Origin of Two Modes of Non-isothermal Crystallization of Glasses Produced by Milling

Re-visitation of Two Models for Predicting Mechanically-Induced Disordering after Cryogenic Impact Milling

PURPOSE

To compare the prediction accuracy of two models used to characterize the complete disordering potential of materials after extensive cryogenic milling.

METHODS

Elastic shear moduli (μs) were simulated in silico. Comparison with available literature values confirmed that computations were reasonable. Complete disordering potential was predicted using the critical dislocation density (ρcrit) and bivariate empirical models. To compare the prediction accuracy of the models, each material added for dataset expansion was cryomilled for up to 5 hr. Mechanical disordering after comminution was characterized using PXRD and DSC, and pooled with previously published results.

RESULTS

Simulated μs enabled predictions using the ρcrit model for 29 materials. This model mischaracterized the complete disordering behavior for 13/29 materials, giving an overall prediction accuracy of 55%. The originally published bivariate empirical model classification boundary correctly grouped the disordering potential for 31/32 materials from the expanded dataset. Recalibration of this model retained a 94% prediction accuracy, with only 2 misclassifications.

CONCLUSIONS

Prediction accuracy of the ρcrit model decreased with dataset expansion, relative to previously published results. Overall, the ρcrit model was considerably less accurate relative to the bivariate empirical model, which retained very high prediction accuracy for the expanded dataset. Although the empirical model does not imply a mechanism, model robustness suggests the importance of glass transition temperature (Tg) and molar volume (Mv) on formation and persistence of amorphous materials following extensive cryomilling.

Molecular Mobility of Terfenadine: Investigation by Dielectric Relaxation Spectroscopy and Molecular Dynamics Simulation

The molecular mobility of an amorphous active pharmaceutical ingredient, terfenadine, was carefully investigated by dielectric relaxation spectroscopy and molecular dynamics simulation for the first time. Comprehensive characterization on a wide frequency (10^-2 to 10⁹ Hz) and temperature (300 K) range highlights the fragile nature of this good glass-former (m = 112) and the relatively large nonexponentiality of the main relaxation (β_KWW = 0.53 ± 0.01). In the glassy state, a particularly broad secondary relaxation of intramolecular origin is evidenced. Terfenadine is a flexible molecule, and from molecular dynamics simulation, a clear link is established between the flexibility of the central part of the molecule (carrying, on the one side, the nitrogen group, and on the other side, the OH group) and the distribution of dipole moments, which explains that broadness. Terfenadine is one of the very few cases for which the molecular mobility of the glass obtained by the quench of the melt or by milling can be compared. From the present study, no major difference in terms of molecular mobility is found between these two glasses. However, terfenadine amorphized by milling (for 1-20 h) clearly shows a lower stability than the quenched liquid as we observed its recrystallization upon heating. Interestingly, it is shown that this recrystallization upon heating is not complete and that the 1-2% of the remaining amorphous phase has an original behavior. Indeed, it exhibits an enhanced main mobility induced by an autoconfinement effect created by the surrounding crystalline phase.

Crystallization of Cyclophosphamide Monohydrate During Lyophilization

The purpose of this study was to investigate the phase behavior of cyclophosphamide (CPA) during various stages of lyophilization, with special emphasis on obtaining crystalline CPA monohydrate (CPA-MH) in the lyophilized product. Subambient differential scanning calorimetry and low-temperature X-ray diffractometry (LTXRD) were used to study the phase behavior of CPA solution (3.7% w/v). In situ lyophilization in LTXRD chamber was used to monitor the phase transitions occurring during the drying stages. Finally, the implications of these findings were confirmed by freeze-drying the aqueous solution in a laboratory-scale freeze-dryer. The results suggested that CPA remains amorphous during freeze concentration, with a T_g' of -50°C. However, its crystallization as CPA-MH can be induced by annealing the frozen solution between -5°C and -10°C. In situ lyophilization in LTXRD showed that the CPA-MH crystallized during annealing, rapidly dehydrated during primary drying, thereby causing structural collapse. The dehydration of CPA-MH can be prevented by lowering the escaping tendency of water molecules from the crystal lattice of CPA-MH by maintaining the chamber pressure to 300, 400, or 500 mTorr. This study highlights the relationship of process parameters used during lyophilization with the solid form of lyophilized CPA.

Coamorphous Loratadine-Citric Acid System with Enhanced Physical Stability and Bioavailability

Coamorphous systems using citric acid as a small molecular excipient were studied for improving physical stability and bioavailability of loratadine, a BCS class II drug with low water solubility and high permeability. Coamorphous loratadine-citric acid systems were prepared by solvent evaporation technique and characterized by differential scanning calorimetry, X-ray powder diffraction, and Fourier transform infrared spectroscopy. Solid-state analysis proofed that coamorphous loratadine-citric acid system (1:1) was amorphous and homogeneous, had a higher T _g over amorphous loratadine, and the intermolecular hydrogen bond interactions between loratadine and citric acid exist. The solubility and dissolution of coamorphous loratadine-citric acid system (1:1) were found to be significantly greater than those of crystalline and amorphous form. The pharmacokinetic study in rats proved that coamorphous loratadine-citric acid system (1:1) could significantly improve absorption and bioavailability of loratadine. Coamorphous loratadine-citric acid system (1:1) showed excellently physical stability over a period of 3 months at 25°C under 0% RH and 25°C under 60% RH conditions. The improved stability of coamorphous loratadine-citric acid system (1:1) could be related to an elevated T _g over amorphous form and the intermolecular hydrogen bond interactions between loratadine and citric acid. These studies demonstrate that the developed coamorphous loratadine-citric acid system might be a promising oral formulation for improving solubility and bioavailability of loratadine.

Preparation of slab-shaped lactose carrier particles for dry powder inhalers by air jet milling

Dry powder inhalers are often formulated by attaching micronized drug particles onto carrier particles, which are generally lactose. In this study, commercially available lactose was air jet milled to produce unique slab-like coarse carrier particles, which have larger and rougher surfaces compared to other commercially available lactose. Two key processing factors, i.e., classifier speed and jet milling pressure, were systematically investigated. The largest fraction of slab-like particles in the resulting powder was obtained at a classifier speed of 3000 rpm. The slab-like coarse carrier particles are expected to exhibit superior performance than commercial lactose due to their unique surface properties.

A study of enhanced ion formation from metal-semiconductor complexes in atmospheric pressure laser desorption/ionization mass spectrometry

The study of the key parameters impacted surface-assisted laser desorption/ionization-mass spectrometry is of broad interest. In previous studies, it has been shown that surface-assisted laser desorption/ionization-mass spectrometry is a complex process depending on multiple factors. In the presented study, we showed that neither porosity, light absorbance nor surface hydrophobicity alone influence the enhancement phenomena observed from the hybrid metal-semiconductor complexes versus individual targets, but small changes in the analyte attaching to the target significantly affect laser desorption ionization-efficiency. By means of Raman spectroscopy and scanning electron microscopy, it was revealed that the formation of an amorphous analyte layer after drying on a solid substrate was essential for the enhanced laser desorption ionization-signal observed from the hybrid metal-semiconductor targets, and the crystallization properties of the analyte appeared as a function of the substrate. Obtained results were used for the screening of regular and lactose-free milk samples through the hybrid metal-semiconductor target. Copyright © 2016 John Wiley & Sons, Ltd.

Molecular Dynamics of Amorphous Sulfamethazine With Structurally Related Sulfonamide Impurities Evaluated Using Thermal Analysis

In this study, the effects of structurally related organic impurities on the molecular dynamics of amorphous sulfamethazine were evaluated using thermal analysis. Sulfanilamide (SNA), sulfamerazine (SMR), and sulfadimethoxine were used as virtual impurities of sulfamethazine. The amorphous state was prepared in situ in differential scanning calorimetry by quenching the melted physical mixtures of sulfamethazine and each impurity compound in the differential scanning calorimetry pan. In the following heating process, the glass transition temperatures (T_g) of each were measured. The fragility parameters were estimated from the width of T_g. The T_g of amorphous sulfamethazine with those impurities changed in accordance with the manner set forth in the Gordon-Taylor equation. The fragility parameter slightly increased when a small amount of SNA or SMR was incorporated. Moreover, the probability of a measurement in which crystallization of sulfamethazine was observed above its T_g, increased at a low-concentration range of SNA, SMR, or sulfadimethoxine. It was considered that the existence of a small amount of impurity would induce heterogeneity in the molecular density of the amorphous state, which would be associated with the local fluctuation. It was suggested that the change in the molecular dynamics would be related to the probability of crystallization of sulfamethazine.

Cocrystallization for successful drug delivery

INTRODUCTION

Cocrystallization is an effective crystal engineering approach for modifying the crystal structure and properties of drugs. The number of examples of solving drug formulation and manufacture problems by cocrystallization is rapidly growing. An updated review that systematically examines the cocrystal research in the context of drug delivery is timely and valuable.

AREAS COVERED

Topics covered in this review include nature of cocrystal, impact of cocrystallization on key pharmaceutical properties (both enhancement and deterioration), cocrystal preparation method and future directions in this field. The focus of this review is on the crystal engineering and pharmaceutical literature in the last 5 years. However, classical literature is also examined when relevant.

EXPERT OPINION

The most effective cocrystal research relies on both in-depth understanding of structure-property relationship and efficient preparation of desired cocrystals. The future cocrystal research will see growth in the areas of designing ternary and higher-order structures, cocrystals between neutral and ionic species, cocrystal polymorphism, cocrystal glasses and thermodynamics of cocrystallization.

Mechanically induced amorphization of drugs: a study of the thermal behavior of cryomilled compounds

The purpose of this work was to determine what aspect of the milled compound influences its thermal profile. For this, six different compounds with different properties were chosen and cryomilled for different times to get an amorphous solid. Differential scanning calorimetry (DSC) and X-ray powder diffraction were used to characterize the material and look at the thermal behavior. Melt-quenched samples were also prepared, and the thermal profile upon milling was determined and correlated with the thermal behavior of the cryomilled samples. Growth rates were determined by hot-stage microscopy. Ketoconazole, when cryomilled, showed only one crystallization exotherm in the DSC profile. Ursodiol, and to some extent indomethacin, initially showed a double exotherm which eventually become a single exotherm on further milling. Griseofulvin, carbamazepine, and piroxicam exhibited a double exotherm in the DSC profile upon cryomilling to the amorphous state. Surface crystal growth rates around T (g) were found to be highest for compounds showing the double exotherm in the DSC. Thus, it was seen that compounds which have high surface crystallization tendency will exhibit the double exotherm during heating.