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PubMed2002

Physical stability and solubility of the thermotropic mesophase of fenoprofen calcium as pure drug and in a tablet formulation.

The aim of this study was to investigate and compare the physical stability and solubility of the liquid crystalline form of fenoprofen calcium as pure drug and in a proprietary tablet formulation (Nalfon), and to investigate if a simple heat treatment of a proprietary tablet containing fenoprofen calcium may lead to a physically stable formulation with enhanced dissolution rate and apparent solubility. The liquid crystalline form of fenoprofen calcium (thermotropic mesophase) was prepared by heating the crystalline drug to 125 degrees C to remove the water of crystallisation. Differential scanning calorimetry investigation revealed an endothermic peak at 89 degrees C upon heating (liquid crystal formation) attributable to water loss from the crystalline dihydrate. The liquid crystalline order was maintained upon cooling. No interference of tablet excipients with the thermal behaviour of the drug in the tablet formulation was observed. The crystalline dihydrate and liquid crystalline forms of fenoprofen calcium could be differentiated by diffuse reflectance infra-red spectroscopy and X-ray powder diffraction, both as pure drug and in tablet formulation. The supercooled liquid crystal (thermotropic reversed hexagonal phase) alone and in preheated and ground tablets was physically stable when stored in a dry environment or at 33% relative humidities (RH) at both 20 and 40 degrees C for 2 months. At 40 degrees C and 75% RH the supercooled mesophase extensively converted to the crystalline dihydrate within 6 days. Liquid crystalline fenoprofen calcium stored at 20 degrees C and 75% RH showed only partial dihydrate conversion after 2 months of storage. The solubility of the crystalline dihydrate alone and from the tablet formulation was 2.8+/-0.2 mg/ml and 3.0+/-0.2 mg/ml (mean+/-s.d.), respectively, (not significantly different), whereas the maximum solubility of the liquid crystal was 5.0+/-0.3 mg/ml (mean+/-s.d.) and 6.9+/-0.6 mg/ml (mean+/-s.d.), respectively (significantly different). The difference in maximum solubility between the crystalline dihydrate form of fenoprofen calcium and the fenoprofen calcium mesophase was highly significant, for both the pure drugs and the tablet formulations. The dissolution rate of the liquid crystalline fenoprofen calcium in preheated, intact tablets was significantly lower than that of the crystalline form in non-preheated tablets. Gross visual changes and scanning electron microscopy indicated that the disintegration properties of the tablet may be detrimentally effected by heating the tablet to 125 degrees C, diminishing the beneficial effect of improved solubility of the liquid crystal. The study has shown that conversion of the crystalline form of fenoprofen calcium to the liquid crystal can enhance the apparent solubility of the pure drug and the drug in presence of tablet excipients, but that the conversion should be performed before tablet formulation in order to increase dissolution of this poorly water-soluble drug.

Chemistry, Pharmaceutical↗
PubMed2002

Prediction of apparent equilibrium solubility of indomethacin compounded with silica by 13C solid state NMR.

The apparent equilibrium solubility (AES) of indomethacin increased by co-grinding with silica. Change in the long- and short range disorder of indomethacin by co-grinding was examined by X-ray powder diffraction and 13C solid state NMR, respectively, to elucidate the increased AES. Since the increase in AES was particularly marked after complete disappearance of X-ray diffraction peaks, we attributed the enhanced AES primarily to the short range disorder on the molecular basis. This was confirmed by a high correlation between the standardized full width at half maximum (SFWHM) of the specific peaks observed by 13C solid state NMR and log (AES). The correlation enables the prediction of AES as well.

Carbon Radioisotopes↗
PubMed2002

Mechanism of increased dissolution of diazepam and temazepam from polyethylene glycol 6000 solid dispersions.

Solid dispersion literature, describing the mechanism of dissolution of drug-polyethylene glycol dispersions, still shows some gaps; (A). only few studies include experiments evaluating solid solution formation and the particle size of the drug in the dispersion particles, two factors that can have a profound effect on the dissolution. (B). Solid dispersion preparation involves a recrystallisation process (which is known to be highly sensitive to the recrystallisation conditions) of polyethylene glycol and possibly also of the drug. Therefore, it is of extreme importance that all experiments are performed on dispersion aliquots, which can be believed to be physico-chemical identical. This is not always the case. (C). Polyethylene glycol 6000 (PEG6000) crystallises forming lamellae with chains either fully extended or folded once or twice depending on the crystallisation conditions. Recently, a high resolution differential scanning calorimetry (DSC)-method, capable of evaluating qualitatively and quantitatively the polymorphic behaviour of PEG6000, has been reported. Unraveling the relationship between the polymorphic behavior of PEG6000 in a solid dispersion and the dissolution characteristics of that dispersion, is a real gain to our knowledge of solid dispersions, since this has never been thoroughly investigated. The aim of the present study was to fill up the three above mentioned gaps in solid dispersion literature. Therefore, physical mixtures and solid dispersions were prepared and in order to unravel the relationship between their physico-chemical properties and dissolution characteristics, pure drugs (diazepam, temazepam), polymer (PEG6000), solid dispersions and physical mixtures were characterised by DSC, X-ray powder diffraction (Guinier and Bragg-Brentano method), FT-IR spectroscopy, dissolution and solubility experiments and the particle size of the drug in the dispersion particles was estimated using a newly developed method. Addition of PEG6000 improves the dissolution rate of both drugs. Mechanisms involved are solubilisation and improved wetting of the drug in the polyethylene glycol rich micro-environment formed at the surface of drug crystals after dissolution of the polymer. Formulation of solid dispersions did not further improve the dissolution rate compared with physical mixtures. X-ray spectra show that both drugs are in a highly crystalline state in the solid dispersions, while no significant changes in the lattice spacings of PEG6000 indicate the absence of solid solution formation. IR spectra show the absence of a hydrogen bonding interaction between the benzodiazepines and PEG6000. Furthermore, it was concluded that the reduction of the mean drug particle size by preparing solid dispersions with PEG6000 is limited and that the influence of the polymorphic behavior of PEG6000 (as observed by DSC) on the dissolution was negligible.

Chemistry, Pharmaceutical↗
PubMed2003

Para-acyl-calix-arene based solid lipid nanoparticles (SLNs): a detailed study of preparation and stability parameters.

The preparation and stability parameters of para-acyl-calix[4]arene based solid lipid nanoparticles (SLNs) have been investigated. Atomic force microscopy (AFM) and photon correlation spectroscopy (PCS) show a mean particle size of 130 nm. In terms of preparation parameters, using the solvent displacement method, the nature and the volume of the organic solvent, the concentration of the amphiphile and the presence of a co-surfactant in the organic phase have been shown to affect significantly the size of the produced SLNs. In contrast, the stirring speed, the viscosity and the acidity of the aqueous phase and the amphiphile hydrophobic chain length have been shown to have no effect. In terms of stability parameters, the ionic strength has been shown to affect the short-time SLN stability depending on both the anion and the cation studied, with sodium sulphate causing precipitation. Ultrasonic, ultraviolet or microwave treatments of the SLN suspensions have no effect on the size of the SLNs. The study of the effects of short time thermal treatment revealed that the SLNs are not affected by one freezing-defreezing cycle and are stable at 100 degrees C in suspension. It is difficult to reconstitute the SLN suspensions after freeze-drying. Finally, the temporal stability of these suspensions in water has been shown to be superior to 1 year. The long-term temporal stability of suspensions stored in saline solution has been investigated. It has been demonstrated that the most destabilising effects arise from the presence in the storage suspension of sulphate ions.1H NMR, X-ray powder diffraction (XPD) and AFM have also been carried out on the calix-arene based SLNs and demonstrate the presence of a semi-organised matrix structure for the SLNs.

Calixarenes↗
PubMed2003

Polymorphic properties of micronized carbamazepine produced by RESS.

Carbamazepine microparticles were produced by the rapid expansion of supercritical carbon dioxide solutions (RESS) method. The characteristics of the resulting particles were studied by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and image analysis. X-ray diffractograms and SEM photomicrographs revealed that the crystalline nature of the produced carbamazepine microparticles depended on operating pressure and temperature conditions. Different polymorphs were obtained under various operating conditions. Under certain temperature (below 40 degrees C) and pressure (below 240 bar) conditions, it was possible to form primarily the carbamazepine polymorph stipulated by US Pharmacopeia. A significant reduction was observed in the particle size and size distribution range of carbamazepine produced by RESS. The processed particles had a mean diameter smaller than 3 microm and a size distribution range between 0.5 and 2.5 microm compared to unprocessed starting material with a mean diameter of approximately 85 microm and a size distribution range between 15 and 336 microm. Thus, this study demonstrates that the polymorphic characteristics of carbamazepine microparticles produced by the RESS method can be controlled by varying operating pressure and temperature parameters.

Calorimetry, Differential Scanning↗
PubMed2003

Formulation design of carbamazepine fast-release tablets prepared by melt granulation technique.

This work describes a new approach to prepare a fast-release dosage form for carbamazepine (CBZ), involving the use of melt granulation process in high shear mixer for the production of tablets. In particular, the granules containing CBZ were prepared using polyethylene glycol (PEG) 4000 as a melting binder and lactose monohydrate as a hydrophilic filler. The potential of the intragranular addition of crospovidone as a dissolution enhancer and a disintegrant agent was also evaluated. After the analysis of their solid state performed by means of X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC), the granules were characterised from the technological and dissolution point of view. The subsequent step encompassed the preparation and the evaluation of the tablets, including the effect of the extragranular introduction of crospovidone. Besides the remarkable enhancement of drug dissolution rate of the granulates in comparison to physical mixtures and pure drug, no significant differences were found between the dissolution profiles of the granulates containing lactose or crospovidone. However, the difficult disintegration and bad dissolution performance of the tablets not containing intragranular crospovidone highlight the necessity of this disintegrant in the granulating mixture. Moreover, the extragranular addition of a small amount of crospovidone gave rise to a further amelioration of the disintegration and dissolution performances.

Carbamazepine↗
PubMed2003

Thermal analysis of the antiretroviral zidovudine (AZT) and evaluation of the compatibility with excipients used in solid dosage forms.

Modern thermal analysis techniques are frequently used because of their ability to provide detailed information about both the physical and the energetic properties of a substance. In the present work, the thermal decomposition of zidovudine (AZT) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). Thermal analysis was supplemented using elemental analysis (C, H, and N), infrared (IR) spectroscopy, and X-ray powder diffraction to characterize the solid intermediates products. Volatile products of the thermal decomposition of AZT were studied by a system composed of the TG/DTA coupled gas chromatography/mass spectrometry (GC/MS). The physical-chemical properties and compatibilities of several commonly used pharmaceutical excipients with AZT were evaluated using thermal methods. The results showed that the product originated from the first thermal decomposition stage corresponds to the cleavage followed by elimination of the azide group and consequent formation of thymine. The second event corresponds to thermal decomposition of thymine. TG/DTA-GC/MS system identified thymine's decomposition products as furan and 2-furanmethanol like volatile species. Comparison of the thermoanalytical profiles of the mixtures with individual compounds did not give any evidence of interactions.

Antiviral Agents↗
PubMed2003

Evaluation of polar lipid-hydrophilic polymer microparticles.

The aim of the present study was to prepare controlled-release tablets of poorly-soluble drug, felodipine. Spray chilling was used to formulate the drug, the polar lipids and the hydrophilic polymers into solid dispersion microparticles, which were then compressed. The microparticles were characterised by Fourier transform infrared and Raman spectroscopies, X-ray powder diffraction, hot-stage microscopy, scanning electron microscopy, and image analysis. The crystallinity of felodipine had decreased in all the samples, and the amount of crystalline felodipine varied depending on the composition of the solid dispersion. The particles were spherical with the median particle diameter ranging from 20 to 35 microm. The addition of hydrophilic polymer into the matrix widened the particle size distribution and increased the amount of agglomerates. Most promising dissolution patterns were obtained from tablets containing glycerides; e.g. from Precirol ATO 5/Pluronic F127 tablets the release was of zero order.

Chemistry, Pharmaceutical↗
PubMed1999

Physicochemical characterization and in vivo properties of Zolpidem in solid dispersions with polyethylene glycol 4000 and 6000.

Solid dispersions and physical mixtures of Zolpidem in polyethylene glycol 4000 (PEG 4000) and 6000 (PEG 6000) were prepared with the aim to increase its aqueous solubility. These PEG based formulations of the drug were characterized in solid state by FT-IR spectroscopy, X-ray powder diffraction, and differential scanning calorimetry. By these physical determinations no drug-polymer interactions were evidenced. Both solubility and dissolution rate of the drug in these formulations were increased. Each individual dissolution profile of PEG based formulation fitted Baker-Lonsdale and first order kinetic models. Finally, significant differences in ataxic induction time were observed between Zolpidem orally administered as suspension of drug alone and as solid dispersion or physical mixture. These formulations, indeed, showed almost two- to three-fold longer ataxic induction times suggesting that, in the presence of PEG, the intestinal membrane permeability is probably the rate-limiting factor of the absorption process.

Animals↗
PubMed1999

Critical properties of lactide-co-glycolide polymers for the use in microparticle preparation by the aerosol solvent extraction system.

The Aerosol Solvent Extraction System (ASES) process uses supercritical carbon dioxide for the production of microparticles. Since the critical temperature for this gas is at 304 K, polymers that are used in this process must fulfil certain requirements in crystallinity, and thermal behavior. This can be achieved by the use of blocked copolymers and thus the presence of semicrystalline microdomains in the polymers. However, changing the sequences of the comonomers dilactide and lactide often leads to polymers of low solubility due to long glycolide blocks. In this study, the critical properties of two blocked co-polymers were investigated, such as the blocked structure itself by (1)H-NMR and (13)C-NMR, the thermal behavior by differential scanning calorimetry (DSC), and the crystallinity by powder diffraction. The impact of these properties on microparticles formed by those polymers was also object of these studies. Additionally, two different model drugs, albumin and estriolm were embedded to investigate the impact of different polymer properties on drug content and release.

Aerosols↗
PubMed1999

Formation and compression characteristics of prismatic polyhedral and thin plate-like crystals of paracetamol.

Prismatic polyhedral crystals of paracetamol were prepared by cooling an aqueous saturated solution of paracetamol from 65 to 25 degrees C. Thin plate-like crystals were prepared by adding a concentrated solution of paracetamol in hot ethanol to water at 3 degrees C. Infrared (IR), X-ray powder diffraction (XPD) and differential scanning calorimetry (DSC) studies confirmed that these two forms of crystals were structurally similar, therefore polymorphic modifications were ruled out. The crystal habit influenced the compression properties during axial compression of paracetamol at different constant rates in a compaction simulator, the Heckel plots and their associated constants being dependent on the habits. The correlation coefficient of the initial part of the Heckel plots, and also the values of strain rate sensitivity (SRS), were lower for thin plate-like crystals, indicative of greater fragmentation for the thin plate-like as compared to polyhedral crystals. Compacts made from thin plate-like crystals exhibited higher elastic recoveries and elastic energies indicating that these crystals underwent less plastic deformation during compression than the polyhedral crystals.

Acetaminophen↗
PubMed2000

Preparation and characterisation of a new insoluble polymorphic form of glibenclamide.

A crystalline form of glibenclamide, with higher melting point (218 degrees C) and lower solubility in simulated gastric and intestinal fluids, was arisen during an attempt to elucidate transitional phases by melting, cooling and reheating. The new form was obtained from the glassy state, by applying sublimation at 130-160 degrees C and was characterised by differential scanning calorimetry (DSC), infrared (IR) spectroscopy, scanning electron microscopy (SEM), hot-stage microscopy (HSM), X-ray powder diffraction (XRD) and solubility studies. Formation of the new crystal form is considered as reason of reduction in dissolution and bioavailability of tablets.

Calorimetry, Differential Scanning↗
PubMed2002

A study of the composition of some eye cosmetics (kohls) used in the United Arab Emirates.

A total of 23 kohl samples was analyzed using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). Nineteen samples were obtained in Abu Dhabi and four in Dubai. None of the samples were made in the United Arab Emirates. The main component of 11 samples was found to be galena (PbS). For the remaining 12 samples, the main component was found to be one of the following: amorphous carbon, zincite (ZnO), sassolite (H(3)BO(3)) or calcite/aragonite (CaCO(3)).

Cosmetics↗
PubMed1998

Composition of eye cosmetics (kohls) used in Oman.

A total of 47 kohl samples, primarily used as traditional eye cosmetics, were analyzed using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). It was found that, of the 18 Omani-made kohls, the main component of five was galena (PbS). Of the other 13, 12 were based on amorphous carbon and one on hematite (Fe2O3). The remaining samples were made in other countries and were found to contain one of the following as the main component: galena, minium (Pb3O4), amorphous carbon, magnetite (Fe3O4), zincite (ZnO), calcite (CaCO3) or sassolite (H3BO3).

Carbon↗
PubMed2000

The use of near-infrared spectroscopy to monitor the mobility of water within the sarafloxacin crystal lattice.

Near-infrared spectroscopy (NIRS) is proposed as a technique to study the mobility of water within the sarafloxacin crystal lattice. An investigation of two samples of sarafloxacin revealed that NIRS can distinguish between acceptable and unacceptable batches for formulation purposes. X-ray powder diffraction (XRPD), mid-infrared (mid-IR) spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) could not detect any differences between the two samples. NIRS detected differences in the location or orientation of the water molecules within the crystal lattices.

Anti-Infective Agents↗
PubMed2000

Solid-state studies on the hemihydrate and the anhydrous forms of flunisolide.

Flunisolide exists in at least two different anhydrous crystalline forms (I and II) and in a hemihydrate form with distinctly different physico-chemical properties. Modification II and the hemihydrate form are the commercial products. Form I was obtained by heating all other forms above 230 degrees C. The different crystalline forms of flunisolide were investigated by FTIR spectroscopy, X-ray powder diffractometry, differential scanning calorimetry (DSC), thermogravimetric analysis and thermomicroscopy both coupled with FTIR spectroscopy (TG-FTIR and FTIR thermomicroscopy). The three forms were easily differentiated by their IR spectra, X-ray powder diffraction patterns and thermal behaviour. Their stability was investigated under different experimental conditions to verify the tendency to solid solid transition and to study the existence range of the three forms. The relationship among the two anhydrous polymorphs and the hemihydrate form and their equilibrium solubilities in water at 20 degrees C were also investigated.

Anti-Asthmatic Agents↗
PubMed2002

Investigation of the effects of grinding and co-grinding on physicochemical properties of glisentide.

The purpose of the present study was to investigate the possibility of improving the dissolution properties of glisentide, a poorly water-soluble antidiabetic drug, by grinding in a high energy micromill, alone or in mixture with polyvinylpyrrolidone (PVP). Conventional and modulated differential scanning calorimetry (DSC, MDSC), thermogravimetry (TGA), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), hot-stage FT-IR thermomicroscopy and scanning electron microscopy (SEM) were used to characterize the drug solid state, whereas its dissolution rates were determined according to the dispersed amount method. The techniques utilized enabled exclusion of polymorphism phenomena as a consequence of mechanical treatment, and revealed a progressive drug amorphization during grinding. In particular, MDSC allowed a clear determination of the glass transition temperature of the amorphous drug, enabling separation of glass transition from enthalpic relaxation. The amorphous state of the ground drug was the main responsible factor for the obtained 100% dissolution efficiency increase in comparison with the untreated drug. Further significant increases in dissolution properties, directly related to the polymer content in the mixture, were obtained by co-grinding with PVP, whose presence clearly favored drug amorphization, allowing a strong reduction of time and frequency of grinding necessary for obtaining complete drug amorphization.

Benzamides↗
PubMed1999

Physico-chemical characterisation of the modifications I and II of (R,S) propranolol hydrochloride: solubility and dissolution studies.

The crystallisation conditions and the physicochemical properties of the modifications I and II of (R,S) propranolol hydrochloride were investigated. Detailed methods of preparation of the two forms were described. Data from FTIR spectroscopy, X-ray powder diffraction, thermal analysis, solubility and dissolution studies were used for the identification and the characterisation of the two forms. The forms I and II were easily differentiated by their IR spectra, X-ray patterns and thermal behaviour. The two polymorphs were found to be enantiotropically related to each other. Their stability was followed at room temperature over a period of 1 year and under different conditions of temperature, grinding and compression to verify the tendency to solid solid transition and to study the existence range of the two forms. The equilibrium solubilities of the two polymorphs in n-octanol were determined as well as their dissolution profiles as pellets in aqueous medium. These studies showed that form I, the less thermodynamically stable, was more soluble (by more than 34%) and dissolved faster than form II in agreement with the thermodynamic rules (A. Burger, R. Ramberger, Mikrochim. Acta II (1979) 259-271).

Crystallization↗