Preparation and evaluation of microencapsulated ion-exchange resin beads

Design and preparation of nanocomposite acrylate coating agents for binder-free dry coating of 100 µm-sized drug-containing particles and their coating performance

For binder-free dry particulate coating to prepare controlled-release micron-sized particles, we designed nanocomposite coating agents with the intention to form a core-shell structure composed of two types of acrylic polymers with different glass transition temperatures (Tg) and evaluated their coating performance. A series of nanocomposite acrylic latexes synthesized by emulsion polymerization was freeze-dried after salting-out to create the powder form. An ion-exchange resin loaded with diclofenac sodium (DS, a model drug) (IER-DS) with a median diameter of approximately 100 µm was used as the core particle. Dry coating of the IER-DS with nanocomposite coating agents was carried out using a laboratory-made coating apparatus assisted with mild-intensity vibration and zirconia bead impaction. The coated particles were cured by heating at a temperature 20 °C higher than the Tg for 12 h to complete the film-forming process. It was found that the highest coating efficiency (more than 70%) and a remarkably prolonged release period of the drug (the time required for 50% release reached approximately 12 h) could be achieved when nanocomposite coating agents with a soft polymeric core (Tg = 30 °C) and a hard polymeric shell (Tg = 80 °C) were applied. In contrast, nanocomposite coating agents with a combination of a hard polymeric core and a soft polymeric shell resulted in lower coating efficiency. These results demonstrate that nanocomposite polymeric coating agents composed of a soft core and hard shell are effective for the production of drug-loaded microparticles with a prolonged release function by a binder-free dry-coating process.

Design and evaluation of taste masked dextromethorphan hydrobromide oral disintegrating tablets

The present study is aimed to develop dextromethorphan hydrobromide (DXM) oral disintegrating tablets (ODT) with acceptable palatability to help patients of all age groups. The bitter taste of the drug was masked by binding the drug to ion exchange resin. The effect of the particle size of resin on drug loading was studied. In vitro and in vivo disintegration time and in vitro drug release studies were performed. Drug loading increased significantly with a decrease in the particle size of the resin. DSC and XRPD studies reveal that the molecular state of the drug changed from crystalline to amorphous form. The dissolution efficiency calculated for optimized ODT and conventional directly compressed tablet were almost comparable, indicating free dissociation of the drug from the resinate. The bitter taste of DXM can be masked by binding with ion exchange resin and the resinate can be successfully formulated into oral disintegrating tablets.

Ion-exchange resins as drug delivery carriers

There are many reports in the literature referring to the utilization of drug bound to ion-exchange resin (drug-resinate), especially in the drug delivery area. Ion-exchange resin complexes, which can be prepared from both acidic and basic drugs, have been widely studied and marketed. Salts of cationic and anionic exchange resins are insoluble complexes in which drug release results from exchange of bound drug ions by ions normally present in body fluids. Resins used are polymers that contain appropriately substituted acidic groups, such as carboxylic and sulfonic for cation exchangers; or basic groups, such as quaternary ammonium group for anion exchangers. Variables relating to the resin are the exchange capacity; degree of cross-linking, which determines the permeability of the resin, its swelling potential, and the access of the exchange sites to the drug ion; the effective pK(a) of the exchanging group, which determines the exchange affinity; and the resin particle size, which controls accessibility to the exchange ions. In this review, the properties of ion-exchange resins, selection of drugs that lend themselves to such an approach, selection of the appropriate resin, preparation of drug-resinate, evaluation of drug release, recent developments of drug-resinates, and applications are discussed.

Preparation of Codeine-Resinate and Chlorpheniramine-Resinate Sustained-Release Suspension and its Pharmacokinetic Evaluation in Beagle Dogs

Using ion exchange resins (IERs) as carriers, a dual-drug sustained release suspension containing codeine, and chlorpheniramine had been prepared to elevate drug safety, effectiveness and conformance. The codeine resinate and chlorpheniramine resinate beads were prepared by a batch process and then impregnated with Polyethylene glycol 4000 (PEG 4000), respectively. The PEG impregnated drug resinate beads were coated with ethylcellulose as the coating polymer and di-n-butyl-phthalate as plasticizer in ethanol and methylene chloride mixture by the Wurster process. The coated PEG impregnated drug resinate beads were dispersed in an aqueous suspending vehicle containing 0.5% w/w xanthan gum and 0.5% w/w of hydroxypropylmethylcellulose of nominal viscosity of 4000 cps, obtaining codeine resinate and chlorpheniramine resinate sustained-release suspension (CCSS). Codeine phosphate and chlorpheniramine maleate were respectively loaded onto AMBERLITE IRP 69, and PEG 4000 was used to impregnate drug resinate beads to maintain their geometry. Ethylcellulose with di-n-butyl-phthalate in ethanol and methylene chloride mixture for the coating of drug resinate beads was performed in Glatt fluidized bed coater, where the coating solution flow rate was 8-12 g/min, the inlet air temperature was 50-60 degrees C, the outlet air temperature was 32-38 degrees C, the atomizing air pressure was 2.0 bar and the fluidized air pressure was adjusted as required. Few significant agglomeration of circulating drug resinate beads was observed during the operation. The film weight gained 20% w/w and 15% w/w were suitable for the PEG impregnated codeine resinate and chlorpheniramine resinate beads, respectively. Residual solvent content increased with coating level, but inprocess drying could reduce residual solvent content. In the present study, the rates of drug release from both drug resinate beads were measured in 0.05 M and 0.5M KCl solutions. The increased ionic strength generally accelerated the release rate of both drugs. But the release of codeine from its resinate beads was much more rapid than chlorpheniramine released from its resinate beads in the same ionic strength release medium. The drug release specification of the CCSS, where release mediums were 0.05 M KCl solution for codeine and 0.5 M KCl solution for chlorpheniramine, was established to be in conformance with in vivo performance. Relative bioavailability and pharmacokinetics evaluation of the CCSS, using commercial immediate-release tablets as the reference preparation, were performed following a randomized two-way crossover design in beagle dogs. The drug concentrations in plasma were measured by a validated LC-MS/MS method to determine the pharmacokinetic parameters of CCSS. This LC-MS/MS method demonstrated high accuracy and precision for bioanalysis, and was proved quick and reliable for the pharmacokinetic studies. The results showed that the CCSS had the longer value of Tmax and the lower value of Cmax, which meant an obviously sustained release effect, and its relative bioavailability of codeine and chlorpheniramine were (103.6 +/- 14.6)% and (98.1 +/- 10.3)%, respectively, compared with the reference preparation. These findings indicated that a novel liquid sustained release suspension made by using IERs as carriers and subsequent fluidized bed coating might provide a constant plasma level of the active pharmaceutical ingredient being highly beneficial for various therapeutic reasons.

Sustained release of propranolol hydrochloride based on ion-exchange resin entrapped within polystyrene microcapsules

Propranolol-HCl, a water soluble drug, was bound to Indion 254, a cation exchange resin, and the resulting resinate was microencapsulated with polystyrene using an oil-in-water emulsion-solvent evaporation method with a view to achieve prolonged drug release in simulated gastric and intestinal fluid. The effect of various formulation parameters on the characteristics of the microcapsules was studied. The diameter of the resinate-loaded polystyrene microcapsules increased with increase in the concentration of emulsion stabilizer and coat/core ratio and decreased with increase in the volume of organic disperse phase. The variation in the size of the microcapsules appeared to be related with the inter-facial viscosity which was influenced by the viscosity of both the aqueous dispersion medium and the organic disperse phase. The resinate encapsulation efficiency and hence the drug entrapment efficiency of the microcapsules increased with increase in the concentration of emulsion stabilizer and coat/core ratio and decreased with increase in the volume of organic disperse phase. These characteristics were found to depend on the extent of formation of fractured microcapsules and subsequent partitioning of the resinate into the aqueous dispersion medium. The degree of fracture on the microcapsules depended on the viscosity of the aqueous dispersion medium and the organic disperse phase. The uncoated resinate discharged the drug quite rapidly following the typical particle diffusion process. Although the desorption of the drug from the resinate was independent of pH of the dissolution media, increase in ionic strength increased the drug desorption. On the other hand, release of drug from the coated resinate was considerably prolonged and followed a diffusion controlled model. The prolongation of drug release was dependent on the uniformity of coating which was influenced by the formulation parameters. The drug release from the microcapsules was also found to be independent of pH of the dissolution media and increased with increase in ionic strength. The pH-independent release of the drug from both the uncoated and microencapsulated resinate was due to pH-independent solubility of the drug and high equilibrium concentration of the resinate in both the dissolution media. Polystyrene appeared to be a suitable polymer to provide prolonged release of propranolol independent of pH of the dissolution media.

Drug release properties of polymer coated ion-exchange resin complexes: experimental and theoretical evaluation

Although ion-exchange resins have been used widely as drug delivery systems, their exact release kinetics has not been reported yet. Usually only the rate-limiting step has been taken into account and the rest of the steps have been ignored as instantaneous processes. To investigate the exact release kinetics of polymer-coated drug/ion-exchange resin complexes for sustained drug delivery, the results of new mathematical modeling were compared with experimental results. Drug/resin complexes with a model drug, dextromethorphan, were prepared and used as cores for fluid-bed coating. An aqueous colloidal dispersion of poly(vinyl acetate) was applied for the coating. A comprehensive mathematical model was developed using a mechanistic approach by considering diffusion, swelling, and ion-exchange processes solved by numerical techniques. The rate-limiting factor of the uncoated resin particles was diffusion through the core matrix. Similarly, in the coated particles the rate-limiting factor was diffusion through the coating membrane. The mathematical model has captured the phenomena observed during experimental evaluations and the release dynamics from uncoated and coated (at different coat levels) particles were predicted accurately (maximum RMSE 2.4%). The mathematical model is a useful tool to theoretically evaluate the drug release properties from coated ion-exchange complexes thus can be used for design purposes.

Preparation and in vitro evaluation of polystyrene-coated diltiazem-resin complex by oil-in-water emulsion solvent evaporation method

The purpose of this study was to examine the suitability of polystyrene-coated (PS-coated) microcapsules of drug-resin complex for achieving prolonged release of diltiazem-HCl, a highly water-soluble drug, in simulated gastric and intestinal fluid. The drug was bound to Indion 254, a cation-exchange resin, and the resulting resinate was microencapsulated with PS using an oil-in-water emulsion-solvent evaporation method. The effect of various formulation parameters on the characteristics of the microcapsules was studied. Mean diameter and encapsulation efficiency of the microcapsules rose with an increase in the concentration of emulsion stabilizer and the coat/core ratio, while the same characteristics tended to decrease with an increase in the volume of the organic disperse phase. The desorption of drug from the uncoated resinate was quite rapid and independent of the pH of the dissolution media. On the other hand, the drug release from the microcapsules was prolonged for different periods of time depending on the formulation parameters and was also found to be independent of the pH of the dissolution media. Both the encapsulation efficiency and the retardation of drug release were found to be dependent on the uniformity of coating, which in turn was influenced by the formulation parameters. Kinetic studies revealed that the desorption of drug from the resinate obeyed the typical particle diffusion process, whereas the drug release from the microencapsulated resinate followed the diffusion-controlled model in accordance with the Higuchi equation. PS appeared to be a suitable polymer to provide prolonged release of diltiazem independent of the pH of the dissolution media.

Indomethacin release from ion-exchange microspheres: impregnation with alginate reduces release rate

Ion-exchange microspheres (MS) designed as a drug delivery system for embolization coupling ability to occlude vessels and chemotherapy were used to evaluate a manufacturing process allowing to control the drug release rate through reduction of diffusion rate of the drug within the particle by impregnation of calcium alginate inside the porous MS. Impregnation was performed by diffusion of sodium alginate inside DEAE-Trisacryl(R) MS, dispersion of the MS in deionised water and gelling alginate by adding CaCl(2) to the dispersed MS. Studied parameters were alginate concentration, alginate diffusion time and calcium concentration. Indomethacin was loaded into the MS by eluting an aqueous indomethacin solution through a chromatographic column packed with impregnated MS. Indomethacin loading was reduced by alginate. Swelling studies showed indomethacin loading enhanced the hydrophobicity of MS while impregnation had no effect. This had an incidence on indomethacin release rate, which was assessed using the rapid elution of PBS through loaded impregnated MS packed in a column. Indomethacin loading reduced its own rate of release. MS impregnated with 2% w/v alginate gelled with a 40 mM calcium solution presented the lower release rate. This work indicated the manufacturing conditions to display a calcium alginate matrix effect on indomethacin release from DEAE-Trisacryl MS.

Swelling and drug release behavior of tablets coated with aqueous hydroxypropyl methylcellulose phthalate (HPMCP) nanoparticles

Organic solvent-based enteric coating technology using hydroxypropyl methyl cellulose phthalate (HPMCP) has been developed for many years due to low water solubility of HPMCP. In this work, aqueous HPMCP nanoparticles (HPMCP-NPs) were prepared by neutralization emulsification method using HPMCP powder and ammonium hydroxide (NH(4)OH) in the absence of any organic solvent and emulsifier. Tablets for enteric use were coated with HPMCP-NP dispersions having different degree of neutralization that was manipulated by ion-exchange process. Disintegration and dissolution behavior of coated tablets were investigated using UV-visible spectrophotometer based on USP method (pH 1.2 and at 37 degrees C) and simulated intestinal fluid (pH 6.8 and at 37 degrees C for 60 min), respectively. The ion-exchange process, which was directly achieved by the protonation of dissociated carboxylic acid group of the aqueous HPMCP-NPs, was introduced as a useful way to control the release rate of drug and hydrophobic nature of HPMCP coating layer with a view for pharmaceutical application. The drug release and swelling were increased with increase in conductivity of aqueous HPMCP-NPs. On the other hand, particle size and polydispersity were decreased with increase in degree of neutralization.

Ion-exchange resins: carrying drug delivery forward

Ion-exchange resins (IER), or ionic polymer networks, have received considerable attention from pharmaceutical scientists because of their versatile properties as drug-delivery vehicles. In the past few years, IER have been extensively studied in the development of novel drug-delivery systems (DDSs) and other biomedical applications. Some of the DDSs containing IER have been introduced into the market. In this review, the applications of IER in drug delivery research are discussed.

Use of ion-exchange resins to prepare 100 microm-sized microcapsules with prolonged drug-release by the Wurster process

Ion-exchange resin (IER)--drug complexes were used as core materials to explore their capability to prepare a 100 microm-sized, highly drug-incorporated microcapsule with a prolonged drug release by the Wurster process. Diclofenac sodium was loaded into Dowex 1-X2 fractionated into 200--400 mesh and subsequently microencapsulated with two types of aqueous colloidal polymer dispersion, Aquacoator Eudragit RS30D. The mass median diameter and drug content of the microcapsules thus obtained were 98 microm and 46% with Aquacoat, and 95 microm and 50% with Eudragit RS30D, respectively. Each microcapsule was obtained at a product yield of 94%. The rate of drug release from the microcapsules was highly dependent on the encapsulating materials. For the microcapsules coated with Aquacoat, diclofenac sodium was found to be rapidly released over 4 h, even at a 25 wt% coating level because of cracks on the microcapsule surfaces resulting from the swelling stress of the drug-loaded IER cores. In contrast, significantly prolonged drug-release was achieved in the microcapsules prepared with Eudragit RS30D: even such a very low coating level as 3 wt% provided an exceptionally prolonged drug-release over 24 h. The results indicated that the use of IER along with a flexible coating material would be a feasible way to prepare a prolonged release type of microcapsules with a diameter of 100 microm and a drug content of more than 50% by the Wurster process.

Synthesis and characterization of surface-hydrophobic ion-exchange microspheres and the effect of coating on drug release rate

Biodegradable, dextran-based ion-exchange microspheres (IE-MS) have been used for localized delivery of anticancer drugs and chemosensitizers. Because of their hydrophilic nature, the IE-MS release their payload quickly. The purpose of this work was to develop an IE-MS system that could provide a broad range of release rates for in vitro and in vivo applications. Sulfopropylated dextran microspheres (SP C25 MS) were surface-modified by acylation. These hydrophobically modified sulfopropylated dextran microspheres (HM-MS) were further coated with the cationic acrylic polymer Eudragit RL100 (EU-MS). The changes in chemical composition after the surface modification and coating were characterized by X-ray photoelectron spectroscopy. The effects of the modification and coating on the surface hydrophobicity, equilibrium swelling, surface morphology, and drug loading capacity were investigated. The HM-MS showed little change in swelling and functionality, despite significantly increased affinity to oil and carbon content on the surface. The coated microspheres (EU-MS) exhibited a profoundly decreased swelling ratio, an even higher affinity to oil, a higher loading capacity, and a lower drug release rate. Through further coating of the EU-MS with different amounts of corn oil, the rate of drug release could be tailored to cover a relatively wide range. These results suggest that a versatile delivery system with various release profiles can be prepared by a combination of hydrophobic modification, polymer coating, and oil coating.

Influence of hydrophobicity on the ion exchange selectivity coefficients for aromatic amines

Hydrophobic effects could play an important role in determining the selectivity of organic ions for ion-exchange resins in aqueous solutions. We used the octanol-water partition coefficient (P) and the chromatographic capacity factor (K') as indices of hydrophobicity of a series of primary and secondary amines, and examined their relationships with the amine selectivity coefficient (K) in binding to the Amberlite IRP-69 ion-exchange resin. Good correlations were found between log K versus log P and log K versus log K', but the relationship appears to be dependent on the degree of substitution at the amino nitrogen. These relationships may be useful for the estimation of selectivity coefficients of various amine drug candidates when they are considered for incorporation with ion-exchange resins in potential controlled-release systems.

Dissolution studies of microencapsulated 4-sulphonamidophenoxyacetic acid: effect of preparative variables on dissolution

Ethylcellulose-walled microcapsules of 4-sulphonamidophenoxyacetic acid were prepared and their in vitro dissolution characteristics were investigated. Different release kinetics must be applied according to the respective average particle size and wall content values of the microcapsule fractions. The 'dissolution model' appears to fit better with small thin-walled microcapsules whereas, for larger thicker-walled microcapsules, Higuchi-type kinetics seem to describe the release of the major part of the drug more adequately.

Preparation and evaluation of microencapsulated and coated ion-exchange resin beads containing theophylline

Anion-exchange resin beads in the theophylline form were prepared and coated with paraffin or encapsulated with ethylcellulose by various methods; one of these products was subsequently coated with paraffin in order to achieve a wide range of release rates and patterns of release. The various products were subjected to rate studies, and it was found that the patterns of release and the rates could be controlled by the cross-linking of the resin and the coating procedures used. A medium and almost constant rate of release was obtained by using ethylcellulose microencapsulation, a coating of hard paraffin, or a combination of both. The amount of coating and the total amount of drug released was also determined.

Influences of matrixes on nylon-encapsulated pharmaceuticals

The preparation and properties of nylon microcapsules containing three different matrixes (formalized gelatin, calcium alginate, and calcium sulfate) are described. Microcapsules containing each matrix were dense and free flowing and could be made of very small diameter by controlling the stirring speed during nylon formation. The preparation of microcapsules containing calcium alginate employed freeze-drying procedures. Lyophilization was not necessary with the formalized gelatin and calcium sulfate systems. Various representative drugs (anionic, cationic, nonionic, quaternary, and amphoteric compounds) were used in the formulation studies. The effects of pH, matrix, and encapsulated species on retention of drug in the microcapsules are described. In addition, the surface morphology of the microcapsules was examined using scanning electron microscopy.