A Comprehensive Review on Pharmaceutical Film Coating: Past, Present, and Future

Designing an effective dissolution test for bilayer tablets tailored for optimal melatonin release in sleep disorder management

This project aims to investigate the release performance of bilayer tablet (BL-Tablet) designed with both fast and slow-release technology, targeting sleep disorders. The tablet incorporates Melatonin, extracts of Eschscholzia californica and Melissa officinalis. In order to validate the effectiveness of the extended-release profile, an advanced dissolution test was herein proposed. This new method utilizes biorelevant intestinal fluid media and incorporates a stomach-to-intestine fluid changing (SIFC) system. To demonstrate the advantages of employing this method for assessing the controlled release profile of active ingredients, the dissolution results were compared with those obtained using the conventional EU Pharmacopoeia approach. Furthermore, the comparative analysis was extended to include a monolayer tablet version (ML-Tablet) lacking the slow-release technology. Technological characterization and bioaccessibility studies, including intestinal permeability test, were conducted as well to assess the pharmacological performance and bioavailability of active ingredients. The dissolution data recovered revealed that the two dissolution methods did not exhibit any significant differences in the release of ML-Tablet's. However, the dissolution profile of the BL-Tablet exhibited notable differences between the two methods particularly when assessing the behavior of the slow-release layer. In this scenario, both methods initially exhibited a similar release pattern within the first approximately 0.5 h, driven by the fast-release layer of the tablet. Following this, distinct gradual and sustained releases were observed, spanning 2.5 h for the EU Pharmacopoeia method and 8 h for the new SIFC-biorelevant dissolution method, respectively. Overall, the novel method demonstrated a substantial improvement compared to conventional EU Pharmacopoeia test in evaluating the performance of a controlled slow-release technology. Remarkably, the prolonged release technology did not have an adverse impact on melatonin intestinal absorption, and, consequently, maintaining its potential bioavailability of around 78%. Concluding, this research provides valuable insights into how the innovative dissolution test can assist formulators in developing controlled release formulations.

Genesis, mechanism, and avoidance of cosmetic coating defects - An industrial case study

Film-coated tablets as solid oral dosage forms are a well-accepted way of administering drugs but are not without specific challenges during manufacturing. One relevant criterion of the final product is the visual integrity and therewith, the absence of cosmetic optical defects such as edge chipping. The aim of the present study was to examine the origin of those edge chipping defects, which were observed during commercial manufacturing of film-coated tablets, and to provide recommendations for process optimization to reduce the defect occurrence. The unraveling of the herein described phenomenon necessitated an interplay of in-depth material characterization, discrete element modeling (DEM) as well as an in-house developed optical measurement system for the automated quantification of tablet defects. As a result of this investigation, the automatic unloading step after the tablet coating process was identified as the most critical step for the occurrence of chipping defects and a replacement by manual unloading was proposed to reduce the defect propensity. The recommended optimization was subsequently confirmed in several manufacturing runs and a reduction of defect propensity by a factor of 5 was observed, highlighting the relevance and the impact of the performed thorough investigation.

Exploring magnesium myristate for its dual functionality as a binder and lubricant in the formulation of tablet

Purpose: To explore 'magnesium myristate' for its dual functionality as a lubricant and binder in the formulation of tablets. Methods: Using (DoE), tablet formulations using magnesium myristate and conventional excipients (magnesium stearate and PVP K30) were developed by wet granulation technique. The prepared granules and formulated tablets were evaluated for pre- and post-compression parameters, respectively. Results: Magnesium myristate exhibited excellent flow properties. The optimized formulations containing magnesium myristate exhibited increased hardness and in vitro drug release in comparison to conventional excipients. f2 similarity index for in vitro drug release showed no significant variations with optimized formulations and with the marketed formulations. Conclusion: Magnesium myristate shows a promising replacement for conventional excipients as both a lubricant and binder in tablet formulation.

Detrimental Effect of the Film Coat Chemistry and Thickness on the Physical Stability of Amorphous Solid Dispersions in Tablet Formulations

Amorphous solid dispersions (ASDs) have been widely utilized to enhance the bioavailability of pharmaceutical drugs with poor aqueous solubility. The role of various excipients on the amorphous drug to crystalline form conversion in ASDs has been widely documented. However, there has been no published study to investigate the role of film coating material on the physical stability of an ASD based tablet formulation, to the best of our knowledge. Here we show that the film coating can potentially have a detrimental impact on the physical stability of spray dried intermediates (SDI) in tablet formulations. The impact of the film coating on the physical stability of SDI was found to be related to the film coat material composition, and an increase in the film coating thickness led to a reduction in the physical stability of SDI in tablets. Oral compressed tablets in which the film coat material was "mixed-in" with the formulation blend showed a similar or worse physical stability than film coated tablets, further underscoring the film coat material impact on physical stability, independent of the film coating process. This study demonstrates a need for careful consideration of the film coat material selection for ASD based pharmaceutical product development.

Impact of Rapid Environmental Changes on Stress Distribution in Tablet Coatings: Simulations

Immediate-release film coatings, also known as "non-functional" film coating, are applied to core tablets to improve product appearance and swallowability, impart taste-masking properties, improve handling and stability of the dosage form, and reduce exposure to active drug substance for caregivers. The coatings have no measurable impact on bio-performance of the drug product but they protect tablets from negative effects of environment such as humidity, oxidation, and light. The mechanical stability and integrity of tablet coatings are therefore important to maintain drug product quality attributes such as appearance and stability. Therefore, environmental conditions under which these coatings may crack are important to understand so as to prevent their occurrence. In this work, we present a novel computational framework to assess the mechanical integrity of tablet coatings exposed to rapid variations in environmental conditions. We perform detailed stress and strain analysis of tablet coatings on tablet surfaces with debossed regions and identify conditions for cracking. Coatings with both elastic and viscoelastic properties are considered. Rapid changes in environmental temperature and humidity can cause differential expansion/contraction of coating and tablet core resulting in stresses that are higher than those experienced during the drying process in a coater. Debossed regions on the tablet surface with sharp surface curvatures act as stress concentrators that nucleate cracks. Small changes in the design of the debossed regions lead to modest reductions in the peak stress. Stress calculations show that coatings that are well bonded to tablet surface can crack only under very extreme conditions.

Studying the dissolution of immediate release film coating using terahertz pulsed imaging

Coated tablets introduce complexity to the dissolution process, even with readily soluble immediate release coating layers. Therefore, a more detailed understanding of the physical steps involved in the dissolution process can improve the efficiency of formulation and process design. The current study uses terahertz pulsed imaging to visualise the hydration process of microcrystalline cellulose (MCC) tablet cores that were film coated with an immediate release coating formulation upon exposure to the dissolution medium. Film coated tablets that were prepared from three levels of core porosity (10%, 20% and 30%) and with coating thickness in the range of 30μm to 250μm were investigated. It was possible to resolve and quantify the distinct stages of wetting of the coating layer, swelling of the MCC particles at the core surface, and dissolution of the coating layer followed by the ingress of dissolution media into the tablet core. The liquid transport process through the coating layer was highly consistent and scalable. The penetration rate through the coating layer and the tablet core both strongly depended on coating thickness and core porosity.

Three-Dimensional Sag Tracking in Falling Liquid Films

Coating defects often arise during application in the flash stage, which constitutes the ∼10 min interval immediately following film application when the solvent evaporates. Understanding the transient rheology and kinematics of a coating system is necessary to avoid defects such as sag, which results in undesirable appearance. A new technique named variable angle inspection microscopy (VAIM) aimed at measuring these phenomena was developed and is summarized herein. The essence of this new, non-invasive, rheological technique is the measurement of a flow field in response to a known gravitational stress. VAIM was used to measure the flow profile through a volume of a liquid thin film at an arbitrary orientation. Flow kinematics of the falling thin film was inferred from particle tracking measurements. Initial benchmarking measurements in the absence of drying tracked the velocity of silica probe particles in ∼140 μm thick films of known viscosity, much greater than water, at incline angles of 5° and 10°. Probe particles were tracked through the entire thickness of the film and at speeds as high as ∼100 μm/s. The sag flow field was well resolved in ∼10 μm thick cross sections, and in general the VAIM measurements were highly reproducible. Complementary profilometer measurements of film thinning were utilized to predict sag velocities with a known model. The model predictions showed good agreement with measurements, which validated the effectiveness of this new method in relating material properties and flow kinematics.

Pharmaceutical Coating and Its Different Approaches, a Review

Coating the solid dosage form, such as tablets, is considered common, but it is a critical process that provides different characteristics to tablets. It increases the value of solid dosage form, administered orally, and thus meets diverse clinical requirements. As tablet coating is a process driven by technology, it relies on advancements in coating techniques, equipment used for the coating process, evaluation of coated tablets, and coated material used. Although different techniques were employed for coating purposes, which may be based on the use of solvents or solvent-free, each of the methods used has its advantages and disadvantages, and the techniques need continued modification too. During the process of film coating, several inter-and intra-batch uniformity of coated material on the tablets is considered a critical point that ensures the worth of the final product, particularly for those drugs that contain an active medicament in the coating layer. Meanwhile, computational modeling and experimental evaluation were actively used to predict the impact of the operational parameters on the final product quality and optimize the variables in tablet coating. The efforts produced by computational modeling or experimental evaluation not only save cost in optimizing the coating process but also saves time. This review delivers a brief review on film coating in solid dosage form, which includes tablets, with a focus on the polymers and processes used in the coating. At the end, some pharmaceutical applications were also discussed.

Silicon Oxycarbide Porous Particles and Film Coating as Strategies for Tenofovir Controlled Release in Vaginal Tablets for HIV Prevention

Sustained release of antiretroviral drugs is currently the most encouraging strategy for the prevention of the sexual transmission of HIV. Vaginal tablets based on hydrophilic gelling polymers are an interesting dosage form for this purpose, since they can be developed to modify the release of the drug depending on the tablet swelling. Tenofovir is a drug with proven activity in the prevention of HIV-1 infection, and it is possible to have it loaded in the surface of γ-aminopropyl trimethoxy silane-functionalized oxycarbide particles. These particles can be incorporated into the tablets, thus providing a sustained release of the drug. Moreover, the presence of the particles modifies the microstructure of the gel formed, as observed in scanning electron microscopy and Hg porosimetry studies, resulting into a gel with a narrow pore size distribution between 10 and 100 µm. This implies a lower volume of fluid incorporated into the gel during swelling studies, and therefore improved mucoadhesion times in ex vivo test. The coating of the formulations with Eudragit® RS modifies the swelling behavior of the tablets, which not only is decreased in magnitude but also extended in time, and as consequence the drug release is also prolonged for up to 7 days.

Real-time coating thickness measurement and defect recognition of film coated tablets with machine vision and deep learning

This paper presents a system, where images acquired with a digital camera are coupled with image analysis and deep learning to identify and categorize film coating defects and to measure the film coating thickness of tablets. There were 5 different classes of defective tablets, and the YOLOv5 algorithm was utilized to recognize defects, the accuracy of the classification was 98.2%. In order to characterize coating thickness, the diameter of the tablets in pixels was measured, which was used to measure the coating thickness of the tablets. The proposed system can be easily scaled up to match the production capability of continuous film coaters. With the developed technique, the complete screening of the produced tablets can be achieved in real-time resulting in the improvement of quality control.

Advanced Analytical Approach Based on Combination of FT-IR and Chemometrics for Quality Control of Pharmaceutical Preparations

Background: The present work represents a feasibility study for the realization of an analytical method finalized to the detection of expired antibiotic tablets. The work focuses on a specific antibiotic drug and represents the preliminary study upstream of a larger-scale work. Methods: attenuated Total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) spectra coupled with sequential preprocessing through an orthogonalization (SPORT) chemometric approach were used to discriminate between expired and compliant tablets. Conclusions: The highest predictive accuracy (93.3% of correct classification rate in external validation, corresponding to 1 misclassified test sample over 15) was achieved by analyzing intact tablets. This represents an excellent result because it gives indications regarding the possibility of determining, in a completely non-destructive way, the presence of expired drugs.

Nanomechanical testing in drug delivery: Theory, applications, and emerging trends

Mechanical properties play a central role in drug formulation development and manufacturing. Traditional characterization of mechanical properties of pharmaceutical solids relied mainly on large compacts, instead of individual particles. Modern nanomechanical testing instruments enable quantification of mechanical properties from the single crystal/particle level to the finished tablet. Although widely used in characterizing inorganic materials for decades, nanomechanical testing has been relatively less employed to characterize pharmaceutical materials. This review focuses on the applications of existing and emerging nanomechanical testing methods in characterizing mechanical properties of pharmaceutical solids to facilitate fast and cost-effective development of high quality drug products. Testing of pharmaceutical materials using nanomechanical techniques holds potential to develop fundamental knowledge in the structure-property relationships of molecular solids, with implications for solid form selection, milling, formulation design, and manufacturing. We also systematically discuss pitfalls and useful tips during sample preparation and testing for reliable measurements from nanomechanical testing.

Visualising liquid transport through coated pharmaceutical tablets using Terahertz pulsed imaging

Dissolution of pharmaceutical tablets is a complex process, especially for coated tablets where layered structures form an additional barrier for liquid transport into the porous tablet matrix. A better understanding of the role of the coating structure in the mass transport processes that govern drug release, starting with the wetting of the coating layer by the dissolution medium, can benefit the formulation design and optimisation of the production. For this study, terahertz pulsed imaging was used to investigate how dissolution medium can penetrate coated tablets. In order to focus on the fundamental process, the model system for this proof-of-principle study consisted of tablet cores made from pure microcrystalline cellulose compacted to a defined porosity coated with Opadry II, a PVA-based immediate release coating blend. The coating was applied to a single side of flat-faced tablets using vacuum compression moulding. It was possible to resolve the hydration of the coating layer and the subsequent liquid ingress into the dry tablet core. The analysis revealed a discontinuity in density at the interface between coating and core, where coating polymer could enter the pore space at the immediate surface of the tablet cores during the coating process. This structure affected the liquid transport of the dissolution medium into the core. We found evidence for the formation of a gel layer upon hydration of the coating polymer. The porosity of the tablet core impacted the quality of coating and thus affected its dissolution performance (r =  0.6932 for the effective liquid penetration rate RP_eff and the core porosity). This study established a methodology and can facilitate a more in-depth understanding of the role of coating on tablet dissolution.

What's next in the use of opacifiers for cosmetic coatings of solid dosage forms? Insights on current titanium dioxide alternatives

The consolidated use of coatings containing E171 (i.e. titanium dioxide, TiO2) as an opacifier has made the white color of the resulting dosage forms a quality standard in the pharmaceutical and dietary supplement fields. This color is also associated with the efficiency of the coating layer in protecting the substrate from the effects of UV rays. However, health risks related to diet exposure to TiO2 has recently been advanced and its addition in coating formulations has been seriously questioned. As a consequence, in principle safer TiO2-free formulations have been recently launched on the market, especially for coatings of dietary supplements. In this work, we evaluated the overall physico-technological characteristics and performance of immediate release tablets coated with a variety of commercial cosmetic formulations free of E171. Moreover, a quantitative method based on the CIELab color space was proposed for the first time for studying the covering/coloring performance of the coating formulations. Based on the results obtained, the possibility to achieve a satisfactory covering capability and a degree of white comparable to that of a standard TiO2-containing reference with all the commercially-available ready-to-use TiO2-free products considered, without affecting the dissolution performance, was demonstrated.

Adsorption modeling of microcrystalline cellulose for pharmaceutical-based micropollutants

Cellulose can be considered as a raw material for the production of filters and adsorbents for the removal of micropollutants, particularly in pharmaceutical-based products. To study its applications, it is important to estimate the adsorptive interaction of cellulose with the targeted chemicals, and develop predictive models for the expandable estimation into various types of micropollutants. Therefore, the adsorption affinity between cellulose and micropollutants was measured through isotherm experiments, and a quantitative structure-adsorption relationship model was developed using the linear free energy relationship (LFER) equation. The results indicate that microcrystalline cellulose has a remarkably high adsorption affinity with cationic micropollutants. Moreover, it has interactions with neutral and anionic micropollutants, although they have relatively lower affinities than those of cations. Through a modeling study, an LFER model - comprising of excess molar refraction, polar interaction, molecular volume, and charge-related terms - was developed, which could be used to predict the adsorption affinity values with an R² of 0.895. To verify the robustness and predictability of the model, internal and external validation studies were performed. The results proved that the model was reasonable and acceptable, with an SE = 0.207 log unit.

Multiscale Shellac-Based Delivery Systems: From Macro- to Nanoscale

Delivery systems play a crucial role in enhancing the activity of active substances; however, they require complex processing techniques and raw material design to achieve the desired properties. In this regard, raw materials that can be easily processed for different delivery systems are garnering attention. Among these raw materials, shellac, which is the only pharmaceutically used resin of animal origin, has been widely used in the development of various delivery systems owing to its pH responsiveness, biocompatibility, and degradability. Notably, shellac performs better on encapsulating hydrophobic active substances than other natural polymers, such as polysaccharides and proteins. In addition, specially designed shellac-based delivery systems can also be used for the codelivery of hydrophilic and hydrophobic active substances. Shellac is most widely used for oral administration, as shellac-based delivery systems can form a compact structure through hydrophobic interaction, protecting transported active substances from the harsh environment of the stomach to achieve targeted delivery in the small intestine or colon. In this review, the advantages of shellac in delivery systems are discussed in detail. Multiscale shellac-based delivery systems from the macroscale to nanoscale are comprehensively introduced, including matrix tablets, films, enteric coatings, hydrogels, microcapsules, microparticles (beads/spheres), nanoparticles, and nanofibers. Furthermore, the hotspots, deficiencies, and future perspectives of shellac-based delivery system development are also analyzed. We hoped this review will increase the understanding of shellac-based delivery systems and inspire their further development.

Enteric-coated bacteriophage tablets for oral administration against gastrointestinal infections

Intestinal Pseudomonas aeruginosa is highly problematic in immunocompromised patients such as those in intensive care units in hospitals. Phage therapy is an attractive alternative or supplementary therapy to antibiotics as it not only kills multidrug-resistant bacteria, but also minimises the disruption of gut microflora. Solid oral dosage forms (i.e., tablets) have the potential to effectively deliver viable phages to the gastrointestinal tract, but formulation studies have been scarce. In this study, Pseudomonas-targeting phage PEV20 was used as a model to produce tablets suitable for oral delivery by utilising industry-scale tablet compression and tablet coating machines. Phage tablets were produced by (i) spray drying of phages, (ii) direct compression of the phage powders into tablets, and then (iii) tablet coating. The resulting phage tablets had negligible phage titre reduction throughout the process and passed the British Pharmacopeia tests, including friability, weight variation, disintegration and dissolution of the tablets as well as weight gain and disintegration (in 0.1 M HCl and pH 7.4 phosphate buffer) of coated tablets. The developed formulation method can be utilised to produce tablets containing other phages and phage cocktails that are effective against enteric bacterial infections.

Sensing technologies and experimental platforms for the characterization of advanced oral drug delivery systems

Complex and miniaturized oral drug delivery systems are being developed rapidly for targeted, controlled drug release and improved bioavailability. Standard analytical techniques are widely used to characterize i) drug carrier and active pharmaceutical ingredients before loading into a delivery device (to ensure the solid form), and ii) the entire drug delivery system during the development process. However, in light of the complexity and the size of some of these systems, standard techniques as well as novel sensing technologies and experimental platforms need to be used in tandem. These technologies and platforms are discussed in this review, with a special focus on passive delivery systems in size range from a few 100 µm to a few mm. Challenges associated with characterizing these systems and evaluating their effect on oral drug delivery in the preclinical phase are also discussed.

Predictive Approach to Understand and Eliminate Tablet Breakage During Film Coating

Pharmaceutical tablets can be susceptible to damage such as edge chipping or erosion of the core during the tablet coating process. The intersection of certain process parameters, equipment design, and tablet properties may induce more significant tablet damage such as complete tablet fracture. In this work, a hybrid predictive approach was developed using discrete element method (DEM) modeling and lab-based tablet impact experiments to identify conditions that may lead to tablet breakage events. The approach was extended to examine potential modifications to the coating equipment and process conditions in silico to mitigate the likelihood of tablet breakage during future batches. The approach is shown to enhance process understanding, identify optimal process conditions within development constraints, and de-risk the manufacture of future tablet coating batches.

3D-printed construct from hybrid suspension as spatially and temporally controlled protein delivery system

Protein delivery systems have been extensively applied in controlled releasing of protein or polypeptides for therapeutic treatment or tissue regeneration. While 3 D printing technology shows great promise in novel dosage form with tailoring dose size and drug release profile, 3 D printable protein delivery system has to face many difficult challenges. In this study, we developed a hybrid suspension combining Eudragit polyacrylate colloid as matrix material and Pluronic polyether hydrogel as diffusion channel for protein release. This hybrid suspension can be 3 D-printed into construct with complex shape and inner structures thanks to its pseudoplastic and thixotropic rheological properties. The protein can be incorporated in hybrid suspension either in its original or nanoparticle capsulated form. The experiment shows that the protein release from construct is a function of drying time, molecular weight (MW) of chitosan, as well as their own structural/diffusional properties. Also, the theoretical derivation suggests polyacrylate matrix tortuosity, chitosan erosion rate as well as hydrogel diffusion coefficient all contributed to the extended duration of release profile. In addition, cytotoxicity test through cell culture confirmed that the construct fabricated from hybrid suspension exhibit relative good bio-compatibility. Finally, heterogeneous constructs with zoned design were fabricated as protein delivery system, which demonstrated the capability of hybrid suspension technique for spatial and temporal release of macromolecular drugs to realize pharmaceutical effectiveness or guild cell organization.