Biomedical subjects

Zeren Wang

Publications and source records attributed to Zeren Wang.

5 recordsLinked to original sources

PubMed2007

Factors affecting the formation of eutectic solid dispersions and their dissolution behavior.

The objective of this work was to obtain a fundamental understanding of the factors, specifically the properties of poorly water-soluble drugs and water-soluble carriers, which influence predominantly, the formation of eutectic or monotectic crystalline solid dispersion and their dissolution behavior. A theoretical model was applied on five poorly water-soluble drugs (fenofibrate, flurbiprofen, griseofulvin, naproxen, and ibuprofen) having diverse physicochemical properties and water-soluble carrier (polyethylene glycol (PEG) 8000) for the evaluation of these factors. Of these, two drugs, fenofibrate and flurbiprofen, and PEG of different molecular weights (3350, 8000, and 20000), were chosen as model drugs and carriers for further investigation. Experimental phase diagrams were constructed and dissolution testing was performed to assess the performance of the systems. The theoretical model predicted the formation of eutectic or monotectic solid dispersions of fenofibrate, griseofulvin, ibuprofen, and naproxen with PEG, holding the contribution of specific intermolecular interactions between compound and carrier to zero. In the case of the flurbiprofen-PEG eutectic system, intermolecular interactions between drug and polymer needed to be taken into consideration to predict the experimental phase diagram. The results of the current work suggest that the thermodynamic function of melting point and heat of fusion (as a measure of crystal energy of drug) plays a significant role in the formation of a eutectic system. Lipophilicity of the compound (as represented by cLog P) was also demonstrated to have an effect. Specific interactions between drug and carrier play a significant role in influencing the eutectic composition. Molar volume of the drug did not seem to have an impact on eutectic formation. The polymer molecular weight appeared to have an impact on the eutectic composition for flurbiprofen, which exhibits specific interactions with PEG, whereas no such impact of polymer molecular weight on eutectic composition was observed for fenofibrate, which does not exhibit specific interactions with PEG. The impact of polymer molecular weight on dissolution of systems where specific drug-polymer interactions are exhibited was also observed. The current work provides valuable insight into factors affecting formation and dissolution of eutectic systems, which can facilitate the rational selection of suitable water-soluble carriers.

Drug Carriers↗

PubMed2006

Use of texture analysis to study hydrophilic solvent effects on the mechanical properties of hard gelatin capsules.

The aim of this work was to explore texture analysis for quantitative evaluation of the effect of hydrophilic solvent systems used as capsule fills on the mechanical properties of hard gelatin capsules. For this purpose, a texture analyzer (Stable Micro Systems, model TA.XT Plus) equipped with a capsule separating rod fixture was used. The tests were conducted in a tension mode. Elastic stiffness, tensile force and elongation at break were determined from the experimental stress-strain curve in order to quantitatively describe both brittleness and softening of capsules. In this paper, it has been demonstrated that the effect of various hydrophilic solvent (i.e. propylene glycol (PG), polyethylene glycol 400 (PEG 400), ethanol) mixtures on the mechanical properties of hard gelatin capsules can be easily monitored using texture analysis. Significant counteractive effects between PG and PEG 400 or ethanol on the integrity of capsule shells were discovered in this study. Texture analysis is found to be a convenient tool for studying formulation compatibility. It can be invaluable in early screening studies of liquid filled hard gelatin capsules.

Capsules↗

PubMed2004

A mechanistic investigation of an amorphous pharmaceutical and its solid dispersions, part I: a comparative analysis by thermally stimulated depolarization current and differential scanning calorimetry.

PURPOSE: To explore using thermally stimulated depolarization current (TSDC), in comparison to differential scanning calorimetry (DSC), for the characterization of molecular mobility of an amorphous pharmaceutical new chemical entity (LAB687), an amorphous polymer (PVPK-30), and their combination as solid dispersions at different % drug loadings. METHODS: Amorphous drug was prepared by quenching from the melt. Solid dispersions containing 10-60% of drug in polymer were prepared by solvent evaporation method. Glass transition temperatures (Tg) were determined by DSC and TSDC. RESULTS: In comparison to a single T. obtained from DSC for the drug substance, TSDC shows two overlapping relaxations. Both peaks correspond to a-relaxations that are associated with the glass transition, with the second peak corresponding to the rigid fraction that is difficult to be detected by DSC because it is associated with only small changes in heat capacity. Two overlapping relaxations were also observed for the polymer vs. one Tg by DSC. The lower temperature relaxation is believed to be a beta-relaxation, whereas the higher temperature transition corresponds to an alpha-relaxation. For the solid dispersions, one single peak was obtained for each of the 20% and 30% dispersions in excellent agreement with the DSC results. However, at the 40% drug load, a small shoulder was observed by TSDC at the low temperature of the main peak. This shoulder becomes more pronounced and overlaps with the main peak as the drug load increases to 50% and 60%. Agreement between the Tg values calculated by the Gordon-Taylor equation and the DSC and TSDC experimental data, especially for the 20% and 30% drug loading, indicate ideal miscibility. At higher drug loads, only by TSDC was it possible to detect the saturation level of the drug in the polymer. CONCLUSIONS: TSDC proved to be very sensitive in detecting small reorientational motions in solids and in separating overlapping events with only slight differences in molecular motion exhibited as broad events in DSC. This allowed for detection of the rigid fraction of the amorphous drug, the sub-glass transition beta- relaxation in the polymer, and the limit of miscibility between the drug and the polymer in the solid dispersions.

Calorimetry, Differential Scanning↗

PubMed2004

A mechanistic investigation of an amorphous pharmaceutical and its solid dispersions, part II: molecular mobility and activation thermodynamic parameters.

PURPOSE: The ability of TSDC to characterize further amorphous materials beyond that possible with DSC was presented in part I (16) of this work. The purpose of part II presented here is to detect and quantitatively characterize time-scales of molecular motions (relaxation times) in amorphous solids at and below the glass transition temperature, to determine distributions of relaxation times associated with different modes of molecular mobility and their temperature dependence, and to determine experimentally the impact upon these parameters of combining the drug with excipients (i.e., solid dispersions at different drug to polymer ratios). The knowledge gleaned may be applied toward a more realistic correlation with physical stability of an amorphous drug within a formulation during storage. METHODS: Preparation of amorphous drug and its solid dispersions with PVPK-30 was described in part I (16). Molecular mobility and dynamics of glass transition for these systems were studied using TSDC in the thermal windowing mode. RESULTS: Relaxation maps and thermodynamic activation parameters show the effect of formulating the drug in a solid dispersion on converting the system (drug alone) from one with a wide distribution of motional processes extending over a wide temperature range at and below Tg to one that is homogeneous with very few modes of motion (20% dispersion) that becomes increasingly less homogeneous as the drug load increases (40% dispersion). This is confirmed by the high activation enthalpy (due to extensive intra- and intermolecular interactions) as well as high activation entropy (due to higher extent of freedom) for the drug alone vs. a close to an ideal system (lower enthalpy), with less extent of freedom (low entropy) especially for the 20% dispersion. The polymer PVPK-30 exhibited two distinct modes of motion, one with higher values of activation enthalpies and entropy corresponding to alpha-relaxations, the other with lower values corresponding to beta-relaxations characterized by local noncooperative motional processes. CONCLUSIONS: Using thermal windowing, a distribution of temperature-dependent relaxation times encountered in real systems was obtained as opposed to a single average value routinely acquired by other techniques. Relevant kinetic parameters were obtained and used in mechanistically delineating the effects on molecular mobility of temperature and incorporating the drug in a polymer. This allows for appropriate choices to be made regarding drug loading, storage temperature, and type of polymer that would realistically correlate to physical stability.

Algorithms↗

PubMed2002

Solubility of E2050 at various pH: a case in which apparent solubility is affected by the amount of excess solid.

The solubility of E2050, supplied as a dihydrochloride salt, in aqueous solutions at different pHs was studied. Two pK(a)s controlling the equilibrium between the various protonated species were determined. The solubility-pH profile of E2050 is expected to be high in acidic solutions because protonated species are formed and to be low in alkaline conditions due to the formation of hydrophobic free base. The solubility is also affected by chloride ion, a common ion for this drug substance. Two solubility products (K(sp)) were determined corresponding to the solubility of di-HCl salt and mono-HCl salt. Based on the pK(a)s (3.10 and 7.71), the solubility products with chloride (2.92 and 3.77 as corresponding pK(sp)), and the solubility of free base (2 x 10(-5) M), the solubility in solutions with different pH and different levels of chloride ion can be predicted. The prediction of the solubility change during the dilution of E2050 parenteral formulations by saline was also demonstrated. Furthermore, the present study presents an interesting example in which an apparent solubility can be different if varying (excess) amounts of salt are added to the solution. In this case, excess chloride ion suppresses the solubility in the pH region where mono-HCl salt controls the solubility.

Chemical Phenomena↗