Effect of calcium ions on the gelling and drug release characteristics of xanthan matrix tablets

Xanthan is a well-known biopolymer. It is an anionic polysaccharide, whose primary structure depends on the bacterial strain and fermentation conditions. Xanthan was extensively studied in combination with galactomannans, and over 90 patents cover the technology of this preparation. Our aim was to investigate the relation between the physical properties of a xanthan matrix in the absence or presence of calcium ions and its influence on the release of pentoxifylline. The release of pentoxifylline from xanthan tablets in purified water was shown to be very slow and governed by the process of polymer relaxation. The presence of calcium ions significantly increased the drug release, changing the release mechanism into a more diffusion controlled one. Xanthan matrices showed substantially faster and more extensive swelling in water than in the presence of Ca2+ ions. Surprisingly, negative correlation between drug release and degree of swelling was obtained for xanthan: the higher the swelling, the slower the drug release. Higher ionic strength led to lower erosion of xanthan tablets, and the gel layers formed were more rigid and of firmer texture, as shown by rheological experiments and textural profiling. The results indicate that the presence of Ca2+ ions in the solution or in matrices does not cause crosslinking of xanthan polymers, but causes charge screening of ionized groups on the trisaccharide side chains of xanthan, leading to lower inter-molecular repulsion and changing water arrangement. The understanding of the parameters influencing drug release leads to the conclusion that xanthan is suitable for controlled release formulations, especially with the incorporation of certain small counterions.     

Controlled delivery of aspirin: effect of aspirin on polymer degradation and in vitro release from PLGA based phase sensitive systems

The objective of this study was to develop poly (d,l-lactide-co-glycolide) (PLGA) based injectable phase sensitive in situ gel forming delivery system for controlled delivery of aspirin, and to characterize the effect of drug/polymer interaction on the in vitro release of aspirin and polymer degradation. Aspirin was dissolved into PLGA solution in 1-methyl-2-pyrrolidone. Poly(ethylene glycol)400 was used as plasticizer to reduce initial burst release. The solution formulation was injected into aqueous release medium to form a gel depot. Released samples were withdrawn periodically and assayed for aspirin content by high performance liquid chromatography. The effect of aspirin on the degradation of PLGA matrix was evaluated using Proton Nuclear Magnetic Resonance and Gel Permeation Chromatography. PLGA based in situ gel forming formulations controlled the in vitro release of aspirin for 7 days only. Analysis of PLGA matrix residuals revealed that PLGA in aspirin loaded formulations exhibited a significantly (p < 0.05) faster degradation compared to blank formulations. These findings suggest that aspirin causes an unusually faster degradation of PLGA. Such faster degradation of PLGA has not been noticed for any other drugs reported in the literature.     

Physicochemical properties of tadalafil solid dispersions – Impact of polymer on the apparent solubility and dissolution rate of tadalafil

To improve solubility of tadalafil (Td), a poorly soluble drug substance (3 μg/ml) belonging to the II class of the Biopharmaceutical Classification System, its six different solid dispersions (1:1, w/w) in the following polymers: HPMC, MC, PVP, PVP-VA, Kollicoat IR and Soluplus were successfully produced by freeze-drying. Scanning electron microscopy showed a morphological structure of solid dispersions typical of lyophilisates. Apparent solubility and intrinsic dissolution rate studies revealed the greatest, a 16-fold, increase in drug solubility (50 μg/ml) and a significant, 20-fold, dissolution rate enhancement for the Td/PVP-VA solid dispersion in comparison with crystalline Td. However, the longest duration of the supersaturation state in water (27 μg/ml) over 24 h was observed for the Td solid dispersion in HPMC. The improved dissolution of Td from Td/PVP-VA was confirmed in the standard dissolution test of capsules filled with solid dispersions. Powder X-ray diffraction and thermal analysis showed the amorphous nature of these binary systems and indicated the existence of dispersion at the molecular level and its supersaturated character, respectively. Nevertheless, as evidenced by film casting, the greatest ability to dissolve Td in polymer was determined for PVP-VA. The crystallization tendency of Td dispersed in Kollicoat IR could be explained by the low T_g (113 °C) of the solid dispersion and the highest difference in Hansen solubility parameters (6.8 MPa^0.5) between Td and the polymer, although this relationship was not satisfied for the partially crystalline dispersion in PVP. Similarly, no correlation was found between the strength of hydrogen bonds investigated using infrared spectroscopy and the physical stability of solid dispersions or the level of supersaturation in aqueous solution.     

Development of orodispersible polymer films with focus on the solid state characterization of crystalline loperamide

The formulation of active pharmaceutical ingredients (API) as orodispersible films is gaining interest among novel oral drug delivery systems due to their small size, enhanced flexibility and improved patient compliance. The aim of this work was the preparation and characterization of orodispersible films containing loperamide hydrochloride (LPH) as model drug. As loperamide hydrochloride is poorly soluble in water it was used in crystalline form with a loading of 2 mg/6 cm² film.Hydroxypropyl methylcellulose (HPMC) and different types of hydroxypropyl cellulose (HPC) in different concentrations were used as film forming polymers whereas arabic gum, xanthan gum and tragacanth served as thickening agents. Films were characterized with respect to the content uniformity, morphology, thermal behavior and crystallinity. Suspensions were investigated regarding their viscosity using a rotational rheometer and the crystal structure of the Active Pharmaceutical Ingredient (API) was analyzed using polarized light microscopy. The development of flexible, non-brittle and homogeneous films of LPH was feasible.Two polymorphic forms of LPH appeared in the film formulations dependent on the utilized polymer. While in presence of HPMC the original polymorphic form I remained stable in suspension and films, the polymorphic form II occurred in presence of HPC. Both polymorphic forms were prepared separately and a solid state characterization was performed. Polymorph I showed isometric crystals whereas polymorph II showed needle shaped crystals. Tragacanth was able to prevent the transformation to polymorph II, if it was dissolved first before HPC. When HPC was added first to the suspension, the conversion to form II occurred irreversibly also after further addition of tragacanth.     

生物医用高分子材料在人造红血球的应用研究与进展

输血作为一种生命救治和人体机能维持的重要手段,已经广泛应用于临床实践当中。人造红血球的研究是解决目前临床使用上存在的诸多弊端（血型、病毒感染、保质期短等）,并可以安全高效的应用于紧急突发事件中的一个重要手段。本文从人体红血球的构造和基本功能出发,详细介绍并评价了人造红血球研究的发展过程和最新进展,归纳了新型人造红血球材料的设计要求,论述了医用高分子材料在人造红血球领域的应用优势,提出了生物可降解高分子与血红蛋白分子结合开发新型人造红血球的设计思路并开展了初步的科研工作。     

Malawian mothers’ attitudes towards the use of two supplementary foods for moderately malnourished children

The efficacy of lipid-based nutrient supplements (LNS) versus corn–soy blend (CSB) in promoting the growth of moderately malnourished children is currently being tested, but information about maternal attitudes towards the two supplements is lacking. This research studied 504 Malawian mothers’ attitudes about LNS and CSB through exit interviews completed at the end of three 12-week clinical trials and compared differences between the groups. Exploratory analyses of factors associated with withholding of supplements during fever, diarrhea, and cough were performed using logistic regression. Mothers generally had similar, positive attitudes towards LNS and CSB. Both supplements were said to be highly acceptable, children learned to eat them within two weeks, and mothers were willing to use them again. Mothers in the LNS group were reportedly more likely to withhold supplements from their children during cough, due to its sweetness, and were willing to pay more for a one-week supply of supplement than mothers in the CSB group. Maternal literacy was negatively and child's weight-for-height z-score was positively associated with withholding of supplements during illness. Our results indicate that the sweetness in LNS should be reduced, and programs using supplements in Malawi could include advice on appropriate feeding of supplements during illness.     

处方工艺对瑞舒伐他汀钙片混合均匀度及含量均匀度的影响

目的 研究处方中的辅料及工艺对瑞舒伐他汀钙片混合均匀度及含量均匀度的影响。方法 采用粉末直接压片工艺，通过单因素试验，考察处方中乳糖的型号、微晶纤维素的型号、乳糖与微晶纤维素的比例、钙盐的种类及交联聚维酮用量对混合均匀度及含量均匀度的影响；同时研究混合工艺对混合均匀度及压片工艺对含量均匀度的影响。结果 不同的乳糖型号（T80、PW80、315）、微晶纤维素型号（PH102、M102、102）、乳糖与微晶纤维素的比例（1:1、3:1、1:3）、钙盐的种类（磷酸钙（细颗粒）、无水磷酸氢钙（细颗粒、细粉）、碳酸钙（细粉））的处方混合均匀度及含量均匀度良好，磷酸钙（粗颗粒）的处方混合均匀度及含量均匀度较差。在混合容器中加入50%的乳糖，之后加入原料药、微晶纤维素、交联聚维酮和磷酸钙，以10 r·min-1混合20~25 min；再加入剩余的乳糖，以10 r·min-1混合15~25 min，物料混合均匀度良好。重力加料器及压片速度（10~20 r·min-1）的含量均匀度良好；强制加料器及压片速度（30 r·min-1）的含量均匀度较差。结论：通过研究筛选出了适合粉末直压工艺的乳糖型号、微晶纤维素型号、乳糖与微晶纤维素比例、钙盐种类及交联聚维酮用量。考察了混合工艺参数范围，优选了重力加料器及压片速度（10~20 r·min-1），获得了良好的混合均匀度和含量均匀度。     

头孢地尼原料及制剂的聚合物杂质分析

目的 建立头孢地尼原料及制剂聚合物杂质的分析方法。方法 分别采用0.1mol/L磷酸盐溶液和氯仿-三乙胺为溶剂,制备头孢地尼降解溶液;采用高效凝胶色谱法(HPSEC, TSK G2000 SWxl)和柱切换-LC/MSn法对头孢地尼降解溶液的弱保留值杂质进行分离和结构鉴定,并评估高效凝胶色谱法分析聚合物杂质的专属性;采用Diamonsil, C18型色谱柱,以0.25%四甲基氢氧化铵溶液(pH5.5)-甲醇-乙腈为流动相进行梯度洗脱,建立头孢地尼聚合物的RP-HPLC分析方法,采用二维色谱法和柱切换-LC/MSn法对其专属性进行分析,并进行方法学验证。结果 在头孢地尼降解物中鉴定出头孢地尼二聚体及其异构体,以及若干小分子杂质;高效凝胶色谱法分离头孢地尼聚合物杂质时,小分子杂质与聚合物杂质共出峰,方法专属性与定量准确性差;RP-HPLC法分析头孢地尼聚合物杂质时,能够检出头孢地尼二聚体及其异构体,头孢地尼三聚体,专属性好。结论 高效凝胶色谱法不能对头孢地尼的聚合物杂质进行有效质控,建立的反相色谱法分析头孢地尼聚合物杂质的专属性良好,可将头孢地尼降解溶液可作为聚合物杂质系统适用性溶液。     

骨组织工程高分子材料和复合材料的研究进展

支架材料是骨组织工程三大因素之一,作为一种载体,为细胞提供生存的三维空间。本文阐述了近年来常见高分子材料及复合材料的国内外研究进展,并分析了各种材料的优缺点。最后,指出了目前支架材料研究中仍存在的问题,并对其发展前景进行了展望。     

Enteric Controlled-Release Pantoprazole-Loaded Microparticles Prepared by Using Eudragit S100 and Poly(ε-caprolactone) Blend

Microparticles of poly(ε-caprolactone) and of its blend with Eudragit® S100 were prepared by emulsion/solvent evaporation technique to provide controlled release and gastro-resistance for an acid labile drug. This drug was sodium pantoprazole, a proton pump inhibitor. Both formulations were successfully prepared, but only the microparticles prepared with the blend were capable of stabilizing the drug in the acid medium. Furthermore, this formulation showed in vivo protection of stomachs against ulceration caused by ethanol in rats. These microparticles were tabletted, and the tablets demonstrated slower drug release and higher acid protection than the microparticles before tabletting.