In Vitro Evaluation of Dexamethasone-β-D-Glucuronide for Colon-Specific Drug Delivery

Dexamethasone--D-glucuronide is a potential prodrug for colonic delivery of the antiinflammatory corticosteroid dexamethasone. Previous studies [T. R. Tozer et al., Pharm. Res. 8:445–454 (1991)] indicated that a glucoside prodrug of dexamethasone was susceptible to hydrolysis in the upper gastrointestinal tract. Resistance of dexamethasone--D-glucuronide to hydrolysis in the upper gastrointestinal tract was therefore assessed. Conventional, germfree, and colitic rats were used to examine enzyme levels along the gastrointestinal tract to compare the stability of two model substrates (p-nitrophenyl--D-glucoside and --D-glucuronide) and to evaluate the prodrug dexamethasone--D-glucuronide. Hydrolytic activity was examined in the luminal contents, mucosa, and underlying muscle/connective tissues in all three types of rats. Enzymatic activity (-D-glucosidase and -D-glucuronidase) was greatest in the lumen of cecum and colon of conventional rats. In contrast, germ-free rats exhibited relatively high levels of -D-glucosidase activity (about 80% of total activity in the conventional rats) in the proximal small intestine (PSI) and the distal small intestine (DSI). Rats with induced colitis (acetic acid) showed reduced levels of luminal -D-glucuronidase activity in the large intestine; however, -D-glucosidase activity was relatively unchanged relative to that of the conventional rat. Mucosal -D-glucuronidase activity was significantly lower in the colitic rats compared with that in the conventional animals. Despite reduced luminal levels of -D-glucuronidase activity in the colitic rats, there was still a sharp gradient of activity between the small and the large intestines. Permeability of the glucoside and glucuronide prodrugs of dexamethasone through a monolayer of Caco-2 cells was relatively low compared to that of dexamethasone. The results indicate that dexamethasone--D-glucuronide should be relatively stable and poorly absorbed in the upper gastrointestinal tract. Once the compound reaches the large intestine, it should be hydrolyzed to dexamethasone and glucuronic acid. Specificity of colonic delivery in humans should be even greater due to lower levels of -D-glucuronidase activity in the small intestine compared with that in the laboratory rat.     

In Vivo Evaluation of a Colon-Specific Drug Delivery System: An Absorption Study of Theophylline from Capsules Coated with Azo Polymers in Rats

Azo polymers based upon 2-hydroxyethyl methacrylate, methyl methacrylate, and methacrylic acid, and containing N,N-bis [(methacryloyloxyethyl)oxy(carbonylamino)]azobenzene as azo aromatic agent were evaluated in vivo as coatings for colon-specific drug delivery. The gastrointestinal absorption of theophylline from capsules coated with the azo polymers was examined in the proximal part of the small intestine and the cecum of male Wistar rats. The capsules were surgically inserted in the region of interest. The plasma concentration of the drug was higher when the capsules were inserted in the cecum as compared to the small intestine. The appearance of theophylline in the plasma when capsules were administered in the small intestine can be attributed to simple diffusion of the drug through the swollen polymer coating. Release and absorption from the cecum is the combined result of diffusion and degradation of the azo polymer coatings by bacterial azo reductase.     

pH依赖型愈肠宁结肠靶向片的制备及体内外释放评价

目的制备用于治疗溃疡性结肠炎的pH依赖型愈肠宁结肠靶向片(pH-dependen t Y uchangn ing T ab let forco lon-spec ific de livery,PYTCSD),并对其体内外释放性能进行评价,探讨制备中药结肠靶向制剂的可行性。方法以苦参碱和氧化苦参碱体外释放度为指标,对制剂的包衣处方进行筛选;采用体外释放度测定法考察该制剂的体外释放性能;采用硫酸钡造影技术对该制剂在人体内的释放性能进行评价。结果拟订了PYTCSD的制备方法:将药物制备得片芯后,以质量浓度3.70%(g/mL)丙烯酸树脂Ⅲ(Eudrag itⅢ)、0.37%(g/mL)邻苯二甲酸二乙酯(DEP)、0.93%(g/mL)滑石粉的乙醇混悬溶液为包衣液,包衣使片芯增重8%,即得;体外释放度测定结果表明,在人工胃液2 h时溶出液中未检测到苦参碱和氧化苦参碱,在人工小肠液4 h时两指标累积溶出率均<10%,而在人工结肠液1 h时苦参碱和氧化苦参碱分别累积溶出86.5%和86.8%;体内释放度试验结果表明,PYTCSD在8名志愿者体内均能完整到达回盲部或升结肠,并在上述部位崩解释放出药物。结论制备得pH依赖型愈肠宁结肠靶向片能达到较好结肠定位释药的目的。     

甲硝唑结肠定位肠溶片的制备及质量控制

目的:研制甲硝唑结肠定位肠溶片的制备工艺和处方,考察其体外释放度并制定该剂型的质量评价标准.方法:模拟服药后该剂型在胃肠道中的生理释药过程,用3种不同pH值的磷酸盐缓冲液作为释放介质,分别在其最大吸收波长277,321和317nm处检测甲硝唑的吸收度,并根据特定时间的药物吸收计算出累计释放度.结果:药片在人工胃液、pH 6.8人工肠液不释药;在pH 7.8人工结肠液中2～20μg穖L-1范围内线性良好,平均回收率104.8%,RSD为0.98%.结论:甲硝唑结肠定位肠溶片的体外释放度检测结果合格.     

肠溶性瑞巴派特壳聚糖胶囊的制备及大鼠口服给药吸收评价

目的评价肠溶性瑞巴派特壳聚糖胶囊的释药作用,考察其结肠定位效果。方法将瑞巴派特1 mg装入壳聚糖胶囊中,并用羟丙基甲基纤维素邻苯二甲酸酯(HPMCP)包裹胶囊,观察胶囊的体外释药性能。在乙醚麻醉下通过聚乙烯管大鼠口服给予瑞巴派特壳聚糖胶囊4 mg,对照组口服同剂量的明胶胶囊和羧甲基纤维素溶液。于给定的时间间隔取血,取出结肠组织,分离提取药物,用HPLC法测定大鼠血液及结肠中药物浓度。结果在6 h体外溶出试验中,即人工胃液2 h和人工肠液4 h中,瑞巴派特从壳聚糖胶囊中的释药量的质量分数小于10%。大鼠口服瑞巴派特壳聚糖胶囊时,在结肠黏膜中的药物含量-时间曲线下面积(AUCLI0-9,16.01 mg.h.L-1)分别是明胶胶囊和羧甲基纤维素溶液的2.5倍和4.4倍。口服瑞巴派特壳聚糖胶囊,大鼠血浆药物含量-时间曲线下面积(AUCPL0-9)为1.02 mg.h.L-1,同剂量的明胶胶囊和羧甲基纤维素溶液分别是2.16 mg.h.L-1和1.89 mg.h.L-1,表明在壳聚糖的作用下,与明胶胶囊或羧甲基纤维素溶液比较,瑞巴派特从胃肠道吸收进入血液循环的量较少。结论在HPMCP的保护下,壳聚糖是瑞巴派特在结肠释药的一种有效的载体。     

结肠定位盐酸小檗碱羧甲基魔芋胶小丸释药机制的研究

目的:研究结肠定位盐酸小檗碱羧甲基魔芋胶小丸的释药机制。方法:采用离子胶凝法制备羧甲基魔芋胶小丸,对小丸在不同释放介质条件下的药物释放度和溶蚀度进行研究。结果:与在不含酶介质中的情况相比,小丸在含酶(大鼠盲、结肠内容物或β-甘露聚糖酶)介质中的药物释放和丸粒溶蚀明显加快,酶对小丸载体材料的降解作用是造成丸粒骨架溶蚀的主要因素;随介质中β-甘露聚糖酶浓度增加,小丸的药物释放和溶蚀均有所增加,药物释放量与丸粒溶蚀量呈近似1∶1的线性相关;药物释放符合Peppas方程,其中释药指数n>1。结论:盐酸小檗碱羧甲基魔芋胶小丸的释药机制为酶降解溶蚀释药,具有结肠定位释药的可能性。     

盐酸小檗碱羧甲基魔芋胶小丸在大鼠体内释药研究

目的：研究盐酸小檗碱羧甲基魔芋胶小丸在大鼠体内的药物吸收及胃，小肠和结肠组织中药物浓度经时变化，评价其结肠定位释药特性。方法：将盐酸小檗碱羧甲基魔芋胶小丸(小丸组)和盐酸小檗碱羧甲基纤维素混悬液(对照组)大鼠灌胃给药(以盐酸小檗碱计，给药剂量50 mg·kg^-1)，采用HPLC测定大鼠体内盐酸小檗碱在血浆，胃，小肠和结肠组织中的浓度，计算药物相对靶向释药指数。结果：盐酸小檗碱在血浆和组织匀浆中线性范围分别为0.0252～2.52 mg·L^-1(r=0.999 2)和0.126～25.22 mg·L^-1(r＞0.99)，血浆和组织匀浆中检测限分别为10，8 mg·L^-1,小丸组血浆中药时曲线下面积(AUC_0→∞)是对照组的0.477倍；小丸组胃，小肠，结肠组织AUC_0→∞分别是对照组的0.187，0.228，2.00倍；小丸组在大鼠胃，小肠，结肠组织的药物相对靶向释药指数分别为0.392 4，0.478 6，4.193。结论：盐酸小檗碱羧甲基魔芋胶小丸具有较好的结肠定位释药特性。     

甲硝唑结肠定位微丸的体外释药机理

目的：研究自制的甲硝唑结肠定位微丸的体外释药机理。方法：用电镜观察微丸在释药前后的变化，通过替换包衣材料来考察微丸的释药行为，通过改变释放介质的渗透压来考察微丸的体外释药特性。结果：乳糖代替HPMC包衣的微丸释药后衣膜也出现破裂；释放介质渗透压升高后微丸释药速率减慢，释药速率与膜内外渗透压差之间有较好的线性关系。结论：微丸的释药机制是介质通过外层EC膜向内渗透，内层的HPMC吸水缓慢水合、溶解，药物及丸心中的水溶性物质也随后溶解，外层EC膜在渗透压作用下发生破裂，药物在渗透压驱动作用下通过EC衣膜裂口向外扩散，从而达到延时释药的效果。     

时间控制型结肠定位释药片体外释放的影响因素

以美沙拉嗪为模型药物，制备含不同有机酸的片芯，依次包内隔离层（HPMC）、胃溶衣层（丙烯酸树脂Ⅳ）、外隔离层（HPMC）和肠溶衣层（HPMCP），制得时间依赖型结肠定位释药片。考察了有机酸种类、用量及内隔离层和胃溶衣层增重对片剂释放时滞的影响。结果表明，片芯含琥珀酸50mg、内隔离层和胃溶衣层增重分别为1．2％和12％的片剂，在模拟胃肠液中的时滞约5h,6h累积释放达85％以上。     

Effect of Colonic Lactulose Availability on the Timing of Drug Release Onset in Vivo from a Unique Colon-Specific Drug Delivery System (CODES™)

Purpose. To test the hypothesis that the onset of drug release in vivo from a unique colon-specific drug delivery system (CODES) would depend on the colonic availability rate of lactulose. The site specificity of drug release in canine GI tract was also estimated. Methods. CODES tablets were prepared by tableting the granulation of acetaminophen and lactulose, followed with film coating. The pharmacokinetic performance of different CODES formulations was evaluated in six beagle dogs under fasted conditions. The release of acetaminophen and lactulose was also characterized in vitro. Results. The onset of acetaminophen release in beagle dogs was found to be dependent on the coating level of Eudragit E and lactulose loading in the core tablet. At Eudragit E coating levels of 4%, 8%, and 12% (coating weight gain), the onset of in vivo drug release occurred 5.5 (±1.9) h, 4.8 (±1.0) h. and 7.5 (±1.0) h, respectively, after dosing. A similar trend was observed when the loading of lactulose in the core tablet decreased from 78% to 58% and 38%. However, the rate and extent of acetaminophen absorption did not vary significantly in each situation based on the values of AUC and C_max. Conclusions. The onset of drug release in vivo from CODES tablets is predominantly dependent on colonic availability rate of lactulose because drug release from this system is triggered by localized drop of colonic pH from the fermentation of lactulose.