The physicochemical characteristics and bioavailability of indomethacin from beta-cyclodextrin, hydroxyethyl-beta-cyclodextrin, and hydroxypropyl-beta-cyclodextrin complexes

In an effort to improve the bioavailability of the insoluble drug indomethacin, three complexes were prepared with indomethacin and the soluble complexing agents β-, hydroxyethyl-β-, and hydroxypropyl-β-cyclodextrin. The indomethacin content was similar among the complexes (P≤0.05). To confirm complex formation, each complex was characterized by ultraviolet, infrared, nuclear-magnetic resonance, powder X-ray diffraction, and differential-scanning calorimetry techniques. Powder diffraction studies show the β-cyclodextrin complex was polycrystalline, and the hydroxyethyl- and hydroxypropyl-β-cyclodextrin complexes were amorphous. Phase-solubility analysis confirmed the formation of complexes and suggested the three complexes were bound similarly. Solubility studies show complexation increased indomethacin solubility, and the hydroxyethyl- and hydroxypropyl-β-cyclodextrin complexes were more soluble than the β-cyclodextrin complex in 0.1N hydrochloric acid and distilled water. Dosage forms were prepared by encapsulating the complexes without the addition of excipients. Dissolution studies show the encapsulated β- and hydroxyethyl-β-cyclodextrin complexes had superior dissolution when compared to the hydroxypropyl-β-cyclodextrin and Indocin^® (50 mg) capsules. Bioavailability studies were performed by administering the indomethacin complex or Indocin capsules to male-albino, New Zealand rabbits. Indomethacin plasma-time concentration data fit best to a compartment-independent model for all capsule formulations. Bioavailability comparisons by ANOVA show no significant difference (P≤0.10) in the peak-plasma time and peak concentration among the capsule formulations. The area-under-the-curve for the β-cyclodextrin complex capsules was found to be significantly higher (P≤0.10) than all other capsule formulations. In conclusion, the bioavailabilty of indomethacin was improved by complexation with only β-cyclodextrin. No correlations were found among the bioavailability, solubility, and dissolution results.     

Use of Biophysical Characterization in Preformulation Development of a Heavy-Chain Fragment of Botulinum Serotype B: Evaluation of Suitable Purification Process Conditions

PURPOSE: The purpose of this study was to investigate the physicochemical and structural characteristics of recombinant botulinum serotype B (rBoNTB(Hc)) under various conditions and to use the information in evaluating suitable purification process conditions. METHODS: The solubility of rBoNTB(Hc) was evaluated at pH 4, 5, 6 7.5, 8, and 9. Secondary structure was evaluated using circular dichroism, and conformational stability was monitored using highsensitivity differential scanning calorimetry. Hydrophobic interaction chromatography, size exclusion chromatography-high performance liquid chromatography (SEC-HPLC), sodium dodecyl sulfate-poly acrylamide gel electrophoresis (SDS-PAGE), peptide mapping, and UV spectroscopy were used to monitor stability under the various conditions. RESULTS: The secondary structure of rBoNTB(Hc) consists predominantly of beta-sheets. Solubility of rBoNTB(Hc) was lowest at its pI and highest at low and high pH. In the presence of NaCl, however, solubility decreased with increase in pH. Conformational and chemical stability are improved below pH 7.5. In the presence of 150 mM NaCl at high pH, conformational and chemical stability of rBoNTB(Hc) are further decreased. The study suggests that the purification process should minimize exposure of rBoNTB(Hc) to high pH and salt conditions. CONCLUSIONS: Optimal stability of rBoNTB(Hc) is achieved at low pH. The biophysical and analytical studies provide us with an understanding of rBoNTB(Hc) stability behavior in solution and assists in developing efficient purification conditions.     

Enthalpy Relaxation of Layered Silicate‐Epoxy Nanocomposites

Using standard and temperature‐modulated differential scanning calorimetry, we have studied the segmental relaxation behavior of montmorillonite‐epoxy nanocomposites. The experimental results showed that the incorporation of clay particles caused the epoxy network to exhibit slower relaxation dynamics compared with the neat epoxy resin. Analysis based on the Tool‐Narayanaswamy‐Moynihan (TNM) model indicated that the nanocomposite systems had greater nonlinearity, higher apparent activation energy, and broader relaxation time distribution than the neat epoxy resin. Further analysis based on the Adam‐Gibbs model indicated that the presence of clay nanoparticles decreased the macroscopic configurational entropy of the epoxy network, and increased the size of the cooperative rearrangement region as well as the fundamental energy barrier. The peculiar relaxation behavior observed in the present experiments was attributed to the confinement effect of nanoparticles on molecular entities during the segmental relaxation. This confinement effect led to a stronger temperature dependence of the relaxation behavior near the glass transition temperature, or greater fragility. An inverse correlation between nonexponentiality and fragility was also observed, which is consistent with the results reported in the literature.

The original MDSC curves: complex heat capacity (C_{\rm P}^* ) versus temperature; the inset shows the nonexponentiality parameters (β) for all the samples.     

Direct Observation of the Enthalpy Relaxation and the Recovery Processes of Maltose-Based Amorphous Formulation by Isothermal Microcalorimetry

Purpose. The applicability of isothermal microcalorimetry (IMC) for evaluating enthalpy relaxation and recovery processes of amorphous material was assessed. Methods. A maltose-based formulation was prepared by freeze-dry method. Differential scanning calorimetry (DSC) was used to investigate its glass transition and relaxation behaviors. IMC was applied to quantitatively analyze the relaxation and the recovery processes. The IMC data were analyzed using a derivative of the Kohlrausch-Williams-Watts equation. Results. The glass transition temperature of the formulation and its fictive temperature stored at 15°C for 1 year were 62 and 32°C, respectively. DSC study showed that annealing below the fictive temperature increased the enthalpy recovery, but it was decreased by annealing at higher temperatures. IMC enabled direct observation of the heat flow during both the relaxation and the recovery processes. The decay constant for the recovery process (recovery time) was much smaller and less sensitive to the temperature than that for the relaxation process (relaxation time). Conclusions. IMC was successfully used to obtain quantitative information on both relaxation and recovery processes of amorphous material. The relaxation parameters obtained by this method could explain the thermodynamic behavior of the formulation.     

Clinical evaluation of a continuous oxygen consumption monitor in mechanically ventilated patients

We measured oxygen consumption using a new noninvasive modular metabolic monitor, M-COVX trade mark, in ventilated critically ill patients. Oxygen consumption was measured continuously as part of routine monitoring for up to 24 h following mechanical ventilation in 27 patients admitted to a general intensive care unit. We explored several possible sources of error. Most errors related to inaccurate tidal volume measurement, which resulted in rejection of a median 14% (interquartile range 8-34%) of data. Water accumulation in the pneumotachograph was responsible and occurred more frequently with water bath humidifiers. After manual removal of erroneous data mean oxygen consumption values were virtually identical to calculated values in 24 of 27 patients. We conclude that in most ventilated patients averaging of continuous oxygen consumption data with the M-COVX module results in small errors.     

Characterisation of elastin and collagen in aortic bioprostheses

Porcine aortic valves used as cardiac valve bioprostheses are well adapted to physiological functions in the short term, but they lack long-term durability. Several multi-step extractions have been performed to obtain a perfectly acellular matrix. A new physical methodology is proposed to evaluate the resulting fibrous protein damage after biochemical extraction (TRI-COL and SDS). Thermal analysis techniques are adapted to collagen and elastin characterisation in the solid state. The aortic tissue thermal transitions are determined by differential scanning calorimetry (DSC): elastin glass transition is observed around 200°C, and collagen denaturation is observed around 230°C. These parameters are characteristic of the elastin network arrangement and of collagen triple-helix stability. The technique of thermostimulated currents (TSC) is well suited to specify the chain dynamics of proteins. The lowtemperature relaxations observed in both collagen and elastin are associated with localised motions, whereas the high-temperature modes are attributed to more delocalised motions of the chains. Therefore TSC and DSC spectrometries allow physical parameters specific to collagen and elastin to be obtained and their interaction in aortic tissues to be determined. According to the significant evolution of these parameters on SDS samples, the destabilising effect of this detergent is highlighted.     

环介导等温扩增快速检测EBV DNA对鼻咽癌诊断的意义

目的:建立环介导等温扩增技术快速检测EB病毒的方法,为鼻咽癌的早期诊断提供辅助手段.方法:利用煮沸法快速提取样品中病毒DNA,使用环介导等温扩增技术检测EB病毒特异基因片段,在等温条件下于1 h内完成检测过程.结果:环介导等温扩增技术在对33份临床标本的检测中显示了较高的特异性,较现有的PCR技术更加简便快速,能在等温条件下进行,不需复杂的仪器设备,检测成本大大降低.结论:本研究为鼻咽癌临床检测提供了一个快速简便的新辅助方法.     

Real Time Detection of Photoreactivity in Pharmaceutical Solids and Solutions with Isothermal Microcalorimetry

Purpose. In this study an irradiation cell made as an accessory for an isothermal microcalorimeter is introduced, and its suitability for detection photoreactivity in pharmaceutical solutions and solids is demonstrated. The pharmaceuticals employed are chosen as sample materials to evaluate the usefulness and stability of the irradiation cell. Methods. An irradiation cell has been constructed and tested in an isothermal microcalorimeter with pharmaceutical solutions and solids known to be sensitive to daylight or UV light. Light is produced with an Xe-arc lamp, split into two parts and introduced into calorimetric vessels with optical light cables. One of the vessels containing the reference sample gives the response to the heat absorbed by the material (radiant power), and the other vessel containing the sample material gives the response also to the photoreaction. The two irradiation cells are positioned in the sample sides of two separate twin microcalorimetric units. Results. Nifedipine and L-ascorbic acid were found to be photosensitive in solutions and solid states, the extent of the degradation depending on the irradiation intensity and wavelength. The threshold values of the wavelength for the photoreactions, as well as the wavelengths for the maximum reaction rates, were estimated via the scanning irradiation measurements. The ability of photons with different energies to produce heat in the photosensitive reaction of nifedipine was calculated using constant measurements. Conclusions. The technique introduced offers a rapid and versatile method to study the photosensitivity of materials in any state. In the measurements, various conditions can be simulated and thus provide information on the real behavior of materials.     

Determination of the Glass Transition Temperatures of Some New Methyl Methacrylate Copolymers Using Modulated Temperature Differential Scanning Calorimetry (MTDSC)

Purpose. The purpose of this study was to determine the glass transition temperatures of new graft copolymers using Modulated Temperature Differential Scanning Calorimetry (MTDSC), and to assess the differences between starch and cellulosic derivatives of methyl methacrylate and between two different drying methods used in their preparation. Methods. Graft copolymers of methyl methacrylate were synthesized and dried by oven or freeze-drying. Surface area measurements and different thermal analysis techniques (Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TGA) and MTDSC) were used to characterize these copolymers. Results. DSC was not sensitive enough to identify the T_gs of the copolymers, however they were clearly identifiable by MTDSC. T_g values obtained may depend on the method of preparation that also altered their physical characteristics e.g. specific surface area. Cellulose derivatives showed lower T_gs than starch derivatives. The results also depended on the drying method used, thus, freeze dried products had slightly lower T_gs than oven dried products. Conclusions. MTDSC represents a useful thermal technique that allows the identification of glass transitions in these new copolymers with higher sensitivity and resolution than conventional DSC, separating the transition from overlapping phenomena such as decomposition or dehydration. The T_g of this new class of copolymers appeared to be dependent on polymer composition and drying method used.     

Complex Formation Between The Anionic Polymer (PAA) and a Cationic Drug (Procaine HC1): Characterization by Microcalorimetric Studies

Purpose. Due to the importance of drug-polymer interactions in, inter alia, drug loading/release, supramolecular assemblies and DNA delivery for gene therapy, the aim of this study was therefore to establish the mechanism of interaction between a model polymer (Polyacrylic acid, PAA) and a model drug (procaine HCl). Methods. This was performed by studying the effect of salt (KCl) concentration on their heat released values using Isothermal Titration Microcalorimetry (ITM). The integrated released heat data were computer fitted to a one class binding model and the thermodynamic parameters (K_obs, H, and N) were determined. Results. As the KC1 concentration was increased, K_obs decreased thus establishing the salt dependence of the interaction. The linear variation of G_obs with S_obs indicated that their interaction was entropically driven. The stoichiometry of the interaction was calculated to be one procaine molecule per monomer of PAA. Dissection of the total observed free energy at each KC1 concentration indicated that the contribution of the non-electrostatic attractions to the interaction of PAA with procaine HC1 was greater than those of the electrostatic attractions. Conclusions. We have shown that the interaction between PAA and procaine HC1 is dependent upon the presence of counterions (monovalent ions) and is mainly entropically driven. The calculated stoichiometry indicated that one procaine HC1 molecule neutralised one carboxylic acid group on PAA. Although electrostatic interactions were necessary for initiating complex formation, the non-electrostatic forces were dominant in stabilising the PAA-procaine HC1 complex.