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Amorphization is a powerful approach for improving the aqueous solubility and bioavailability of poorly water-soluble compounds. However, it can cause chemical and physical instability, the latter of which can lead to crystallization during storage, diminishing the solubility advantage of the amorphous state. As there is no standard method for predicting the physical stability of amorphous materials, a long-term stability study is needed in drug development. This study investigated the correlation between the physical stability of amorphous compounds and molecular mobility based on the assumption that physical stability is governed by the diffusional motion of a molecule. Model compounds were evaluated for crystallization onset time, structural relaxation time, fragility, and fictive temperature. The crystallization onset time of acetaminophen glass correlated with its relaxation time calculated from the Adam-Gibbs-Vogel equation; however, that of felodipine glass correlated with the relaxation time calculated from the Vogel-Tammann-Fulcher equation. The different crystallization tendencies of these compounds can be explained by the differences in the rate limiting steps in their crystallization processes, indicating the importance of distinguishing the critical process associated with crystallization. These findings will be useful for more accurate prediction of long-term physical stability of amorphous materials.

N -nitrosodimethylamine (NDMA) contamination in several drugs has been reported since 2018, and there is also a potential risk of the NDMA contamination in various other drug substances and their pharmaceutical products. To quantitate NDMA in various drugs having diverse physicochemical properties, a specific, sensitive and durable analytical method is required, in addition to methods that can be applied to a class of nitrosamines. We aimed to develop an off-line isolation method for NDMA in drug substances using solid-phase extraction (SPE) for quantification using high-performance liquid chromatography (HPLC)–atmospheric pressure chemical ionization (APCI)–tandem mass spectrometry (MS/MS).Impediments to accurate quantitation of NDMA in drug substances using LC–MS/MS and insufficient durability of the system is due to the extremely large amounts (≈ 10 8 times) of active pharmaceutical ingredients (APIs) in sample solutions in comparison to the trace amount of NDMA. It is occasionally possible to encounter a reduced retention of NDMA and/or decreased separation from other substances in LC, matrix effect in MS detection, and undesirable contamination of instruments with API and other substances, which consequently results in deterioration of system performance and generation of unreliable data even in the cases where divert valve is configured between the column and ion source of the MS instrument.To address the problems, an off-line isolation methodology for NDMA from APIs having diverse physicochemical properties, namely ranitidine hydrochloride (ranitidine), metformin hydrochloride (metformin), nizatidine, valsartan, and telmisartan , was developed. The applicability of the method was confirmed by batch analysis of metformin and ranitidine. Furthermore, contrary to previous reports, NDMA was found to be stable over a wide pH range. The methodology and information would contribute the control of NDMA concentration in various drugs to realize the safe delivery of pharmaceuticals to patients.

N-Nitrosodimethylamine (NDMA) has been detected in some drug substances and pharmaceutical products containing sartans, ranitidine and metformin, and a potential risk of NDMA contamination exists in other drug substances and their pharmaceutical products. To quantitate NDMA in various drugs having diverse physicochemical properties, a specific, sensitive, and reliable analytical method is required, in addition to methods that can be applied to a class of nitrosamines. We aimed to develop an off-line isolation method for NDMA in drug substances using SPE for quantification with LC-APCI-MS/MS. Impediments to accurate quantitation of NDMA in drug substances using LC-MS/MS and insufficient durability of the system are attributed to the extremely large amounts of active pharmaceutical ingredients (APIs) in sample solutions in comparison to the trace amount of NDMA. A reduced retention of NDMA and/or decreased separation from other substances in LC, matrix effect in MS detection, and undesirable contamination of instruments with API and other substances may be occasionally encountered, all of which consequently result in deterioration of system performance and generation of unreliable data, even in the cases where a divert valve is configured between the column and ion source of the MS instrument. To address these problems, an off-line NDMA isolation methodology from APIs exhibiting diverse physicochemical properties, namely ranitidine hydrochloride (ranitidine), metformin hydrochloride (metformin), nizatidine, valsartan, and telmisartan, was developed. The applicability of the method was confirmed by batch analysis of metformin and ranitidine. Furthermore, contrary to previous reports, NDMA was found to be stable over a wide pH range. The proposed methodology and data from this study would contribute to the control of NDMA contamination in various drugs to realize the safe delivery of pharmaceuticals to patients.

A non-destructive discrimination method for crystals in solid dosage drug forms was first developed using a combination of Raman spectroscopy and X-ray micro-computed tomography (X-ray CT). Identification of the crystal form of an active pharmaceutical ingredient (API) at the appropriate pharmaceutical dosage is crucial, as the crystal form is a determinant of the quality and performance of the final formulation. To develop a non-destructive analytical methodology for the discrimination of solid API crystals in a solid dosage form, we utilized a combination of Raman spectroscopy and X-ray CT to differentiate between ranitidine crystal polymorphs (forms 1 and 2) in tablet formulations containing three excipients. The difference in electron density correlated with the true density between ranitidine polymorphs, thereby enabling the discrimination of crystal forms and visualization of their three-dimensional spatial localization inside the tablets through X-ray CT imaging. Furthermore, X-ray CT imaging revealed that the crystal particles were of varying densities, sizes, and shapes within the same batch. These findings suggest that X-ray CT is not only an imaging tool but also a unique method for quantitative physicochemical characterization to study crystal polymorphs and solid dosage forms.

Amorphous nifedipine (NFD), which has a smooth surface immediately after preparation, was shown to have structures resembling clusters of curling and branching fibers approximately 1 μm wide by atomic force microscopy (AFM) after storage at 25°C. The size of the cluster‐like structures increased with storage over time, implying crystal growth. The average elongation rate of the fibers determined by AFM at ambient room temperature was 1.1 × 10 −9 m/s, and this agreed well with the crystal growth rate of 1.6 × 10 −9 m/s determined by polarized light microscopy. The crystal growth rate of NFD in solid dispersions with 5% polyethylene glycol (PEG) was found to be 5.0 × 10 −8 m/s by AFM. Although this value was approximately the same as that obtained by polarized light microscopy, three‐dimensional information obtained by AFM for the crystallization of NFD in a solid dispersion with PEG revealed that the changes in topography were not a consequence of surface crystal growth, but rather attributable to the growth of crystals formed in the amorphous bulk. For solid dispersions with α,β‐poly(N‐5‐hydroxypentyl)‐l‐aspartamide, acceleration of NFD crystallization by tapping with an AFM probe was observed. The present study has demonstrated the feasibility and application of AFM for interpretation of surface crystallization data. © 2011 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:4413–4420, 2011

To clarify the contribution of drug-polymer interaction to the physical stability of amorphous solid dispersions, we studied the crystallization rates of nitrendipine (NTR) enantiomers with identical physicochemical properties in the presence of hydroxypropylmethylcellulose (HPMC), hydroxypropylmethylcellulose phthalate (HPMCP) and polyvinylpyrrolidone (PVP). The overall crystallization rate at 60°C and the nucleation rate at 50-70°C of (+)-NTR were lower than those of (-)-NTR in the presence of 10-20% HPMC or HPMCP. In contrast, similar crystallization profiles were observed for the NTR enantiomers in solid dispersions containing PVP. The similar glass transition temperatures for solid dispersions of (-)-NTR and (+)-NTR suggested that the molecular mobility of the amorphous matrix did not differ between the enantiomers. These results indicate that the interaction between the NTR enantiomers and HPMC or HPMCP is stereoselective, and that differences in the stereoselective interaction create differences in physical stability between (-)-NTR and (+)-NTR at 50-70°C. However, no difference in physical stability between the enantiomers was obvious at 40°C. Loss of the difference in physical stability between the NTR enantiomers suggests that the stereoselective interaction between NTR and the polymers may not contribute significantly to the physical stabilization of amorphous NTR at 40°C.

The relative influences of chemical activation energy and molecular mobility in determining chemical reactivity were evaluated for insulin lyophilized with α,β-poly( N -hydroxyethyl)- L -aspartamide (PHEA), and compared with that for insulin lyophilized with trehalose, which had been found to have the ability to decrease the molecular mobility of insulin at low humidity. The ratio of the observed rate constant k obs to the chemical activation energy-controlled rate constant k act ( k obs / k act ) at glass transition temperature ( T g ) was estimated to be approximately 0.6 and 0.8 at 6% RH and 12% RH, respectively, indicating that the degradation rate is significantly affected by molecular mobility at lower humidity conditions. However, these k obs / k act values at T g were larger than those for the insulin-trehalose system, and changes in the temperature-dependent slope around T g were less obvious than those for the insulin-trehalose system. Thus, the contribution of molecular mobility to the degradation rate in the insulin-PHEA system appeared to be less intense than that in the insulin-trehalose system. The subtle change in the temperature-dependent slope around T g observed in the insulin-PHEA system brought about a significant bias in shelf-life estimation when the reaction rate was extrapolated from temperatures above T g according to the Arrhenius equation.

The purpose of this study is to confirm the speculation which arose in our previous study that the degradation rate of insulin lyophilized with poly(vinylpyrrolidone) is mainly governed by the chemical activational barrier rather than molecular mobility. This speculation was based on the degradation data of insulin lyophilized with poly(vinylpyrrolidone) K-30 (PVP K-30), which was obtained at temperatures well below the glass transition temperature ( T g ). In this study, the degradation rate of insulin at temperatures below and above T g was determined using PVP 10k as an excipient, instead of PVP K-30, in order to examine whether or not the temperature dependence of the degradation rate changes around T g . The relative contributions of molecular mobility and the activational barrier, calculated from the temperature- and T g -dependence of the degradation rate, indicated that the contribution of molecular mobility to the degradation rate was negligible. Furthermore, the negligible contribution of molecular mobility was confirmed by the lack of significant change observed in the temperature- and T g -dependence of the rate around T g .