Properties of drug-containing spherical pellets produced by a hot-melt extrusion and spheronization process

The objectives of this study were to investigate the particle size distribution, morphology and dissolution properties of spherical pellets produced by hot-melt extrusion and spheronization and to compare the properties of hot-melt extruded pellets with beads manufactured by a traditional wet-mass extrusion and spheronization method. Spherical pellets were produced by hot-melt extrusion without the use of water or other solvents. A powder blend of theophylline, Eudragit Preparation 4135 F, microcrystalline cellulose and polyethylene glycol 8000 was hot melt-extruded and the resulting composite rod was cut into cylindrical pellets. The pellets were then spheronized in a traditional spheronizer at an elevated temperature. The same powder blend was processed using conventional wet-mass techniques. Unlike wet-mass extruded pellets, pellets prepared from hot-melt extrusion displayed both a narrow particle size distribution and controlled drug release in dissolution media less than pH 7.4. Scanning electron microscopy, X-ray diffraction and porosity measurements were employed to explain the differences in drug release rates of theophylline from pellets produced by the two processing techniques. Theophylline release from the hot-melt extruded pellets was described using the Higuchi diffusion model, and drug release rates from wet-granulated and melt-extruded pellets did not change after post-processing thermal treatment.     

Characterization of ibuprofen as a nontraditional plasticizer of ethyl cellulose

This study describes the characterization of the plasticizing properties of ibuprofen (IBP) on hot-melt extruded ethyl cellulose (EC). The thermal behavior of hot-melt extrudates containing 0, 5, 10, and 20% (w/w) IBP was evaluated using modulated temperature differential scanning calorimetry. By means of comparison, co-evaporates containing the same concentrations of IBP and EC, were also evaluated. Both methods yielded solid solutions having one glass transition temperature indicating compatibility between drug and polymer. A similar decrease in glass transition temperature was noticed with increasing IBP concentration in the solid solutions prepared via both methods, indicating its plasticizing effect. The plasticizing efficiency was of the same magnitude as for the traditionally used plasticizers. Infrared spectroscopy was performed for better understanding of the chemical interactions in the molecular dispersions and confirmed the existence of hydrogen bonds between IBP and EC. Overall, the study has highlighted the plasticizing properties of IBP on EC during hot-melt extrusion.     

The effect of polymer properties on direct compression and drug release from water-insoluble controlled release matrix tablets

The objective of this study was to identify and evaluate key polymer properties affecting direct compression and drug release from water-insoluble matrices. Commonly used polymers, such as Kollidon^® SR, Eudragit^® RS and ethyl cellulose, were characterized, formulated into tablets and compared with regard to their properties in dry and wet state. A similar site percolation threshold of 65% v/v was found for all polymers in dry state. Key parameters influencing polymer compactibility were the surface properties and the glass transition temperature (T_g), affecting polymer elasticity and particle size-dependent binding. The important properties observed in dry state also governed matrix characteristics and therefore drug release in wet state. A low T_g (Kollidon^® SR < Eudragit^® RS) decreased the percolation threshold, particle size effect and tortuosity, but increased permeability and sensitivity to heat/humidity treatment. Hence, lower permeability and higher stability are benefits of a high-T_g polymer (ethyl cellulose). However, release retardation was observed in the same order as matrix integrity (Eudragit^® RS < ethyl cellulose < Kollidon^® SR), as the high permeability was counteracted by PVP in case of Kollidon^® SR. Therefore, the T_g and composition of a polymer need to be considered in polymer design and formulation of controlled-release matrix systems.     

Influence of Plasticizer Level on the Drug Release from Sustained Release Film Coated and Hot-Melt Extruded Dosage Forms

In the current study, the influence of plasticizer level on drug release was investigated for solid dosage forms prepared by hot-melt extrusion and film coating. The properties of two highly water-soluble compounds, diltiazem hydrochloride (DTZ) and chlorpheniramine maleate (CPM), and a poorly water-soluble drug, indomethacin (IDM), were investigated in the melt extrudates containing either Eudragit® RSPO or Eudragit® RD 100 and triethyl citrate (TEC) as the plasticizer. In addition, pellets containing DTZ were film coated with Eudragit® RS 30D and varying levels of TEC using a fluidized bed coating unit. Differential scanning calorimetry (DSC) demonstrated that both CPM and IDM exhibited a plasticization effect on the acrylic polymers, whereas no plasticizing effect by DTZ on Eudragit® RSPO was observed. Thermogravimetric analysis (TGA) was used to investigate the thermal stability of the DTZ, Eudragit® RSPO and TEC at 140 °C, the maximum temperature used in the hot-melt extrusion process. The chemical stability of DTZ and IDM in the extrudate following hot-melt processing was determined by high pressure liquid chromatography (HPLC). Drug release rates of both DTZ and CPM from hot-melt extrudates increased with an increase in the TEC level in the formulations, while the release rate of DTZ from the Eudragit® RS 30D–coated pellets decreased with an increase in TEC in the coating dispersion. This phenomenon was due to the formation of a reservoir polymeric structure as a result of the thermal stress and shear stress involved in the hot-melt extrusion process regardless of the TEC level. In contrast, coalescence of the polymer particles in the film coating process was enhanced with higher levels of TEC, as demonstrated by scanning electron microscopy (SEM). The addition of TEC (0% to 8%) in the IDM hot-melt extrudate formulation had no influence on the drug release rate as the drug release rate was controlled by drug diffusion through the inside of the polymeric materials rather than between the polymer particles.     

Solid lipid extrusion of sustained release dosage forms.

The applicability of the solid lipid extrusion process as preparations method for sustained release dosage forms was investigated in this study. Two lipids with similar melting ranges but of different composition, glyceryl palmitostearate (Precirol ATO 5) and glyceryl trimyristate (Dynasan 114), and mixtures of each lipid with 50% or 75% theophylline were extruded at temperatures below their melting ranges. Extrudates were analyzed using differential scanning calorimetry, scanning electron microscopy, porosity measurements and in vitro drug dissolution studies. The possibility of processing lipids by softening instead of complete melting and without subsequent formation of low-melting, metastable polymorphs could be demonstrated. Extrudates based on formulations of glyceryl palmitostearate/theophylline (50:50) and glyceryl trimyristate/theophylline (50:50) showed sustained release properties. An influence of extrusion conditions on the matrix structure was shown for extrudates based on a mixture of glyceryl trimyristate and theophylline (50:50). Glyceryl trimyristate tended to solidify in porous structures after melting. Exceeding a material temperature of 50.5 degrees C led to porous extrudate matrices with a faster drug release. The production of novel, non porous sustained release matrices was possible at a material temperature of 49.5 degrees C. Extrudates based on glyceryl trimyristate/theophylline (50:50) only slight changes in melting enthalpy and stable drug release profiles.     

热熔挤出技术提高水飞蓟素溶出度的初步研究

目的:研究热熔挤出技术是否提高难溶性药物溶出度.方法:以难溶性水飞蓟素为模型药物,以泊洛沙姆-188为亲水性载体,采用热熔挤出技术和熔融法分别制备挤出物和固体分散体,比较两者的差示扫描量热(DSC)图谱和累积溶出曲线.结果:挤出物是分散程度较高的固体分散体,DSC图谱中药物的吸热峰均消失,载体泊洛沙姆-188的吸热峰向低温方向移动,挤出物中的移行程度大于固体分散体;药物在90 min时从挤出物中溶出90.63%,而在固体分散体中的溶出量为71.06%.结论:热熔挤出技术可提高水飞蓟素的溶出度,且效果优于熔融法.     

Influence of plasticizer level on the drug release from sustained release film coated and hot-melt extruded dosage forms

In the current study, the influence of plasticizer level on drug release was investigated for solid dosage forms prepared by hot-melt extrusion and film coating. The properties of two highly water-soluble compounds, diltiazem hydrochloride (DTZ) and chlorpheniramine maleate (CPM), and a poorly water-soluble drug, indomethacin (IDM), were investigated in the melt extrudates containing either Eudragit RSPO or Eudragit RD 100 and triethyl citrate (TEC) as the plasticizer. In addition, pellets containing DTZ were film coated with Eudragit RS 30D and varying levels of TEC using a fluidized bed coating unit. Differential scanning calorimetry (DSC) demonstrated that both CPM and IDM exhibited a plasticization effect on the acrylic polymers, whereas no plasticizing effect by DTZ on Eudragit RSPO was observed. Thermogravimetric analysis (TGA) was used to investigate the thermal stability of the DTZ, Eudragit RSPO and TEC at 140 degrees C, the maximum temperature used in the hot-melt extrusion process. The chemical stability of DTZ and IDM in the extrudate following hot-melt processing was determined by high pressure liquid chromatography (HPLC). Drug release rates of both DTZ and CPM from hot-melt extrudates increased with an increase in the TEC level in the formulations, while the release rate of DTZ from the Eudragit RS 30D-coated pellets decreased with an increase in TEC in the coating dispersion. This phenomenon was due to the formation of a reservoir polymeric structure as a result of the thermal stress and shear stress involved in the hot-melt extrusion process regardless of the TEC level. In contrast, coalescence of the polymer particles in the film coating process was enhanced with higher levels of TEC, as demonstrated by scanning electron microscopy (SEM). The addition of TEC (0% to 8%) in the IDM hot-melt extrudate formulation had no influence on the drug release rate as the drug release rate was controlled by drug diffusion through the inside of the polymeric materials rather than between the polymer particles.     

Formulation of 3D Printed Tablet for Rapid Drug Release by Fused Deposition Modeling: Screening Polymers for Drug Release,Drug-Polymer Miscibility and Printability

The primary aim of this study was to identify pharmaceutically acceptable amorphous polymers for producing 3D printed tablets of a model drug, haloperidol, for rapid release by fused deposition modeling. Filaments for 3D printing were prepared by hot melt extrusion at 150°C with 10% and 20% w/w of haloperidol using Kollidon^® VA64, Kollicoat^® IR, Affinsiol^?15 cP, and HPMCAS either individually or as binary blends (Kollidon^® VA64 + Affinisol^? 15 cP, 1:1; Kollidon^® VA64 + HPMCAS, 1:1). Dissolution of crushed extrudates was studied at pH 2 and 6.8, and formulations demonstrating rapid dissolution rates were then analyzed for drug-polymer, polymer-polymer and drug-polymer-polymer miscibility by film casting. Polymer-polymer (1:1) and drug-polymer-polymer (1:5:5 and 2:5:5) mixtures were found to be miscible. Tablets with 100% and 60% infill were printed using MakerBot printer at 210°C, and dissolution tests of tablets were conducted at pH 2 and 6.8. Extruded filaments of Kollidon^® VA64-Affinisol^? 15 cP mixtures were flexible and had optimum mechanical strength for 3D printing. Tablets containing 10% drug with 60% and 100% infill showed complete drug release at pH 2 in 45 and 120 min, respectively. Relatively high dissolution rates were also observed at pH 6.8. The 1:1-mixture of Kollidon^® VA64 and Affinisol^?15 cP was thus identified as a suitable polymer system for 3D printing and rapid drug release.     

Properties of lipophilic matrix tablets containing phenylpropanolamine hydrochloride prepared by hot-melt extrusion.

The objective of the present study was to investigate the influence of formulation factors on the physical properties of hot-melt extruded granules and compressed tablets containing wax as a thermal binder/retarding agent, and to compare the properties of granules and tablets with those prepared by a high-shear melt granulation (MG) method. Powder blends containing phenylpropanolamine hydrochloride, Precirol and various excipients were extruded in a single-screw extruder at open-end discharge conditions. The extrudates were then passed through a 14-mesh screen to form granules. The extrusion conditions and the optimum amount of wax to function as the thermal binder were dependent on the properties of the filler excipients. At the same wax level, drug release from tablets decreased in the order of using microcrystalline cellulose (MCC), lactose and Emcompress as the filler excipient. The observed differences in the dissolution properties of the tablets were due to the differences in the solubility, swellability and density of the filler excipients. Replacing Precirol with Sterotex K, a higher melting point wax, resulted in slightly increased dissolution rates, when the extrusion was performed at the same temperature conditions. Hot-melt extruded granules were observed to be less spherical than high-shear melt granules and showed lower values of bulk/tap densities. However, tablets containing MCC or lactose granules prepared by hot-melt extrusion (HME) exhibited higher hardness values. Slower drug release rates were found for tablets containing MCC by HME compared with MG. Analysis of the hot-melt extruded granules showed better drug content uniformity among granules of different size ranges compared with high-shear melt granules, resulting in a more reproducible drug release from the corresponding tablets.     

In situ formation of nanoparticles upon dispersion of melt extrudate formulations in aqueous medium assessed by asymmetrical flow field-flow fractionation

In recent years melt extrudates (e.g. Meltrex^®) have proven to be a promising formulation tool for poorly water-soluble and poorly bioavailable drugs. During the hot-melt extrusion process solid dispersions are formed. For several of these formulations improved bioavailabilities have been reported; the mechanism behind, however is still not very well understood. The aim of this study was to investigate whether solid dispersions prepared by melt extrusion upon dispersion in aqueous medium form particles and/or supramolecular assemblies. The formulation investigated here contained the human immunodeficiency virus (HIV) protease inhibitors lopinavir and ritonavir, polyvinylpyrrolidone–vinyl acetate copolymer (Kollidon^® VA64), sorbitan monolaurate (Span^® 20) and hydrophilic fumed silica (Aerosil^® 200). The aqueous dispersions originating from both, API-containing and placebo formulation were investigated using photon correlation spectroscopy (PCS) and asymmetrical flow field-flow fractionation (AsFlFFF) with subsequent online multi-angle light-scattering (MALS) particle size analysis. The content of both APIs in the AsFlFFF-fractions was quantified using high performance liquid chromatography–mass spectrometry.     

Production of spherical pellets by a hot-melt extrusion and spheronization process

Controlled-release theophylline containing spherical pellets were successfully produced by a hot-melt extrusion (HME) and spheronization process. A powder blend of anhydrous theophylline, Eudragit Preparation 4135 F, microcrystalline cellulose and polyethylene glycol 8000 powder was sieved, blended and then melt-extruded in a Randcastle Microtruder. The hot-melt extruded pellets were prepared by first cutting a thin, extruded composite rod into symmetrical pellets. The pellets were then spheronized in a traditional spheronizer at an elevated temperature. Thermal properties of the pellet formulation components and the hot-melt extrudate were studied to determine suitability of the formulation for HME. Pellets were examined using scanning electron microscopy to determine the effect of spheronization time on surface morphology. The rate of release of theophylline from the hot-melt extruded spherical pellets was characterized using USP 24 Apparatus 2 dissolution testing after initial pellet production and after 1 year storage in sealed HDPE containers at 25 degrees C/60% RH.     

Effect on the nasal bioavailability of co-processing drug and bioadhesive carrier via spray-drying

A mucoadhesive combination of a maize starch (Amioca^®, mainly consisting of amylopectine) and a cross-linked acrylic acid-based polymer (Carbopol^® 974P) was spray-dried with metoprolol tartrate (used as model molecule) in order to develop a powder suitable for nasal drug delivery via a one-step manufacturing process. The bioavailability of metoprolol tartrate after nasal administration of this powder to rabbits was compared with powders manufactured via other procedures: (a) freeze-drying of a dispersion prepared using the co-spray-dried powder, (b) freeze-drying of a dispersion prepared using a physical mixture of drug and mucoadhesive polymers. After co-processing via spray-drying a low bioavailability (BA 10.8 ± 2.3%) was obtained, whereas manufacturing procedures based on freeze-drying yielded a higher BA: 37.9 ± 12.8% using the co-processed powder and 73.6 ± 24.9% using the physical mixture. The higher bioavailability was due to the deprotonation of poly(acrylic acid) during neutralisation of the dispersion prior to freeze-drying. This induced repulsion of the ionised carboxyl groups and a lower interaction between poly(acrylic acid) and starch, creating a less compact matrix upon hydration of the polymer and allowing an easier escape of metoprolol tartrate from the matrix. This study showed that co-processing of a mucoadhesive Amioca^®/Carbopol^® 974P formulation with metoprolol tartrate via co-spray-drying did not provide any added value towards the bioavailability of the drug after nasal administration of the mucoadhesive powder.     

Crystal growth formation in melt extrudates

The purpose of the study was to investigate the physical state of hot-melt extruded guaifenesin tablets containing either Acryl-EZE or Eudragit L100-55 and to study the physicochemical factors influencing crystal growth of guaifenesin on the surface of the extrudates. The powder mixtures containing Acryl-EZE were extruded on a single-screw Randcastle Microtruder at 20rpm and at temperatures of 90, 95, 110 degrees C (zones 1, 2, 3, respectively) and 115 degrees C (die), before being manually cut into tablets (250+/-5mg). Extrudates containing Eudragit L100-55, TEC and guaifenesin were extruded at temperatures ranging from 60 to 115 degrees C. Modulated differential calorimetry (DSC) was used to demonstrate the plasticizing effect of guaifenesin on Eudragit L100-55. Powder X-ray diffraction (PXRD) showed that while the drug powder is crystalline, extrudates containing up to 25% drug exhibited an amorphous diffraction profile. Extrudates containing higher drug concentrations showed an amorphous profile with some crystalline peaks corresponding to guaifenesin, indicating that the limit of solubility of drug in the matrix had been exceeded. Scanning electron microscopy was used to demonstrate that drug crystallization was a surface phenomenon and dependent on the drug concentration. In vitro dissolution testing showed no effect of surface crystallization of guaifenesin on drug release rates of extruded matrix tablets. The influence of hydrophilic polymeric additives including PVP K25, polycarbophil, PEG 3,350, poloxamer 188 or poly(ethylene oxide) as crystal growth inhibitors was investigated at a level of 10% based on the drug content. The extent of crystal growth was reduced for all additives. Complete drug release in pH 6.8 phosphate buffer was prolonged from 4h in extrudates containing Acryl-EZE and guaifenesin to 8h in extrudates containing Eudragit L100-55, TEC and guaifenesin. Drug release in extrudates containing Eudragit L100-55 and guaifenesin was not affected by the presence of hydrophilic additives present at 10% based on the drug content. In vitro drug release studies showed no significant change during storage for up to 6 months at 25 degrees C/60% relative humidity and 40 degrees C/75% relative humidity.     

Diclofenac sodium sustained release hot melt extruded lipid matrices

Abstract

Sustained release diclofenac sodium (Df-Na) solid lipid matrices with Compritol® 888 ATO were developed in this study. The drug/lipid powders were processed via cold and hot melt extrusion at various drug loadings. The influence of the processing temperatures, drug loading and the addition of excipients on the obtained dissolution rates was investigated. The physicochemical characterization of the extruded batches showed the existence of crystalline drug in the extrudates with a small amount being solubilized in the lipid matrix. The drug content and uniformity on the tablet surface were also investigated by using energy dispersive X-ray microanalysis. The dissolution rates were found to depend on the actual Df-Na loading and the nature of the added excipients, while the effect of the processing temperatures was negligible. The dissolution mechanism of all extruded formulations followed Peppas–Korsemeyer law, based on the estimated determination coefficients and the dissolution constant rates, indicating drug diffusion from the lipid matrices.     

Investigating the relationship between drug distribution in solid lipid matrices and dissolution behaviour using raman spectroscopy and mapping

In this study, in situ and mapping Raman spectroscopic measurements were used to investigate the physical structure of solid lipid extrudates and relate the structure to dissolution behaviour. Theophylline anhydrate was extruded with tripalmitin, with and without the water‐soluble polymer, polyethylene glycol 10000. Raman mapping of the extrudate cores revealed that drug particles of diverse size were dispersed in a continuous lipid phase with or without polyethylene glycol. At the surface, there was evidence of more mixing between the components. Previous characterisation by other methods suggested that the extrudate surface is covered predominantly by lipid, and the Raman mapping suggested that such a layer is in general less than a few micrometres thick. Nevertheless, the lipid layer dramatically reduced the drug dissolution rate. The extrudate cores were also mapped after a period of dissolution testing, and there was no evidence of a uniformly receding drug boundary in the extrudates during drug release. In situ Raman spectroscopy analysis during dissolution testing revealed that the drug distribution in the extrudate affected the formation of theophylline monohydrate. However, the drug release rate was primarily determined directly by drug distribution, with the solid‐state behaviour of the drug having a smaller influence. © 2009 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1464–1475, 2010     

Influence of sulfobutyl ether beta-cyclodextrin (Captisol) on the dissolution properties of a poorly soluble drug from extrudates prepared by hot-melt extrusion

The aim of this study was to investigate the influence of sulfobutyl ether β-cyclodextrin (SBE₇-β-CD; Captisol^®) on the dissolution properties of a poorly water-soluble drug from extrudates prepared by hot-melt extrusion. Ketoprofen was employed as a model drug. Extrudates containing the parent β-cyclodextrin (β-CD) were also produced for comparative evaluation to assess the benefits of SBE₇-β-CD. Hot-melt extrudates were produced at 100 °C, which was close to the melting point of ketoprofen. The physiochemical properties and the in vitro drug release properties of ketoprofen from extrudates were investigated and compared with samples prepared by physical mixing, co-grinding, freeze-drying and heat-treatment. The solubilizing effects and the interactions of ketoprofen with SBE₇-β-CD and β-CD were investigated using phase solubility and NMR studies, respectively. The dissolution rate of ketoprofen from samples prepared by hot-melt extrusion with SBE₇-β-CD was significantly faster than both the physical mixture and the hot-melt extrudates prepared with the parent β-CD. Moisture absorption studies revealed that the hygroscopic nature of SBE₇-β-CD led to particle aggregation and a corresponding decrease in drug release rate for all samples. However, the samples prepared by melt extrusion were least affected by exposure to elevated humidity.     

Influence of methylparaben as a solid-state plasticizer on the physicochemical properties of Eudragit RS PO hot-melt extrudates.

The purpose of this study was to investigate the properties of methylparaben as a solid-state plasticizer for Eudragit RS PO during a hot-melt extrusion process. Extruded matrices containing different levels of methylparaben and Eudragit RS PO, were prepared by feeding the powder blend through a hot melt extruder. The melt viscosity of the polymer blends was assessed by torque rheometry using a Brabender Plasticorder. The physicochemical properties of the extruded methylparaben-containing polymer matrix were characterized by differential scanning calorimetry and X-ray diffraction. Solid state nuclear magnetic resonance spectroscopy (NMR) was used to study the possible interaction between methylparaben and Eudragit RS PO polymer. The results demonstrated that the glass transition temperature of the Eudragit RS PO decreased with increasing levels of methylparaben in the extrudate, due to an increase in the chain mobility of Eudragit RS PO. The crystallinity of methylparaben was absent following hot-melt processing. At increasing levels of methylparaben in the extrudates, a decrease in the melt viscosity was seen due to a plasticization of the polymer. Rheological properties of the extrudates containing methylparaben were compared with the extrudates containing conventional plasticizers. It was found that methylparaben was as effective as triethyl citrate (TEC) in reducing torque during the extrusion process. Solid state NMR spectra indicated a change in the chemical shift of Eudragit RS PO plasticized with methylparaben, which could be ascribed to an interaction between the hydroxyl group of the methylparaben and the ester group of the Eudragit RS PO polymer. The results of this study demonstrated that methylparaben could be used as a solid-state plasticizer for the Eudragit RS PO polymer when a hot melt extrusion technique was employed in the preparation of sustained release tablets.     

Solid-state plasticization of an acrylic polymer with chlorpheniramine maleate and triethyl citrate

The influence of in situ plasticization of chlorpheniramine maleate (CPM) on Eudragit RS PO from hot-melt extruded matrix tablets, and from compressed granules prepared by thermal processing was investigated. CPM was studied as both a model drug substance and as a solid-state plasticizer for the acrylic polymer. Triethyl citrate (TEC) was incorporated into the polymer blend as a liquid plasticizer for the polymer. The influence of TEC and CPM concentration on the dissolution properties of CPM tablets was investigated. The glass transition temperature (T(g)) of the samples was determined by modulated differential scanning calorimetry (MDSC). The morphologies of the granules formed by hot-melt extrusion and hot-melt granulation processes were investigated by scanning electron microscopy. The addition of 12% TEC to the polymer reduced the T(g) by 32.5 degrees C, while the reduction in the T(g) for the same level of CPM was 16.4 degrees C. The effect of TEC levels on drug release was dependent on the tablet preparation method. At high TEC levels, the release rate of CPM decreased in tablets prepared by direct compression and tablets made from compressed granules that had been prepared by high shear hot-melt granulation. However, the CPM release rate increased from hot-melt extruded tablets with increasing blends of plasticizer in the extruded tablets. An increase in the CPM content in the tablets resulted in an increase in the drug release rate. During high shear hot-melt granulation, the model drug adhered to the polymer to form a porous discontinuous structure. Following hot-melt extrusion, the drug was distributed at a molecular level in the continuous polymeric structure. The influence of both CPM and TEC levels on the drug release rate from these polymeric drug delivery systems was shown to be a function of whether the granules or tablets were formed by either hot-melt granulation or hot-melt extrusion, as well as the plasticization effects of both TEC and CPM on the acrylic polymer.     

Ethylene vinyl acetate as matrix for oral sustained release dosage forms produced via hot-melt extrusion

Different ethylene vinyl acetate grades (EVA9, EVA15, EVA28 and EVA40 having a VA content of 9%, 15%, 28% and 40%, respectively) were characterized via differential scanning calorimetry. Glass transition temperature (T_g), polymer crystallinity, melting point and polymer flexibility were positively influenced by the vinyl acetate content. The processability of EVA-based formulations produced by means of hot-melt extrusion (2 mm die) was evaluated in function of VA content, extrusion temperature (60–140 °C) and metoprolol tartrate (MPT, used as model drug) concentration (10–60%). Matrices containing 50% MPT resulted in smooth-surfaced extrudates, whereas at 60% drug content severe surface defects (shark skinning) were observed. Drug release from EVA/MPT matrices (50/50, w/w) was affected by the EVA grades: 90% after 24 h for EVA15 and 28, while EVA9 and EVA40 formulations released 80% and 60%, respectively. Drug release also depended on drug loading and extrusion temperature. For all systems, the total matrix porosity (measured by X-ray tomography) was decreased after dissolution due to elastic rearrangement of the polymer. However, the largest porosity reduction was observed for EVA40 matrices as partial melting of the structure (melt onset temperature: 34.7 °C) also contributed (thereby reducing the drug release pathway and yielding the lowest release rate from EVA40 formulations).The Simulator of the Human Intestinal Microbial Ecosystem (SHIME) used to evaluate the stability of EVA during gastrointestinal transit showed that EVA was not modified during GI transit, nor did it affect the GI ecosystem following oral administration.