000 1:10 ratio) was used for the preparation of solid dispersion-based rofecoxib tablets by the direct compression method. Solid dispersion-based rofecoxib tablets obtained by direct compression, with a hardness of 8.1 Kp exhibited rapid drug dissolution and produced quick anti-inflammatory activity when compared to conventional tablets containing pure rofecoxib at the same drug dosage. This indicated that the improved dissolution rate and quick anti-inflammatory activity of rofecoxib can be obtained from its solid dispersion-based oral tablets.     

(噁)丙嗪固体分散体的制备

目的:制备噁丙嗪固体分散体.方法:以聚乙二醇(PEG 6000)为载体,采用熔融法制备噁丙嗪固体分散体,桨法测定体外溶出度,X-射线衍射法分析结构状态.结果:噁丙嗪-PEG 6000固体分散体是一种简单低共熔混合物,噁丙嗪以超细结晶状态分散在PEG载体中.1:5,1:7,1:9,1:11比例固体分散体的标示含量均在98%～106%范围.与原料药及物理混合物相比,固体分散体的溶出速度和程度均显著增加(P＜0.01);且随着载体比例的逐渐增大,固体分散体的药物溶出加快.结论:以PEG 6000为载体制备的噁丙嗪固体分散体体外溶出迅速,可用于制备速效、高效的噁丙嗪口服制剂.     

Characterization of nifedipine solid dispersions

The sublingual administration of nifedipine (NIF) is currently used in clinical practice. The sublingual administration of NIF solid dispersions (SD), by using a suitable dispenser, appears an interesting approach in the treatment of moderate and severe hypertensive emergencies. With this aim nine SD made of NIF and a low viscosity hydroxypropylmethylcellulose (HPMC) in different ratio were prepared by means of spray-drying technique and their structure was studied. Moreover, the drug dissolution properties from SD were verified. The characteristic peaks of crystalline NIF were not detectable by using the X-ray analysis when the NIF/HPMC ratios were lower than 50/50 w/w. In thermograms obtained from SD, the NIF melting endothermic peak disappeared when NIF/HPMC ratios were lower than 30/70 w/w; the experimental Tg values of SD were lower than the Tg values predicted by Gordon Taylor equation suggesting some type of non-ideality of mixing. In the SD FTIR spectra the NH stretching vibrations and the C=O stretch in esteric groups of NIF shift to free NH and C=O regions indicating the rupture of intermolecular hydrogen bond in the crystalline structure of NIF. The prepared SD improved the NIF dissolution rate in comparison with that of commercial NIF or NIF/HPMC physical mixtures. Moreover, the concentration of NIF in the dissolution medium increased decreasing the NIF content.     

Dissolution rate of p-aminobenzoates from solid xylitol dispersions.

Xylitol was studied as a carrier in solid dispersions because of its low melting point and stability up to 180 degrees. It is more stable than sucrose and does not enter into Maillard reactions. Solid dispersions were prepared from esters of p-aminobenzoic acid and xylitol by the melting method and were compressed into tablets. The p-aminobenzoate dissolution rates were determined by a modified beaker method. The increase in the dissolution rates was greatest at the lowest drug levels. When the dispersion drug content exceeded 20-30%, the dissolution rate per unit area remained nearly constant. In the latter case, the increase in the dissolution rate was primarily due to an increase in area. When the carbon chain length was increased in the homologous series, the dissolution rate from the xylitol dispersions showed a nearly linear decrease.     

A comparison of spray drying and milling in the production of amorphous dispersions of sulfathiazole/polyvinylpyrrolidone and sulfadimidine/polyvinylpyrrolidone

Formulations containing amorphous active pharmaceutical ingredients (APIs) present great potential to overcome problems of limited bioavailability of poorly soluble APIs. In this paper, we directly compare for the first time spray drying and milling as methods to produce amorphous dispersions for two binary systems (poorly soluble API)/excipient: sulfathiazole (STZ)/polyvinylpyrrolidone (PVP) and sulfadimidine (SDM)/PVP. The coprocessed mixtures were characterized by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and intrinsic dissolution tests. PXRD and DSC confirmed that homogeneous glassy solutions (mixture with a single glass transition) of STZ/PVP were obtained for 0.05 ≤ X(PVP) (PVP weight fraction) < 1 by spray drying and for 0.6 ≤ X(PVP) < 1 by milling (at 400 rpm), and homogeneous glassy solutions of SDM/PVP were obtained for 0 < X(PVP) < 1 by spray drying and for 0.7 ≤ X(PVP) < 1 by milling. For these amorphous composites, the value of T(g) for a particular API/PVP ratio did not depend on the processing technique used. Variation of T(g) versus concentration of PVP was monotonic for all the systems and matched values predicted by the Gordon-Taylor equation indicating that there are no strong interactions between the drugs and PVP. The fact that amorphous SDM can be obtained on spray drying but not amorphous STZ could not be anticipated from the thermodynamic driving force of crystallization, but may be due to the lower molecular mobility of amorphous SDM compared to amorphous STZ. The solubility of the crystalline APIs in PVP was determined and the activities of the two APIs were fitted to the Flory-Huggins model. Comparable values of the Flory-Huggins interaction parameter (χ) were determined for the two systems (χ = -1.8 for SDM, χ = -1.5 for STZ) indicating that the two APIs have similar miscibility with PVP. Zones of stability and instability of the amorphous dispersions as a function of composition and temperature were obtained from the Flory-Huggins theory and the Gordon-Taylor equation and were found to be comparable for the two APIs. Intrinsic dissolution studies in aqueous media revealed that dissolution rates increased in the following order: physical mix of unprocessed materials < physical mix of processed material < coprocessed materials. This last result showed that production of amorphous dispersions by co-milling can significantly enhance the dissolution of poorly soluble drugs to a similar magnitude as co-spray dried systems.     

Stability study of piroxicam and cinnoxicam in solid pharmaceuticals

The pseudo-first order rate constant for the hydrolysis of cinnoxicam as a function of temperature was obtained by variable-temperature kinetic experiments. The method used is on a generalization of non-isothermal analysis, and takes advantage of the capabilities of modern data collection and processing systems. A spectrophotometric method under non isothermal conditions was carried out. The results obtained are identical to those obtained under the same conditions by using traditional constant-temperature kinetic runs. This provides the possibility of reducing the amount of time spent and chemicals usually used in collecting kinetic data in mechanistic studies in solution by an order of magnitude.     

尼群地平固体分散体的休外溶出特性

目的：制备尼群地平固体分散体,增加其溶解度和溶出速度。方法：以聚乙二醇6000（PEG6000）、聚乙二醇4000（PEG4000）、聚乙烯吡咯烷酮（PVPk30)为载体,以溶剂－熔融法和共沉淀法制备尼群地平固体分散体。应用差热分析鉴别药物在载体中的存在状态,同时进行溶解测定和溶出度研究。结果：尼群地平与载体形成了共熔物,药物以微细结晶存在于载体中,载体比例越大,药物溶出越快,溶解度越大,结论：尼群地平与3种载体形成的固体散全在水中的溶解度均有显著增加（P＜0．05）。当尼群地平－载体比例达1：4时,尼群地平从固体分散体中的溶出速度明显大于尼群地平纯药和尼发群地平－载体（1：8）物理混合物（P＜0．05）。3种载体中以PVPK30对尼群地平的溶解度及溶出速度增加最为显著。     

Solubility of erythromycin from solid dispersions

The effect of solid dispersion (SD) formation on the solubility of the antibiotic erythromycin has been studied using the parent substance of erythromycin and its SDs with polyethyleneglycol (PEG-1500), polyvinylpyrrolidone (PVP-10000), and β-cyclodextrin. It is established that SD formation increases the solubility of the antibiotic by a factor of 1.3 – 1.8; the dissolution rate, 1.5 – 2.0. Results using a complex of physical and chemical methods suggest that the increase in erythromycin release from SDs takes place due to a decrease in the degree of crystallinity and the formation of intermolecular complexes.     

Solid-state characterization of nifedipine solid dispersions

The purpose of this study is to characterize the nature and solid-state properties of a solid dispersion system of nifedipine (33.3% w/w) in a polymer matrix consisting of Pluronic F68 (33.3% w/w) and Gelucire 50/13 (33.3% w/w). The nature of nifedipine dispersed in the matrix was studied by powder X-ray diffractometry (PXRD), differential scanning calorimetry (DSC) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The rate and extent of water uptake of the solid dispersion were determined by weight gain. The dissolution rate of nifedipine solid dispersion was determined using Apparatus 2 of USP XXIII (1995). Quantitative PXRD showed that the saturation solubility of nifedipine in the polymer matrix is 2.1-3.0% w/w and indicated an excess of crystalline nifedipine in the solid dispersion. The maximum water uptake by the solid dispersion exposed to 75% RH at 45 degrees C was 3.3 times higher than for the dispersion exposed to 65% RH at 25 degrees C. Over 8 weeks, PXRD and DRIFTS of the nifedipine matrix stored at 25 or 4 degrees C were unchanged, showing constancy of crystallinity and intermolecular interactions. For a given mass of nifedipine (20 mg) and for a given particle size of nifedipine (<850 microm), the initial release rate of nifedipine from the solid dispersion was faster (46.2% of the nifedipine dissolved in 20 min) than that of the pure drug (1.2% of the nifedipine dissolved in 20 min). The results indicate that the nifedipine solid dispersion is physically stable over 8 weeks. Nifedipine is released faster from the solid dispersion than from the pure crystalline drug of the same particle size.     

Phase equilibria and stability characteristics of chlorpropamide-urea solid dispersions.

Physical mixtures and melts of various compositions of chlorpropamide and urea have been prepared. The phase diagrams and the effects of ageing of the systems have been measured by differential scanning calorimetry. The eutectic composition was found to contain 89% w/w chlorpropamide. Greater concentrations of chlorpropamide produced solid solutions of urea in chlorpropamide, whereas solid solution formation did not occur at compositions less than 89%. Melts in the range 50-100% chlorpropamide, which included the eutectic, existed as glass solids. The effect of ageing produced generally an increase in the liquidus peak temperature which was considered to be due to a gradual increase in crystal size.