Dissolution rate enhancement and physicochemical characterization of carbamazepine-poloxamer solid dispersions

This study investigates the potential of poloxamers as solid dispersions (SDs) carriers in improving the dissolution rate of a poorly soluble drug, carbamazepine (CBZ). Solid dispersions were prepared with poloxamer 188 (P188) and poloxamer 407 (P407) by melting method in different drug:carrier ratios (1:1, 1:2 and 1:3). Prepared samples were characterized using differential scanning calorimetry (DSC), hot-stage polarized light microscopy (HSM), powder X-ray diffraction (PXRD) and Fourier transform infrared spectroscopy (FT-IR) to investigate drug physical state within the SDs matrix, possible polymorphic transitions and drug-polymer interactions. The interactions between CBZ molecules and polymeric chains were also evaluated using molecular dynamics simulation (MDS) technique. The most thermodynamically stable polymorphic form III of CBZ was present in all SDs, regardless of the type of poloxamer and drug-to-carrier ratio. The absence of drug-polymer interactions was observed by FT-IR analysis and additionally confirmed by MDS. Formation of persistent hydrogen bond between two CBZ molecules, observed by MDS indicate high tendency of CBZ molecules to aggregate and form crystalline phase within dispersion. P188 exhibit higher efficiency in increasing CBZ dissolution rate due to its more pronounced hydrophilic properties, while increasing poloxamers concentration resulted in decreasing drug release rate, as a consequence of their thermoreversible gelation.     

Dissolution and precipitation behavior of amorphous solid dispersions

Amorphous solid dispersions (ASDs) are widely utilized in the pharmaceutical industry for bioavailability enhancement of low solubility drugs. The important factors governing the dissolution behavior of these systems are still far from adequately understood. As a consequence, it is of interest to investigate the behavior of these systems during the dissolution process. The purpose of this research was twofold. First, the degree of supersaturation generated upon dissolution as a function of drug-polymer composition was investigated. Second, an investigation was conducted to correlate physical behavior upon dissolution with polymer loading. Felodipine and indomethacin were selected as model drugs and hydroxypropylmethylcellulose (HPMC) and polyvinylpyrrolidone (PVP) were used to form the dispersions. Diffusion and nuclear magnetic resonance spectroscopy experiments revealed that the extent of bulk supersaturation generated on dissolution of the ASD did not depend on the drug-polymer ratio. Interestingly, the maximum supersaturation generated was similar to the predicted amorphous solubility advantage. However, dynamic light scattering measurements revealed that particles on the submicron scale were generated during dissolution of the solid dispersions containing 90% polymer, whereas solid dispersions at a 50% polymer loading did not yield these nanoparticles. The nanoparticles were found to result in anomalous concentration measurements when using in situ ultraviolet spectroscopy. The supersaturation generated upon dissolution of the solid dispersions was maintained for biologically relevant timeframes for the HPMC dispersions, whereas PVP appeared to be a less effective crystallization inhibitor.     

Dissolution behaviour of nalidixic acid solid dispersions using water soluble dispersion carriers

The oral bioavailability of nalidixic acid (NA) is low due to its poor solubility and slow dissolution. Solid dispersions of NA containing varying concentrations of polyvinylpyrrolidone (PVP), beta-cyclodextrin (BCD) and sodium starch glycolate (SSG) were prepared by solvent evaporation technique in an attempt to improve dissolution rate of NA. Physical characterization of NA, physical mixtures (PM) and solid dispersions were investigated by a variety of analytical methods including scanning electron microscopy (SEM), infrared (IR) spectroscopy and powder X-ray diffraction (XRD). SEM was useful in the verification of possible nalidixic acid inclusion in the dispersion system by studying its surface and shape characteristics of different samples. IR analysis demonstrated no strong interaction between the drug and the carrier exists in the solid dispersions. The degree of crystallinity of nalidixic acid decreased and also differed with the dispersion systems of different carriers. Disolution studies indicated that the dissolution rate and percent dissolution efficiency (DE) were significantly increased in the solid dispersions compared with drug alone. The relative potency of the carriers to enhance the dissolution rate of nalidixic acid was in the order: BCD > PVP > SSG. The dissolution rate of the drug in the solid dispersions was faster when the ration of the drug to carrier was smaller. F-test suggests that first order model may be used for explaining the kinetics of drug release from all the solid dispersion systems.     

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.     

依托泊苷固体分散体的溶出与大鼠在体肠吸收研究

目的:制备依托泊苷(VP-16)固体分散体,对其在大鼠小肠各部位的吸收进行研究,以期提高口服生物利用度.方法:采用溶剂-熔融法制备VP-16-硬脂酸聚氧烃酯(S-40)或泊洛沙姆188(F68)固体分散体,按中华人民共和国药典2005年版溶出度第二法测定VP-16固体分散体的溶出,以差示扫描量热法(DSC)法和X-射线衍射法鉴定VP-16在体系中的状态,运用大鼠在体肠循环模型,采用HPLC法测定药物浓度,考察药物的吸收.结果:固体分散体中VP-16的溶出比原料药和物理混合物均有显著提高,随着载体质量比增加而增大.DSC图谱显示VP-16的特征峰消失,X-射线衍射图谱显示VP-16的结晶衍射峰消失,药物以无定形或分子状态分散在固体分散体中.VP-16在小肠上半段吸收较好,当载体对药物质量比≥3时,固体分散体在空肠段吸收有显著增加,且VP-16/S-40固体分散体的吸收比VP-16/F68固体分散体的吸收好.结论:S-40和F68两种表面活性剂均能显著提高VP-16的溶出度,并对VP-16在大鼠小肠的吸收有明显促进作用,S-40的吸收促进作用显著大于F68.     

Dissolution properties and in vivo behaviour of triamterene in solid dispersions with polyethylene glycols

The applicability of the solid dispersion technique as a method for enhancing the GI absorption of a drug has been explored in order to procure better dissolution characteristics and better bioavailability for triamterene. The physicochemical characterization of the systems has shown the absence of chemical reaction between the drug and the polymers during the solid dispersion elaboration process (melting carrier method). In vitro release profiles have been studied and quantified in terms of dissolution efficiency over the first 30 min (DE₃₀) and dissolution percentage over the first 30 min (DP₃₀). The results have shown that there were no significant differences between the three polyethylene glycols (PEGs) under test. The in vivo effectiveness of the different preparations was also investigated by means of the urinary volumetric excretion (UVE) — pharmacologie effect — and by the estimation of K_c, t_max, and MRT — pharmacokinetic parameters. At end, an analysis of the relative bioavailabilities between formulations has been performed.     

Dissolution and bioavailability improvement of bioactive apigenin using solid dispersions prepared by different techniques

Apigenin (APG) is a poorly soluble bioactive compound/nutraceutical which shows poor bioavailability upon oral administration. Hence, the objective of this research work was to develop APG solid dispersions (SDs) using different techniques with the expectation to obtain improvement in its in vitro dissolution rate and in vivo bioavailability upon oral administration. Different SDs of APG were prepared by microwave, melted and kneaded technology using pluronic-F127 (PL) as a carrier. Prepared SDs were characterized using “thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infra-red (FTIR) spectrometer, powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM)”. After characterization, prepared SDs of APG were studied for in vitro drug release/dissolution profile and in vivo pharmacokinetic studies. The results of TGA, DSC, FTIR, PXRD and SEM indicated successful formation of APG SDs. In vitro dissolution experiments suggested significant release of APG from all SDs (67.39–84.13%) in comparison with control (32.74%). Optimized SD of APG from each technology was subjected to in vivo pharmacokinetic study in rats. The results indicated significant improvement in oral absorption of APG from SD prepared using microwave and melted technology in comparison with pure drug and commercial capsule. The enhancement in oral bioavailability of APG from microwave SD (319.19%) was 3.19 fold as compared with marketed capsule (100.00%). Significant enhancement in the dissolution rate and oral absorption of APG from SD suggested that developed SD systems can be successfully used for oral drug delivery system of APG.     

Some factors influencing dissolution from salicylic acid-urea solid dispersions.

Solid dispersion systems of salicylic acid-urea have been prepared using a fusion method. Two different methods of cooling the melt were employed, rapid cooling in liquid nitrogen and slow cooling in air. Differential scanning calorimetry and an X-ray diffraction technique were employed to investigate the nature of the fused mixture. Evidence was found of compound formation between the constituents. Dissolution rates of drug from non-disintegrating discs of solid dispersion systems were measured. Rapid cooling of the melt resulted in a much faster drug dissolution rate than from a corresponding mixture prepared by a slow cooling method. This phenomenon is explained by a difference in the sizes of drug particles produced under the different cooling conditions. Rapid cooling favoured the generation of many nucleation sites for the solid drug particles as the liquid was cooled, and hence many small particles were obtained. Conversely, slow cooling favoured the growth of the first few nuclei or solid drug particles, rather than the production of new nuclei, and hence large drug particles were obtained.     

Enhancement of dissolution rate of rofecoxib using solid dispersions with urea

The aim of this study was to enhance the dissolution rate of rofecoxib using solid dispersions (SDs) with urea. In preliminary studies, the solubility behavior of rofecoxib in the presence of polyethylene glycol (PEG)‐4000, polyvinylpyrrolidone (PVP) K30, mannitol, and urea in water was obtained at 37°C to choose an effective carrier for preparing its SDs. A systematic increase in the solubility behavior of rofecoxib was observed with increasing concentrations of these carriers in water except mannitol. The Gibbs free energy (ΔG) values were negative indicating the spontaneous nature of rofecoxib solubilization, and it decreased with increases in concentration, demonstrating that the reaction became more favorable as the concentration of these carriers increased. Since, urea exhibited higher solubilizing power than the other carriers, SDs of rofecoxib with urea were prepared at 1:1, 1:2, 1:5, and 1:10 (rofecoxib:urea) ratios by the fusion method. Evaluation of the properties of the SDs was performed using dissolution studies, fourier‐transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), X‐Ray diffraction (XRD), and scanning electron microscopy (SEM). The dissolution rate of rofecoxib was enhanced rapid by its SDs with urea and increased with increasing concentrations of urea in SDs. The mean dissolution time (MDT) of rofecoxib decreased after preparation of SDs and physical mixtures with urea. FTIR spectroscopic studies showed the stability of rofecoxib and the absence of a well‐defined rofecoxib‐urea interaction. DSC and XRD studies confirmed the amorphous state of rofecoxib in SDs of rofecoxib with urea. SEM pictures showed the formation of effective SDs of rofecoxib with urea since well‐defined changes in the surface nature of rofecoxib, SDs, and physical mixture were observed. Drug Dev Res 63:181–189, (2004). © 2004 Wiley‐Liss, Inc.     

The influence of beta-cyclodextrin on the solubility and dissolution rate of paracetamol solid dispersions.

The effect of cyclodextrin (beta-CD) on the solubility and dissolution rate of various paracetamol dispersion powders (1:1 w/w), and tablets was studied. Lower solubility was exhibited by a spray dried solid dispersion made from paracetamol-Ethocel-Macrogol 6000 (95:2:3). The improvement in solubility was influenced by complexation with beta-CD and the crystalline nature of the powder products made by different procedures. The difference in crystallinity was confirmed by X-ray powder diffraction patterns. The dissolution rate of paracetamol from tablets made from the solid dispersions was satisfactory compared with paracetamol alone. The differences between the dissolution rate from the examined paracetamol tablets resulted from the different solubility of each powder and from the structural changes of particles which influenced the consolidation of the tablet mass.     

Dissolution properties and anticonvulsant activity of phenytoin-polyethylene glycol 6000 and -polyvinylpyrrolidone K-30 solid dispersions

The purpose of the present study was to investigate the effects of molecular weight (MW) of polyvinylpyrrolidone (PVP) on glass transition and crystallization of sucrose. Thus, sucrose was co-lyophilized with 2.5 and 5.0% w/w PVP of different molecular weights, which were characterized using gel permeation chromatography. Freeze drying was carried out for 48 h at a shelf temperature of -40 degrees C and a pressure of about 36 Pa. The samples were then dried in a vacuum oven at 24 degrees C for 12 h before drying for a further 12 h at 40 degrees C. Differential scanning calorimetry (DSC) was employed to measure the glass transition temperature (Tg), dynamic crystallization temperature (Tc) and isothermal crystallization induction time (tc) at 85 degrees C of sucrose. Isothermal water vapour sorption of each sample was also measured at different relative humidities. Tg values of sucrose varied from 48.3+/-0.8 degrees C for freeze-dried (FD) sucrose alone to 58.8+/-0.8 degrees C for the mixture containing 5.0% PVP of nominal MW 300 K. PVP increased sucrose T(g) significantly (ANOVA P<0.05). Although there was no significant difference (P>0.05) in Tg of the mixtures containing 2.5% w/w PVP of different MW, samples with 5.0% PVP of MW 300 K produced a significantly higher (P<0.05) Tg than the other mixtures. All mixtures were shown to possess higher (P<0.01) Tc than FD sucrose alone, which exhibited a T(c) of approximately 85 degrees C. PVP of MW 300 K consistently induced a significantly (P<0.05) higher Tc of sucrose than PVP of smaller MW. Increasing PVP concentration from 2.5 to 5.0% also resulted in a substantial increase in sucrose Tc. Using isothermal water vapour absorption, sucrose tc was found to increase up to over 10 times when it was co-lyophilized with 2.5% PVP, the actual value of tc being dependent upon the MW of the PVP. For example, PVP of MW 300 K resulted in a sucrose tc at 85 degrees C (89.1-95.6 min), which was approximately seven times higher than that of 2.5% PVP of MW 24 or 40 K. A longer tc of sucrose was also observed for mixtures containing PVP of MW 300 K than when sucrose was mixed with PVP of smaller MW. Thus the effect of PVP on sucrose Tg, Tc and tc was found to be dependent upon MW. PVP of higher MW was more efficient in inhibiting sucrose crystallization and by stabilizing glassy structures of the sugar, these polymers may improve the stability of co-lyophilized proteins and peptides.     

Dissolution, stability, and absorption characteristics of dicumarol in polyethylene glycol 4000 solid dispersions

The dissolution characteristics of dicumarol were markedly enhanced by preparing dispersions of drug in polyethylene glycol 4000. Solid dispersions of varying weight fractions were formed by a melt method without measurable drug degradation or evaporation. There were no significant differences in dissolution rates among weight fractions, with dynamic solubilities being approximately 2.5 times greater than dicumarol's equilibrium solubility. No indications of drug polymer complexation were noted from equilibrium or in situ absorption experiments. Incorporation of solid dispersions into direct compression tablets provided dosage forms with fast-release properties relative to test tablets of physical mixtures and a commercially available product. Percentages dissolved in 30 min were 370% greater for 1:3 and 1:5 (w/w) solid dispersion tablets compared to a commercial tablet at 37 degrees with a pH 7.5 dissolution buffer. X-ray diffraction of test powder revealed that the crystalline nature of the drug had altered during fusion preparation. Dissolution traits and drug stability for solid dispersions were maintained over 1 year of storage.     

尼美舒利固体分散体的非pH依赖性释放研究

目的以尼美舒利为难溶弱酸性模型药物,研究提高该类药物释放速率的方法。方法以聚乙二醇6000(PEG6000)为载体,采用熔融法制备尼美舒利固体分散体;测定含不同碱化剂(包括NaOH、KOH、Ca(OH)2、Na2CO3、CaCO3)的尼美舒利固体分散体中药物的释放速率。结果加入碱化剂能显著增加尼美舒利在蒸馏水中的释放度,碱化剂不同,药物的释放度不同;碱化剂的碱性越强,分散体的颜色越深,其吸湿性也相对越大。结论在尼美舒利PEG6000固体分散体中加入碱化剂可显著改善该类药物的体外释放特点,并呈现明显的非pH依赖性。     

Solution thermodynamics of alkyl p-aminobenzoates.

Equilibrium solubilities of the first four homologous alkyl p-aminobenzoate esters were determined in methanol, ethanol, and 1-propanol at 25, 33, and 40 degrees; the esters and the alcohols comprise separate homologous series. The solution process of a solute may be considered to be the summation of two sequential steps, melting and mixing, and the magnitude of solubility depends upon temperature and the extent of interactions between solute and solvent molecules. Quantitative solute concentrations, obtained from spectrophotometric analysis, were converted to mole fractions. Statistical analysis of the logarithmic mole fraction solubilities of the aminobenzoates, which were linear with respect to both reciprocal absolute temperature and the logarithm of absolute temperature, generated enthalpies and entropies of solution, respectively. The heats of fusion and the melting points of these aminobenzoates were determined to calculate their ideal solubilities. Excess free energies and partial molal free energies of each solution were calculated from the activity coefficients of the solutes; the thermodynamic elements for these systems are discussed.     

Humid storage conditions increase the dissolution rate of diazepam from solid dispersions prepared by melt agglomeration

The purpose of this study is to investigate the effect of cooling mode and storage conditions on the dissolution rate of a solid dispersion prepared by melt agglomeration. The aim has been to relate this effect to the solid state properties of the agglomerates. The cooling mode had an effect on the dissolution rate, probably due to several factors such as the morphology of the agglomerates and crystallinity of the carrier. The dissolution increased with increasing temperature and relative humidity which increased the amount of water sorbed in the carrier. The processing and storage conditions were shown to have a complex interplay.     

The mechanisms of drug release from solid dispersions in water-soluble polymers.

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. However, despite the publication of numerous original papers and reviews on the subject, the mechanisms underpinning the observed improvements in dissolution rate are not yet understood. In this review the current consensus with regard to the solid-state structure and dissolution properties of solid dispersions is critically assessed. In particular the theories of carrier- and drug-controlled dissolution are highlighted. A model is proposed whereby the release behaviour from the dispersions may be understood in terms of the dissolution or otherwise of the drug into the concentrated aqueous polymer layer adjacent to the solid surface, including a derivation of an expression to describe the release of intact particles from the dispersions. The implications of a deeper understanding of the dissolution mechanisms are discussed, with particular emphasis on optimising the choice of carrier and manufacturing method and the prediction of stability problems.     

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.