Interrogating erosion-based drug liberation phenomena from hydrophilic matrices using near infrared (NIR) spectroscopy

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Application of Focus Variation Microscopy and Dissolution Imaging in Understanding the Behaviour of Hydrophilic Matrices

Hydrophilic matrix systems can be found in a wide range of extended release pharmaceutical formulations. The main principle of these systems is that upon contact with water, the hydrophilic component swells to form a hydrated gel layer which controls drug release. The following work demonstrates an explorative study into the use of dissolution imaging and focus variation microscopy with hydrophilic polymers. This study investigated the surface properties of xanthan gum (XG), polyethylene oxide (PEO), and hypromellose (hydroxypropyl methylcellulose, HPMC) compacts with each of these three hydrophilic polymers from one of each classification of natural, semi-synthetic, or synthetic polymer using a focus variation instrument. The auto correlation length (Sal) showed all surface profiles from the compacts displayed a value below 0.1 mm, indicating that only high frequency components (i.e., roughness) were considered and that the analysis had been successful. The developed interfacial area ratio (Sdr) displayed values below 5% in line with ISO guidelines for all the polymers studied with their texture aspect ratio values (Str) > 0.5, indicating uniformity of the surfaces of the produced compacts. Of the various parameters studied, areal material ratio (Smr2) predicted XG to wet and hydrate quicker than PEO, with PEO also wetting and hydrating quicker than the HPMC. The dissolution imaging and initial swelling studies proved to concur with the findings from the areal material ratio (Smr2) parameter, suggesting porosity was not an indicator for the ease with which water ingress occurs. This study suggests the Smr2 surface parameter to potentially predict wetting and initial hydration of hydrophilic polymers, however care should be taken as this study consists of a selected number of hydrophilic polymers.

Towards functional characterization of excipients for oral solid dosage forms using UV-vis imaging. Liberation, release and dissolution

The purpose of this study was to investigate whole-dosage form UV-vis imaging as a potential tool for functional characterization of excipients used in solid oral dosage forms. To this end, tablets (average mass 260.0 mg, 224.5 mg and 222.1 mg) containing theophylline anhydrate (20 % w/w), 1% (w/w) magnesium stearate, and 79 % (w/w) of either microcrystalline cellulose (MCC, Avicel PH 101) or hydroxypropyl methylcellulose (HPMC, Methocel K15 M or K100 M) were prepared as model systems. Drug liberation from tablets was studied in 0.01 M HCl at 37 °C using a Sirius SDi2 equipped with a USP IV type flow cell comprising a UV-vis imaging detector operating at 255 nm and 520 nm. The effluent from the flow cell was passed through a downstream spectrophotometer, and UV-vis spectra in the wavelength range 200-800 nm were recorded every 2 min. The erosion and swelling behavior of the MCC tablets and HPMC K15 M and K100 M tablets were visualized in real time. The swelling of HPMC K15 M and K100 M containing tablets was assessed quantitatively as changes in tablet diameter measured at 520 nm, and was clearly distinguished from the swelling of the MCC tablets. Namely, an increment of 2.5 mm in diameter was determined for the HPMC tablets while the MCC tablets increased by 0.5-1 mm in diameter. Gel layers of variable thickness were observed only for the HPMC K15 M and K100 M tablets. In addition, a relatively high initial liberation rate of theophylline was found for the MCC tablets as compared to the HPMC tablets. UV-vis imaging revealed features of liberation not revealed by simply measuring drug concentration in the dissolution media or by visual assessment. It may be sufficiently sensitive to be further developed for functional characterization of excipients and provide insights into drug-excipient interactions likely to be useful in formulation development.

Development of a novel method utilising dissolution imaging for the measurement of swelling behaviour in hydrophilic matrices

A variety of imaging techniques are currently used within the field of pharmaceutics to help understand and determine a wide range of phenomena associated with drug release from hydrophilic matrix tablets. This work for the first time aims at developing an appropriate testing imaging methodology using a surface dissolution imaging instrument (SDI2) for determining the swelling of whole compacts using hypromellose as a model hydrophilic matrix former. The influence of particle morphology (CR and DC grades) and two compressional forces (5 and 15 kN) on the initial swelling behaviour of hypromellose were investigated. The results showed that a lower absorbance of 50 mAu with a wider measurement zone proved successful in determining the edge of the gel layer and growth measurements in real-time with high level of details under flow. Despite the differences in the morphology of the grades of hypromellose tested, it was however discovered that gel growth was statistically similar between them which may be attributed to their similar chemistry. This novel method also highlighted differences in the hydrated polymer's appearance which may have been as a result of differences in porosity and solid fraction. This information is of great importance to a formulator as gel growth plays a crucial role in determining drug release from polymer compacts.

Advances in mechanistic understanding of release rate control mechanisms of extended-release hydrophilic matrix tablets

Approaches to characterizing and developing understanding around the mechanisms that control the release of drugs from hydrophilic matrix tablets are reviewed. While historical context is provided and direct physical characterization methods are described, recent advances including the role of percolation thresholds, the application on magnetic resonance and other spectroscopic imaging techniques are considered. The influence of polymer and dosage form characteristics are reviewed. The utility of mathematical modeling is described. Finally, how all the information derived from applying the developed mechanistic understanding from all of these tools can be brought together to develop a robust and reliable hydrophilic matrix extended-release tablet formulation is proposed.