Application of X-ray microtomography for the characterisation of hollow polymer-stabilised spray dried amorphous dispersion particles

Recent Advances in Amorphous Solid Dispersions: Preformulation, Formulation Strategies, Technological Advancements and Characterization

Amorphous solid dispersions (ASDs) are among the most popular and widely studied solubility enhancement techniques. Since their inception in the early 1960s, the formulation development of ASDs has undergone tremendous progress. For instance, the method of preparing ASDs evolved from solvent-based approaches to solvent-free methods such as hot melt extrusion and Kinetisol^®. The formulation approaches have advanced from employing a single polymeric carrier to multiple carriers with plasticizers to improve the stability and performance of ASDs. Major excipient manufacturers recognized the potential of ASDs and began introducing specialty excipients ideal for formulating ASDs. In addition to traditional techniques such as differential scanning calorimeter (DSC) and X-ray crystallography, recent innovations such as nano-tomography, transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray microscopy support a better understanding of the microstructure of ASDs. The purpose of this review is to highlight the recent advancements in the field of ASDs with respect to formulation approaches, methods of preparation, and advanced characterization techniques.

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

Graphical Abstract.

Microstructure, Quality, and Release Performance Characterization of long-Acting Polymer Implant Formulations with X-Ray Microscopy and Quantitative AI Analytics

Long-acting implants are typically formulated using carrier(s) with specific physical and chemical properties, along with the active pharmaceutical ingredient (API), to achieve the desired daily exposure for the target duration of action. In characterizing such formulations, real-time in-vitro and in-vivo experiments that are typically used to characterize implants are lengthy, costly, and labor intensive as these implants are designed to be long acting. A novel characterization technique, combining high resolution three-dimensional X-Ray microscopy imaging, image-based quantification, and transport simulation, has been employed to provide a mechanistic understanding of formulation and process impact on the microstructures and performance of a polymer-based implant. Artificial intelligence-based image segmentation and image data analytics were used to convert morphological features visualized at high resolution into numerical microstructure models. These digital models were then used to calculate key physical parameters governing drug transport in a polymer matrix, including API uniformity, API domain size, and permeability. This powerful new tool has the potential to advance the mechanistic understanding of the interplay between drug-microstructure and performance and accelerate the therapeutic development long-acting implants.

Combining Co-Amorphous-Based Spray Drying with Inert Carriers to Achieve Improved Bioavailability and Excellent Downstream Manufacturability

It is crucial to improve poorly water-soluble orally administered drugs through both preclinical and therapeutic drug discovery. A co-amorphous formulation consisting of two low molecular weight (MW) molecules offers a solubility/dissolubility advantage over its crystalline form by maintaining their amorphous status. Here, we report on a co-amorphous solid dispersion (SD) system that includes inert carriers (lactose monohydrate or microcrystalline cellulose) and co-amorphous sacubitril (SAC)-valsartan (VAL) using the spray drying process. The strong molecular interactions between drugs were the driving force for forming robust co-amorphous SDs. Our system provided the highest solubility with more than ~11.5- and 3.12-times solubility increases when compared with the physical mixtures. Co-amorphous lactose monohydrate (LM) SDs showed better bioavailability of APIs (~356.27.8% and 154.01% for the relative bioavailability of LBQ 657 and valsartan, respectively). Co-amorphous inert carrier SDs possessed an excellent compressibility for the production of a direct compression pharmaceutical product. In conclusion, these brand-new co-amorphous SDs could reduce the number of unit processes to produce a final pharmaceutical product for downstream manufacturability.

Characterization of Controlled Release Microspheres Using FIB-SEM and Image-Based Release Prediction

For polymer-based controlled release drug products (e.g. microspheres and implants), active pharmaceutical ingredient distribution and microporosity inside the polymer matrix are critical for product performance, particularly drug release kinetics. Due to the decreasing domain size and increasing complexity of such products, conventional characterization and release test techniques are limited by their resolution and speed. In this study, samples of controlled release poly(lactic-co-glycolic acid) microspheres in the diameter range of 30-80 μm are investigated with focused ion beam scanning electron microscope imaging at 20 nm or higher resolution. Image data is quantified with artificial intelligence-based image analytics to provide size distributions of drug particles and pores within the microsphere sample. With an innovative image-based numerical simulation method, release profiles are predicted in a matter of days regardless of the designed release time. A mechanistic understanding on the impact of porosity to the interplays of drug, formulation, process, and dissolution was gained.

Effect of Spray-Dried Particle Morphology on Mechanical and Flow Properties of Felodipine in PVP VA Amorphous Solid Dispersions

Amorphous solid dispersions (ASDs) are commonly used to enhance the oral absorption of drugs with solubility or dissolution rate limitations. Although the ASD formulation is typically constrained by physical stability and in vivo performance considerations, ASD particles can be engineered using the spray-drying process to influence mechanical and flow properties critical to tableting. Using the ASD formulation of 20% w/w felodipine dispersed in polyvinyl pyrrolidone vinyl acetate, spray-drying atomization and drying conditions were tuned to achieve 4 different powders with varying particle properties. The resulting particles ranged in volume moment mean diameter from 4 to 115 μm, bulk density from 0.05 to 0.38 g cm^-3, and morphologies of intact, collapsed, and fractured hollow spheres. Powder flowability by shear cell ranged from poor to easy flowing, whereas mechanical property tests suggested all samples will produce strong tablets at reasonable solid fractions and compression pressures. In addition, Hiestand dynamic tableting indices showed excellent dynamic bonding for 3 powders, and low viscoelasticity with high brittleness for all powders. This work demonstrates the extent spray-dried ASD particle morphologies can be engineered to achieve desired powder flow and mechanical properties to mitigate downstream processing risks and increase process throughput.

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.

Recent strategies in spray drying for the enhanced bioavailability of poorly water-soluble drugs

Poorly water-soluble drugs are a significant and ongoing issue for the pharmaceutical industry. An overview of recent developments for the preparation of spray-dried delivery systems is presented. Examples include amorphous solid dispersions, spray dried dispersions, microparticles, nanoparticles, surfactant systems and self-emulsifying drug delivery systems. Several aspects of formulation are considered, such as pre-screening, choosing excipient(s), the effect of polymer structure on performance, formulation optimisation, ternary dispersions, fixed-dose combinations, solvent selection and component miscibility. Process optimisation techniques including nozzle selection are discussed. Comparisons are drawn with other preparation techniques such as hot melt extrusion, freeze drying, milling, electro spinning and film casting. Novel analytical and dissolution techniques for the characterization of amorphous solid dispersions are included. Progress in understanding of amorphous supersaturation or recrystallisation from solution gathered from mechanistic studies is discussed. Aspects of powder flow and compression are considered in a section on downstream processing. Overall, spray drying has a bright future due to its versatility, efficiency and the driving force of poorly soluble drugs.

Moisture-Induced Amorphous Phase Separation of Amorphous Solid Dispersions: Molecular Mechanism, Microstructure, and Its Impact on Dissolution Performance

Amorphous phase separation (APS) is commonly observed in amorphous solid dispersions (ASD) when exposed to moisture. The objective of this study was to investigate: (1) the phase behavior of amorphous solid dispersions composed of a poorly water-soluble drug with extremely low crystallization propensity, BMS-817399, and PVP, following exposure to different relative humidity (RH), and (2) the impact of phase separation on the intrinsic dissolution rate of amorphous solid dispersion. Drug-polymer interaction was confirmed in ASDs at different drug loading using infrared (IR) spectroscopy and water vapor sorption analysis. It was found that the drug-polymer interaction could persist at low RH (≤75% RH) but was disrupted after exposure to high RH, with the advent of phase separation. Surface morphology and composition of 40/60 ASD at micro-/nano-scale before and after exposure to 95% RH were also compared. It was found that hydrophobic drug enriched on the surface of ASD after APS. However, for the 40/60 ASD system, the intrinsic dissolution rate of amorphous drug was hardly affected by the phase behavior of ASD, which may be partially attributed to the low crystallization tendency of amorphous BMS-817399 and enriched drug amount on the surface of ASD. Intrinsic dissolution rate of PVP decreased resulting from APS, leading to a lower concentration in the dissolution medium, but supersaturation maintenance was not anticipated to be altered after phase separation due to the limited ability of PVP to inhibit drug precipitation and prolong the supersaturation of drug in solution. This study indicated that for compounds with low crystallization propensity and high hydrophobicity, the risk of moisture-induced APS is high but such phase separation may not have profound impact on the drug dissolution performance of ASDs. Therefore, application of ASD technology on slow crystallizers could incur low risks not only in physical stability but also in dissolution performance.