Glass-forming ability of compounds in marketed amorphous drug products

Different or the same? exploring the physicochemical properties and molecular mobility of celecoxib amorphous forms

The influence of different preparation methods on the physicochemical properties of amorphous solid forms have gained considerable attention, especially with recent publications on pharmaceutical polyamorphism. In the present study, we have investigated the possible occurrence of polyamorphism in the drug celecoxib (CEL) by investigating the thermal behavior, morphology, structure, molecular mobility and physical stability of amorphous CEL obtained by quench-cooling (QC), ball milling (BM) and spray drying (SD). Similar glass transition temperatures but different recrystallization behaviors were observed for CEL-QC, CEL-BM and CEL-SD using modulated differential scanning calorimetry analysis. A correlation between the different recrystallization behaviors of the three CEL amorphous forms and the respective distinct powder morphologies, was also found. Molecular dynamics simulations however, reveal that CEL presents similar molecular conformational distributions when subjected to QC and SD. Moreover, the obtained molecular conformational distributions of CEL are different from the ones found in its crystal structure and also from the ones found in the lowest-energy structure obtained by quantum mechanical calculations. The type and strength of CEL hydrogen bond interactions found in CEL-QC and CEL-SD systems are almost identical, though different from the ones presented in the crystal structure. Pair distribution function analyses and isothermal microcalorimetry show similar local structures and structural relaxation times, respectively, for CEL-QC, CEL-BM and CEL-SD. The present work shows that not only similar physicochemical properties (glass transition temperature, and structural relaxation time), but also similar molecular conformational distributions were observed for all prepared CEL amorphous systems. Hence, despite their different recrystallization behaviors, the three amorphous forms of CEL did not show any signs of polyamorphism.

Surface Enrichment and Depletion of Components in a Ternary Drug-Surfactant-Polymer Amorphous Solid Dispersion

Amorphous solid dispersions (ASDs) can be used to enhance the solubility and bioavailability of poorly soluble drugs. An ASD is often a ternary system containing a drug, a surfactant, and a polymer. Recent work on binary ASDs has observed significant differences between surface and bulk compositions, with impacts on wettability and stability. Here we investigate a ternary ASD composed of the antifungal posaconazole, the surfactant Span 80, and a dispersion polymer (PVP or PVP/VA). The surfactant loading was fixed at the typical level of 5 wt %, and the drug/polymer ratio was varied. We observed strong surface enrichment of the surfactant and simultaneous depletion of the drug. This effect is already pronounced in the binary drug-surfactant system and is enhanced by the addition of the polymers. Between the two polymers, the more hydrophilic PVP causes a stronger enhancement of the surface enrichment effect. These results demonstrate the impact of component interactions on the surface composition of ASDs and the performance.

Long-Term Physical Stability of Amorphous Solid Dispersions: Comparison of Detection Powers of Common Evaluation Methods for Spray-Dried and Hot-Melt Extruded Formulations

Although physical stability can be a critical issue during the development of amorphous solid dispersions (ASDs), there are no established protocols to predict/detect their physical stability. In this study, we have prepared fenofibrate ASDs using two representative manufacturing methods, hot-melt extrusion and spray-drying, to investigate their physical stability for one year. Intentionally unstable ASDs were designed to compare the detection power of each evaluation method, including X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and dissolution study. Each method did not provide the same judgment results on physical stability in some cases because of their different evaluation principles and sensitivity, which has been well-comprehended only for one-component glass. This study revealed that the detection powers of each evaluation method significantly depended on the manufacturing methods. DSC was an effective method to detect a small amount of crystals for both types of ASDs in a quantitative manner. Although the sensitivity of XRPD was always lower compared to that of DSC, interpretation of the data was the easiest. SEM was very effective for observing the crystallization of the small amount of drug for hot-melt extruded products, as the drug crystal vividly appeared on the large grains. The dissolution performance of spray-dried products could change even without any indication of physical change including crystallization. The advantage/disadvantage and complemental roles of each evaluation method are discussed for deeper understanding on the physical stability data of ASDs.

Drug-Polymer Nanodroplet Formation and Morphology Drive Solubility Enhancement of GDC-0810

Nanodroplet formation is important to achieve supersaturation of active pharmaceutical ingredients (APIs) in an amorphous solid dispersion. The aim of the current study was to explore how polymer composition, architecture, molar mass, and surfactant concentration affect polymer-drug nanodroplet morphology with the breast cancer API, GDC-0810. The impact of nanodroplet size and morphology on dissolution efficacy and drug loading capacity was explored using polarized light microscopy, dynamic light scattering, and cryogenic transmission electron microscopy. Poly(N-isopropylacrylamide-stat-N,N-dimethylacrylamide) (PND) was synthesized as two linear derivatives and two bottlebrush derivatives with carboxylated or PEGylated end-groups. Hydroxypropyl methylcellulose acetate succinate grade MF (HPMCAS-MF) and poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA) were included as commercial polymer controls. We report the first copolymerization synthesis of a PVPVA bottlebrush copolymer, which was the highest performing excipient in this study, maintaining 688 μg/mL GDC-0810 concentration at 60 wt % drug loading. This is likely due to strong polymer-drug noncovalent interactions and the compaction of GDC-0810 along the PVPVA bottlebrush backbone. Overall, it was observed that the most effective formulations had a hydrodynamic radius less than 25 nm with tightly compacted nanodroplet morphologies.

Design Principles for Balancing Lipophilicity and Permeability in beyond Rule of 5 Space

An ab initio conformational analysis of oral beyond Rule of 5 (bRo5) drugs was complemented with measured permeability and logP(octanol) to derive design principles conferring oral bioavailability. 3D polar surface area (PSA) thresholds for oral bRo5 drugs coincided with those reported for Ro5 space. The majority of oral bRo5 drugs exceeded the Ro5 logP threshold of 5, reflecting a bias for permeability. Above 500 Da molecular weight (MW), oral drugs and highly permeable Novartis compounds occupy a narrow polarity range (topological or TPSA/MW) of 0.1-0.3 Å2 /Da, whose upper half coincides with the lower 90 percentiles of the Novartis logP set. This TPSA/MW range and 3D PSA below 100 Å2 define the "Rule of ~1 /₅" for balancing lipophilicity and permeability. Neutral TPSA, defined as TPSA minus 3D PSA occurs independent of conformation, intramolecular hydrogen bonds (IMHB) and MW, suggesting it is an intrinsic molecular property. Neutral TPSA increased in the lead optimization (LO) campaigns of three first in class de novo designed bRo5 drugs and may be a useful design parameter in bRo5 space.

Formulation strategies for the development of high drug-loaded amorphous solid dispersions

Amorphous solid dispersions (ASD) have gained tremendous attention over the past two decades as one of the most promising techniques for enhancing the solubility of poorly water-soluble drugs. However, low drug loading is one of the major challenges of ASD technology that limits its commercialization to only a few drug candidates. Increasing the drug loading increases the risk of recrystallization during storage (solid state) and/or during dissolution (solution state). Various formulation and process-related strategies have been explored that open the possibility of formulating high drug-loaded ASDs without the risk of recrystallization. Here, we review various formulation approaches, such as the use of surfactants, mesoporous silicas, polymer combinations, in situ thermal crosslinking, structural modification of polymeric carriers, and surface nanocoating using minerals. We also discuss the mechanisms by which these approaches inhibit solid state and/or solution state recrystallization.

Tailored ASD destabilization - Balancing shelf life stability and dissolution performance with hydroxypropyl cellulose

Amorphous solid dispersion (ASD) formulations are preferred enabling formulations for poorly water soluble active pharmaceutical ingredients (API) as they reliably enhance the dissolution behavior and solubility. Balancing a high stability against unwanted transformations such as crystallization and amorphous phase separation during storage on the one hand and optimizing the dissolution behavior of the formulation (high supersaturation and maintenance for long time) on the other hand are essential during formulation development. This study assessed the potential of ternary ASDs (one API and two polymers) containing the polymers hydroxypropyl cellulose together with poly(vinylpyrrolidone-co-vinyl acetate) (PVP VA64) or hydroxypropyl cellulose acetate succinate to stabilize the amorphously embedded APIs fenofibrate and simvastatin during storage and to enhance the dissolution performance. Thermodynamic predictions using the PC-SAFT model revealed for each combination of polymers the optimal polymer ratio, maximum API load that is thermodynamically stable as well as miscibility of the two polymers. The stability predictions were validated by three months enduring stability tests, followed by a characterization of the dissolution behavior. The thermodynamically most stable ASDs were found to be the ASDs with deteriorated dissolution performance. Within the investigated polymer combinations, physical stability and dissolution performance opposed each other.

Strategies to improve the stability of amorphous solid dispersions in view of the hot melt extrusion (HME) method

Oral administration of drugs is preferred over other routes for several reasons: it is non-invasive, easy to administer, and easy to store. However, drug formulation for oral administration is often hindered by the drug's poor solubility, which limits its bioavailability and reduces its commercial value. As a solution, amorphous solid dispersion (ASD) was introduced as a drug formulation method that improves drug solubility by changing the molecular structure of the drugs from crystalline to amorphous. The hot melt extrusion (HME) method is emerging in the pharmaceutical industry as an alternative to manufacture ASD. However, despite solving solubility issues, ASD also exposes the drug to a high risk of crystallisation, either during processing or storage. Formulating a successful oral administration drug using ASD requires optimisation of the formulation, polymers, and HME manufacturing processes applied. This review presents some important considerations in ASD formulation, including strategies to improve the stability of the final product using HME to allow more new drugs to be formulated using this method.

Crystallization of Amorphous Nifedipine Under Isothermal Conditions: Inter-laboratory Reproducibility and Investigation of the Factors Affecting Reproducibility

High inter-laboratory reproducibility is required for conducting collaborative experiments among several laboratories. The primary aim of our evaluation of the physical stability of amorphous drugs, conducted in co-operation with eight laboratories, was to establish a protocol for isothermal storage tests to obtain data of the same quality from all the participating laboratories. Sharing a protocol that contained the same level of detail as the experimental section of general papers was insufficient for high inter-laboratory reproducibility. We investigated the causes of variations in the data from the various laboratories and restricted the protocol step-by-step to achieve high inter-laboratory reproducibility. The various experimentalists had very different levels of awareness regarding how to control the temperature of a sample as the samples were transferred into and out of thermostatic chambers. Specific instructions on how to conduct this operation, such as regarding the time required for the transfer and thermal protection of the container during the transfer, helped to reduce variation. Improved inter-laboratory reproducibility revealed that the physical stabilities of amorphous drugs differed when samples were prepared in differently shaped aluminum pans designed for various differential scanning calorimeters.

Review of industrially recognized polymers and manufacturing processes for amorphous solid dispersion based formulations

Evolving therapeutic landscape through combinatorial chemistry and high throughput screening have resulted in an increased number of poorly soluble drugs. Drug delivery strategies quickly adapted to convert these drugs into successful therapies. Amorphous solid dispersion (ASD) technology is widely employed as a drug delivery strategy by pharmaceutical industries to overcome the challenges associated with these poorly soluble drugs. The development of ASD formulation requires an understanding of polymers and manufacturing techniques. A review of US FDA-approved ASD-based products revealed that only a limited number of polymers and manufacturing technologies are employed by pharmaceutical industries. This review provides a comprehensive guide for the selection and overview of polymers and manufacturing technologies adopted by pharmaceutical industries for ASD formulation. The various employed polymers with their underlying mechanisms for solution-state and solid-state stability are discussed. ASD manufacturing techniques, primarily implemented by pharmaceutical industries for commercialization, are presented in Quality by Design (QbD) format. An overview of novel excipients and progress in manufacturing technologies are also discussed. This review provides insights to the researchers on the industrially accepted polymers and manufacturing technology for ASD formulation that has translated these challenging drugs into successful therapies.

Nucleation During Storage Impeded Supersaturation in the Dissolution Process of Amorphous Celecoxib

The aqueous solubility of active pharmaceutical ingredients (APIs) is one of the most critical factors in determining the absorption of orally administered drugs. Amorphization of API may offer better drug absorption than the crystalline state owing to enhanced solubility. However, if crystal nuclei are formed during storage, they may develop into crystals upon contact with water, thus limiting the dissolution advantage. In an earlier study, we found that the nuclei of amorphous celecoxib (CEL) could be formed at freezing temperatures (FT) without further crystal growth. Following this finding, we compared the dissolution performances of amorphous CEL annealed at room temperature (RT, 25 °C) or FT (-20 °C). We found that only the RT-annealed CEL could achieve a supersaturated state effectively during the dissolution process, which could be explained by the fast conversion of the FT-annealed amorphous CEL to a crystalline state owing to the presence of nuclei. Investigation of the residual solids revealed that supersaturation could be maintained for a while after the appearance of the crystals, which could be explained by heterogeneous nucleation and competition between the dissolution of amorphous parts and crystallization. In addition, a new crystalline form of CEL was observed during dissolution.

Physiological Buffer Effects in Drug Supersaturation - A Mechanistic Study of Hydroxypropyl Cellulose as Precipitation Inhibitor

Phosphate buffer is predominantly used instead of the more physiological bicarbonate buffer, as the latter requires a technical solution of adequate gas mixing. Recent pioneering work on how bicarbonate buffer affected drug supersaturation revealed interesting effects that call for more mechanistic understanding. Therefore, this study used hydroxypropyl cellulose as a model precipitation inhibitor and real-time desupersaturation testing was conducted with the drugs bifonazole, ezetimibe, tolfenamic acid and triclabendazole. Specific buffer effects for the different compounds were noted and overall, statistical significance was found for the precipitation induction time (p = 0.0088). Interestingly, molecular dynamics simulation revealed a conformational effect of the polymer in the presence of the different buffer types. Subsequent molecular docking trials suggested a stronger interaction energy of drug and polymer in the presence of phosphate compared to bicarbonate buffer (p =0.0010). In conclusion, a better mechanistic understanding of how different buffers affect drug-polymer interactions regarding drug supersaturation was achieved. Further mechanisms may account for the overall buffer effects and additional research on drug supersaturation is certainly needed, but it can already be concluded that bicarbonate buffering should be used more often for in vitro testing in drug development.

Predicting Glass-Forming Ability of Pharmaceutical Compounds by Using Machine Learning Technologies

Low aqueous solubility is a common and serious challenge for most drug substances not only in development but also in the market, and it may cause low absorption and bioavailability as a result. Amorphization is an intermolecular modification strategy to address the issue by breaking the crystal lattice and enhancing the energy state. However, due to the physicochemical properties of the amorphous state, drugs are thermodynamically unstable and tend to recrystallize over time. Glass-forming ability (GFA) is an experimental method to evaluate the forming and stability of glass formed by crystallization tendency. Machine learning (ML) is an emerging technique widely applied in pharmaceutical sciences. In this study, we successfully developed multiple ML models (i.e., random forest (RF), XGBoost, and support vector machine (SVM)) to predict GFA from 171 drug molecules. Two different molecular representation methods (i.e., 2D descriptor and Extended-connectivity fingerprints (ECFP)) were implemented to process the drug molecules. Among all ML algorithms, 2D-RF performed best with the highest accuracy, AUC, and F1 of 0.857, 0.850, and 0.828, respectively, in the testing set. In addition, we conducted a feature importance analysis, and the results mostly agreed with the literature, which demonstrated the interpretability of the model. Most importantly, our study showed great potential for developing amorphous drugs by in silico screening of stable glass formers.

Combining drug salt formation with amorphous solid dispersions - a double edged sword

Glass transition temperature (T_g) is important for amorphous compounds because it can have implications on their physical and chemical stability. With drugs that possess ionizable acidic or basic groups, salt formation is a potential strategy to reduce re-crystallization tendency through T_g elevation. While salt formation has been reported to impact re-crystallization tendency, it is not known if this holds true for all drugs and if it is useful in the context of amorphous solid dispersion (ASD) formulations. In addition, little information on the impact of salt formation on drug release performance of ASD is available. Herein, the influence of salt formation and T_g elevation on the release performance of lumefantrine (T_g = 19.7 °C) when formulated as an ASD with copovidone (PVPVA) was examined. Lumefantrine salts and lumefantrine salt-PVPVA ASDs with drug loadings (DLs) ranging from 5 to 30% were prepared. The acids used for salt formation were benzoic acid, benzenesulfonic acid, camphorsulfonic acid, hydrochloric acid, p-toluenesulfonic acid, poly(ethylene) glycol 250 diacid (PEG 250 diacid), and sulfuric acid. Salt formation resulted in an elevation of T_g compared to lumefantrine free base, with the largest increase in T_g observed with lumefantrine sulfate. With a lower T_g salt, ASDs could be formulated at higher DLs while ensuring drug release. In contrast, drug release ceased at a DL as low as 5% when T_g of the salt was high. However, ASDs with lower T_gs such as the benzoate and PEG 250 diacid salts showed poor stability against re-crystallization when stored under stress storage conditions. When using a salt in an ASD formulation, attention should be paid to the T_g of the salt, since it may show opposing effects on physical stability and drug release, at least for PVPVA-based ASDs.

Bioavailability Enhancement Techniques for Poorly Aqueous Soluble Drugs and Therapeutics

The low water solubility of pharmacoactive molecules limits their pharmacological potential, but the solubility parameter cannot compromise, and so different approaches are employed to enhance their bioavailability. Pharmaceutically active molecules with low solubility convey a higher risk of failure for drug innovation and development. Pharmacokinetics, pharmacodynamics, and several other parameters, such as drug distribution, protein binding and absorption, are majorly affected by their solubility. Among all pharmaceutical dosage forms, oral dosage forms cover more than 50%, and the drug molecule should be water-soluble. For good therapeutic activity by the drug molecule on the target site, solubility and bioavailability are crucial factors. The pharmaceutical industry’s screening programs identified that around 40% of new chemical entities (NCEs) face various difficulties at the formulation and development stages. These pharmaceuticals demonstrate less solubility and bioavailability. Enhancement of the bioavailability and solubility of drugs is a significant challenge in the area of pharmaceutical formulations. According to the Classification of Biopharmaceutics, Class II and IV drugs (APIs) exhibit poor solubility, lower bioavailability, and less dissolution. Various technologies are discussed in this article to improve the solubility of poorly water-soluble drugs, for example, the complexation of active molecules, the utilization of emulsion formation, micelles, microemulsions, cosolvents, polymeric micelle preparation, particle size reduction technologies, pharmaceutical salts, prodrugs, the solid-state alternation technique, soft gel technology, drug nanocrystals, solid dispersion methods, crystal engineering techniques and nanomorph technology. This review mainly describes several other advanced methodologies for solubility and bioavailability enhancement, such as crystal engineering, micronization, solid dispersions, nano sizing, the use of cyclodextrins, solid lipid nanoparticles, colloidal drug delivery systems and drug conjugates, referring to a number of appropriate research reports.

Kinetics of Surface Enrichment of a Polymer in a Glass-Forming Molecular Liquid

X-ray photoelectron spectroscopy has been used to measure the surface concentration and the surface enrichment kinetics of a polymer in a glass-forming molecular liquid. As a model, the bulk-miscible system of maltitol-polyvinylpyrrolidone (PVP) was studied. The PVP concentration is significantly higher at the liquid/vapor interface than in the bulk by up to a factor of 170, and the effect increases with its molecular weight. At a freshly created liquid/vapor interface, the concentration of PVP gradually increases from the bulk value at a rate controlled by bulk diffusion. The polymer diffusion coefficient obtained from the kinetics of surface enrichment agrees with that calculated from viscosity and the Stokes-Einstein equation. Our finding allows prediction of the rate at which the surface composition equilibrates in an amorphous material after milling, fracture, and a change in ambient temperature.

Physical stability and dissolution behaviors of amorphous pharmaceutical solids: Role of surface and interface effects

Amorphous pharmaceutical solids (APS) are single- or multi-component systems in which drugs exist in high-energy states with long-range disordered molecular packing. APSs have become one of the most effective and widely used pharmaceutical delivery approaches for poorly water-soluble drugs in the last several decades. Considerable efforts have been made to investigate the physical stability and dissolution behaviors of APSs, however, the underlying mechanisms remain imperfectly understood. Recent studies reveal that surface and interface properties of APSs could strongly affect the physical stability and dissolution behaviors. This paper provides a comprehensive overview of recent studies focusing on the physical stability and dissolution behaviors of APSs from both surface and interface perspectives. We highlight the role of surface or interface properties in nucleation, crystal growth, phase separation, dissolution, and supersaturation. Meanwhile, the challenges and scope of research on surface and interface properties in the future are also briefly discussed. This review contributes to a better understanding of the surface- and interface-facilitated processes, which will provide more efficient and rational guidance for the design of APSs.

Hydroxypropyl Cellulose for Drug Precipitation Inhibition: From the Potential of Molecular Interactions to Performance Considering Microrheology

There has been recent interest in using hydroxypropyl cellulose (HPC) for supersaturating drug formulations. This study investigated the potential for molecular HPC interactions with the model drug celecoxib by integrating novel approaches in the field of drug supersaturation analysis. Following an initial polymer characterization study, quantum-chemical calculations and molecular dynamics simulations were complemented with results of inverse gas chromatography and broadband diffusing wave spectroscopy. HPC performance was studied regarding drug solubilization and kinetics of desupersaturation using different grades (i.e., HPC-UL, SSL, SL, and L). The results suggested that the potential contribution of dispersive interactions and hydrogen bonding depended strongly on the absence or presence of the aqueous phase. It was proposed that aggregation of HPC polymer chains provided a complex heterogeneity of molecular environments with more or less excluded water for drug interaction. In precipitation experiments at a low aqueous polymer concentration (i.e., 0.01%, w/w), grades L and SL appeared to sustain drug supersaturation better than SSL and UL. However, UL was particularly effective in drug solubilization at pH 6.8. Thus, a better understanding of drug-polymer interactions is important for formulation development, and polymer blends may be used to harness the combined advantages of individual polymer grades.

Recent Advances in Enhancement of Dissolution and Supersaturation of Poorly Water-Soluble Drug in Amorphous Pharmaceutical Solids: A Review

Amorphization is one of the most effective pharmaceutical approaches to enhance the dissolution and oral bioavailability of poorly water-soluble drugs. In recent years, amorphous formulations have been experiencing rapid development both in theoretical and practical application. Based on using different types of stabilizing agents, amorphous formulations can be mainly classified as polymer-based amorphous solid dispersion, coamorphous formulation, mesoporous silica-based amorphous formulation, etc. This paper summarizes recent advances in the dissolution and supersaturation of these amorphous formulations. Moreover, we also highlight the roles of stabilizing agents such as polymers, low molecular weight co-formers, and mesoporous silica. Maintaining supersaturation in solution is a key factor for the enhancement of dissolution profile and oral bioavailability, and thus, the strategies and challenges for maintaining supersaturation are also discussed. With an in-depth understanding of the inherent mechanisms of dissolution behaviors, the design of amorphous pharmaceutical formulations will become more scientific and reasonable, leading to vigorous development of commercial amorphous drug products.

Pharmaceutical profiling and molecular dynamics simulations reveal crystallization effects in amorphous formulations

Robust and reliable in vivo performance of medicines based on amorphous solid dispersions (ASDs) depend on maintenance of physical stability and efficient supersaturation. However, molecular drivers of these two kinetic processes are poorly understood. Here we used molecular dynamics (MD) simulations coupled with experimental assessments to explore supersaturation, nucleation, and crystal growth. The effect of drug loading on physical stability and supersaturation potential was highly drug specific. Storage under humid conditions influenced crystallization, but also resulted in morphological changes and particle fusion. This led to increased particle size, which significantly reduced dissolution rate. MD simulations identified the importance of nano-compartmentalization in the crystallization rate of the ASDs. Nucleation during storage did not inherently compromise the ASD. Rather, the poorer performance resulted from a combination of properties of the compound, nanostructures formed in the formulation, and crystallization.

Polyelectrolyte Matrices in the Modulation of Intermolecular Electrostatic Interactions for Amorphous Solid Dispersions: A Comprehensive Review

Polyelectrolyte polymers have been widely used in the pharmaceutical field as excipients to facilitate various drug delivery systems. Polyelectrolytes have been used to modulate the electrostatic environment and enhance favorable interactions between the drug and the polymer in amorphous solid dispersions (ASDs) prepared mainly by hot-melt extrusion. Polyelectrolytes have been used alone, or in combination with nonionic polymers as interpolyelectrolyte complexes, or after the addition of small molecular additives. They were found to enhance physical stability by favoring stabilizing intermolecular interactions, as well as to exert an antiplasticizing effect. Moreover, they not only enhance drug dissolution, but they have also been used for maintaining supersaturation, especially in the case of weakly basic drugs that tend to precipitate in the intestine. Additional uses include controlled and/or targeted drug release with enhanced physical stability and ease of preparation via novel continuous processes. Polyelectrolyte matrices, used along with scalable manufacturing methods in accordance with green chemistry principles, emerge as an attractive viable alternative for the preparation of ASDs with improved physical stability and biopharmaceutic performance.

Impact of Laser Speed and Drug Particle Size on Selective Laser Sintering 3D Printing of Amorphous Solid Dispersions

This research demonstrates the influence of laser speed and the drug particle size on the manufacturing of amorphous solid dispersions (ASD) and dosage forms thereof using selective laser sintering 3-dimensional (3D) printing. One-step manufacturing of ASD is possible using selective laser sintering 3D printing processes, however, the mechanism of ASD formation by this process is not completely understood and it requires further investigation. We hypothesize that the mechanism of ASD formation is the diffusion and dissolution of the drug in the polymeric carrier during the selective laser sintering (SLS) process and the drug particle size plays a critical role in the formation of said ASDs as there is no mixing involved in the sintering process. Herein, indomethacin was used as a model drug and introduced into the feedstock (Kollidon® VA64 and Candurin® blend) as either unprocessed drug crystals (particle size > 50 µm) or processed hot-melt extruded granules (DosePlus) with reduced drug particle size (<5 µm). These feedstocks were processed at 50, 75, and 100 mm/s scan speed using SLS 3D printing process. Characterization and performance testing were conducted on these tablets which revealed the amorphous conversion of the drug. Both MANOVA and ANOVA analyses depicted that the laser speed and drug particle size significantly impact the drug's apparent solubility and drug release. This significant difference in performance between formulations is attributed to the difference in the extent of dissolution of the drug in the polymeric matrix, leading to residual crystallinity, which is detrimental to ASD's performance. These results demonstrate the influence of drug particle size on solid-state and performance of 3D printed solid dispersions, and, hence, provide a better understanding of the mechanism and limitations of SLS 3D printing of ASDs and its dosage forms.

Analytical and Computational Methods for the Determination of Drug-Polymer Solubility and Miscibility

In the pharmaceutical industry, poorly water-soluble drugs require enabling technologies to increase apparent solubility in the biological environment. Amorphous solid dispersion (ASD) has emerged as an attractive strategy that has been used to market more than 20 oral pharmaceutical products. The amorphous form is inherently unstable and exhibits phase separation and crystallization during shelf life storage. Polymers stabilize the amorphous drug by antiplasticization, reducing molecular mobility, reducing chemical potential of drug, and increasing glass transition temperature in ASD. Here, drug-polymer miscibility is an important contributor to the physical stability of ASDs. The current Review discusses the basics of drug-polymer interactions with the major focus on the methods for the evaluation of solubility and miscibility of the drug in the polymer. Methods for the evaluation of drug-polymer solubility and miscibility have been classified as thermal, spectroscopic, microscopic, solid-liquid equilibrium-based, rheological, and computational methods. Thermal methods have been commonly used to determine the solubility of the drug in the polymer, while other methods provide qualitative information about drug-polymer miscibility. Despite advancements, the majority of these methods are still inadequate to provide the value of drug-polymer miscibility at room temperature. There is still a need for methods that can accurately determine drug-polymer miscibility at pharmaceutically relevant temperatures.

Application of a Physiologically Based Pharmacokinetic Model to Develop a Veterinary Amorphous Enrofloxacin Solid Dispersion

Zoonotic intestinal pathogens threaten human health and cause huge economic losses in farming. Enrofloxacin (ENR) shows high antibacterial activity against common intestinal bacteria. However, its poor palatability and low aqueous solubility limit the clinical application of ENR. To obtain an ENR oral preparation with good palatability and high solubility, a granule containing an amorphous ENR solid dispersion (ENR-SD) was prepared. Meanwhile, a PBPK model of ENR in pigs was built based on the physiological parameters of pigs and the chemical-specific parameters of ENR to simulate the pharmacokinetics (PK) of ENR-SD granules in the intestinal contents. According to the results of parameter sensitivity analysis (PSA) and the predicted PK parameters at different doses of the model, formulation strategies and potential dose regimens against common intestinal infections were provided. The DSC and XRD results showed that no specific interactions existed between the excipients and ENR during the compatibility tests, and ENR presented as an amorphous form in ENR-SD. Based on the similar PK performance of ENR-SD granules and the commercial ENR soluble powder suggesting continued enhancement of the solubility of ENR, a higher drug concentration in intestinal contents could not be obtained. Therefore, a 1:5 ratio of ENR and stearic acid possessing a saturated aqueous solubility of 1190 ± 7.71 µg/mL was selected. The predictive AUC24h/MIC90 ratios against Campylobacter jejuni, Salmonella, and Escherichia coli were 133, 266 and 8520 (>100), respectively, suggesting that satisfactory efficacy against common intestinal infections would be achieved at a dose of 10 mg/kg b.w. once daily. The PSA results indicated that the intestinal absorption rate constant (Ka) was negatively correlated with the Cmax of ENR in the intestine, suggesting that we could obtain higher intestinal Cmax using P-gp inducers to reduce Ka, thus obtaining a higher Cmax. Our studies suggested that the PBPK model is an excellent tool for formulation and dose design.

Rational Selection of Bio-Enabling Oral Drug Formulations - A PEARRL Commentary

New drug candidates often require bio-enabling formation technologies such as lipid-based formulations, solid dispersions, or nanosized drug formulations. Development of such more sophisticated delivery systems generally requires higher resource investment compared to a conventional oral dosage form, which might slow down clinical development. To achieve the biopharmaceutical objectives while enabling rapid cost effective development, it is imperative to identify a suitable formulation technique for a given drug candidate as early as possible. Hence many companies have developed internal decision trees based mostly on prior organizational experience, though they also contain some arbitrary elements. As part of the EU funded PEARRL project, a number of new decision trees are here proposed that reflect both the current scientific state of the art and a consensus among the industrial project partners. This commentary presents and discusses these, while also going beyond this classical expert approach with a pilot study using emerging machine learning, where the computer suggests formulation strategy based on the physicochemical and biopharmaceutical properties of a molecule. Current limitations are discussed and an outlook is provided for likely future developments in this emerging field of pharmaceutics.

Diffusion-controlled and `diffusionless' crystal growth: relation between liquid dynamics and growth kinetics of griseofulvin

Understanding how liquid dynamics govern crystallization is critical for maintaining the physical stability of amorphous pharmaceutical formulations. In the present study, griseofulvin (GSF), a classic antifungal drug, was used as the model system to investigate the correlations between crystal growth kinetics and liquid dynamics. The temperature dependence of the kinetic part of the bulk crystal growth in a supercooled liquid of GSF was weaker than that of the structural relaxation time τα and scaled as τα −0.69. In the glassy state, GSF exhibited the glass-to-crystal (GC) growth behavior, whose growth rate was too fast to be under the control of the α-relaxation process. Moreover, from the perspective of τα, the GC growth of GSF also satisfied the general condition for GC growth to exist: D/u < 7 pm, where D is the diffusion coefficient and u the speed of crystal growth. Also compared were the fast surface crystal growth rates u s and surface relaxation times τsurface predicted by the random first-order transition theory. Here, the surface crystal growth rate u s of GSF exhibited a power-law dependence upon the surface structural relaxation time: u s ∝ τsurface −0.71, which was similar to that of the bulk growth rate and τα. These findings are important for understanding and predicting the crystallization of amorphous pharmaceutical solids both in the bulk and at the surface.

Impact of the Chain Length and Topology of the Acetylated Oligosaccharide on the Crystallization Tendency of Naproxen from Amorphous Binary Mixtures

The impact of the chain length or dispersity of polymers in controlling the crystallization of amorphous active pharmaceutical ingredients (APIs) has been discussed for a long time. However, because of the weak control of these parameters in the majority of macromolecules used in pharmaceutical formulations, the abovementioned topic is poorly understood. Herein, four acetylated oligosaccharides, maltose (acMAL), raffinose (acRAF), stachyose (acSTA), and α-cyclodextrin (ac-α-CD) of growing chain lengths and different topologies (linear vs cyclic), mimicking the growing backbone of the polymer, were selected to probe the influence of these structural factors on the crystallization of naproxen (NAP)—an API that does not vitrify regardless of the cooling rate applied in our experiment. It was found that in equimolar systems composed of NAP and linear acetylated oligosaccharides, the progress and activation barrier for crystallization are dependent on the molecular weight of the excipient despite the fact that results of Fourier transform infrared studies indicated that there is no difference in the interaction pattern between measured samples. On the other hand, complementary dielectric, calorimetric, and X-ray diffraction data clearly demonstrated that NAP mixed with ac-α-CD (cyclic saccharide) does not tend to crystallize even in the system with a much higher content of APIs. To explain this interesting finding, we have carried out further density functional theory computations, which revealed that incorporation of NAP into the cavity of ac-α-CD is hardly possible because this state is of much higher energy (up to 80 kJ/mol) with respect to the one where the API is located outside of the saccharide torus. Hence, although at the moment, it is very difficult to explain the much stronger impact of the cyclic saccharide on the suppression of crystallization and enhanced stability of NAP with respect to the linear carbohydrates, our studies clearly showed that the chain length and the topology of the excipient play a significant role in controlling the crystallization of this API.

Development of Remdesivir as a Dry Powder for Inhalation by Thin Film Freezing

Remdesivir exhibits in vitro activity against SARS-CoV-2 and was granted approval for emergency use. To maximize delivery to the lungs, we formulated remdesivir as a dry powder for inhalation using thin film freezing (TFF). TFF produces brittle matrix nanostructured aggregates that are sheared into respirable low-density microparticles upon aerosolization from a passive dry powder inhaler. In vitro aerodynamic testing demonstrated that drug loading and excipient type affected the aerosol performance of remdesivir. Remdesivir combined with optimal excipients exhibited desirable aerosol performance (up to 93.0% FPF_{< 5 µm}; 0.82 µm mass median aerodynamic diameter). Remdesivir was amorphous after the TFF process, which benefitted drug dissolution in simulated lung fluid. TFF remdesivir formulations are stable after one month of storage at 25 °C/60% relative humidity. An in vivo pharmacokinetic evaluation showed that TFF remdesivir–leucine was poorly absorbed into systemic circulation while TFF remdesivir-Captisol^® demonstrated increased systemic uptake compared to leucine. Remdesivir was hydrolyzed to the nucleoside analog GS-441524 in the lung, and levels of GS-441524 were greater in the lung with leucine formulation compared to Captisol^®. In conclusion, TFF technology produces high-potency remdesivir dry powder formulations for inhalation that are suitable to treat patients with COVID-19 on an outpatient basis and earlier in the disease course where effective antiviral therapy can reduce related morbidity and mortality.

Physical stability of amorphous pharmaceutical solids: Nucleation, crystal growth, phase separation and effects of the polymers

Compared to their crystalline forms, amorphous pharmaceutical solids present marvelous potential and advantages for effectively improving the oral bioavailability of poorly water-soluble drugs. A central issue in developing amorphous pharmaceutical solids is the stability against crystallization, which is particularly important for maintaining their advantages in solubility and dissolution rate. This review provides a comprehensive overview of recent studies focusing on the physical stability of amorphous pharmaceutical solids affected by nucleation, crystal growth, phase separation and the addition of polymers. Moreover, we highlight the novel technologies and theories in the field of amorphous pharmaceutical solids. Meanwhile, the challenges and strategies in maintaining the physical stability of amorphous pharmaceutical solids are also discussed. With a better understanding of physical stability, the more robust amorphous pharmaceutical formulations with desired pharmaceutical performance would be easier to achieve.

The Solubility-Permeability Interplay for Solubility-Enabling Oral Formulations

The Biopharmaceutical classification system (BCS) classifies the drugs based on their intrinsic solubility and intestinal permeability. The drugs with good solubility and intestinal permeability have good bioavailability. The drugs with poor solubility and poor permeability have solubility dependent and permeability dependent bioavailability, respectively. In the current pharmaceutical field, most of the drugs have poor solubility. To solve the problem of poor solubility, various solubility enhancement approaches have been successfully used. The effects of these solubility enhancing approaches on the intestinal permeability of the drugs are a matter of concern, and must not be overlooked. The current review article focuses on the effect of various solubility enhancing approaches viz. cyclodextrin, surfactant, cosolvent, hydrotropes, and amorphous solid dispersion, on the intestinal permeability of drugs. This article will help in the designing of the optimized formulations having balanced solubility enhancement without affecting the permeability of drugs.

Microwave-Induced In Situ Amorphization: A New Strategy for Tackling the Stability Issue of Amorphous Solid Dispersions

The thermodynamically unstable nature of amorphous drugs has led to a persistent stability issue of amorphous solid dispersions (ASDs). Lately, microwave-induced in situ amorphization has been proposed as a promising solution to this problem, where the originally loaded crystalline drug is in situ amorphized within the final dosage form using a household microwave oven prior to oral administration. In addition to circumventing issues with physical stability, it can also simplify the problematic downstream processing of ASDs. In this review paper, we address the significance of exploring and developing this novel technology with an emphasis on systemically reviewing the currently available literature in this pharmaceutical arena and highlighting the underlying mechanisms involved in inducing in situ amorphization. Specifically, in order to achieve a high drug amorphicity, formulations should be composed of drugs with high solubility in polymers, as well as polymers with high hygroscopicity and good post-plasticized flexibility of chains. Furthermore, high microwave energy input is considered to be a desirable factor. Lastly, this review discusses challenges in the development of this technology including chemical stability, selection criteria for excipients and the dissolution performance of the microwave-induced ASDs.

Using thin film freezing to minimize excipients in inhalable tacrolimus dry powder formulations

We investigated the feasibility of preparing high-potency tacrolimus dry powder for inhalation using thin film freezing (TFF). We found that using ultra-rapid freezing can increase drug loading up to 95% while maintaining good aerosol performance. Drug loading affected the specific surface area and moisture sorption of TFF formulations, but it did not affect the chemical stability, physical stability, and dissolution of tacrolimus. Tacrolimus remained amorphous after storage at 40 °C/75% RH, and 25 °C/60% RH for up to 6 months. Lactose functioned as a bulking agent, and it had little to no effect as a stabilizer for amorphous tacrolimus due to a lack of interaction between the drug and excipient. Additionally, the aerosol performance of TFF tacrolimus/lactose (95/5) did not significantly change after six months of storage at 25 °C/60% RH. For processing parameters, the solids content and the processing temperature did not affect the aerosol performance of tacrolimus. Furthermore, both low- and high-resistance RS01 showed optimal and consistent aerosol performance over the 1-4 kPa pressure drop range. In conclusion, TFF is a suitable technology for producing inhalable powder that contain high drug loading and have less flow rate dependence.

Influence of the Internal Structure and Intermolecular Interactions on the Correlation between Structural (α) and Secondary (β-JG) Relaxation below the Glass Transition Temperature in Neat Probucol and Its Binary Mixtures with Modified Saccharides

Broadband dielectric spectroscopy (BDS) has been used to study the molecular dynamics and aging process in neat probucol (PRO) as well as its binary mixtures with selected acetylated saccharides. In particular, we applied the Casalini and Roland approach to determine structural relaxation times in the glassy state of the examined systems (so-called isostructural times, τ_iso). Next, using the calculated τ_iso, primitive relaxation times of the coupling model were obtained and compared to the experimental secondary β (Johari-Goldstein (JG) type) relaxation times. Interestingly, it turned out that there is a correlation between the β-JG and the structural (α)-relaxation processes below the glass transition temperature (T < T_g) in each investigated sample. This is a new observation compared to previous studies demonstrating that such a relationship exists only in the supercooled liquid state of neat PRO. Moreover, it was revealed that the stretching parameters obtained from the aging procedure are very close to the ones determined by fitting the dielectric data above the T_g with the use of the Kohlrausch-Williams-Watts function, indicating that the aging process is governed by the α-relaxation. Complementary Fourier transform infrared and X-ray diffraction measurements allowed us to find a possible reason for these findings. It was demonstrated that although there are very weak intermolecular interactions between PRO and modified saccharides, the intra- and intermolecular structure of PRO is practically unaffected by the presence of modified saccharides.

Degrees of order: A comparison of nanocrystal and amorphous solids for poorly soluble drugs

Poor aqueous solubility is currently a prevalent issue in the development of small molecule pharmaceuticals. Several methods are possible for improving the solubility, dissolution rate and bioavailability of Biopharmaceutics Classification System (BCS) class II and class IV drugs. Two solid state approaches, which rely on reductions in order, and can theoretically be applied to all molecules without any specific chemical prerequisites (compared with e.g. ionizable or co-former groups, or sufficient lipophilicity), are the use of the amorphous form and nanocrystals. Research involving these two approaches is relatively extensive and commercial products are now available based on these technologies. Nevertheless, their formulation remains more challenging than with conventional dosage forms. This article describes these two technologies from both theoretical and practical perspectives by briefly discussing the physicochemical backgrounds behind these approaches, as well as the resulting practical implications, both positive and negative. Case studies demonstrating the benefits and challenges of these two techniques are presented.

Influence of Annealing in the Close Vicinity of Tg on the Reorganization within Dimers and Its Impact on the Crystallization Kinetics of Gemfibrozil

In this paper, broadband dielectric spectroscopy (BDS) has been applied to study the molecular dynamics and crystallization kinetics of the antihyperlipidemic active pharmaceutical ingredient (API), gemfibrozil (GEM), as well as its deuterated (dGEM) and methylated (metGEM) derivatives, characterized by different types and strengths of intermolecular interactions. Moreover, calorimetric and infrared measurements have been carried out to characterize the thermal properties of examined samples and to probe a change in the H-bonding pattern in GEM, respectively. We found that the dielectric spectra of all examined compounds, collected below the glass transition temperature (T_g), reveal the presence of two secondary relaxations (β, γ). According to the coupling model (CM) predictions, it was assumed that the slower process (β) is of JG type, whereas the faster one (γ) has an intramolecular origin. Interestingly, the extensive crystallization kinetics measurements performed after applying two paths, i.e., the standard procedure (cooling and subsequently heating up to the appropriate temperature, T_c), as well as annealing at two temperatures in the vicinity of T_g and further heating up to T_c, showed that the annealing increases the crystallization rate in the case of native API, while the thermal history of the sample has no significant impact on the pace of this process in the two derivatives of GEM. Analysis of the dielectric strength (Δε) of the α-process during annealing, together with the results of Fourier transform infrared spectroscopy (FTIR) measurements, suggested that the reorganization within dimeric structures formed between the GEM molecules is responsible for the observed behavior. Importantly, our results differ from those obtained by Tominaka et al. (Tominaka, S.; Kawakami, K.; Fukushima, M.; Miyazaki, A.Physical Stabilization of Pharmaceutical Glasses Based on Hydrogen Bond Reorganization under Sub-T_g Temperature Mol. Pharm. 2017 14 264 273 10.1021/acs.molpharmaceut.6b00866.), who demonstrated that the sub-T_g annealing of ritonavir (RTV), which is able to form extensive supramolecular hydrogen bonds, protects this active substance against crystallization. Therefore, based on these contradictory reports, one can hypothesize that materials forming H-bonded structures, characterized by varying architecture, may behave differently after annealing in the vicinity of the glass transition temperature.

Enhanced Physical Stability and Synchronized Release of Febuxostat and Indomethacin in Coamorphous Solids

Coamorphous formulation, a homogeneous monophasic amorphous system composed of multiple components, has been demonstrated as an effective approach for delivering drugs with poor aqueous solubility. In this study, we prepared the coamorphous system composed of two poorly soluble drugs febuxostat (FEB) and indomethacin (IMC) by using cryogenic milling. The combination of these two drugs in the coamorphous form can attain a synergistic effect, especially on gout therapy. Coamorphous solid of FEB and IMC in 1:1 molar ratio exhibited superior physical stability compared with the individual amorphous components, as evidenced by X-ray powder diffractions after 30 days of storage at ambient and elevated temperature. In addition, the FEB-IMC coamorphous system has been demonstrated to show enhanced dissolution performance. The intrinsic dissolution rates of two components in the coamorphous system exhibited the synchronized drug release. Based on the FT-IR spectroscopy, the excellent physical stability and synchronized release of FEB-IMC coamorphous system could be attributed to the heterodimer structure formed by strong hydrogen bonding interactions between these drugs. Furthermore, the supersaturation potential of FEB-IMC coamorphous solids was also investigated through the cosolvent quenching method. The FEB-IMC coamorphous system can effectively inhibit the fast crystallization of FEB in the supersaturated solution. However, the maximum achievable supersaturation of IMC in the coamorphous system decreases to only one fifth of that achieved for the pure amorphous IMC. These results are relevant for understanding the physical stability and complex solution behaviors of the coamorphous formulation.

Manufacturing strategies to develop amorphous solid dispersions: An overview

Since the past several decades, poor water solubility of existing and new drugs in the pipeline have remained a challenging issue for the pharmaceutical industry. Literature describes several approaches to improve the overall solubility, dissolution rate, and bioavailability of drugs with poor water solubility. Moreover, the development of amorphous solid dispersion (SD) using suitable polymers and methods have gained considerable importance in the recent past. In the present review, we attempt to discuss the important and industrially scalable thermal strategies for the development of amorphous SD. These include both solvent (spray drying and fluid bed processing) and fusion (hot melt extrusion and KinetiSol®) based techniques. The current review also provides insights into the thermodynamic properties of drugs, their polymer miscibility and solubility, and their molecular dynamics to develop stable and more efficient amorphous SD.

A Novel Rheological Method to Assess Drug-Polymer Interactions Regarding Miscibility and Crystallization of Drug in Amorphous Solid Dispersions for Oral Drug Delivery

Solid dispersions provide a key technology to formulate poorly water-soluble drugs, and a main task of early development is appropriate selection of polymer. This study investigates the use of a novel rheology-based approach to evaluate miscibility and interactions of drugs with polymers regarding amorphous solid drug dispersions for oral administration. Tacrolimus was used as model drug and hydroxypropyl cellulose, ethylcellulose, Soluplus^®, polyethyleneglycol 6000, Poloxamer-188 (Koliphor-188), and Eudragit^® S100 were used as excipients. Solvent-based evaporation methods were used to prepare binary solid dispersions of drug and polymer. Data of the dilute solution viscosimetry were compared with in silico calculations of the Hansen solubility parameter (HSP), as well as phase separation/crystallization data obtained from X-ray diffraction and differential scanning calorimetry. HSP calculations in some cases led to false positive predictions of tacrolimus miscibility with the tested polymers. The novel rheology-based method provided valuable insights into drug-polymer interactions and likely miscibility with polymer. It is a rather fast, inexpensive, and robust analytical approach, which could be used complementary to in silico-based evaluation of polymers in early formulation development, especially in cases of rather large active pharmaceutical ingredients.

Opportunities for Successful Stabilization of Poor Glass-Forming Drugs: A Stability-Based Comparison of Mesoporous Silica Versus Hot Melt Extrusion Technologies

Amorphous formulation technologies to improve oral absorption of poorly soluble active pharmaceutical ingredients (APIs) have become increasingly prevalent. Currently, polymer-based amorphous formulations manufactured by spray drying, hot melt extrusion (HME), or co-precipitation are most common. However, these technologies have challenges in terms of the successful stabilization of poor glass former compounds in the amorphous form. An alternative approach is mesoporous silica, which stabilizes APIs in non-crystalline form via molecular adsorption inside nano-scale pores. In line with these considerations, two poor glass formers, haloperidol and carbamazepine, were formulated as polymer-based solid dispersion via HME and with mesoporous silica, and their stability was compared under accelerated conditions. Changes were monitored over three months with respect to solid-state form and dissolution. The results were supported by solid-state nuclear magnetic resonance spectroscopy (SS-NMR) and scanning electron microscopy (SEM). It was demonstrated that mesoporous silica was more successful than HME in the stabilization of the selected poor glass formers. While both drugs remained non-crystalline during the study using mesoporous silica, polymer-based HME formulations showed recrystallization after one week. Thus, mesoporous silica represents an attractive technology to extend the formulation toolbox to poorly soluble poor glass formers.

Preparation of Amorphous Composite Particles of Drugs with Ursodeoxycholic Acid as Preclinical Formulations

We studied the possibility of using ursodeoxycholic acid (UDCA) as an excipient to create an amorphous composite that can be administered to animals in preclinical studies of experimental drugs. Three UDCA-based amorphous samples composed of nifedipine (NIF), indomethacin (IND), and naproxen (NAP) were found by screening. The UDCA-based formulations were adjudged amorphous by solid-state analysis using X-ray powder diffraction and differential scanning calorimetry. In addition, amorphous samples of NIF-UDCA, IND-UDCA, and NAP-UDCA did not crystallize while in 1% methyl cellulose (MC) solution for 120 min, although an amorphous solid dispersion of NIF-poly(vinylpyrrolidone) (PVP) crystallized rapidly. The low hygroscopicity of UDCA helps NIF maintain an amorphous state in 1% MC solution. The UDCA-based amorphous composites can be administered as suspended formulations to animals in preclinical studies.

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.

Long-Term Physical (In)Stability of Spray-Dried Amorphous Drugs: Relationship with Glass-Forming Ability and Physicochemical Properties

This study shows the importance of the chosen method for assessing the glass-forming ability (GFA) and glass stability (GS) of a drug compound. Traditionally, GFA and GS are established using in situ melt-quenching in a differential scanning calorimeter. In this study, we included 26 structurally diverse glass-forming drugs (i) to compare the GFA class when the model drugs were produced by spray-drying with that when melt-quenching was used, (ii) to investigate the long-term physical stability of the resulting amorphous solids, and (iii) to investigate the relationship between physicochemical properties and the GFA of spray-dried solids and their long-term physical stability. The spray-dried solids were exposed to dry (<5% RH) and humid (75% RH) conditions for six months at 25 °C. The crystallization of the spray-dried solids under these conditions was monitored using a combination of solid-state characterization techniques including differential scanning calorimetry, Raman spectroscopy, and powder X-ray diffraction. The GFA/GS class assignment for 85% of the model compounds was method-dependent, with significant differences between spray-drying and melt-quenching methods. The long-term physical stability under dry condition of the compounds was predictable from GFA/GS classification and glass transition and crystallization temperatures. However, the stability upon storage at 75% RH could not be predicted from the same data. There was no strong correlation between the physicochemical properties explored and the GFA class or long-term physical stability. However, there was a slight tendency for compounds with a relatively larger molecular weight, higher glass transition temperature, higher crystallization temperature, higher melting point and higher reduced glass transition temperature to have better GFA and better physical stability. In contrast, a high heat of fusion and entropy of fusion seemed to have a negative impact on the GFA and physical stability of our dataset.