Evaluation of the performance characteristics of bilayer tablets: Part I. Impact of material properties and process parameters on the strength of bilayer tablets

The Effect of Compression Pressure on the First Layer Surface Roughness and Delamination of Metformin and Evogliptin Bilayer and Trilayer Tablets

The objectives of this study were to evaluate the delamination of convex-shaped metformin HCl (MF) and evogliptin tartrate (EG) multi-layer tablets depending on the pre-compression and main compression pressures and simultaneously correlate these results with those of a surface roughness analysis. Free-flowing MF and EG (median diameters of 38.3 and 44.7 μm, respectively) granules prepared using the wet granulation method were pre-compressed and subsequently compressed into bilayer and trilayer tablets using a universal testing machine. The compaction force required to break the tablets increased linearly as the main compression pressure increased (30-150 MPa). Conversely, the interfacial strength and compaction breaking force decreased as the pre-compression pressure increased (10-110 MPa). A surface roughness analysis employing a profilometer revealed that the first layer (MF) roughness drastically decreased from 5.89 to 0.51 μm (Ra, arithmetic average of profile height deviations from the mean line) as the pre-compression pressure increased from 10 to 150 MPa in the bilayer tablet. Accordingly, the decrease in the roughness of the first layer reduced the inter-penetration at the interface, as observed via energy dispersive spectrometer (EDS)-equipped scanning electron microscopy, decreasing the interfacial bonding strength and causing delamination of the MF/EG multi-layer tablets. These findings indicate the significance of roughness control in the actual preparation of multi-layer tablets and the usefulness of profilometer- and EDS-based surface analyses for interpreting the delamination of multi-layer tablets.

Implementation of Quality by Design (QbD) for development of bilayer tablets

Bilayer tablets offer various drug release profiles for individual drugs incorporated in each layer of a bilayer tablet, which is rarely achievable by conventional tablets. These tablets also help avoid physicochemical incompatibilities between drugs and excipients. Successful manufacturing of such more complex dosage forms depends upon screening of material attributes of API and excipients as well as optimization of processing parameters of individual unit operations of the manufacturing process that must be strictly monitored and controlled to obtain an acceptable drug product quality and performance in order to achieve safety and efficacy per regulatory requirements. Optimizing formulation attributes and manufacturing processes during critical stages, such as blending, granulation, pre-compression, and main compression, can help avoid problems such as weight variation, segregation, and delamination of individual layers, which are frequently faced during the production of bilayer tablets. The main objective of this review is to establish the basis for the implementation of Quality by Design (QbD) system principles for the design and development of bilayer tablets, encompassing the preliminary and systematic risk assessment of critical material attributes (CMAs) and critical process parameters (CPPs) with respect to in-process and finished product critical quality attributes (CQAs). Moreover, the applicability of the QbD methodology based on its purpose is discussed and complemented with examples of bilayer tablet technology.

Bilayer fixed-dose combination tablet for curcumin microparticles and piroxicam and in vitro evaluation

Aim: In the present work, fixed-dose combination of bilayer tablets for piroxicam as and curcumin as immediate-release and sustained-release layer (SRL) respectively for management of inflammatory response. Materials & methods: The SRL include Curcumin polycaprolactone microparticles from spray drying. The tablet layers include Pearlitol 200SD, Microcrystalline cellulose PH101, Aerosil 200, talc each layer. Results: SEM studies confirm spherical microparticles. PXRD and DSC studies confirm the amorphous microparticles. In vitro studies exhibit, an immediate release and sustained release for Piroxicam and Curcumin after 2 h. Cellular uptake studies on RAW 264.7 cells confirm the complete internalization of microparticles. Conclusion: Therefore, it was concluded that microparticles can be formulated into a unit dosage form for the management of inflammation.

Optimization of bilayer tablet manufacturing process for fixed dose combination of sustained release high-dose drug and immediate release low-dose drug based on quality by design (QbD)

A fixed dose combination (FDC) bilayer tablet, consisting of high-dose metformin HCl in a sustained release layer and low-dose evogliptin tartrate in an immediate release layer, was developed based on a quality by design (QbD) approach. To implement QbD approach, the bilayer tableting process parameters judged as high risk through risk analysis were optimized by a central composite face-centered design as a design of experiment (DOE) methodology. Using DOE, the optimized conditions of the tableting process for drug products that satisfy the established quality target product profiles were obtained. The content uniformity of low-dose evogliptin tartrate in the optimized bilayer tablet prepared on a large scale was confirmed by at-line transmittance Raman spectroscopy as a process analytical technology. In addition, the in vitro drug release and in vivo pharmacokinetic studies showed that metformin HCl and evogliptin tartrate in the bilayer tablet is bioequivalent to those of the respective reference drugs. Furthermore, the physicochemical stability of the optimized bilayer tablet during storage under long-term and accelerated conditions was also confirmed. Therefore, it can be concluded that the QbD approach is an effective way to develop a new FDC bilayer tablet that is easy to scale up for successful commercialization.

Challenges in technology of bilayer and multi-layer tablets: a mini-review

Bilayer and multi-layer tablets are enjoying growing popularity among original drug and generic product manufacturers. Multi-layer tablets have many key benefits compared to classic immediate-release tablets. The use of such solid oral dosage forms simplifies dosing regimens in combination therapy, and thus improves patient compliance. However, the technology of multilayer tablets is demanding and requires precise choice of excipients and production parameters with regard to each technological step. The main benefits of multi-layer tablets, certain aspects of their production and the challenges encountered during the compression process are reviewed in this paper.

Interfacial bonding in formulated bilayer tablets

To take full advantage of the drug delivery benefits offered by bilayer tablets, the common issue of weak interfacial bonding strength (IBS) with manufacturing must be overcome. This work seeks to characterize the effects of composition in individual layers and compaction pressure on the IBS. Mixtures of MCC and lactose in different ratios with and without HPMC were used where the first layer was compacted with two different pressures (20 and 100 MPa) followed by a second layer compaction pressure of 200 MPa. After identifying the failure mode as either at the interface or within a layer, the complex trends of bilayer tablet IBS as a function of MCC content were explained by considering the interplay between particle bonding strength and bonding area at the interface.

The influence of core tablets rheology on the mechanical properties of press-coated tablets

Press-coating (also called compression coating or dry coating) consists of a second compression of an outer layer of material over a preformed tablet core. Despite being old, this technology has returned to popularity due to its widespread use in preparation of chronotherapeutic dosage forms. The literature available on press-coated tablets has mainly investigated drug release kinetics, while there is a lack of information about their mechanical properties. Here we study, for the first time, the effect of material properties and manufacturing parameters on the mechanical characteristics of press-coated tablets. Firstly, we show that the stiffness of the bare core tablets depends on the material type and, in case of viscoelastic materials, also depends on the compression pressure. We then demonstrate that less stiff (i.e. more viscoelastic) core tablets deform to a greater extent upon the second compression and thus allow the formation of less porous, harder coats and with a more homogenous density distribution. Finally, we find that changes in the mechanical properties of press-coated tablets over one month storage are almost negligible. Our data suggest that viscoelastic rather than stiff cores should be used in dry coating, as they promote the formation of more homogenous coats and with better mechanical properties.

Matrix systems for oral drug delivery: Formulations and drug release

In this current article matrix formulations for oral drug delivery are reviewed. Conventional dosage forms and novel applications such as 3D printed matrices and aerogel matrices are discussed. Beside characterization, excipients and matrix forming agents are also enlisted and classified. The incorporated drug could exist in crystalline or in amorphous forms, which makes drug dissolution easily tunable. Main drug release mechanisms are detailed and reviewed to support rational design in pharmaceutical technology and manufacturing considering the fact that R&D members of the industry are forced to obtain knowledge about excipients and methods pros and cons. As innovative and promising research fields of drug delivery, 3D printed products and highly porous, low density aerogels with high specific surface area are spreading, currently limitlessly. These compositions can also be considered as matrix formulations.

On Identification of Critical Material Attributes for Compression Behaviour of Pharmaceutical Diluent Powders

As one of the commonly-used solid dosage forms, pharmaceutical tablets have been widely used to deliver active drugs into the human body, satisfying patient's therapeutic requirements. To manufacture tablets of good quality, diluent powders are generally used in formulation development to increase the bulk of formulations and to bind other inactive ingredients with the active pharmaceutical ingredients (APIs). For formulations of a low API dose, the drug products generally consist of a large fraction of diluent powders. Hence, the attributes of diluents become extremely important and can significantly influence the final product property. Therefore, it is essential to accurately characterise the mechanical properties of the diluents and to thoroughly understand how their mechanical properties affect the manufacturing performance and properties of the final products, which will build a sound scientific basis for formulation design and product development. In this study, a comprehensive evaluation of the mechanical properties of the widely-used pharmaceutical diluent powders, including microcrystalline cellulose (MCC) powders with different grades (i.e., Avicel PH 101, Avicel PH 102, and DG), mannitol SD 100, lactose monohydrate, and dibasic calcium phosphate, were performed. The powder compressibility was assessed with Heckel and Kawakita analyses. The material elastic recovery during decompression and in storage was investigated through monitoring the change in the dimensions of the compressed tablets over time. The powder hygroscopicity was also evaluated to examine the water absorption ability of powders from the surroundings. It was shown that the MCC tablets exhibited continuous volume expansion after ejection, which is believed to be induced by (1) water absorption from the surrounding, and (2) elastic recovery. However, mannitol tablets showed volume expansion immediately after ejection, followed by the material shrinkage in storage. It is anticipated that the expansion was induced by elastic recovery to a limited extent, while the shrinkage was primarily due to the solidification during storage. It was also found that, for all powders considered, the powder compressibility and the elastic recovery depended significantly on the particle breakage tendency: a decrease in the particle breakage tendency led to a slight decrease in the powder compressibility and a significant drop in immediate elastic recovery. This implies that the particle breakage tendency is a critical material attribute in controlling the compression behaviour of pharmaceutical powders.

Understanding the Delamination Risk of a Trilayer Tablet Using Minipiloting Tools

A multilayer tablet is one of the formulation options used to mitigate chemical and physical incompatibility between different drug substances. Feasibility studies of multilayer tablets are often conducted using round flat-faced punch tooling. However, the link between different tooling designs and multilayer tablet performance is not well established. This study uses a prototype trilayer tablet and examines tooling design considerations when conducting small-scale studies to gauge the risk of interfacial defects. The impact of tablet weight and dimensions was evaluated to gain understanding of the effect of scale-up/down of tablet size. The factors in tooling selection, including tablet shape, cup depth, and size of embossing were evaluated to gain insight on the impact of tooling design on the interfacial strength of the trilayer tablet. It was found that tablet weight and dimensions can significantly affect the interfacial strength due to their impact on force transmission during compression and the retardation force from the die wall during ejection. Round flat-faced tooling generated trilayer tablets of the strongest interfacial strength compared to typical commercial tablets-oval shaped with concave surfaces. These factors should be accounted for when using round flat compacts to assess the interface risks of a multilayer tablet.

Effect of the Curvature of the Punches on the Shape of the Interface and the Delamination Tendency of Bilayer Tablets

Bilayer tablets are of special interest in the pharmaceutical industry. The main problem during their manufacturing is the occurrence of delamination during or after the ejection from the die. This work studies the influence of using punches with a curvature on the interfacial strength and thus on the delamination tendency of bilayer tablets. Bilayer tablets were produced with a compaction simulator using different flat and concave punches with different radii of curvature. The main compaction pressure was kept constant but the tamping force was varied. Two bilayer model systems were studied. The interfacial strength was determined using a previously described indentation test. The factors studied were analyzed for statistical significance with respect to the responses. The curvature of the interface was found to be higher when the curvature of the punch and the tamping force increased. Breaking tests then demonstrated that, for bilayer tablets obtained using the same compression parameters, the interfacial strength was lower when the curvature of the interface increased. As a consequence, when producing bilayer tablets with concave punches, it is important to choose properly the tableting parameters in order to have an interface between the layers as flat as possible to avoid delamination issues.

Single Layer Extended Release Two-in-One Guaifenesin Matrix Tablet: Formulation Method, Optimization, Release Kinetics Evaluation and Its Comparison with Mucinex® Using Box-Behnken Design

Guaifenesin, a highly water-soluble active (50 mg/mL), classified as a BCS class I drug. Owing to its poor flowability and compressibility, formulating tablets especially high-dose one, may be a challenge. Direct compression may not be feasible. Bilayer tablet technology applied to Mucinex®, endures challenges to deliver a robust formulation. To overcome challenges involved in bilayer-tablet manufacturing and powder compressibility, an optimized single layer tablet prepared by a binary mixture (Two-in-one), mimicking the dual drug release character of Mucinex^® was purposed. A 3-factor, 3-level Box-Behnken design was applied to optimize seven considered dependent variables (Release "%" in 1, 2, 4, 6, 8, 10 and 12 h) regarding different levels of independent one (X₁: Cetyl alcohol, X₂: Starch 1500^®, X₃: HPMC K100M amounts). Two granule portions were prepared using melt and wet granulations, blended together prior to compression. An optimum formulation was obtained (X₁: 37.10, X₂: 2, X₃: 42.49 mg). Desirability function was 0.616. F2 and f1 between release profiles of Mucinex® and the optimum formulation were 74 and 3, respectively. An n-value of about 0.5 for both optimum and Mucinex® formulations showed diffusion (Fickian) control mechanism. However, HPMC K100M rise in 70 mg accompanied cetyl alcohol rise in 60 mg led to first order kinetic (n = 0.6962). The K values of 1.56 represented an identical burst drug releases. Cetyl alcohol and starch 1500^® modulated guaifenesin release from HPMC K100M matrices, while due to their binding properties, improved its poor flowability and compressibility, too.

Effect of the surface free energy of materials on the lamination tendency of bilayer tablets

Dosage forms with fixed dose combinations of drugs is a frequent and advantageous mode of administration, but their production involves a number of technological problems. Numerous interactions in a homogeneous vehicle may be avoided through the use of layered tablets. The mechanical properties of these dosage forms depend on numerous process parameters and material characteristics. The aim of the present study was a detailed investigation of the relationships between the surface characteristics and deformation properties of tableting materials and the tendency of bilayer tablets to undergo lamination. Bilayer tablets were compressed from unlubricated materials with different plastic-elastic properties and surface free energies according to a mixed 2 and 3-level half-replicated factorial design. The results revealed that the surface characteristics play the main role in the lamination of layered tablets and the effect of the plastic-elastic behavior cannot be interpreted without a knowledge of these properties.

Evaluation of the performance characteristics of bilayer tablets: Part II. Impact of environmental conditions on the strength of bilayer tablets

Ambient air humidity and temperature are known to influence the mechanical strength of tablets. The objective of this work is to understand the influence of processing parameters and environmental conditions (humidity and temperature) on the strength of bilayer tablets. As part of this study, bilayer tablets were compressed with different layer ratios, dwell times, layer sequences, material properties (plastic and brittle), first and second layer forces, and lubricant concentrations. Compressed tablets were stored in stability chambers controlled at predetermined conditions (40C/45%RH, 40C/75%RH) for 1, 3, and 5 days. The axial strength of the stored tablets was measured and a statistical model was developed to determine the effects of the aforementioned factors on the strength of bilayer tablets. As part of this endeavor, a full 3 × 2(4) factorial design was executed. Responses of the experiments were analyzed using PROC GLM of SAS (SAS Institute Inc, Cary, North Carolina, USA). A model was fit using all the responses to determine the significant interactions (p < 0.05). Results of this study indicated that storage conditions and storage time have significant impact on the strength of bilayer tablets. For Avicel-lactose and lactose-Avicel tablets, tablet strength decreased with the increasing humidity and storage time. But for lactose-lactose tablets, due to the formation of solid bridges upon storage, an increase in tablet strength was observed. Significant interactions were observed between processing parameters and storage conditions on the strength of bilayer tablets.