Critical factors in the release of drugs from sustained release hydrophilic matrices

The relationship between drug release rate, particle size and swelling of silicone matrices

Oral solid drug delivery continues to be the gold standard in pharmaceutical formulations, owing to its cost-effectiveness, ease of administration, and high patient compliance. Tablets, the most widely used dosage form, are favored for their precise dosing, simplicity, and economic advantages. Among these, controlled release (CR) tablets stand out for their ability to maintain consistent drug levels, enhance therapeutic efficacy, and reduce dosing frequency, thereby improving patient adherence and treatment outcomes. A well-designed CR system ensures a sustained and targeted drug supply, optimizing therapeutic performance while minimizing side effects. This review delves into the latest advancements in CR formulations, with a particular focus on hydrophilic matrix systems, which regulate drug release through mechanisms such as swelling, diffusion, and erosion. These systems rely on a variety of polymers as drug-retarding agents to achieve tailored release profiles. Recent breakthroughs in crystal engineering and polymer science have further enhanced drug solubility and bioavailability, addressing critical challenges associated with poorly soluble drugs. In terms of manufacturing, direct compression has emerged as the most efficient method for producing CR tablets, streamlining production while ensuring consistent drug release. The integration of the Quality by Design framework has been instrumental in optimizing product performance by systematically linking formulation and process variables to patient-centric quality attributes. The advent of cutting-edge technologies such as artificial intelligence and 3D printing is revolutionizing the field of CR formulations. AI enables predictive modeling and data-driven optimization of drug release profiles, while 3D printing facilitates the development of personalized medicines with highly customizable release kinetics. These innovations are paving the way for more precise and patient-specific therapies. However, challenges such as regulatory hurdles, patent constraints, and the need for robust in vivo validation remain significant barriers to the widespread adoption of these advanced technologies. This succinct review underscores the synergistic integration of traditional and emerging strategies in the development of CR matrix tablets. It highlights the potential of hydrophilic and co-crystal matrix systems, particularly those produced via direct compression, to enhance drug bioavailability, improve patient adherence, and deliver superior therapeutic outcomes. By bridging the gap between established practices and innovative approaches, this field is poised to address unmet clinical needs and advance the future of oral drug delivery.

Influence of drug:hydroxypropylmethylcellulose ratio, drug and polymer particle size and compression force on the release of diclofenac sodium from HPMC tablets

This study aimed to develop diclofenac sodium sustained-release tablets using different matrix systems and to evaluate their physicochemical properties. Diclofenac sodium was characterized for solubility, flowability, and particle size. Solubility in water and phosphate buffer (pH 7.5) was determined by UV-Vis spectrophotometry, while flowability was assessed via angle of repose, Hausner ratio, and Carr’s index. Product X SR 75 mg tablets were analyzed as a reference for uniformity, hardness, and dissolution. Two matrix approaches were explored: a hydrophobic system (carnauba wax and cetyl alcohol) via melt granulation and a hydrophilic system (Arabic gum) via direct compression. The research results indicate that diclofenac sodium exhibited slight solubility and poor flowability. Formulations based on both hydrophobic and hydrophilic systems were developed, meeting the physical, quantitative, and dissolution criteria of the United States Pharmacopeia (USP). The formulation exhibited a drug release profile in USP pH 7.5 medium equivalent to that of the reference product, Product X SR 75. The hydrophobic matrix formulations followed zero-order release kinetics, whereas the hydrophilic matrix formulations followed the Higuchi release model and showed stability over 3 months under accelerated and long-term aging conditions. Hydrophobic matrices provided a more sustained drug release compared to hydrophilic matrices. Both systems effectively modulated drug release, indicating their potential for once-daily extended-release diclofenac formulations.

Design of sustained-release matrix systems for a highly water-soluble compound, ABT-089

In recent years, controlled and sustained release drug delivery system has become the focus of pharmaceutical researchers. Some technologies aimed to develop the controlled and sustained release of the drug, which used to be administered several times a day and generate plasma concentration fluctuation. As all, a controlled drug release rate has always been a goal pursued by researchers. This paper introduced a controlled delivery hydrophilic matrix system, and evaluated their relevance between in vitro and in vivo behaviors. The matrix tablets were fabricated by direct powder compression method. Single-factor test and the orthogonal experimental design were used to find out the optimal formulation. And the in vivo pharmacokinetics study was also evaluated in this paper. The amount of WSR N301 and low viscosity materials significantly affect the drug release. Compared with commercially available sustained-release tablets Diamicron®, the pharmacokinetics parameters of these matrix tablets exhibited similar blood profiles, and other parameters such as prolonged Tmax, Cmax, MRT and similar bioavailability. However, this matrix system showed unstable blood profiles in comparison with two-layer-core osmotic pump tablet. The IVIVC study suggested that there was a good correlation between absorption in vivo and drug release in vitro. Zero-order controlled drug release of hydrophilic matrix system has the simpler manufacture process. And it will be a promising system to control drug release. Due to the disadvantage of hydrophilic matrix tablets in vivo release, for further research the zero-order delivery of PEO matrix tablets system, some pharmaceutical technology are needed to decrease the influence of gastrointestinal peristalsis. Therefore, the study of polyethylene oxide hydrophilic matrix tablets provides a promising formulation for promoting the development of a drug delivery system.

The aim of this study was to design a polyethylene oxide (PEO) binary hydrophilic matrix controlled system and investigate the most important influence(s) on the in vitro water-insoluble drug release behavior of this controlled system. Direct-compressed PEO binary matrix tablets were obtained from a variety of low viscosity hydrophilic materials as a sustained agent, using anhydrous drugs as a model drug. Water uptake rate, swelling rate, and erosion rate of matrices were investigated for the evaluation of the PEO hydrophilic matrix systems. The effect of the dose, the solubility of water-insoluble drug, and the rheology of polymers on in vitro release were also discussed. Based on the in vitro release kinetics study, three optimized PEO binary matrices were selected for further research. And, these PEO binary matrices had shown the similar release behavior that had been evaluated by the similarity factor f 2. Further study indicated that they had identical hydration, swelling, and erosion rate. Moreover, rheology study exhibited the similar rheological equation of Herschel-Bulkley and their viscosity was also within the same magnitude. Therefore, viscosity plays the most important role to control drug release compared to other factors in PEO binary matrix system. This research provides fundamental understanding of in vitro drug release of PEO binary hydrophilic matrix tablets and helps pharmaceutical workers to develop a hydrophilic controlled system, which will effectively shorten the process of formulation development by reducing trial-and-error.

Analysis of macromolecular changes and drug release from hydrophilic matrix systems

Solid dispersions are dynamic systems, a careful control of processing variables is required to produce desired physicochemical properties of these systems.The influence of drug particle size, dispersion temperature and compression force on the release rate of theophylline from solid dispersed system tablets was studied. Theophylline base (micronized and granulate) were embedded into a polymeric mixture of PEG and acrylic/methacrylic esters at controlled temperature and shock cooled. Tablets were made at two compressional forces and drug release was measured spectrophotometrically over a period of fifteen hours.The release rate of drug dispersed in these insoluble matrices was independent of particle size but not of hardness.However, variations in ratios of polymeric mixture and dispersion temperature controls the drug release rate from inert matrix more effectively than such factors as drug particle size and lower range of tablet hardness. The fast cooling produced excellent reproducibility of drug content throughout the entire entrapment product. X-ray diffraction study demonstrated no changes in crystalline form of theophylline.

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.

The purpose of this work was to understand the formulation effect on the drug release from a hydrophilic matrix tablet of niacin using a multivariate statistical technique and Near Infrared Chemical Imaging (NIR-CI). Tablets were composed of ethyl cellulose (EC) and polyethylene oxide (PEO) as release retarding polymers and lactose as the release modulator. D-optimal experimental design was composed of three formulation variables: the content of EC(X1), PEO (X2), and lactose (X3). Response surface methodology (RSM) and multiple response optimization utilizing the polynomial equation were used to predict the optimal formulation. Results showed that the interaction effect of lactose with the polymers PEO and EC and lactose by itself were the most influential factors on the drug release rate. While lactose enhances the drug release rate by forming pores it also promotes water penetration into the tablet core. This in turn helps the formation of the gel layer which acts as barrier to drug diffusion. NIR-CI showed that tablets with higher level of PEO swells at a faster rate and greater extent than formulations with higher level of EC. NIR-CI was thus found to be a very useful technique to predict the drug release rate from hydrophilic matrix systems.

The particle size of HPMC is a critical factor that can influence drug release rate from hydrophilic matrix systems. Percolation theory is a statistical tool which is used to study the disorder of particles in a lattice of a sample. The percolation threshold is the point at which a component is dominant in a cluster resulting in significant changes in drug release rates. Mini-tablets are compact dosage forms of 1.5–4 mm diameter, which have potential benefits in the delivery of drug to some patient groups such as pediatrics. In this study, the effect of HPMC particle size on hydrocortisone release and its associated percolation threshold for mini-tablets and tablets was assessed. For both mini-tablets and tablets, large polymer particles reduced tensile strength, but increased the drug release rate and the percolation threshold. Upon hydration, compacts with 45–125 μm HPMC particles formed a strong gel layer with low porosity, reducing hydrocortisone release rates. In comparison, faster drug release rates were obtained when 125–355 µm HPMC particles were used, due to the greater pore sizes that resulted in the formation of a weaker gel. Using 125–355 µm HPMC particles increased the percolation threshold for tablets and to a greater extent for mini-tablets. This work has demonstrated the importance of HPMC particle size in ER matrices, the effects of which are even more obvious for mini-tablets.

A hydrophilic matrix tablet containing 300 mg of propylthiouracil was formulated with several types of hydroxypropylmethylcellulose. The influence of polymer and drug granule particle size, polymer concentration, crystallinity and geometry of the polymer particles, the polymer incorporation outside or inside the granule, addition of a filler and tablet hardness were studied. Polymer concentration, polymer particle size and geometry, filler addition and type of the filler used had a major influence on in vitro drug dissolution profiles. The bioavailability of propylthiouracil in dogs from the hydrophilic matrices investigated was low, because of the short gastro-intestinal transit times of the matrix tablets in the dogs. The matrix tablets reached the colon in fasted dogs within 2-3 hours after administration. The results indicated the poor predictability of bioavailability experiments in dogs with hydrophilic matrices. Although the bioavailability data in pigs seemed promising, a transit time study revealed a long stomach residence time of the matrix tablets in pigs. These data suggested that pigs are an inappropriate animal model for bioavailability studies of erodible matrix tablets.

This chapter discusses the application of twin-screw hot-melt extrusion as an enabling technology to overcome well-known, physical limitations of hydrophilic controlled-release matrix tablets manufactured by conventional means, such as direct compression and wet and dry granulation. Polymers that are particularly useful in hydrophilic matrix systems that are produced by extrusion include hydroxypropylcellulose, hypromellose, polyethylene oxide, and copovidone. Case studies are presented that show enhanced tablet compactibility, smaller tablets, and greater drug retardation for hydrophilic matrix tablets comprising up to 75 % highly soluble drug (metformin) made by melt extrusion as opposed to conventional methods. In the case of poorly soluble drugs, hot-melt extrusion enables the combination of amorphous drug polymer dispersions and hydrophilic matrix technology in a single manufacturing step, to simultaneously deliver drug over an extended period, enhance equilibrium drug solubility, and prevent the dissolved drug from precipitating out of saturated solution in the simulated GIT fluids for periods as long as 8 h. Twin-screw extrusion is a versatile enabling technology that is increasingly relevant in commercial solid oral dosage form manufacturing.KeywordsDrug ReleaseSolid DispersionPolyvinyl AcetateSoluble DrugMatrix TabletThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The aim of this work was to design new hydrophilic matrix (HM) systems by cross-linking Mesquite Seed Gum (MSG), a galactomannan that occurs in the endosperm layer of the seeds of a Brazilian tree,Prosopis juliflora DC, with two well-known polysaccharides with the ability of retarding drug release, chitosan and xanthan gum. This had in mind the idea of using these new compounds in the preparation of extended-release dosage oral forms. The first part of this study was dedicated to the evaluation of MSG in terms of its functionality as a hydrophilic matrix (HM) system for extended-release purposes. Next, we started the study of water uptake profile of all polymers of interest (MSG, Xanthan Gum and Chitosan), in the following media: water, SGF and SIF. Following, we searched for the best cross-linking agent between Glutharaldehyde (GA) and Hexamethylenediisocyanate (HMDI), which turned out to be the GA. Next step we begun to prepare new hydrophilic matrices of MSG_Chitosan and MSG_Xanthan Gum, with different ratios, 1:1, 1:2 and 2:1. Finally, after deciding which new HM system presented best results, by using statistics tools, we investigated the mechanism controlling the rate release of the model drug, from tablets made with this new matrix. As a final result we concluded that the best combination of polysaccharides was achieved with MSG and Xanthan Gum, with mass ratio of 1:2, using glutharaldehyde aqueous solution as cross-linking agent. It presented a prevalent zero order kinetics, which is a very important feature when thinking about an extended-release oral dosage.