The Effect of Water Plasticization on the Molecular Mobility and Crystallization Tendency of Amorphous Disaccharides

Stability Studies of Amorphous Ibrutinib Prepared Using the Quench-Cooling Method and Its Dispersions with Soluplus®

The successful development of an amorphous form of a drug demands the use of process conditions and materials that reduce their thermodynamic instability. For the first time, we have prepared amorphous ibrutinib using the quench-cooling method with very high process efficiency. In the presented study, different formulations of amorphous active pharmaceutical ingredient (API) with Soluplus (SOL) in various weight ratios 1:9, 3:7, and 1:1 were prepared. The obtained samples were stored under long-term (25 ± 2 °C/60%RH ± 5% RH, 12 months) and accelerated (40 ± 2 °C/75%RH ± 5% RH, 6 months) storage conditions. The physical stability of amorphous ibrutinib and ibrutinib-Soluplus formulations was analyzed using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction analysis (XRPD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The lack of significant interactions between the ingredients of the formulation was confirmed by FTIR analysis. An increase in moisture content with an increasing SOL weight ratio was observed under accelerated aging and long-term conditions. Additionally, a slight increase in the moisture content of the stored sample compared to that at the initial time was observed. The results revealed the physical strength of the polymeric systems in the presence of high humidity and temperature. The observed high thermal stability allows the use of various technological processes without the risk of thermal degradation.

Screening of novel excipients for freeze-dried protein formulations

The typical excipients used as bulking agents and lyoprotectants for freeze-drying are usually limited to only a few selected substances, such as sucrose and mannitol. Considering the sheer diversity amongst proteins, it is doubtful that this limited choice should, in every case, provide the best possible option in order to achieve the most stable product. In this work, a screening of 12 proteins with 64 excipients was conducted in order to increase the knowledge space of potential excipients. Three critical quality attributes (CQAs) of the freeze-dried products, namely the solid state, the cake appearance and the protein integrity based on changes in tryptophan fluorescence were investigated by high throughput X-ray powder diffraction, image analysis and intrinsic fluorescence spectroscopy, respectively. It was found, that in some cases the excipient had a dominating influence on the CQAs, whilst in other cases the CQAs were primarily protein dependent, or that the CQAs were dependent on the combination of both. In the course of this investigation, a general view of potentially relevant excipients, and their interplay with various proteins, was obtained, thereby furthermore paving the way for the use of novel freeze-drying excipients.

The use of hydrophobic amino acids in protecting spray dried trehalose formulations against moisture-induced changes

Trehalose is commonly used as a protein stabilizer in spray dried protein formulations delivered via the pulmonary route. Spray dried trehalose formulations are highly hygroscopic, which makes them prone to deliquescence and recrystallization when exposed to moisture, leading to impairment in aerosolization performance. The main aim of this study was to investigate and compare the effect of hydrophobic amino acids (i.e. L-leucine and L-isoleucine) in enhancing aerosolization performance and in mitigating moisture-induced changes in spray dried trehalose formulations. Trehalose was spray dried with 20-60% w/w of amino acid (i.e. L-leucine or L-isoleucine). The spray dried formulations were stored at 25 °C/50% RH for 28 days. Solid state characterization and in vitro aerosolization performance studies were performed on the spray dried formulations before and after storage. The addition of 20-60% w/w of amino acid (i.e. L-leucine or L-isoleucine) improved the emitted fractions of spray dried trehalose formulations from a dry powder inhaler. However, ≥ 40% w/w of L-leucine/L-isoleucine was needed to prevent recrystallization of trehalose in the formulations when exposed to 25 °C/50% RH for 28 days. X-ray photoelectron spectroscopy (XPS) demonstrated that samples with 40-60% w/w L-isoleucine had more amino acid on the surfaces of the particles compared to their L-leucine counterparts. This may explain the greater ability of the L-isoleucine (40-60% w/w) samples to cope with elevated humidity compared to L-leucine samples of the same concentrations, as observed in the dynamic vapour sorption (DVS) studies. In conclusion, this study demonstrated that both L-leucine and L-isoleucine were effective in enhancing aerosolization performance and mitigating moisture-induced reduction in aerosolization performance in spray dried trehalose formulations. L-isoleucine proved to be superior to L-leucine in terms of its moisture protectant effect when incorporated at the same concentration in the formulations.

Correlation between molecular dynamics and physical stability of two milled anhydrous sugars: Lactose and sucrose

The process of milling often results in amorphization and the physical stability of amorphous phase is linked with its molecular dynamics. This study focuses on a propensity of two disaccharides (lactose and sucrose) to amorphize on ball milling and the stability of the resultant amorphous phase. The amorphous content in milled sugars is estimated by Differential Scanning Calorimetry (DSC) and the stability was measured in terms of the tendency to recrystallize by Broadband Dielectric Spectroscopy (BDS). The results show that the amorphous content increases with milling time and is greater for lactose than sucrose. At the same degree of amorphization, sucrose recrystallize at temperature ∼15 °C higher than lactose, indicating higher stability. The molecular dynamics (beta relaxation process), suggest that milled sucrose is more stable with higher activation energy (∼9 kJ mol^-1) than that of lactose. The moisture content of amorphous phase also impacts its molecular dynamics in terms of increase in activation energy as the moisture decrease with increasing the milling times. The study suggests a greater stability of amorphous sucrose and susceptibility of milled lactose to recrystallize, however, on extended milling when the moisture content decreases, lactose was seen to become relatively more stable.

Merits and Limitations of Dynamic Vapor Sorption Studies on the Morphology and Physicochemical State of Freeze-Dried Products

The goal of the present study was to assess the applicability of dynamic vapor sorption analysis of freeze-dried products. Water vapor sorption profiles of intact and ground cakes were recorded to determine the relevance of powder handling. Grinding prior to measurements appeared to be related with a more rapid uptake of water vapor and crystallization. Crystallization may be prevented when analyzing intact cakes. More hygroscopic materials appeared to require a longer time to achieve a constant mass. The specific surface area of different freeze-dried products was calculated from the sorption isotherms using water, organic solvents, and krypton. The specific surface areas calculated for mannitol with water and ethanol was in good agreement with krypton data. False high values were obtained from water vapor sorption of the investigated amorphous materials. The results were slightly improved by the application of vacuum. For trehalose and sucrose, no sorption and thus faulty results were detected with the studied organic solvents. The degree of crystallinity of mannitol within a binary formulation could not be determined by dynamic vapor sorption. Differences in sorption and crystallization tendencies of mannitol and sucrose that were freeze-dried separately and in a binary mixture were considered as the root cause.

Experimental Studies and Modeling of the Drying Kinetics of Multicomponent Polymer Films

The process of drying thin polymer films is an important operation that influences the film structure and solid state, and the stability of the product. The purpose of this work was to study and model the drying kinetics of multicomponent films based on two polymers: hydroxypropyl methylcellulose (HPMC, amorphous) and polyvinyl alcohol (PVA, semicrystalline). The isothermal drying kinetics of the films at different temperatures (40, 60, and 80°C) were studied using thermo-gravimetric analysis (TGA) and convection oven methods. Solid-state characterization tools used in the study included polarization and hot-stage microscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The drying kinetics of HPMC and PVA films in the TGA apparatus and convection oven were comparable. The three-parameter (W _max, τ, n) Hill equation successfully modeled the experimental drying kinetics. The time factor τ in the Hill equation nicely explained two drying phases in the films. Solid-state phase changes occurring in the films during dehydration had a bearing on the drying kinetics and mechanisms. TGA can be used as a simple tool to determine the end points in drying processes using ovens or tunnels. The three-parameter Hill equation explained the drying kinetics and diffusion mechanisms of the solvent through the polymer films for the first time. This study advances our understanding of film drying, in particular for pharmaceutically relevant thin films.

Spray-dried amorphous isomalt and melibiose, two potential protein-stabilizing excipients

The possibility of producing amorphous isomalt and melibiose by spray drying was studied. The impact of process parameters on yield and solid-state stability was compared to sucrose and trehalose. All powders remained amorphous during 2-3 weeks. Processing was challenging due to powder stickiness. Low-temperature and low-humidity drying processes generally performed best. Most isomalt and sucrose powder was retrieved when using 60°C inlet temperature, 800L/h atomizing rate, 1.4ml/min feed rate, 15% concentration and 100% aspirator rate, giving 42-43°C outlet temperature. Isomalt was the most problematic, because it had the lowest Tg and became sticky very easily, therefore process parameters needed to be precisely balanced. There was more freedom in designing processes for melibiose but best yields were obtained with low-temperature (50°C inlet temperature, 800L/h atomizing rate, 4.9ml/min feed rate, 10% concentration and 100% aspirator, 39°C outlet temperature). Trehalose was different in that higher temperatures resulted in better yields. Yet, trehalose generally contained the highest moisture contents. The possibility to produce amorphous isomalt and melibiose at low-temperature process conditions makes them promising considering spray drying applications for heat-sensitive proteins. Melibiose is a better candidate than isomalt because of easier processability and superior solid-state stability.

Physical Stability of Freeze-Dried Isomalt Diastereomer Mixtures

PURPOSE

Isomalt is a sugar alcohol used as an excipient in commercially available solid oral dosage forms. The potential of isomalt as a novel freeze-drying excipient was studied in order to increase knowledge of the behavior of isomalt when it is freeze-dried.

METHODS

Isomalt was freeze-dried in four different diastereomer compositions and its physical stability was investigated with differential scanning calorimetry, Fourier-transform infrared and Raman spectroscopy, X-ray powder diffraction, Karl-Fischer titration and thermogravimetric analysis in order to verify the solid state form of isomalt after freeze-drying and observe any changes occurring during storage in three different relative humidity conditions.

RESULTS

Isomalt was successfully transformed into the amorphous form with freeze-drying and three diastereomer combinations remained stable as amorphous during storage; one of the diastereomer compositions showed signs of physical instability when stored in the highest relative humidity condition. The four different crystalline diastereomer mixtures showed specific identifiable solid state properties.

CONCLUSIONS

Isomalt was shown to be a suitable excipient for freeze-drying. Preferably a mixture of the diastereomers should be used, as the mixture containing only one of the isomers showed physical instability. A mixture containing a 1:1 ratio of the two diastereomers showed the best physical stability in the amorphous form.

Hot Melt Extrusion: Development of an Amorphous Solid Dispersion for an Insoluble Drug from Mini-scale to Clinical Scale

The objective of the study was to develop an amorphous solid dispersion (ASD) for an insoluble compound X by hot melt extrusion (HME) process. The focus was to identify material-sparing approaches to develop bioavailable and stable ASD including scale up of HME process using minimal drug. Mixtures of compound X and polymers with and without surfactants or pH modifiers were evaluated by hot stage microscopy (HSM), polarized light microscopy (PLM), and modulated differential scanning calorimetry (mDSC), which enabled systematic selection of ASD components. Formulation blends of compound X with PVP K12 and PVP VA64 polymers were extruded through a 9-mm twin screw mini-extruder. Physical characterization of extrudates by PLM, XRPD, and mDSC indicated formation of single-phase ASD's. Accelerated stability testing was performed that allowed rapid selection of stable ASD's and suitable packaging configurations. Dissolution testing by a discriminating two-step non-sink dissolution method showed 70-80% drug release from prototype ASD's, which was around twofold higher compared to crystalline tablet formulations. The in vivo pharmacokinetic study in dogs showed that bioavailability from ASD of compound X with PVP VA64 was four times higher compared to crystalline tablet formulations. The HME process was scaled up from lab scale to clinical scale using volumetric scale up approach and scale-independent-specific energy parameter. The present study demonstrated systematic development of ASD dosage form and scale up of HME process to clinical scale using minimal drug (∼500 g), which allowed successful clinical batch manufacture of enabled formulation within 7 months.

Evaluation of the recrystallization kinetics of hot-melt extruded polymeric solid dispersions using an improved Avrami equation

The recrystallization of an amorphous drug in a solid dispersion system could lead to a loss in the drug solubility and bioavailability. The primary objective of the current research was to use an improved kinetic model to evaluate the recrystallization kinetics of amorphous structures and to further understand the factors influencing the physical stability of amorphous solid dispersions. Amorphous solid dispersions of fenofibrate with different molecular weights of hydroxypropylcellulose, HPC (Klucel™ LF, EF, ELF) were prepared utilizing hot-melt extrusion technology. Differential scanning calorimetry was utilized to quantitatively analyze the extent of recrystallization in the samples stored at different temperatures and relative humidity (RH) conditions. The experimental data were fitted into the improved kinetics model of a modified Avrami equation to calculate the recrystallization rate constants. Klucel LF, the largest molecular weight among the HPCs used, demonstrated the greatest inhibition of fenofibrate recrystallization. Additionally, the recrystallization rate (k) decreased with increasing polymer content, however exponentially increased with higher temperature. Also k increased linearly rather than exponentially over the range of RH studied.

Mapping Moisture Sorption Through Carbohydrate Composite Glass with Fourier Transform Near-Infrared (FT-NIR) Hyperspectral Imaging

Inherent changes in foods during storage are often caused by water sorption or desorption that often results in product matrix instability. Water sorption behavior differs depending on the matrix through which it moves. Often, concurrent phenomenon such as crystallization modifies water's movement. We describe a novel use of hyperspectral imaging combined with Fourier Transform Near Infrared (FT-NIR) spectroscopy to map where water molecules are in two dimensions while concurrently quantifying the crystallization motif as water sorbs into a carbohydrate matrix over a month's storage time. This methodology allows us to identify and quantify sucrose crystals formed within a carbohydrate matrix while also mapping water migration through this complex matrix. We compared corn syrup/sucrose blends where sucrose is supersaturated (high sucrose, HS), sucrose is below saturation (low sucrose, LS), sucrose below saturation with embedded sucrose crystals (LSS) and maltotriose is supersaturated within a corn syrup matrix (high maltotriose, LSM). This FT-NIR method was used to characterize water sorption through a carbohydrate matrix over time and measured both the propensity of the systems to form sucrose crystals and the influence sucrose crystals have on water sorption. We observed water diffusion was slower in lower sugar carbohydrate glasses, and the process of sorption was different. Amorphous systems supersaturated in sucrose allow crystallization when sufficient water is sorbed and thus, this concurrent action disrupts normal Fickian diffusion. The water front compresses to a narrow band as it sorbs through the matrix. The presence of embedded crystals in an amorphous matrix slows overall water penetration through the matrix by convoluting the path of moving water molecules. This did not appear to change the rate of diffusion. Experiments with maltotriose at supersaturation concentration showed the crystallization rate was slower than sucrose. Thus, pure maltotriose is not a practical solution as a potential replacement for sucrose to slow sorption in food systems.

Amorphous solid dispersions of piroxicam and Soluplus(®): Qualitative and quantitative analysis of piroxicam recrystallization during storage

The conversion of active pharmaceutical ingredient (API) from amorphous to crystalline form is the primary stability issue in formulating amorphous solid dispersions (SDs). The aim of the present study was to carry out qualitative and quantitative analysis of the physical solid-state stability of the SDs of poorly water-soluble piroxicam (PRX) and polyvinyl caprolactam-polyvinyl acetate-polyethylene-glycol graft copolymer (Soluplus(®)). The SDs were prepared by a solvent evaporation method and stored for six months at 0% RH/6 °C, 0% RH/25 °C, 40% RH/25 °C and 75% RH/25 °C. Fourier transform infrared spectroscopy equipped with attenuated total reflection accessory (ATR-FTIR) and Raman spectroscopy were used for characterizing the physical solid-state changes and drug-polymer interactions. The principal component analysis (PCA) and multivariate curve resolution alternating least squares (MCR-ALS) were used for the qualitative and quantitative analysis of Raman spectra collected during storage. When stored at 0% RH/6 °C and at 0% RH/25 °C, PRX in SDs remained in an amorphous form since no recrystallization was observed by ATR-FTIR and Raman spectroscopy. Raman spectroscopy coupled with PCA and MCR-ALS and ATR-FTIR spectroscopy enabled to detect the recrystallization of amorphous PRX in the samples stored at higher humidity.

Counter-intuitive effect of non-crystallizing sugars on the crystallization of gemcitabine HCl in frozen solutions

In this study, the effect of four non-crystallizing sugars, namely fructose, trehalose, sucrose and raffinose, was assessed on the crystallization of gemcitabine hydrochloride (GHCl) in frozen solutions. Aqueous solutions containing GHCl (50 mg/mL) and a sugar at varying concentrations (10-60 mg/mL) were frozen in situ in DSC and analyzed in the subsequent heating run. Crystallization propensity of GHCl was quantified in terms of reduced crystallization temperature (RCT) as a function of sugar type and concentration. Multivariate analysis option in JMP(®) software was employed for calculating correlation between the variables. All sugars inhibited GHCl crystallization in a concentration dependent manner. At equal concentration, fructose (with the lowest Tg') exerted the strongest inhibitory effect, whereas raffinose (with the highest Tg') exerted the weakest inhibitory effect. Additionally, RCT showed a poor correlation with Tg' (r=0.2327). Thus, the inhibitory effect of sugars could not be described by their anti-plasticization effect. This counter-intuitive behavior was explained by the inhibitory effect of sugars on ice crystallization, which increased the unfrozen water content (UWC) in the freeze concentrate, thereby lowering the supersaturation of GHCl. This was established by observing a good correlation (r=0.9666) between RCT and ln(1/UWC). Additionally, reduced diffusion kinetics of GHCl in presence of sugar molecules was also postulated. This study highlights the importance of unfrozen water towards governing the crystallization behavior of solutes in multi-component frozen systems.

Scalable organic solvent free supercritical fluid spray drying process for producing dry protein formulations

In this study, we evaluated the influence of supercritical carbon dioxide (scCO2) spray drying conditions, in the absence of organic solvent, on the ability to produce dry protein/trehalose formulations at 1:10 and 1:4 (w/w) ratios. When using a 4L drying vessel, we found that decreasing the solution flow rate and solution volume, or increasing the scCO2 flow rate resulted in a significant reduction in the residual water content in dried products (Karl Fischer titration). The best conditions were then used to evaluate the ability to scale the scCO2 spray drying process from 4L to 10L chamber. The ratio of scCO2 and solution flow rate was kept constant. The products on both scales exhibited similar residual moisture contents, particle morphologies (SEM), and glass transition temperatures (DSC). After reconstitution, the lysozyme activity (enzymatic assay) and structure (circular dichroism, HP-SEC) were fully preserved, but the sub-visible particle content was slightly increased (flow imaging microscopy, nanoparticle tracking analysis). Furthermore, the drying condition was applicable to other proteins resulting in products of similar quality as the lysozyme formulations. In conclusion, we established scCO2 spray drying processing conditions for protein formulations without an organic solvent that holds promise for the industrial production of dry protein formulations.

Characterization and performance assessment of solid dispersions prepared by hot melt extrusion and spray drying process

The present study investigated effect of manufacturing methods such as hot melt extrusion (HME) and spray drying (SD) on physicochemical properties, manufacturability, physical stability and product performance of solid dispersion. Solid dispersions of compound X and PVP VA64 (1:2) when prepared by SD and HME process were amorphous by polarized light microscopy, powder X-ray diffractometry, and modulated differential scanning calorimetry analyses with a single glass transition temperature. Fourier transform infrared (FT-IR) and Raman spectroscopic analyses revealed similar molecular level interactions between compound X and PVP VA64 as evident by overlapping FT-IR and FT Raman spectra in SD and HME solid dispersions. The compactibility, tabletability, disintegration and dissolution performance were similar for solid dispersions prepared by both processing techniques. Differences in material properties such as surface area, morphological structure, powder densities, and flow characteristics were observed between SD and HME solid dispersion. The SD solid dispersion was physically less stable compared to HME solid dispersion under accelerated stability conditions. Findings from this study suggest that similar product performance could be obtained if the molecular properties of the solid dispersion processed by two different techniques are similar. However differences in material properties might affect the physical stability of the solid dispersions.

Water-solid interactions in amorphous maltodextrin-crystalline sucrose binary mixtures

Amorphous and crystalline solids are commonly found together in a variety of pharmaceutical and food products. In this study, the influence of co-formulation of amorphous maltodextrins (MDs) and crystalline sucrose (S) on moisture sorption, deliquescence, and glass transition (Tg) properties of powder blends was investigated. Individual components and binary mixtures of four different molecular weight MDs with sucrose in 1:1 w/w ratios were exposed to various relative humidity (RH) environments and their equilibrium and dynamic moisture contents were monitored. The deliquescence point (RH0) and dissolution behavior of sucrose alone and in blends was also monitored by polarized light microscopy and second harmonic generation imaging. In S:MD blends, the deliquescence RH of sucrose was lower than the RH0 of sucrose alone, and synergistic moisture sorption also occurred at RHs lower than the RH0. Intimate contact of sucrose crystals with the amorphous MDs resulted in complete dissolution of sucrose at RH < RH0. When blends were stored at conditions exceeding the Tg of the individual MDs (25 °C and 60%, 49% and 34%RH for MD21, MD29 and MD40, respectively), the Tg of the blends was lower than that of individual MDs. Thus, co-formulation of amorphous MDs with crystalline sucrose sensitizes the blend to moisture, potentially leading to deleterious changes in the formulation if storage conditions are not adequately controlled.

The effect of relative humidity on the physical properties of two melibiose monohydrate batches with differing particle size distributions and surface properties

Melibiose monohydrate has shown promise when employed as a pharmaceutical excipient, but its physical properties have not been adequately characterized. Therefore, two different melibiose monohydrate batches were analyzed as received or after storage under different relative humidity (RH) atmospheres. The particle size distributions and specific surface areas of the two batches were shown to differ considerably, which also had an effect on their water sorption tendencies and on the intermolecular structure of melibiose after storage. The relatively large primary particles that were more abundant in one of the batches were shown to possess a porous surface structure, and water evaporation from them occurred in two phases when heated. Furthermore, storing the batch with smaller mean particle size under dry conditions affected the crystal structure and molecular vibrations of the sample more than in the case of the batch with larger mean particle size. It was concluded that the physical properties of melibiose monohydrate after storage at different RH atmospheres is largely governed by the primary particle size and porosity.