In vitro and in vivo evaluation of ranitidine hydrochloride loaded hollow microspheres in rabbits

Orally Administrated Olsalazine-Loaded Multilayer Pectin/Chitosan/Alginate Composite Microspheres for Ulcerative Colitis Treatment

The pathogenesis of inflammatory bowel diseases (IBDs) including ulcerative colitis (UC) and Crohn's disease is extremely cloudy. Maintaining the level of remission lesions in colitis is the default treatment attitude at present. Epithelial barrier restoration is considered as the same important strategy as colonic targeted drug delivery in UC treatment. In this paper, we developed a multilayer natural polysaccharide microsphere (pectin/chitosan/alginate) with pH and enzyme dual sensitivity to reduce the loss of medication in the upper digestive tract and preferentially adhere to exposed epithelial cells in colonic tissues by electrostatic forces for efficiently targeted UC treatment. Olsalazine as an inflammatory drug was efficiently loaded in the chitosan layer and realized a colonic pH-responsive drug release. Furthermore, the multilayer microspheres exhibited excellent capability in suppressing harmful flora and a bio-adhesion effect to extend the duration of local medicine. In the in vivo anti-colitis study, the downregulated levels of pro-inflammatory factors and the increase of tight junction protein indicated the excellent anti-inflammation effect of the olsalazine-loaded microspheres. In summary, these results showed that the multilayer natural polysaccharide microspheres could be a powerful candidate in the targeted drug delivery system for UC therapy.

In vitro and in vivo evaluation of curcumin loaded hollow microspheres prepared with ethyl cellulose and citric acid

Curcumin (CUR) demonstrates a variety of biological activities; however, the poor oral bioavailability limits its clinical application. The objective of this study was to develop and evaluate characteristics and bioavailability of hollow microspheres loading curcumin (CUR-HPs). CUR-HPs were prepared by solvent diffusion and evaporation method. The effect of viscosity of ethyl cellulose (EC), amount of EC, citric acid (CA) and CUR on physicochemical characteristics and in vitro release profile of CUR-HPs were evaluated. Scanning electron microscopy (SEM) showed microspheres had smooth surfaces with hollow structures. The yield of CUR-HPs was (96 ± 1.80) %. The floating rate at 24 h was (89.67 ± 4.91) % and the drug loading was (3.41 ± 0.21) %. Nearly 95% of CUR was released from the HPs at 24 h. In vitro release profiles of CUR-HPs fitted the Korsmeyer et al.'s equation and indicated that CUR was released through the combination of diffusion and erosion mechanisms. The bioavailability of CUR-HPs was 12-fold higher than that of CUR. The peak time was delayed for 7.5 h and peak concentration of CUR-HPs was 3.21 times than that of free CUR. The CUR-HPs might be a promising strategy to achieve sustained release and increase oral bioavailability of CUR.

Polymer blends used to develop felodipine-loaded hollow microspheres for improved oral bioavailability

Felodipine (FD) has been widely used in anti-hypertensive treatment. However, it has extremely low aqueous solubility and poor bioavailability. To address these problems, FD hollow microspheres as multiple-unit dosage forms were synthesized by a solvent diffusion evaporation method. Particle size of the hollow microspheres, types of ethylcellulose (EC), amounts of EC, polyvinyl pyrrolidone (PVP) and FD were investigated based on an orthogonal experiment of three factors and three levels. In addition, the release kinetics in vitro and pharmacokinetics in beagle dogs of the optimized FD hollow microspheres was investigated and compared with Plendil (commercial FD sustained-release tablets) as a single-unit dosage form. Results showed that the optimal formulation was composed of EC_{10 cp}:PVP:FD (0.9:0.16:0.36, w/w). The FD hollow microspheres were globular with a hollow structure and have high drug loading (17.69±0.44%) and floating rate (93.82±4.05%) in simulated human gastric fluid after 24h. Pharmacokinetic data showed that FD hollow microspheres exhibited sustained-release behavior and significantly improved relative bioavailability of FD compared with the control. Pharmacodynamic study showed that the FD hollow microspheres could effectively lower blood pressure. Therefore, these findings demonstrated that the hollow microspheres were an effective sustained-release delivery system for FD.

A 5-fluorouracil-loaded floating gastroretentive hollow microsphere: development, pharmacokinetic in rabbits, and biodistribution in tumor-bearing mice

5-Fluorouracil (5-FU) was loaded in hollow microspheres to improve its oral bioavailability. 5-FU hollow microspheres were developed by a solvent diffusion-evaporation method. The effect of Span 80 concentration, ether/ethanol volume ratio, and polyvinyl pyrrolidone/ethyl cellulose weight ratio on physicochemical characteristics, floating, and in vitro release behaviors of 5-FU hollow microspheres was investigated and optimized. The formulation and technology composed of Span 80 (1.5%, w/v), ether/ethanol (1.0:10.0, v/v), and polyvinyl pyrrolidone/ethyl cellulose (1.0:10.0, w/w) were employed to develop three batch samples, which showed an excellent reproducibility. The microspheres were spherical with a hollow structure with high drug loading amount (28.4%±0.5%) and production yield (74.2%±0.6%); they exhibited excellent floating and sustained release characteristics in simulated gastric and intestinal fluid. Pharmacokinetic studies demonstrated that 5-FU hollow microspheres significantly enhanced oral bioavailability (area under curve, [AUC](0-t): 12.53±1.65 mg/L(*)h vs 7.80±0.83 and 5.82±0.83 mg/L(*)h) with longer elimination half-life (t1/2) (15.43±2.12 hours vs 2.25±0.22 and 1.43±0.18 hours) and mean residence time (7.65±0.97 hours vs 3.61±0.41 and 2.34±0.35 hours), in comparison with its solid microspheres and powder. In vivo distribution results from tumor-bearing nude mice demonstrated that the animals administered with 5-FU hollow microspheres had much higher drug content in tumor, plasma, and stomach at 1 and 8 hours except for 0.5 hours sample collection time point in comparison with those administered with 5-FU solid microspheres and its powder. These results suggested that the hollow microspheres would be a promising controlled drug delivery system for an oral chemotherapy agent like 5-FU.

Recent advances in testing of microsphere drug delivery systems

INTRODUCTION

This review discusses advances in the field of microsphere testing.

AREAS COVERED

In vitro release-testing methods such as sample and separate, dialysis membrane sacs and USP apparatus IV have been used for microspheres. Based on comparisons of these methods, USP apparatus IV is currently the method of choice. Accelerated in vitro release tests have been developed to shorten the testing time for quality control purposes. In vitro-in vivo correlations using real-time and accelerated release data have been developed, to minimize the need to conduct in vivo performance evaluation. Storage stability studies have been conducted to investigate the influence of various environmental factors on microsphere quality throughout the product shelf life. New tests such as the floating test and the in vitro wash-off test have been developed along with advancement in characterization techniques for other physico-chemical parameters such as particle size, drug content, and thermal properties.

EXPERT OPINION

Although significant developments have been made in microsphere release testing, there is still a lack of guidance in this area. Microsphere storage stability studies should be extended to include microspheres containing large molecules. An agreement needs to be reached on the use of particle sizing techniques to avoid inconsistent data. An approach needs to be developed to determine total moisture content of microspheres.

Floating microspheres: a review

Gastric emptying is a complex process, one that is highly variable and that makes in vivo performance of drug delivery systems uncertain. A controlled drug delivery system with prolonged residence time in the stomach can be of great practical importance for drugs with an absorption window in the upper small intestine. The main limitations are attributed to the inter- and intra-subject variability of gastro-intestinal (GI) transit time and to the non-uniformity of drug absorption throughout the alimentary canal. Floating or hydrodynamically controlled drug delivery systems are useful in such applications. Various gastroretentive dosage forms are available, including tablets, capsules, pills, laminated films, floating microspheres, granules and powders. Floating microspheres have been gaining attention due to the uniform distribution of these multiple-unit dosage forms in the stomach, which results in more reproducible drug absorption and reduced risk of local irritation. Such systems have more advantages over the single-unit dosage forms. The present review briefly addresses the physiology of the gastric emptying process with respect to floating drug delivery systems. The purpose of this review is to bring together the recent literature with respect to the method of preparation, and various parameters affecting the performance and characterization of floating microspheres.

Ranitidine Hydrochloride-loaded Ethyl Cellulose and Eudragit RS 100 Buoyant Microspheres: Effect of pH Modifiers

A floating type of dosage form of ranitidine hydrochloride in the form of microspheres capable of floating on simulated gastric fluid was prepared by solvent evaporation technique. Microspheres prepared with ethyl cellulose, Eudragit(®) RS100 alone or in combination were evaluated for percent yield, drug entrapment, percent buoyancy and drug release and the results demonstrated satisfactory performance. Microspheres exhibited ranitidine hydrochloride release influenced by changing ranitidine hydrochloride-polymer and ranitidine hydrochloride-polymer-polymer ratio. Incorporation of a pH modifier has been the usual strategy employed to enhance the dissolution rate of weakly basic drug from floating microspheres. Further citric acid, fumaric acid, tartaric acid were employed as pH modifiers. Microspheres prepared with ethyl cellulose, Eudragit(®) RS100 and their combination that showed highest release were utilized to study the effect of pH modifiers on ranitidine hydrochloride release from microspheres which is mainly affected due to modulation of microenvironmental pH. In vitro release of ranitidine hydrochloride from microspheres into simulated gastric fluid at 37° showed no significant burst effect. However the amount of release increased with time and significantly enhanced by pH modifiers. 15% w/w concentration of fumaric acid provide significant drug release from ranitidine hydrochloride microspheres prepared with ranitidine hydrochloride:ethyl cellulose (1:3), ranitidine hydrochloride:Eudragit(®) RS100 (1:2) and ranitidine hydrochloride:ethyl cellulose:Eudragit(®) RS100 (1:2:1) whereas citric acid, tartaric acid showed significant cumulative release at 20% w/w. In all this study suggest that ethyl celluose, Eudragit(®) RS100 alone or in combination with added pH modifiers can be useful in floating microspheres which can be proved beneficial to enhance the bioavailability of ranitidine hydrochloride.

Polymer blends used to prepare nifedipine loaded hollow microspheres for a floating-type oral drug delivery system: in vitro evaluation

The aim of this study was to investigate whether hollow microspheres prepared from polymer blends of polyvinyl pyrrolidone (PVP) and ethyl cellulose (EC) could improve the vitro release behavior of the poorly water-soluble drug nifedipine. Hollow microspheres containing nifedipine were prepared by a solvent diffusion-evaporation method using various ratios of PVP and EC codissolved with drug in ethanol/ether (5:1, v/v). The hollow microspheres could float in release medium for more than 24 h, and floating capacities were not be influenced by mixing PVP. In vitro release profiles of hollow microspheres prepared using EC along showed an initial burst release to some extent, and the cumulative release percentage was less than 55% after 24 h. But, not only the slope but also the shape of the release curves was affected by using mixture of PVP and EC. What's more important, when the ratio (PVP/EC) increased to 1.5:8.5, the cumulative release percentage could be increased to 95.8%. Furthermore, the release rate of microspheres showed a zero order approximate dynamic model and could be expressed by the following equation: Q=3.78t+8.52 (r=0.990). Consequently, hollow microspheres prepared using polymer blends of PVP and EC (1.5:8.5, w/w) could be suitable for floating-type controlled-release delivery systems for the oral administration of nifedipine.