Hydrophilic Hydroxypropyl Methylcellulose Research Articles

Polymer Tablet Matrix Systems for the Controlled Release of Dry Betula pendula Leaf Extract.

The aim of the study was to develop polymer matrix tablets with modified release of dry Betula pendula leaf extract and to investigate basic parameters influencing the drug release pattern. To fully assess the statistical significance of the influence of the individual factors in the tablet formulation development as well as the combination of them, Tukey's tests and a complete 33 factor analysis of variance (ANOVA) were applied. The following three factors were studied at three levels (low, medium and high): influence of the hydrophobic/hydrophilic polymer ratio Ethylcellulose (EC)/Hydroxypropyl methylcellulose (HPMC) (40/60, 25/75 and 10/90), influence of HPMC molecular weight (500 kDa, 750 kDa and 1150 kDa), and influence of the compression force applied (1 t, 1.5 t and 2 t). The effect of these varied parameters on the drug release parameter t80 was evaluated statistically. Twenty-seven tablet models were formulated, including all possible combinations of the variables. The obtained drug release profiles demonstrated that a 25/75 (EC/HPMC) ratio was the most suitable for prolonging the release process. Increasing the molecular weight of HMPC from 500 kDa to 750-1150 kDa and applying higher compression force significantly influenced the studied t80 values and caused sustained drug release (t80 up to 7.97 h). The combination of the hydrophilic HPMC polymer with the hydrophobic EC can result in the formation of a promising drug-carrying matrix, offering effective control of the drug release process.

New Insight into the Impact of Effervescence on Gel Layer Microstructure and Drug Release of Effervescent Matrices Using Combined Mechanical and Imaging Characterisation Techniques

Gel layer characteristics play a crucial role in hydrophilic hydroxypropyl methylcellulose (HPMC) matrix development. Effervescent agents have the potential to affect the gel layer microstructures. This study aimed to investigate the influence of effervescence on the microstructure of the gel layer around HPMC matrices using a combination of texture analysis and imaging techniques. The relationship with drug release profile and release mechanisms were also examined. The high amounts of effervescent agents promoted a rapid carbonation reaction, resulting in a high gel layer formation with a low gel strength through texture analysis. This finding was ascribed to the enhanced surface roughness and porosity observed under digital microscopy and microporous structure of the gel layer under scanning electron microscopy. The reconstructed three-dimensional images from synchrotron radiation X-ray tomographic microscopy notably exhibited the interconnected pores of various sizes from the carbonation reaction of effervescent and microporous networks, indicating the gel layer on the tablet surface. Notably, effervescence promoted the increase in interconnected porosities, which directly influenced the strength of the gel layer microstructure, drug release patterns and release mechanism of the effervescent matrix tablet. Therefore, combined mechanical characterisation and imaging techniques can provide new insights into the role of effervescent agents on the gel layer microstructure, and describe the relationship of drug release patterns and release mechanism of matrix tablets.

Release Kinetics of Hydroxypropyl Methylcellulose Governing Drug Release and Hydrodynamic Changes of Matrix Tablet.

Hydrophilic Hydroxypropyl Methylcellulose (HPMC) matrix tablets are the standard role model of the oral controlled-release formulation. Nevertheless, the HPMC kinetics for the mechanistic understanding of drug release and hydrodynamic behaviors are rarely investigated. This study aims to investigate the release behaviors of both HPMC and paracetamol (model drug) from the hydrophilic matrix tablet. Two different viscosity grades of HPMC were used (Low viscosity: 6 cps, High viscosity: 4,000 cps). Three different ratios of drug/HPMC (H:38.08%, M:22.85%, and L:15.23% (w/w) of HPMC amounts in total weight) matrix tablets were prepared by wet granulation technique. The release profiles of the drug and HPMC in a matrix tablet were quantitatively analyzed by HPLC and 1H-Nuclear Magnetic Resonance (NMR) spectroscopy. The hydrodynamic changes of HPMC were determined by the gravimetric behaviors such as swelling and erosion rates, gel layer thickness, front movement data,and distributive Near-Infrared (NIR) chemical imaging of HPMC in a matrix tablet during the dissolution process. High viscosity HPMC tablets showed slower release of HPMC than the release rate of drug, suggesting that drug release preceded polymer release.Different hydration phenomenon was qualitatively identified and corresponded to the release profiles. The release behaviors of HPMC and drug in the tablet could be distinguished with the significant difference with fitted dissolution kinetics model (Low viscosity HPMC 6cps; Korsmeyer-Peppas model, High viscosity HPMC 4000cps; Hopfenberg model, Paracetamol; Weibull model) according to the weight of ingredients and types of HPMC. The determination of HPMC polymer release correlating with drug release, hydrodynamic behavior, and NIR chemical imaging of HPMC can provide new insights into the drug release- modulating mechanism in the hydrophilic matrix system.

DEVELOPMENT AND EVALUATION OF FLOATING TABLET OF METOPROLOL SUCCINATE FOR INCREASED BIOAVAILABILITY VIA IN VIVO STUDY

Objective: This study was performed to formulate a floating tablet using hydrophobic glyceryl behenate (GB) and hydrophilic hydroxypropyl methylcellulose polymers, optimization of the same for retention in stomach and sustained drug delivery over a period of 20 h from upper gastrointestinal tract so as to increase its oral bioavailability.
 Methods: Granules of GB with the metoprolol succinate (MS) was formulated and compressed with the other ingredients to formulate a floating tablet. Physiochemical parameters of an optimized formulation along with its in vitro buoyancy study, dissolution study, in vivo studies in rabbit, and stability studies were performed.
 Results: Differential scanning calorimetry data show no interaction between polymers and the drug MS. A 32 factorial design was applied for optimization purpose, and from ANOVA and surface response plot the best formulation (F3) was obtained. In vitro dissolution study shows sustained drug release for 20 h for all the formulations and in vivo studies using rabbit model show increased bioavailability of an optimized formulation F3 as compared to the marketed sustained release formulation of MS (25 mg). Stability study shows no comparable differences in physical parameters and the drug release of initial formulation and the one which is kept for accelerated stability testing.
 Conclusion: Hence, we can conclude that a floating tablet containing a combination of hydrophilic and hydrophobic polymers can be used for gastric retention for more than 20 h which will increase the oral bioavailability of MS.

DEVELOPMENT AND EVALUATION OF FLOATING TABLET OF METOPROLOL SUCCINATE FOR INCREASED BIOAVAILABILITY VIA IN VIVO STUDY

Objective: This study was performed to formulate a floating tablet using hydrophobic glyceryl behenate (GB) and hydrophilic hydroxypropyl methylcellulose polymers, optimization of the same for retention in stomach and sustained drug delivery over a period of 20 h from upper gastrointestinal tract so as to increase its oral bioavailability.Methods: Granules of GB with the metoprolol succinate (MS) was formulated and compressed with the other ingredients to formulate a floating tablet. Physiochemical parameters of an optimized formulation along with its in vitro buoyancy study, dissolution study, in vivo studies in rabbit, and stability studies were performed.Results: Differential scanning calorimetry data show no interaction between polymers and the drug MS. A 32 factorial design was applied for optimization purpose, and from ANOVA and surface response plot the best formulation (F3) was obtained. In vitro dissolution study shows sustained drug release for 20 h for all the formulations and in vivo studies using rabbit model show increased bioavailability of an optimized formulation F3 as compared to the marketed sustained release formulation of MS (25 mg). Stability study shows no comparable differences in physical parameters and the drug release of initial formulation and the one which is kept for accelerated stability testing.Conclusion: Hence, we can conclude that a floating tablet containing a combination of hydrophilic and hydrophobic polymers can be used for gastric retention for more than 20 h which will increase the oral bioavailability of MS.

Sustained Release of Poorly Water-Soluble Drug from Hydrophilic Polymeric Film Sandwiched Between Hydrophobic Layers.

This proof-of-concept study explores the feasibility of using a drug-loaded hydrophilic polymeric layer sandwiched between two hydrophobic layers for improving film drug load while achieving sustained release of poorly water-soluble drug. Such films having total thickness in range ~ 146-250μm were prepared by slurry-based casting using hydrophilic hydroxypropyl methylcellulose (HPMC) as matrix layer containing fenofibrate (FNB) as the model drug, encased between two very thin rate-limiting layers of 10μm each of hydrophobic poly-ɛ-caprolactone (PCL). Film precursor slurry consisted of HPMC with plasticizer and water along with micronized FNB powders, which were dry-coated with hydrophilic silica. Characterization techniques demonstrated the presence of homogeneously dispersed crystalline FNB in films. The films are very thin and hence two-dimensional; hence, average drug load per unit area in range ~ 5 to ~ 9mg/cm2 could be achieved by altering the thickness of the drug matrix layer. Drug amount and drug content uniformity were measured through assay of ten circular samples ~ 0.712cm2 in area punched out using a circular-shaped punch tool. Drug release rate was investigated using USP IV flow-through cell and surface dissolution imaging system. Thinner films followed Fickian diffusion, and thicker films followed non-Fickian anomalous diffusion. Overall, the application of middle layer thickness could be used as a tool to manipulate drug load without the need for altering its formulation or precursor preparation by changing its thickness, hence achieving relatively high drug loading yet having sustained release of drug.

Jute cellulose nano-fibrils/hydroxypropylmethylcellulose nanocomposite: A novel material with potential for application in packaging and transdermal drug delivery system

Nowadays, bio-derived cellulose nano-fibrils based nanocomposites is gaining utmost interest in the area of barrier films for food packaging, as reinforcing filler to make biodegradable nanocomposites with different biopolymers for various applications such as transdermal drug delivery, edible packaging and tissue scaffolding. Ultrasound-assisted preparation of hydroxypropylmethylcellulose based nanocomposites with cellulose nano-fibrils were carried out following solution mixing technique. The crystalline nature of cellulose nano-fibrils has been scrutinized by X-ray diffraction study. The field emission-scanning electron micrographs of cellulose nano-fibrils revealed a network of nano-fibrillar morphology. The Fourier transform infrared spectroscopy results of cellulose nano-fibrils confirmed the removal of lignin and hemicellulose from raw jute (Corchorus olitorius L.) fibres. The storage modulus and tensile properties of hydroxypropyl methylcellulose films increased up to the addition of 1.00 wt% cellulose nano-fibrils. The moisture affinity of hydrophilic hydroxypropylmethylcellulose has also been reduced at 1.00 wt% cellulose nano-fibrils loading. The impact of cellulose nano-fibrils loading on the cumulative percentage of drug release from prepared nanocomposites films has been explored accordingly. By utilizing these versatilities of cellulose nano-fibrils, the fabricated nanocomposites are expected to be highly promising in the area of packaging and transdermal drug delivery system.

Novel Controlled Release Polymer-Lipid Formulations Processed by Hot Melt Extrusion.

The aim of the study was to investigate the effect of novel polymer/lipid formulations on the dissolution rates of the water insoluble indomethacin (INM), co-processed by hot melt extrusion (HME). Formulations consisted of the hydrophilic hydroxypropyl methyl cellulose polymer (HPMCAS) and stearoyl macrogol-32 glycerides-Gelucire 50/13 (GLC) were processed with a twin screw extruder to produce solid dispersions. The extrudates characterized by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and hot stage microscopy (HSM) indicated the presence of amorphous INM within the polymer/lipid matrices. In-line monitoring via near-infrared (NIR) spectroscopy revealed significant peak shifts indicating possible interactions and H-bonding formation between the drug and the polymer/lipid carriers. Furthermore, in vitro dissolution studies showed a synergistic effect of the polymer/lipid carrier with 2-h lag time in acidic media followed by enhanced INM dissolution rates at pH > 5.5.

Development of Oral Fast-Disintegrating Levothyroxine Films for Management of Hypothyroidism in Pediatrics

Purpose: To develop fast disintegrating films of levothyroxine (LVX) using hydrophilic hydroxypropyl methylcellulose (HPMC), croscarmellose sodium (CCS) as superdisintegrant, and propylene glycol (PG) as a plasticizer.Methods: Fast-disintegrating films were formulated by solvent casting evaporation method using 3-factor, 2-level full factorial design. The films were evaluated for disintegration time, in vitro drug release, physical appearance, thickness, weight variation, folding endurance, drug content uniformity, The effect of concentration of dependent variables (HPMC, CCS and PG) on disintegration time and in vitro drug release was studied.Results: Suitable fast-disintegrating films were obtained using HPMC, CCS and PG. The minimum disintegration time (DT) was 15 s and maximum drug release (DR) in 1 h was 97.56 %. All independent variables selected for the study were statistically significant (p < 0.5). Increase in the concentrations of independent variables increased DR and DT.Conclusion: The findings of this study indicate that the developed fast-disintegrating film is suitable for levothyroxine in the management of hypothyroidism in pediatrics.Keywords: Hypothyroidism, Superdisintegrant, Fast-disintegrating, Levothyroxine, Oral films, Hydroxypropyl methylcellulose, Croscarmelose sodium, Propylene glycol

Drug Release-Modulating Mechanism of Hydrophilic Hydroxypropylmethylcellulose Matrix Tablets: Distribution of Atoms and Carrier and Texture Analysis

Although release profiles of drug from hydrophilic matrices have been well recognized, the visual distribution of hydroxypropylmethylcellulose (HPMC) and atoms inside of internal structures of hydrophilic HPMC matrices has not been characterized. In this paper, drug release mechanism from HPMC matrix tablet was investigated based on the release behaviors of HPMC, physical properties of gelled HPMC tablet and atomic distributions of formulation components using diverse instruments. A matrix tablet consisting of hydroxypropyl methylcellulose (HPMC 6, 4,000 and 100,000 mPa·s), chlorpheniramine maleate (CPM) as a model and fumed silicon dioxide (Aerosil(®) 200) was prepared via direct compression. The distribution of atoms and HPMC imaging were characterized using scanning electron microscope (SEM)/ energy-dispersive X-ray spectroscopy (EDX), and near-infrared (NIR) analysis, respectively as a function of time. A texture analyzer was also used to characterize the thickness and maintenance of gel layer of HPMC matrix tablet. The HPMC matrix tablets showed Higuchi release kinetics with no lag time against the square root of time. High viscosity grades of HPMC gave retarded release rate because of the greater swelling and gel thickness as characterized by texture analyzer. According to the NIR imaging, low-viscosity-grade HPMC (6 mPa·s) quickly leached out onto the surface of the tablet, while the high-viscosity-grade HPMC (4000 mPa·s) formed much thicker gel layer around the tablet and maintained longer via slow erosion, resulting in retarded drug release. The atomic distribution of the drug (chlorine, carbon, oxygen), HPMC (carbon, oxygen) and silicon dioxide (silica, oxygen) and NIR imaging of HPMC corresponded with the dissolution behaviors of drug as a function of time. The use of imaging and texture analyses could be applicable to explain the release- modulating mechanism of hydrophilic HPMC matrix tablets.

Development of diclofenac potassium gel from hydrophobically modified HPMC

An improved topical gel was developed which could allow fast release of drug and having appropriate organoleptic (texture) and rheological properties (viscosity). In vitro release of diclofenac potassium from hydrophobically modified hydroxypropyl methyl cellulose (hm-HPMC, 90L grade) based gels (F1, F2 and F3 at 1, 1.5 and 2 % (w/v) concentration, respectively) was compared with conventional hydrophilic hydroxypropyl methylcellulose (HPMC, 50 mPa s) based gels (F4 and F5 at 12 and 15 % (w/v) concentration, respectively). This study was performed in Franz diffusion cell using cellulose dialysis membrane. The hm-HPMC-based gels of higher viscosity release remarkable quantity of the drug in comparison to conventional hydrophilic HPMC-based gels of lower viscosity. So in the drug-release process polymer concentration is more important and a determinant factor compared to viscosity. Texture profile and viscosity of hm-HPMC-based gels were compared with a commercial gel and all the rheological data obtained from the experiments confirm the suitability of these hm-HPMC-based gels for use as a topical drug delivery system. In order to achieve percutaneous penetration of drug, permeation enhancers (n-octanol and propylene glycol) were added in hm-HPMC-based gels. Both enhancers have shown enhancement of drug penetration through rat skin. Propylene glycol at both lower concentration (2 %) and higher concentration (5 %) exhibited a greater increase in the permeation flux as well as more antinociceptive activity than formulations without enhancer or with n-octanol as enhancer.

The effect of hydrophilic and hydrophobic polymers on release profiles of diclofenac sodium from matrix tablets

Objective: The current study aimed to develop a matrix type sustained release Diclofenac tablet, using hydrophilic hydroxypropyl methylcellulose (HPMC) and hydrophobic polymer cetyl alcohol (CA). Materials and Methods: Two different polymers, that is, Methocel K15MCR ® and CA were used in various proportions as release controlling factor. Matrix tablets were prepared by wet granulation technique. The physicochemical properties of the granules and tablets were evaluated. In vitro dissolution studies of prepared matrix tablet and patent product Voltaren SR ® tablet (VSR) were performed at pH 7.4 phosphate buffer at 100 rpm, and at 37 ± 0.5°C, and subjected to in vitro bioequivalence study in terms of similarity and difference factors. Stability studies were conducted for 6 months using optimized formulation for extended period of time, both at room temperature and accelerated conditions. The dissolution data were fit to Zero‑order, First‑order, Higuchi, and Korsmeyer‑Peppas’ equations. Results: The formulated tablets showed acceptable weight variation, hardness, drug content uniformity with sustained release matrix characteristics. Hydrophilic Methocel K15 MCR ® matrices‑based tablets showed zero‑order and hydrophobic CA matrices‑based tablets followed first‑order kinetics except for formulation six (F6 showed zero‑order profile). It was found that formulations containing CA showed better dissolution properties with respect to formulations containing Methocel K15 MCR ® in terms of similarity and difference factor. Furthermore, the formulations F4, F5, and F6 exhibited similar drug release profile as compared with VSR tablet, which indicated that these formulations could be bioequivalent with VSR tablet in vitro. Tablets were stable both at room temperature and as well as at accelerated conditions. Conclusion: The present study demonstrated that Diclofenac could be successfully prepared using an appropriate amount of Methocel K15 MCR ® and CA in the form of matrix tablets with similar dissolution profile of patent product Voltaren SR ® . The type of polymers used was found to induce a profound effect on release rate and mechanism.

Development and <i>in Vitro-in Vivo</i> Evaluation of Controlled Release Matrix Tablets of Desvenlafaxine

The objective of this investigation was to prepare extended release tablet containing matrix granules of Desvenlafaxine succinate monohydrate and to study its in vitro release and in vivo absorption. The design of dosage form was performed by choosing hydrophilic hydroxypropyl methyl cellulose (HPMC K100M), sodium carboxyl methyl cellulose (Blanose), microcrystalline cellulose (MCC) and lactose monohydrate polymers as matrix builders and polyvinyl pyrolidine (Kollidon K30) as granulating polymers. Granules were prepared by composing drug with HPMC K100M, sodium CMC, MCC and lactose monohydrate by spray drying method. Optimized formulation of Desvenlafaxine succinate monohydrate was formed by using 20% HPMC K100M, 26.6% MCC, 6.6% of sodium CMC (Blanose), 13.3% of lactose monohydrate and 5% ratio of Kollidon K30 as binder. Tablets were compressed with free flowing optimized granules of uniform drug content. This extended the release period up to 24 h in vitro study. Similarity factor and mean dissolution time were also reported to compare various dissolution profiles. The network formed by HPMC, MCC and Blanose had been coupled satisfactorily with the controlled resistance. Biopharmaceutical study of this optimized dosage form in rabbit model showed 24 h prolonged drug release in vivo. A close correlation (R2 = 0.9833) was established between the in vitro release and the in vivo absorption of drug. The results suggested that wet granulation with spray dried technique, is a suitable method to formulate sustained release Desvenlafaxine succinate monohydrate and it can Perform therapeutically better than conventional immediate release dosage form.

Preparation and evaluation of mucoadhesive hydrophilic hydroxy propyl methyl cellulose based extended release matrix tablets of Niacin (Nicotinic acid)

The aim of this study is to develop a once-daily extended release matrix tablet of Niacin using Hydroxy Propyl Methyl Cellulose i.e. Methocel K4M CR as release controlling factor and to evaluate drug release parameters as per various release kinetic models and also to find the best fitted extended release matrix formulation of Niacin. In order to achieve required extended release profile, tablets were prepared by wet granulation technique using different formulations (F-1, F-2, F-3, F-4, F-5 and F-6) with different amount of Methocel K4M CR. The formulated tablets were also characterized by physical and chemical parameters and results were found in acceptable limits. Different release kinetic models were applied in order to evaluate release of Niacin from the prepared matrix tablets. Criteria for selecting the most appropriate model were based on linearity (coefficient of correlation) and diffusion exponent of the respective kinetic model. Among all the formulations, F-5 was found as the best fitted matrix tablet for extended release of Niacin. Drug release mechanism was found as a complex mixture of diffusion, swelling and erosion.

Development of Sustained Release Capsules Containing “Coated Matrix Granules of Metoprolol Tartrate”

The objective of this investigation was to prepare sustained release capsule containing coated matrix granules of metoprolol tartrate and to study its in vitro release and in vivo absorption. The design of dosage form was performed by choosing hydrophilic hydroxypropyl methyl cellulose (HPMC K100M) and hydrophobic ethyl cellulose (EC) polymers as matrix builders and Eudragit® RL/RS as coating polymers. Granules were prepared by composing drug with HPMC K100M, EC, dicalcium phosphate by wet granulation method with subsequent coating. Optimized formulation of metoprolol tartrate was formed by using 30% HPMC K100M, 20% EC, and ratio of Eudragit® RS/RL as 97.5:2.5 at 25% coating level. Capsules were filled with free flowing optimized granules of uniform drug content. This extended the release period upto 12 h in vitro study. Similarity factor and mean dissolution time were also reported to compare various dissolution profiles. The network formed by HPMC and EC had been coupled satisfactorily with the controlled resistance offered by Eudragit® RS. The release mechanism of capsules followed Korsemeyer-Peppas model that indicated significant contribution of erosion effect of hydrophilic polymer. Biopharmaceutical study of this optimized dosage form in rabbit model showed 10 h prolonged drug release in vivo. A close correlation (R(2) = 0.9434) was established between the in vitro release and the in vivo absorption of drug. The results suggested that wet granulation with subsequent coating by fluidized bed technique, is a suitable method to formulate sustained release capsules of metoprolol tartrate and it can perform therapeutically better than conventional immediate release dosage form.

In vitro controlled release of vinpocetine–cyclodextrin–tartaric acid multicomponent complexes from HPMC swellable tablets

The objective of this study was to investigate the effect of multicomponent complexation (MCC) of vinpocetine (VP), a poorly soluble base-type drug, with β-cyclodextrin (βCD), sulfobutylether β-cyclodextrin (SBEβCD), tartaric acid (TA), polyvinylpyrrolidone (PVP) and hydroxypropylmethylcellulose (HPMC), on the design of controlled release hydrophilic HPMC tablets and to evaluate their in vitro release profiles by a pH gradient method. Multicomponent complexation led to enhanced dissolution properties of VP both in simulated gastric and intestinal fluids, and became possible the development of HPMC tablet formulations with more independent pH dissolution profiles. Drug release process was investigated experimentally using USP apparatus 3 and by means of model-independent parameters. Responses studied included similarity of dissolution profiles, time for 60% of the drug to dissolve ( T 60%), percent of VP released after 7h (PD 7 h) and the dissolution efficiency parameter at 12 h (DE 12 h). Influence of multicomponent complexation was proved to increase the release of VP from HPMC tablets and superior PD 7 h and DE 12 h values were obtained in formulations containing VP–CD–TA complexes. Results supported the use of HPMC matrices to provide a useful tool in retarding the release of VP and that dissolution characteristics of the drug may be modulated by multicomponent complexation in these delivery systems, suggesting an improvement on VP bioavailability.

Dissolution of diclofenac sodium from matrix tablets

Several parameters were studied for their effect on the dissolution of diclofenac sodium from Voltaren SR and hydroxypropylmethylcellulose (HPMC) based matrix tablets. The results indicate that addition of sodium or potassium chloride to the dissolution medium decreases the solubility of the drug and slows the dissolution rate, with the effect of sodium chloride being greater. The dissolution of the drug was studied in a medium which simulates the changing pH of the pathway followed by the drug as it passes from the stomach to the intestine. Dissolution was found to be inversely related to the rate at which the pH was changed. This may be caused by the deposition of an insoluble drug layer when contact is made with an acid medium. When higher viscosity grades of HPMC are used, slower release rates result. Drug release from Voltaren SR is best described as non-Fickian in an aqueous medium irrespective of whether salt is added; however, a zero-order dependence became evident in pH-changing media. The release of diclofenac sodium from the hydrophilic HPMC matrices follows a non-Fickian transport in all media.

Modelling of drug diffusion through swellable polymeric systems

A drug diffusion model for the case of diffusion of an initially uniformly distributed drug through a polymeric matrix is presented and solved. Drug diffusion from a single surface is analyzed for the case of countercurrent diffusion of a solvent which is thermodynamically compatible with the polymer. Due to swelling, considerable volume expansion is observed leading to a moving-boundary diffusion problem. Drug concentration profiles within the polymer and drug release rates can be determined. The results are in agreement with experimental data obtained for the system of KCl distributed in hydrophilic hydroxypropyl methyl cellulose matrices, in the form of tablets.