Coating of pharmaceutical powders by fluidized bed process. I. Aqueous enteric coating with methacrylic acid-ethylacrylate copolymer and the dissolution behavior of products

Influences of Crystal Anisotropy in Pharmaceutical Process Development

Crystalline materials are of crucial importance to the pharmaceutical industry, as a large number of APIs are formulated in crystalline form, occasionally in the presence of crystalline excipients. Owing to their multifaceted character, crystals were found to have strongly anisotropic properties. In fact, anisotropic properties were found to be quite important for a number of processes including milling, granulation and tableting. An understanding of crystal anisotropy and an ability to control and predict crystal anisotropy are mostly subjects of interest for researchers. A number of studies dealing with the aforementioned phenomena are grounded on over-simplistic assumptions, neglecting key attributes of crystalline materials, most importantly the anisotropic nature of a number of their properties. Moreover, concepts such as the influence of interfacial phenomena in the behaviour of crystalline materials during their growth and in vivo, are still poorly understood. The review aims to address concepts from a molecular perspective, focusing on crystal growth and dissolution. It begins with a brief outline of fundamental concepts of intermolecular and interfacial phenomena. The second part discusses their relevance to the field of pharmaceutical crystal growth and dissolution. Particular emphasis is given to works dealing with mechanistic understandings of the influence of solvents and additives on crystal habit. Furthermore, comments and perspectives, highlighting future directions for the implementation of fundamental concepts of interfacial phenomena in the rational understanding of crystal growth and dissolution processes, have been provided.

Research Advances of Microencapsulation and Its Prospects in the Petroleum Industry

Additives in the petroleum industry have helped form an efficient system in the past few decades. Nowadays, the development of oil and gas has been facing more adverse conditions, and smart response microcapsules with the abilities of self-healing, and delayed and targeted release are introduced to eliminate obstacles for further exploration in the petroleum industry. However, limited information is available, only that of field measurement data, and not mechanism theory and structural innovation data. Thus we propose that the basic type, preparation, as well as mechanism of microcapsules partly depend on other mature fields. In this review, we explore the latest advancements in evaluating microcapsules, such as X-ray computed tomography (XCT), simulation, and modeling. Finally, some novel microencapsulated additives with unparalleled advantages, such as flexibility, efficiency, and energy-conservation are described.

Review : Biodegradable Microcapsular Drug Delivery Systems: Manufacturing Methodology, Release Control and Targeting Prospects

An overview of the subject of biodegradable microcapsular drug delivery systems is presented from a polymer chemist's viewpoint. Various polymerization and microencapsulation techniques (including emulsion polymerization, interfacial polycondensation, suspension crosslinking, coacer vation/phase separation and solvent evaporation/extraction) suitable for the preparation of biodegradable microcapsules based on proteins, polysaccharides, polyesters, polyamides, or cyanoacrylates are described. Drug release from biodegradable microcapsules is discussed, and examples are presented to illus trate how the rate of drug release can be controlled by adjusting parameters such as microcapsule size, porosity, and crosslinking. Prospects of site-specific chemotherapy by means of passive and active targeting of microcapsular drug carriers are also analyzed.

Ammonio Polymethacrylate-Coated Diltiazem: Drug Release from Single Pellets, Media Dependence, and Swelling Behavior

Drug release from single pellets was measured on an easily assembled flow-through system. Despite heterogeneity between pellets, the sum of the individual results resembled drug release from an ensemble. A typical pellet displayed a long lag followed by rapid release. Heterogeneity appeared to result from substrate properties rather than coating uniformity. Swelling behavior in acid and buffer was measured by dynamic image analysis and related to drug release. Drug release was sensitive to dissolution temperature but swelling was not. A description of the drug release process was proposed.

Granulation of core particles suitable for film coating by agitation fluidized bed II. A proposal of a rapid dissolution test for evaluation of bitter taste of ibuprofen

To prepare powdered drugs that do not have a bitter taste, a film coating covering the surfaces of the core particles is required. The dissolution rate of ibuprofen from the coated particles changes according to the physical properties of the core particles. In this study, the effects of the physical properties of granules prepared by using several scales of agitation fluidized beds on the drug dissolution rate were investigated. The dissolution rate of ibuprofen decreased when the apparent density and shape factor of the granules increased. In contrast, the dissolution rate of the drug increased with the friablility of the granules increased. Thus, the structures of the granules appear to affect the dissolution rate of the drug to a large degree. A rapid dissolution test that can be used to investigate the early dissolution rate of ibuprofen in vitro was proposed to evaluate the taste-masking level of the coated particles. The bitter taste-masking level of the coated particles was successfully confirmed by using this novel test method.

Granulation of Core Particles Suitable for Film Coating by Agitation Fluidized Bed I. Optimum Formulation for Core Particles and Development of a Novel Friability Test Method

To prepare powdered medicines without bitter taste, film coating is required to cover the surface of core particles. In this study, effect of formulation and operating conditions of agitation fluidized bed on the core particle properties was investigated. In order to prevent breakage of the core particles during coating process, which sometimes causes variation of drug dissolution rate, addition of maltose syrup powder during the formulation process of the core particles was investigated. Also, a method for friability test in which the core particles were subjected to strong impact was proposed to evaluate strength of the core particles. The friability of the core particles determined by this test method correlated well with the actual friability of the particles during the coating process. Based on this result, we confirmed this novel friability test method could predict the core particle endurance during the coating process.

Suppression of agglomeration in fluidized bed coating. IV. Effects of sodium citrate concentration on the suppression of particle agglomeration and the physical properties of HPMC film

We previously reported that sodium citrate (Na citrate), which is a high order salt in the Hofmeister's series, greatly suppressed particle agglomeration in fluidized bed coating (Pharm. Res., 16 (1999), 1616-1620). In this paper, we studied the effects of Na citrate concentration on the particle agglomeration in fluidized bed coating and on the structure of coated film on the particles. Spherical granules made of crystalline cellulose (Celphere) containing phenacetin were coated in a fluidized bed with the aqueous coating solution of hydroxypropylmethyl cellulose (HPMC) containing Na citrate at various concentrations. The particle diameter and drug release profile of coated particles, and the physical properties, i.e. tensile strength, elongation percentage at break, porosity and pore size distribution, of the HPMC cast film were investigated. The particle agglomeration was suppressed with the increasing Na citrate concentration. It is considered that the increase in the suppression effect was caused by the salting-out effect of the increased Na citrate. In the HPMC cast film system, the tensile strength and elongation percentage decreased and the porosity and cumulative pore volume increased with an increase in Na citrate concentration. It is considered that the increase in the porosity by adding Na citrate resulted from a phase separation due to the salting-out during the film forming process. The drug release rate from coated particles also increased with the increasing Na citrate concentration. It can be concluded that the increase in the release rate was due to the increase in porosity of the HPMC coated film caused by the increased Na citrate concentration.

Preparation of microcapsules masking the bitter taste of enoxacin by using one continuous process technique of agglomeration and microencapsulation

In order to mask the bitter taste of drugs, a novel microencapsulation process combined with the wet spherical agglomeration (WSA) technique was developed by using a modified phase separation method. The spherical agglomerates of enoxacin (ENX) with various additives including disintegrants were successfully produced in the system of acetone-n-hexane-ammonia water or acetone-n-hexane-distilled water by the WSA, using flocculation phenomena of particles in liquid. Resultant agglomerates could be microencapsulated continuously with Eudragit RS utilizing the phase separation method in the same system as agglomeration under stirring. 'Explosible' microcapsules which were free from the bitter taste could be produced in formulating finer particle size of ENX and 50 per cent of Primojel in core agglomerates, using distilled water as a bridging liquid, and treating with 20 per cent polymer coating level. These microcapsules were bioequivalent to the commercial ENX 100 mg tablets in beagle dogs. One continuous process technique of agglomeration and microencapsulation was useful for the design of ENX powders which masked the bitter taste and controlled the drug release rate.

Microcapsules for food

A systematic description of various processes employed for microencapsulation of food additives is presented. Microencapsulation methods covered include spray drying, fluidized bed coating, extrusion, solvent extraction, coacervation, cocrystallization, liposome formation and molecular inclusion. Basic features of microcapsular products, such as morphology, particle size, core/coat characteristics, and release behaviour, are also highlighted.