Titanium Dioxide (E171 Grade) and the Search For Replacement Opacifiers and Colorants: Supplier Readiness Survey, Case Studies and Regulatory Perspective

Titanium dioxide (TiO2) is used primarily as an opacifier in solid dosage forms and is present in the majority of tablet and capsule dosage forms on the market. The IQ* TiO2 Working Group has previously shown that titanium dioxide has unique properties which are necessary for its function in these formulations and noted that, as the potential replacements lack the semi-conductor properties, high refractive index and whiteness of E171, it might be hard to replicate these properties with alternative materials. In this paper we detail the results of readiness surveys and practical assessments that have been conducted with alternative materials by IQ member companies. A range of technical challenges and regulatory hurdles were identified which mean that, in the short term, it may be difficult to replace titanium dioxide with the currently available alternative materials while readily achieving the same drug product quality attributes, especially for some of the marketed formulations that titanium dioxide is currently used for. We note the higher technical complexity, due to the variability, color fading and identified scale up risk, of E171 free film coatings and the likely impact on development costs and timelines. We also highlight several regulatory hurdles that would have to be overcome if a titanium dioxide replacement was required for some markets but was not mandated by others.

Determining the Impact of Roller Compaction Processing Conditions on Granulate and API Properties: Impact of Formulation API Load

Previous work demonstrated that roller compaction of a 40%w/w theophylline-loaded formulation resulted in granulate consisting of un-compacted fractions which were shown to constitute between 34 and 48%v/v of the granulate dependent on processing conditions. The active pharmaceutical ingredient (API) primary particle size within the un-compacted fraction was also shown to have undergone notable size reduction. The aim of the current work was to test the hypothesis that the observations may be more indicative of the relative compactability of the API due to the formulation being above the percolation threshold. This was done by assessing the impact of varied API loads in the formulation on the non-granulated fraction of the final granulate and the extent of attrition of API particles within the non-granulated fraction. The influence of processing conditions for all formulations was also investigated. The results verify that the observations, both of this study and the previous work, are not a consequence of exceeding the percolation threshold. The volume of un-compacted material within the granulate samples was observed to range between 34.7 and 65.5% depending on the API load and roll pressure, whilst the API attrition was equivalent across all conditions.

Non-contact Laser Interferometer Method to Characterize Tablet Punches: New Methodology to Assess Surface Roughness

Sticking to tablet punches is a major issue during drug product manufacturing. Research has shown that sticking involves the interrelationship of powder properties, compression force, length of manufacturing runs and punch quality. Here, we present a novel non-destructive methodology to study the surface metrology of punches to monitor them over their lifetime. This investigation used a non-contact laser interferometer to characterise roughness of commercial standard S7 steel punches coated with chrome that were originally used for commercial scale production that developed a sticking issue. During the development, this phenomenon had not been observed and was not considered a scale-up risk. The profilometer was used to examine the complete surface of these punches to investigate whether they met the acceptability criteria based on BS_ISO_18804 tooling standard. To improve data analysis during changeover, a 3D-printed holder was designed to enable analysis with minimal set-up requirements. Upon investigation, the punches were found to be of an unacceptable roughness and, particularly rough areas of the punch surface profiled, correlated well with areas of visually pronounced sticking. This non-destructive method can be used to produce a more detailed characterisation of punch roughness to ensure surfaces are of an acceptable quality after treatment with coatings.

Comparative Evaluation of the Powder and Tableting Properties of Regular and Direct Compression Hypromellose from Different Vendors

Hypromellose, a widely used polymer in the pharmaceutical industry, is available in several grades, depending on the percentage of substitution of the methoxyl and hydroxypropyl groups and molecular weight, and in various functional forms (e.g., suitable for direct compression tableting). These differences can affect their physicomechanical properties, and so this study aims to characterise the particle size and mechanical properties of HPMC K100M polymer grades from four different vendors. Eight polymers (CR and DC grades) were analysed using scanning electron microscopy (SEM) and light microscopy automated image analysis particle characterisation to examine the powder's particle morphology and particle size distribution. Bulk density, tapped density, and true density of the materials were also analysed. Flow was determined using a shear cell tester. Flat-faced polymer compacts were made at five different compression forces and the mechanical properties of the compacts were evaluated to give an indication of the powder's capacity to form a tablet with desirable strength under specific pressures. The results indicated that the CR grades of the polymers displayed a smaller particle size and better mechanical properties compared to the DC grade HPMC K100M polymers. The DC grades, however, had better flow properties than their CR counterparts. The results also suggested some similarities and differences between some of the polymers from the different vendors despite the similarity in substitution level, reminding the user that care and consideration should be given when substitution is required.

Morphological distribution mapping: Utilisation of modelling to integrate particle size and shape distributions

The aim of this work was to develop approaches to utilize whole particle distributions for both particle size and particle shape parameters to map the full range of particle properties in a curated dataset. It is hoped that such an approach may enable a more complete understanding of the particle landscape as a step towards improving the link between particle properties and processing behaviour. A 1-dimensional principal component analysis (PCA) approach was applied to create a 'morphological distribution landscape'. A dataset of imaged APIs, intermediates and excipients encompassing particle size, particle shape (elongation, length and width) and distribution shape was curated between 2008 and 2022. The curated dataset encompassed over 200 different materials, which included over 150 different APIs, and approximately 3500 unique samples. For the purposes of the current work, only API samples were included. The morphological landscape enables differentiation of materials of equivalent size but varying shape and vice versa. It is hoped that this type of approach can be utilised to better understand the influence of particle properties on pharmaceutical processing behaviour and thereby enable scientists to leverage historical knowledge to highlight and mitigate risks associated to materials of similar morphological nature.

Particle Property Characterization and Data Curation for Effective Powder Property Modeling in the Pharmaceutical Industry

Computational modeling, machine learning, and statistical data analysis are increasingly utilized to mitigate chemistry, manufacturing, and control failures related to particle properties in solid dosage form manufacture. Advances in particle characterization techniques and computational approaches provide unprecedented opportunities to explore relationships between particle morphology and drug product manufacturability. Achieving this, however, has numerous challenges such as producing and appropriately curating robust particle size and shape data. Addressing these challenges requires a harmonized strategy from material sampling practices, characterization technique selection, and data curation to provide data sets which are informative on material properties. Herein, common sources of error in particle characterization and data compression are reviewed, and a proposal for providing robust particle morphology (size and shape) data to support modeling efforts, approaches for data curation, and the outlook for modeling particle properties are discussed.

Characterization of the Morphological Nature of Hollow Spray Dried Dispersion Particles Using X-ray Submicron-Computed Tomography

Graphical Abstract.

Determining the Impact of Roller Compaction Processing Conditions on Granule and API Properties

The attrition of drug particles during the process of dry granulation, which may (or may not) be incorporated into granules, could be an important factor in determining the subsequent performance of that granulation, including key factors such as sticking to punches and bio-performance of the dosage form. It has previously been demonstrated that such attrition occurs in one common dry granulation process train; however, the fate of these comminuted particles in granules was not determined. An understanding of the phenomena of attrition and incorporation into granule will improve our ability to understand the performance of granulated systems, ultimately leading to an improvement in our ability to optimize and model the process. Unique feeding mechanisms, geometry, and milling systems of roller compaction equipment mean that attrition could be more or less substantial for any given equipment train. In this work, we examined attrition of API particles and their incorporation into granule in an equipment train from Gerteis, a commonly used equipment train for dry granulation. The results demonstrate that comminuted drug particles can exist free in post-milling blends of roller compaction equipment trains. This information can help better understand the performance of the granulations, and be incorporated into mechanistic models to optimize such processes.

Enhanced Understanding of Pharmaceutical Materials Through Advanced Characterisation and Analysis

The impact of pharmaceutical materials properties on drug product quality and manufacturability is well recognised by the industry. An ongoing effort across industry and academia, the Manufacturing Classification System consortium, aims to gather the existing body of knowledge in a common framework to provide guidance on selection of appropriate manufacturing technologies for a given drug and/or guide optimization of the physical properties of the drug to facilitate manufacturing requirements for a given processing route. Simultaneously, material scientists endeavour to develop characterisation methods such as size, shape, surface area, density, flow and compactibility that enable a stronger understanding of materials powder properties. These properties are routinely tested drug product development and advances in instrumentation and computing power have enabled novel characterisation methods which generate larger, more complex data sets leading to a better understanding of the materials. These methods have specific requirements in terms of data management and analysis. An appropriate data management strategy eliminates time-consuming data collation steps and enables access to data collected for multiple methods and materials simultaneously. Methods ideally suited to extract information from large, complex data sets such as multivariate projection methods allow simpler representation of the variability contained within the data and easier interpretation of the key information it contains. In this review, an overview of the current knowledge and challenges introduced by modern pharmaceutical material characterisation methods is provided. Two case studies illustrate how the incorporation of multivariate analysis into the material sciences workflow facilitates a better understanding of materials.

Multivariate analysis as a method to understand variability in a complex excipient, and its contribution to formulation performance

A key part of the Risk Assessment of excipients is to understand how raw material variability could (or does) contribute to differences in performance of the drug product. Here we demonstrate an approach which achieves the necessary understanding for a complex, functional, excipient. Multivariate analysis (MVA) of the certificates of analysis of an ethylcellulose aqueous dispersion (Surelease) formulation revealed low overall variability of the properties of the systems. Review of the scores plot to highlight batches manufactured using the same ethylcellulose raw material in the formulation, indicated that these batches tend to be more closely related than other randomly selected batches. This variability could result in potential differences in the quality of drug product lots made from these batches. Manufacture of a model drug product from Surelease batches coated using different lots of starting material revealed small differences in the release of a model drug, which could be detected by certain model dependent dissolution modeling techniques, but they were not observed when using model-independent techniques. This illustrates that the techniques are suitable for detecting and understanding excipient variability, but that, in this case, the product was still robust.

Use of similarity scoring in the development of oral solid dosage forms

In the oral solid dosage form space, material physical properties have a strong impact on the behaviour of the formulation during processing. The ability to identify materials with similar characteristics (and thus expected to exhibit similar behaviour) within the company's portfolio can help accelerate drug development by enabling early assessment and prediction of potential challenges associated with the powder properties of a new active pharmaceutical ingredient. Such developments will aid the production of robust dosage forms, in an efficient manner. Similarity scoring metrics are widely used in a number of scientific fields. This study proposes a practical implementation of this methodology within pharmaceutical development. The developed similarity metrics is based on the Mahalanobis distance. Scanning electron microscopy was used to confirm morphological similarity between the reference material and the closest matches identified by the metrics proposed. The results show that the metrics proposed are able to successfully identify material with similar physical properties.

An investigation into the impact of magnesium stearate on powder feeding during roller compaction

A systematic evaluation on the effect of magnesium stearate on the transmission of a placebo formulation from the hopper to the rolls during screw fed roller compaction has been carried out. It is demonstrated that, for a system with two 'knurled' rollers, addition of 0.5% w/w magnesium stearate can lead to a significant increase in ribbon mass throughput, with a consequential increase in roll gap, compared to an unlubricated formulation (manufactured at equivalent process conditions). However, this effect is reduced if one of the rollers is smooth. Roller compaction of a lubricated formulation using two smooth rollers was found to be ineffective due to a reduction in friction at the powder/roll interface, i.e. powder was not drawn through the rollers leading to a blockage in the feeding system. An increase in ribbon mass throughput could also be achieved if the equipment surfaces were pre-lubricated. However this increase was found to be temporary suggesting that the residual magnesium stearate layer was removed from the equipment surfaces. Powder sticking to the equipment surfaces, which is common during pharmaceutical manufacturing, was prevented if magnesium stearate was present either in the blend, or at the roll surface. It is further demonstrated that the influence of the hopper stirrer, which is primarily used to prevent bridge formation in the hopper and help draw powder more evenly into the auger chamber, can lead to further mixing of the formulation, and could therefore affect a change in the lubricity of the carefully blended input material.

Active and intelligent inhaler device development

The dry powder inhaler, which has traditionally relied on the patient's inspiratory force to deaggregate and deliver the active agent to the target region of the lung, has been a successful delivery device for the provision of locally active agents for the treatment of conditions such as asthma and chronic obstructive pulmonary disease (COPD). However, such devices can suffer from poor delivery characteristics and/or poor reproducibility. More recently, drugs for systemic delivery and more high value compounds have been put into DPI devices. Regulatory, dosing, manufacturing and economic concerns have demanded that a more efficient and reproducible performance is achieved by these devices. Recently strategies have been put in place to produce a more efficient DPI device/formulation combination. Using one novel device as an example the paper will examine which features are important in such a device and some of the strategies required to implement these features. All of these technological advances are invisible, and may be irrelevant, to the patient. However, their inability to use an inhaler device properly has significant implications for their therapy. Use of active device mechanisms, which reduce the dependence on patient inspiratory flow, and sensible industrial design, which give the patient the right clues to use, are important determinants of performance here.