Effects of wet-granulation process parameters on the dissolution and physical stability of a solid dispersion

Amorphous Solid Dispersions (ASDs): The Influence of Material Properties, Manufacturing Processes and Analytical Technologies in Drug Product Development

Poorly water-soluble drugs pose a significant challenge to developability due to poor oral absorption leading to poor bioavailability. Several approaches exist that improve the oral absorption of such compounds by enhancing the aqueous solubility and/or dissolution rate of the drug. These include chemical modifications such as salts, co-crystals or prodrugs and physical modifications such as complexation, nanocrystals or conversion to amorphous form. Among these formulation strategies, the conversion to amorphous form has been successfully deployed across the pharmaceutical industry, accounting for approximately 30% of the marketed products that require solubility enhancement and making it the most frequently used technology from 2000 to 2020. This article discusses the underlying scientific theory and influence of the active compound, the material properties and manufacturing processes on the selection and design of amorphous solid dispersion (ASD) products as marketed products. Recent advances in the analytical tools to characterize ASDs stability and ability to be processed into suitable, patient-centric dosage forms are also described. The unmet need and regulatory path for the development of novel ASD polymers is finally discussed, including a description of the experimental data that can be used to establish if a new polymer offers sufficient differentiation from the established polymers to warrant advancement.

Enteric complex layer-coated controlled release of capsaicin from phytosterol/γ-cyclodextrin microparticles via guest exchange reaction with taurocholic acid

Phytosterol (PSE)/γ-cyclodextrin (γ-CD) microparticles have a capsule-like structure, wherein the hydrophobic PSE core is surrounded by outer layers of the hydrophilic PSE/γ-CD inclusion complex crystal. The microparticles could mask the undesirable taste of capsaicin (CAP) by encapsulation of CAP into the microparticles. In the present study, the dissolution of CAP from PSE/γ-CD microparticles into artificial intestinal fluids was examined using the paddle method. The dissolution of CAP from the microparticles was suppressed at pH 1.2 and 5.0. On the other hand, the dissolution was significantly enhanced in fasted and fed state simulated intestinal fluid (FaSSIF and FeSSIF) . Taurocholate (TCA), contained in these artificial fluids, induced rapid dissolution of CAP from microparticles. The mechanism of CAP dissolution from the microparticles in the presence of TCA was investigated using in situ¹H NMR spectroscopy. During the incubation of the mixed suspension of the microparticles and TCA, γ-CD peaks started to appear, and the TCA peak showed a gradual upfield shift. Quantitative analysis of NMR results showed that the TCA/γ-CD inclusion complex could form during incubation, according to the dissolution of γ-CD from the microparticles via the guest exchange reaction of PSE by TCA. The collapse of the PSE/γ-CD inclusion complex crystal at the outer shell of microparticles could trigger the release of CAP into the intestinal fluid. Thus, PSE/γ-CD microparticles can be used as an enteric controlled-release system that releases encapsulated drugs not via the conventional pH changes but via guest exchange reaction with TCA.

Injection-Molded Coamorphous Tablets: Analysis of Intermolecular Interaction and Crystallization Propensity

The processing steps involved in converting from a powder to a tablet entail numerous operations in a which the coamorphous system is recrystallized and dissociated easily. This research focused on (i) a single-step preparation of a coamorphous tablet during injection molding (IM) from the bulk powder, and (ii) a mechanistic characterization of the coamorphous formulation. We selected several organic acids [citric acid, succinic acid, tartaric acid, and malic acid] in an effort to compound with basic loratadine (a poorly water-soluble drug). Loratadine-acids coamorphous tablets were produced via an IM process, and the dissolution was more enhanced than in the pure loratadine amorphous. The interaction was analyzed by FT-IR and terahertz spectroscopies. Each tablet was stored at 40 °C/75%RH, and then XRD patterns were acquired at the desired timepoints. In summary, loratadine exhibited ionic interaction with each acid, and the physical stability of the coamorphous tablet was in proportion to the loratadine-acids interaction strength. Terahertz spectra detected the molecular mobility, which plays an important role in the crystallization propensity of a coamorphous system. This understanding offers a framework for robust coamorphous tablet formulation using the IM methodology.

A Semi-Mechanistic Prediction of Residence Time Metrics in Twin Screw Granulation

This work is concerned with the semi-mechanistic prediction of residence time metrics using historical data from mono-component twin screw wet granulation processes. From the data, several key parameters such as powder throughput rate, shafts rotation speed, liquid binder feed ratio, number of kneading elements in the shafts and the stagger angle between the kneading elements were identified and physical factors were developed to translate those varying parameters into expressions affecting the key intermediate phenomena in the equipment, holdup, flow and mixing. The developed relations were then tested across datasets to evaluate the performance of the model, applying a k-fold optimization technique. The semi-mechanistic predictions were evaluated both qualitatively through the main effects plots and quantitatively through the parity plots and correlations between the tuning constants across datasets. The root mean square error (RMSE) was used as a metric to compare the degree of goodness of fit for different datasets using the developed semi-mechanistic relations. In summary this paper presents a new approach at estimating both the residence time metrics in twin screw wet granulation, mean residence time (MRT) and variance through semi-mechanistic relations, the validity of which have been tested for different datasets.

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.