Kinetics of drug release from polylactic acid—hydrocortisone microcapsules

Abstract

Polylactic acid microcapsules of similar particle size distribution containing various drug loadings of hydrocortisone were prepared. The microcapsules, which contained randomly dispensed drug particles, showed a dissolution pattern which consists of a fast first-stage and a slow second-stage drug release. Our studies showed that the kinetics of drug release from the microcapsules can be adequately described by a spherical matrix model based on a flux mechanism involving the diffusion of dissolved drug at the penetrating front of the dissolution medium. Drug loading played an important role in the control of drug release rate. An empirical relationship between drug loading and drug diffusi-bility through the polymeric matrix was developed and showed that the rate of drug release increased exponentially with the increase in drug loading. The microcapsules were further shown to exhibit increased rate of drug release in dissolution medium containing either cetylpyridium chloride or aerosol OT. The effect of the surfactants was attributed to surface tension lowering and improved wetting of the microcapsule particles.     

制备条件对丝裂霉素微囊载药量及释放度的影响

目的:筛选制备高载药量和释放性能良好的丝裂霉素微囊的条件。方法:以溶剂非溶剂法制备了丝裂霉素微囊,用高效液相色谱法和紫外分光光度法测定丝裂霉素微囊载药量及释放度。结果:随着囊材用量减少,载药量升高,释放显现突释效应;随着吐温-80用量的增加,释放度逐渐加快,直至无规律释药;随着搅拌速度的加快,载药量先增加后减少,释放度增大。结论:以正己烷、环己烷为溶剂,最佳制备工艺条件是:0.8%的乙基纤维素,4%的吐温-80,100 r.min-1的搅拌速度。     

Microencapsulation using poly(DL-lactic acid) I: Effect of preparative variables on the microcapsule characteristics and release kinetics

Abstract

Poly(DL-lactic acid) (DL-PLA, molecular weight 20 500) microcapsules containing phenobarbitone (PB) as a reference core were prepared using a water/oil (W/O) emulsion system. Surface morphology, particle size and ‘encapsulation efficiency’ of the microcapsules prepared using different preparative variables have been investigated. Buffer pH 9 was used as a dissolution medium to determine the affect of preparative variables on the release rate from these microcapsules.

With an increase in temperature of evaporation the microcapsule surface became increasingly irregular and porous, due to deposition of phenobarbitone crystals near the vicinity of the microcapsule surface leading to rapid release of the core. The normalized release rate was found to increase exponentially with an increase in the temperature of evaporation. Microcapsule morphology was also severely affected due to differences in polymer concentration in the disperse phase solvent. With the increase in polymer concentration, the microcapsule surface was found to be increasingly irregular and non-continuous, due to rapid precipitation of the polymer. Increased polymer concentrations also increased mean microcapsule diameter. The release rate increased with the increase in polymer concentration due to surface defects and did not exhibit a straight line correlation. When core loading was very high (e.g. C:P, 2:1 and 1:1), crystals of phenobarbitone appeared at the surface and these caused a very rapid burst effect. However, microcapsules containing a lower phenobarbitone content were found to follow t^1/2 dependent release. The encapsulation efficiency was not seriously affected due to variations in temperature of preparation and polymer concentration. However, with the decrease in initial core loading the encapsulation efficiency of microcapsules was found to be reduced.     

海藻酸钠-壳聚糖微囊成型机理及其对大分子药物的载药、释药研究海藻酸钠-壳聚糖微囊成型机理及其对大分子药物的载药、释药研究

目的考察海藻酸钠-壳聚糖微囊成型机理及其对大分子药物的载药及释药特性。方法采用乳化胶凝法制备海藻酸钠-壳聚糖微囊,通过差示扫描量热法(DSC)探讨其成型机理。以牛血清白蛋白(BSA)为模型药,研究微囊对大分子药物的包载能力及释药特性。结果DSC分析结果显示,组成微囊的各材料间发生静电相互作用而成型。随药载比增加,微囊中BSA的载药量由9.20％增至35.08％;随壳聚糖浓度升高,载药量由30.29％升至38.12％。载药微囊中BSA在PBS(pH 7.4)与0.1 mol·L^-1 HCl中均呈两相释放;随CTS浓度增大,BSA在0.1 mol·L^-1 HCl中的释放减慢。结论制备的微囊圆整且分散性好,微囊对BSA具较高包载能力,并具一定的缓释作用。     

Kinetics of drug release from polylactic acid-hydrocortisone microcapsules

Polylactic acid microcapsules of similar particle size distribution containing various drug loadings of hydrocortisone were prepared. The microcapsules, which contained randomly dispensed drug particles, showed a dissolution pattern which consists of a fast first-stage and a slow second-stage drug release. Our studies showed that the kinetics of drug release from the microcapsules can be adequately described by a spherical matrix model based on a flux mechanism involving the diffusion of dissolved drug at the penetrating front of the dissolution medium. Drug loading played an important role in the control of drug release rate. An empirical relationship between drug loading and drug diffusibility through the polymeric matrix was developed and showed that the rate of drug release increased exponentially with the increase in drug loading. The microcapsules were further shown to exhibit increased rate of drug release in dissolution medium containing either cetylpyridium chloride or aerosol OT. The effect of the surfactants was attributed to surface tension lowering and improved wetting of the microcapsule particles.     

Gastroresistant microcapsules: new approaches for site-specific delivery of ketoprofen

Ketoprofen is a potent non-steroidal anti-inflammatory drug (NSAID) that has been widely used in the treatment of rheumatoid arthritis and other related conditions. However, it carries the risk of undesirable systemic side effects and gastrointestinal irritation at the usual dose of oral administration. The aim of this study was to prepare and evaluate gastroresistant microcapsules containing ketoprofen. Microcapsules were obtained by a spray-drying process starting from an O/A emulsion in the presence of different pH-dependent materials (Eudragit^® L100, Eudragit^® S100, and stearic acid) dissolved in the external phase. The influence of formulation factors (oily phase employed for drug solubilization, type of coating) on the morphology, particle size distribution, drug loading capacity, in-vitro release, and ex-vivo permeation characteristics were investigated. Drug loading capacity was very high for all the microcapsules prepared. Formulation factors did not significatively influence the mean particle size, but modified microcapsule in-vitro and ex-vivo behavior.     

Cry8Ca2-containing layer-by-layer microcapsules for the pH-controlled release of crystal protein

Abstract

To extend the activity of crystal proteins by protection from environmental stress, we developed a new type of microcapsule containing Cry8Ca2 protoxins. Layer-by-layer (LbL) microcapsules containing Cry8Ca2 were successfully prepared for the first time by the alternate deposition of poly(acrylic acid) (PAH) and Cry8Ca2 at pH 6 on the surface of poly(styrene sulphonate) (PSS)-doped CaCO₃ microbeads. Scanning electron microscopy (SEM) photos showed that microparticles were spherical in shape, approximately 2?μm in diameter. After removing the templates, the loading results were observed with a confocal laser scattering microscope (CLSM) by using fluorescein-labelled Cry8Ca2. The Cry8Ca2 protoxins were released from the microcapsules when they were exposed to a pH higher than 6 due to the loss of the electrostatic attraction. The microcapsules displayed resistance to proteinase K. Bioassay result demonstrated that the microcapsules with Cry8Ca2 displayed approximately equivalent insecticidal activity to the larvae of Anomala corpulenta compared to the free Cry8Ca2.     

对乙酰氨基酚复合微囊缓释栓的制备及体外释放度研究

目的:采用复凝聚法制备对乙酰氨基酚(AAP)微囊并考察其体外释药行为。制备AAP复合微囊栓剂,具有良好释放效果。方法:考察复凝聚法制备AAP微囊过程的处方和工艺因素,并进行正交试验设计,筛选出最佳条件制备AAP微囊并考察其体外释药行为。同时采用复合缓释技术(速释部分+微囊缓释)制备复合微囊缓释栓剂,考察其释药行为。结果:建立了复凝聚法制备AAP微囊方法,优化后的制备条件为:明胶阿拉伯胶囊材用量各为7 g(溶液浓度7%),药物用量为8 g,搅拌速度为300 r·min^-1,制备温度55℃。此条件制备的微囊形态圆整,粒径均匀,重复性好,包封率为(79.71±0.10)%,载药量为23.11±0.69%。微囊有缓释效果,拟合缓释方程符合一级方程。制备的复合微囊栓与普通栓剂相比,具有更好的释放效果,其中缓释过程药物释放符合Higuchi方程。结论:基于普通栓剂与复合微囊技术制备的新型AAP栓具有更佳的释药特性。     

Preparation and in vitro dissolution of salbutamol sulphate microcapsules and tabletted microcapsules

Abstract

Salbutamol sulphate is a sympathomimetic amine having a rather short plasma half-life. Aiming to achieve sustained release of this drug through microencapsu-lation, the coacervation method with a 1:1 core-shell ratio was used. In vitro release rate experiments were performed on the microcapsules prepared using ethyl cellulose as the coating agent and compared to the results of intact drug, the tabletted microcapsules and a commercial tablet. The release rate of salbutamol sulphate could be controlled through microencapsulation. The time for the 50% release of the drug was 15 and 90 min for the tabletted microcapsules and microcapsules respectively. The specific surface area of the intact drug was 0.35m²/cc while it reduced to 0.06m²/cc after encapsulation.     

利用喷雾干燥技术制备氯雷他定透明质酸微囊和微球及其评价

目的：制备氯雷他定（LOR）透明质酸（HA）微囊和微球,并对其进行体外评价。方法：HA和聚乙二醇6000（PEG 6000）为材料,以粒径,载药量,载药率,溶解度,体外累积释放度来评价载药微囊和微球;利用DSC和XRD考察载药微囊和微球中LOR的晶型变化。结果：HA、PEG 6000和LOR的比例为16：1：2时,LOR的溶解度和溶出效果最佳。LOR微囊的水中溶解度为（23.12±0.15） μg·mL^-1,载药量为（8.07±0.44）%,载药率为（76.69±0.44）%,体外累积释放度达到（87.00±3.34）%;LOR微球的水中溶解度为（5.58±0.15） μg·mL^-1,载药量为（11.87±0.46）%,载药率为（112.78±0.46）%,体外累积释放度达到（63.16±0.63）%。晶型变化分析结果,微囊中LOR大部分以无定型状态存在,小部分以结晶状态存在;微球中LOR以无定型状态存在。结论：采用喷雾干燥法成功制备LOR-HA微囊和微球,显著改善LOR的溶解度和体外释放度的,利用此方法制备微囊（或微球）成本较低、操作简单,易于实现大规模工业化生产。     

Production of BSA-loaded alginate microcapsules: Influence of spray dryer parameters on the microcapsule characteristics and BSA release

The aim of this study was to optimize the production of BSA-loaded alginate microcapsules by spray drying and to study the release of bovine serum albumin fraction V (BSA) under gastric simulated conditions. Microcapsule yield, BSA release, microcapsule size and size distribution were characterized following the application of different production parameters including inlet air temperature, inlet air pressure and liquid feed rate. The microcapsules were incubated in 0.1?N HCl and BSA release was quantified over time. The yields were higher with the pressure of 3?bar compared to 4?bar and with a feed rate of 0.45 vs. 0.2?ml s^?1. A high feed rate (0.45 vs. 0.2?ml s^?1) allows one to obtain microcapsules with a low BSA release (p?=?0.0327). The increase of the atomizer inlet temperature leads to microcapsules with a higher BSA release (p?=?0.0230). A higher air pressure of 4?bar compared to 3?bar resulted in a lower microcapsule size (2.55 vs. 2.80?µm) and led to a narrower size distribution (0.92 vs. 1.07). In conclusion, the spray dryer parameters influenced the alginate microcapsule characteristics as well as subsequent protein release into a simulated gastric medium.     

Production of BSA-loaded alginate microcapsules: Influence of spray dryer parameters on the microcapsule characteristics and BSA release

The aim of this study was to optimize the production of BSA-loaded alginate microcapsules by spray drying and to study the release of bovine serum albumin fraction V (BSA) under gastric simulated conditions. Microcapsule yield, BSA release, microcapsule size and size distribution were characterized following the application of different production parameters including inlet air temperature, inlet air pressure and liquid feed rate. The microcapsules were incubated in 0.1?N HCl and BSA release was quantified over time. The yields were higher with the pressure of 3?bar compared to 4?bar and with a feed rate of 0.45 vs. 0.2?ml?s^?1. A high feed rate (0.45 vs. 0.2?ml?s^?1) allows one to obtain microcapsules with a low BSA release (p?=?0.0327). The increase of the atomizer inlet temperature leads to microcapsules with a higher BSA release (p?=?0.0230). A higher air pressure of 4?bar compared to 3?bar resulted in a lower microcapsule size (2.55 vs. 2.80?µm) and led to a narrower size distribution (0.92 vs. 1.07). In conclusion, the spray dryer parameters influenced the alginate microcapsule characteristics as well as subsequent protein release into a simulated gastric medium.     

含ZnS的壳聚糖-阿拉伯胶含药微囊的制备及研究

目的本文以壳聚糖和阿拉伯胶为囊材,利用复凝聚法制备包裹非甾体抗炎药物布洛芬的微囊,引入ZnS纳米,增强其缓控释性能。方法将含乙酸锌的壳聚糖溶液与含Na2S的阿拉伯胶溶液混合,以布洛芬为模型药物,通过复凝聚法制备包裹非甾体抗炎药物布洛芬的复合微囊,以微囊的药物包封率与载药量为制备工艺优化指标,通过L9（34）正交实验得出微囊的最佳制备工艺条件。同时用转篮法在肠液条件下进行体外溶出的测定。结果壳聚糖浓度为0.2%、成囊pH为4.5、成囊温度为45℃、搅拌速度为200 rpm。交联剂戊二醛用量0.6mL,乙酸锌0.05M,硫化钠0.05M为最佳工艺。引入纳米ZnS的微囊比未引入纳米ZnS的微囊及市售的片剂具有更好的缓控释性能。结论引入纳米ZnS离子,并以最佳制备工艺条件制备含药微囊,工艺稳定,具有良好的缓控释作用。     

Poly(D,L-lactide-co-glycolide) encapsulated poly(vinyl alcohol) hydrogel as a drug delivery system

Purpose. The efficiency of encapsulation of water-soluble drugs in biodegradable polymer is often low and occasionally these microcapsules are associated with high burst effect. The primary objective of this study is to develop a novel microencapsulation technique with high efficiency of encapsulation and low burst effect. Method. Pentamidine was used as a model drug in this study. Pentamidine/polyvinyl alcohol (PVA) hydrogel was prepared by freeze-thaw technique. Pentamidine loaded hydrogel was later microencapsulated in poly(lactide-co-glycolide) (PLGA) using solvent evaporation technique. The microcapsules were evaluated for the efficiency of encapsulation, particle size, surface morphology, thermal characteristic, and drug release. Results. Scanning Electron Microscope (SEM) studies revealed that the microcapsules were porous. The microcapsules were uniform in size and shape with the median size of the microcapsules ranging between 27 and 94 m. The samples containing 10% PLGA showed nearly three times increase in drug loading (18-53%) by increasing the hydrogel content from 0-6%. The overall drug release from the microencapsulated hydrogel, containing 3% and 6% PVA, respectively, was significantly lower than the control batches. Conclusions. The use of a crosslinked hydrogel such as PVA can significantly increase the drug loading of highly water-soluble drugs. In addition, incorporation of the PVA hydrogel significantly reduced the burst effect and overall dissolution of pentamidine.     

Suspensions of prolonged-release diclofenac-Eudragit® and ion-exchange resin microcapsules: II. Improved dissolution stability

Purpose:?The stability of prolonged release 100?µm -size ion-exchange resin (IER) diclofenac microcapsules (prepared by the Wurster process) and coated with Eudragit® RS30D was evaluated using dissolution analysis.

Methods:?The IER microcapsules were suspended in 0.1% methylcellulose and stored at 23 and 37°C and the dissolution study conducted over a 6-month period. The surface morphology of the microcapsules was examined using scanning electron microscopy (SEM).

Results:?The dissolution of the suspensions stored at 23°C on day 1 or 7 and was similar to that of day 30 with slightly faster dissolution on day 60. In contrast, release from suspensions stored at 37°C decreased with storage. The decrease in dissolution with increased temperature was possibly due to the polymer relaxation (micromelting) that was enough to seal the drug within the matrix, resulting in slow dissolution. SEM of the suspended microcapsules correlated with the dissolution data, i.e. the surfaces of microcapsule stored at 37°C showed decreased roughness or smoothening and closing of pores with time and, hence, retardation of drug release, compared with samples stored at 23°C. The dissolution kinetics (shown by the linearity of Bt vs. time profiles) indicated that release mechanism was diffusion.

Conclusions:?The suspensions of diclofenac IER microcapsules were stable up to 30 days at ambient temperature, which makes the formulation potentially useful as reconstitutable product.     

正交实验设计优化岩白菜素微囊的制备工艺

目的优化岩白菜素微囊的制备工艺,并对制备的岩白菜素微囊进行质量评价。方法以明胶为囊材,单凝聚法制备岩白菜素微囊,通过正交实验设计优化其制备工艺,并对包封率、载药量、平均粒径、体外溶出率进行研究。结果明胶制备岩白菜素微囊的最佳工艺条件为:明胶质量分数为6%,囊心囊材质量比为1∶2,搅拌速度为750r·min^-1。此最佳工艺制备的岩白菜素微囊包封率为75.90%,载药量为23.09%,体外溶出度测定30min为28.6%,12h累计释放达到90%以上。结论以最佳工艺条件制备岩白菜素微囊工艺稳定,包封率高,同时体外释放实验表明,该微囊具有较好的缓释作用。     

Release profile comparison and stability of diltiazem-resin microcapsules in sustained release suspensions

A sustained release suspension of diltiazem, a short half-life calcium channel blocker, was developed to reduce frequency of drug administration, ease of dose adjustment and improve patient compliance. In this study, the sustained release of diltiazem was obtained by complexing the drug with Dowex 50W x 4 and Dowex 50W x 8, strong cationic exchange resins with 4% and 8% degree of cross-linking, respectively. The diltiazem-Dowex 50W x 4 complexes provided the highest drug release and were subsequently used to prepare the microcapsules by emulsion-solvent evaporation method, using 0.75-5.00% cellulose acetate butyrate (CAB) in methylene chloride as a coating solution. As the concentration of CAB increased, the size of microcapsule increased and the drug release from the microcapsule was retarded. From release profile comparison using f(1) and f(2) factors, it was found that the microcapsules coated with 1.75% CAB provided a release profile equivalent to the commercial product of diltiazem sustained release capsule, Herbesser 90SR. Furthermore, sustained release suspensions of the diltiazem microcapsules were formulated with the use of 0.8% sodium carboxymethylcellulose or 0.4% xanthan gum as a suspending agent. The suspension of 0.4% xanthan gum showed superior in physical appearance after 120-day storage at 30 and 45 degrees C. In addition, all sustained release suspensions possessed good stability with low drug leaching and their release profiles were unchanged when compared with the dried microcapsules for 120 days at 30 and 45 degrees C.     

氨基噻唑(噁唑)类化合物的合成及抗K562细胞活性研究

目的 设计、合成一系氨基噻唑（噁唑）类似物,并测试新衍生物对人类慢性粒细胞白血病细胞系K562的体外抑制作用。方法 以dasatinib为先导化合物设计新衍生物,通过亲核取代和关环缩合得到目标化合物,其结构通过¹H-NMR、¹³C-NMR、IR和MS测定。结果 发现5个目标化合物抑制活性高于对照药伊马替尼。4个化合物抗K562细胞活性高于dasatinib。结论 保持药效基团不变,用五元噻唑环取代芳香苯环,活性能得以改善。     

Polyacrylate resin microcapsules for taste masking of antibiotics

Abstract

Various microencapsulated dosage forms were prepared to limit the release of an antibiotic in solution for up to 3 days and in the oral cavity following per oral administration. An experimental antibiotic, clarithromycin (TE-031), was used in these studies. The drug was first encapsulated in gelatin followed in some cases by crosslinking with glutaraldehyde. The gelatin microcapsules were then coated with acrylic resins (Eudragit®), whose solubility properties vary according to pH. A non-solvent coacervation technique was used to apply the Eudragit resins. It was found that crosslinking the gelatin retarded release of TE-031 somewhat relative to that from uncrosslinked gelatin microcapsules in a 72 h release experiment conducted at room temperature. Coating the gelatin microcapsules with Eudragit resins L100, S100, or E100 slowed the release of TE-031 further still; less TE-031 was released over 72 h from the Eudragit-coated formulations prepared with crosslinked gelatin compared with formulations prepared with uncrosslinked gelatin. The Eudragit ElOO-coated crosslinked gelatin microcapsule formulation was most effective in preventing release of the TE-031 under simulated conditions of storage in an aqueous solution.     

Preparation of double-encapsulated microcapsules for mitigating drug loss and extending release.

The double-encapsulated microcapsules were prepared by the non-solvent addition, phase-separation method to form core material and, encapsulated with the O/W emulsion non-solvent addition method to increase drug loading and regulate drug release rate. The drug used was theophylline, which is water-soluble. Dichloromethane and n-hexane were used as the solvent and non-solvent, respectively. This study investigated how various core material and microcapsule EC/TH ratios affect the drug loss, particle size, surface morphology and release rate. The drug loss of the double-encapsuLated microcapsules was 12.8% less than that of microcapsules prepared by the O/W emulsion non-solvent addition method alone. The particle size of these double-encapsulated microcapsules decreased as the concentration of EC polymer was increased in the second encapsulation process. The roughness of their surface was also in proportion to the concentration of polymer solution used in the second encapsulation process. The dissolution study showed that the T20 of the double-encapsulated microcapsules ranged from 2-35.4 h, while that of the O/W emulsion non-solvent addition method microcapsules was from 2.7-7.7 h. The greater the level of EC in the polymer solution, the slower the release rate of the drug from the microcapsules when the EC was not over the critical amount.