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

Development and evaluation of sustained release tablet of betahistine hydrochloride using ion exchange resin tulsion t344

An attempt was made to sustain the release of Betahistine hydrochloride by complexation technique using strong cation-exchange resin, Tulsion T344. The drug loading onto ion-exchange resin was optimized for mixing time, activation, effect of pH, swelling time, ratio of drug : resin, and temperature. The resinate was evaluated for micromeritic properties and characterized using XRPD and IR. For resinate sustained release tablets were formulated using hydoxypropyl methylcellulose K100M. The tablets were evaluated for hardness, thickness, friability, drug content, weight variation, and in vitro drug release. Tablets thus formulated (Batch T-3) provided sustained release of drug over a period of 12 h. The release of Betahistine HCl from resinate controls the diffusion of drug molecules through the polymeric material into aqueous medium. Results showed that Betahistine HCl was formulated into a sustained dosage form as an alternative to the conventional tablet.

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.

Simple preparation of coated resin complexes and their incorporation into fast-disintegrating tablets

Even though ion-exchange resins are good drug carriers to get sustained release properties, it may not be good enough only with themselves. For further sustained release effect, a diffusion barrier or coating on the resins' surface can be utilized. Initially, microencapsulation using a w/o/w double emulsion method was used to apply ethylcellulose (EC) onto the drug/resin complexes. Typical pharmaceutical waxes can be alternative materials to delay the drug release from the complex. After the coating, the coated resin particles were incorporated into fast-disintegrating tablets to get an idea regarding the effects of wet granulation and compression on the release. Among the different grades of ECs tested (Ethocel 20, 45, and 100), more viscous EC resulted in better morphologies and sustained release effects. Because the drug release rate was significantly dependent on the coating level, the release rate can be modified easily by changing different levels of the coating. The drug release rate was also strongly dependent on the granulation and compaction process as the coated particles were incorporated into the tablet dosage form. Among the tested waxes, stearic acid had an effect on the sustained release together with lubrication and wetting properties. Even though microencapsulation or wax coating may not be practical for real manufacturing, the results may give valuable information how to formulate sustained release dosage forms and their properties on the tablet preparation.

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.

Controlled release of theophylline through semi-interpenetrating network microspheres of chitosan-(dextran-g-acrylamide)

Semi-interpenetrating network microspheres of chitosan-(dextran-g-acrylamide) were prepared by emulsion-crosslinking method using glutaraldehyde (GA) as a crosslinking agent. Graft copolymerization of dextran with acrylamide (Dx-g-AAm) was carried out by aqueous free-radical polymerization using ceric ammonium nitrate (CAN) as initiator. The grafting efficiency was found to be 92%. Theophylline (TH), antiasthmatic drug, was successfully encapsulated into semi-INP microspheres by varying the ratio of Dx-g-AAm and amount of GA. The laser light scattering technique shows that the particles size increased with increasing amount of graft copolymer and decrease with increasing amount of GA. The % encapsulation efficiency was found to vary between 50 and 78. MPs were characterized by FTIR spectroscopy and differential scanning calorimetry (DSC) techniques to confirm the graft copolymer, formation of semi-IPN structure of MPs and molecular distribution of the drug molecules in the polymer matrix. In vitro release studies of TH from these matrices have been investigated at Ph 1.2 and 7.4 media and the slow release were extended up to 18 h at 37 degrees C. The release rates were fitted to an empirical equation to estimate the diffusion exponent n, which indicated that the release from the MPs follows non-Fickian type.

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.

Cellulose acetate butyrate microcapsules containing dextran ion-exchange resins as self-propelled drug release system

Sulfopropylated dextran microspheres (SP-Ms), (Dm = 80 microm) loaded with a water soluble drug (Tetracycline HCl), were included in cellulose acetate butyrate (CAB) microcapsules. Spherical CAB microcapsules were obtained by oil in water (o/w) solvent evaporation method in the presence of an inert solvent as cyclohexane (CyH) or n-hexane (N-Hex), and different excipients (Phospholipon, Tween, Span, Eudragit RS 100). Chloroform was found to be the best solvent for the preparation of the microcapsules. Also, the sphericity as well as the porosity of the microcapsules was controlled by the presence of an inert solvent. The final concentration of the drug in CAB microparticles was up to 25% (w/w). The key factors for the successful preparation were also the viscosity of the polymer, while the wettability of the resulted microcapsules, the temperature of the preparation, and the porosity have modulated the release of the drug. The higher is the amount of encapsulated microspheres the thinner is the CAB wall between the compartments created by their incorporation. When these microspheres come in contact with the release medium, the pressure created by their swelling breaks the polymer film and the drug starts to be released. The more drug is released in phosphate buffer the higher is the swelling degree of the encapsulated ion exchange resins and the force created by their supplementary swelling will break the more resistants walls. In this way a self-propelled drug release is achieved, until almost all drug was eliberated.

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.

Controlled-release liquid suspensions based on ion-exchange particles entrapped within acrylic microcapsules

Eudragit RS/RL polymers were used to prepare microcapsules containing terbutaline-loaded ion-exchange resins, with the final aim of formulating this anti-asthmatic drug in a controlled-release liquid form. Oil-in-oil (o/o) and oil-in-water (o/w) solvent evaporation procedures were conveniently modified in order to encapsulate the resin cores. The microcapsules were then suspended in a hydroxypropylmethylcellulose solution of adequate viscosity and palatability, and stored at 20 degrees C and ambient humidity conditions for a 6-month period. Stability studies of the dispersed microparticles were performed in order to evaluate the changes occurred in the diffusion of the drug to the suspending medium and in the dissolution behaviour during storage. The morphological alterations of the stored microcapsules were followed throughout the duration of the study by scanning electron microscopy. The polymer coatings of microcapsules prepared by the o/o method broke up on the first day of storage, while those made by the aqueous procedure remained intact during all the storage period. This agreed with the modification observed in the controlled-release profiles of terbutaline in the case of microcapsules prepared by the o/o method, which completely changed after the first week of storage. On the contrary, the microcapsules prepared by the aqueous method showed identical controlled-release profiles for all the stability study. The different behaviour of both types of microcapsules was attributed to the swelling suffered by the resin particles in contact with the aqueous suspending medium, which was higher in the microcapsules prepared by the o/o technique. In fact, in the anhydrous procedure, the microencapsulation was carried out on the shrunken resin particles, whereas in the o/w method, the presence of water during the microencapsulation process allowed the coating of the swollen particles, thus avoiding the further problem of rupture of the polymer coating.

Evaluation of an aliphatic polyurethane as a microsphere matrix for sustained theophylline delivery

In spite of several biomedical applications of polyurethanes, very little attention has been focused on these polymers for controlled drug delivery. In this study, an aliphatic polyurethane, Tecoflex, was evaluated as a microsphere matrix for the controlled release of theophylline. Polyurethane microspheres containing theophylline were prepared using a solvent evaporation technique from a dichloromethane solution of the polymer containing the drug. A dilute solution of poly(vinyl alcohol) served as the dispersion medium. Microspheres of good spherical geometry having theophylline content of 35% could be prepared by the technique. The release of the drug from the microspheres was examined in simulated gastric and intestinal fluids at 37 degrees C. While a large burst effect was observed in gastric fluid, in the intestinal fluid a close to zero-order release was seen. Attempts were made to modulate the release by incorporating poly(ethylene glycol) in the matrix and also coating the spheres with paraffin wax. Preliminary data indicate that polyurethanes could be interesting matrices for controlled drug delivery.

Glutaraldehyde cross-linked bovine casein microspheres as a matrix for the controlled release of theophylline: in-vitro studies

A controlled release dosage form of theophylline in the form of microspheres using the milk protein casein as the matrix is described. Glutaraldehyde cross-linking of an aqueous alkaline solution of the protein containing the drug, dispersed in a mixture of dichloromethane/hexane having ca. 1% of an aliphatic polyurethane as the suspension stabilizer, led to the formation of the drug-loaded microspheres. Drug incorporation efficiency of around 80% could be achieved by the technique. Release profiles of the drug were examined in simulated gastric and intestinal fluids at 37 degrees C. It was observed that the release was diffusion-controlled and followed the Higuchi model. Release characteristics were influenced by the cross-linking density, particle size and the extent of loading. Data obtained indicate that the natural milk protein casein could be used as a matrix for sustained release oral dosage forms.

Microencapsulation studies on aminophylline involving spherical crystallization, spheronization and drug loading on to non-pareil seeds

Aminophylline was formulated as small spherical cores for subsequent coating in an attempt to develop a competitor microencapsulated product to the commercial available sustained-release tablet, Phyllocontin. Optimum spherical crystallization conditions yielded cores of loosely adhering crystals of active, with highly irregular surface morphology and poor mechanical strength during pan coating. Aqueous spheronization yielded satisfactory cores in high yield when microcrystalline cellulose and liquid paraffin were used. However, application of large amounts of controlled-release coatings based on Eudragit RL and RS failed to produce a product with retarded drug dissolution comparable to the commercial product. Drug loaded non-pareils were easily formed, but required application of about 20 per cent Eudragit RL/RS coating to achieve adequate prolonged-release properties. Application of 10 per cent hydrogenated castor oil/ethylcellulose based coating gave acceptable in vitro release only if the microcapsules formed were tableted and annealed. All products investigated rapidly discoloured during storage and none were considered to represent a realistic alternative to tableting technology for the production of a sustained-release oral dosage form of aminophylline.

Formulation parameters affecting the preparation and properties of microencapsulated ion-exchange resins containing theophylline

A method of microencapsulating theophylline ion-exchange resins with ethylcellulose was developed to produce smooth and uniform coats which were predominantly mononucleated. This was achieved by controlling the amount of ethylcellulose and the particle size, and through the use of a protective colloid, polyisobutylene. The rate of release of theophylline was influenced by the ion-exchange resin crosslinking, the amount of ethylcellulose, and the smoothness of the coat. Mesh size and polyisobutylene did not appear to affect the rate in a regular manner. It was found that the release rate from coated resins with low crosslinking followed a logarithmic plot, indicating membrane-controlled release, whereas coated resins with high crosslinking fitted a t1/2 plot, suggesting particle diffusion control.

Rate of release of organic carboxylic acids from ion-exchange resins

Organic anions with similar properties, but different molecular weights, were bound to anion-exchange resins with different cross-linking. It was found that the capacity of the ion-exchange resin for the anions, the percentage of organic anion released, and the rate of release depends on the crosslinking of the ion-exchange resin, the molecular weight of the anion, and the moisture content of the resin. Self-diffusion coefficients for the release rates were determined.

Formation and in-vitro evaluation of theophylline-loaded poly(methyl methacrylate) microspheres

Theophylline-loaded poly(methyl methacrylate) (PMM) microspheres were prepared by the solvent evaporation method. Increasing the drug to polymer ratio increased both the mean particle size of the microspheres and the release rate. Polyethylene glycol (PEG) 4000 was used to improve the release rate of theophylline from the microspheres. No marked effect was observed on particle size distribution of the microspheres as a function of PEG concentration but there was a pronounced effect on drug release. The different particle sizes of microspheres prepared from the same drug to polymer ratio showed no significant difference in drug content, indicating that the ratio between theophylline and PMM remained practically constant regardless of the size of microspheres. Release characteristics of the microspheres were influenced by drug to polymer ratio, the amount of PEG incorporated and the particle size of microspheres. The release rate was slightly higher in simulated gastric fluid than in simulated intestinal fluid. The release profiles of the drug were modified by mixing microspheres of different formulations in different ratios.

Ion-exchange resins as potential phosphate-binding agents for renal failure patients: effect of the physicochemical properties of resins on phosphate and bile salt binding

The effect of resin type, degree of cross-linking, bead size, and surface area on the phosphate and bile salt binding characteristics of five strongly basic Dowex anion-exchange resins in the chloride form was studied. The maximum uptake of phosphate (expressed as uptake of phosphorus) from sodium phosphate solutions was 137, 82, 86, 138, and 76 mg of phosphorus per gram of dry Dowex resins XF 43311, XY 40013, XF 43254, XY 40011, and XY 40012, respectively. The presence of simulated gastric or intestinal fluids resulted in small but insignificant alterations in phosphorus uptake by the resins. The resins all bound similar amounts of phosphorus and taurocholate (80-100% of the total phosphorus and taurocholate in solution) at physiological concentrations of phosphate and bile salt. Dowex resins XY 40013 and XF 43254, with identical physicochemical properties, but different bead sizes and surface areas, bound similar amounts of the bile salt sodium taurocholate at all taurocholate concentrations, indicating that binding was not restricted to the surface sites on the resin bead. The 2% cross-linked resins bound 3-4 times more taurocholate than the 8% cross-linked resins (at high taurocholate concentrations); the smaller pore size of the latter resins probably presents a greater mechanical exclusion barrier than the larger pore size of the 2% cross-linked resins.