Impact of Solid-State Form on the Disproportionation of Miconazole Mesylate

Effect of Physicochemical Properties on the Basic Drug-Acid-Polymer Interactions and Miscibility in PVA Based Orodispersible Films

Salts of weakly basic drugs can partially dissociate in formulations, to give basic drugs and counter acids. The aim of the present study was to clarify the effect of physicochemical properties on the basic drug-acid-polymer interactions and salt-polymer miscibility, and to explain the influence mechanism at the molecular level. Six maleate salts with different physicochemical properties were selected and PVA was used as the film forming material. The relationship between the physicochemical properties and the miscibility was presented with multiple linear regression analysis. The existence state of salts in formulations were determined by XRD and Raman imaging. The stability of salts was characterized by NMR and XPS. The intermolecular interactions were investigated by FTIR and NMR. The results showed that the salt-PVA miscibility was related to polar surface area of salts and Tg of free bases, which represented hydrogen bond interaction and solubility potential. The basic drug-acid-PVA intermolecular interactions determined the existence state and bonding pattern of the three molecules. Meanwhile, the decrease of the stability after formulation increased the number of free bases in orodispersible films, which in turn affected the miscibility with PVA. The study provided references for the rational design of PVA based orodispersible films.

A triclinic polymorph of miconazole

The crystal structure of the new triclinic polymorph of miconazole {MIC; C18H14Cl4N2O; systematic name: (RS)-1-[2-(2,4-di-chloro-benz-yloxy)-2-(2,4-di-chloro-phen-yl)eth-yl]-1H-imidazole} is reported and compared with the monoclinic form of solvent-free miconazole previously reported [Kaspiaruk & Chęcińska (2022 ▸). Acta Cryst. C78, 343-350]. A comparison shows a different orientation of imidazole and one di-chloro-phenyl ring between polymorphic mol-ecules. In the crystal structure of the title compound, only weak halogen bonds and C-H⋯π(arene) inter-actions are found. Hirshfeld surface analysis and energy framework calculations complement the comparison of the two polymorphic forms of the miconazole drug.

Kinetic Barriers to Disproportionation of Salts of Weakly Basic Drugs

Disproportionation is a major issue in formulations containing salts of weakly basic drugs. Despite considerable interest in risk assessment approaches for disproportionation, the prediction of salt-to-base conversion remains challenging. Recent studies have highlighted several confounding factors other than pHmax that appear to play an important role in salt disproportionation and have suggested that kinetic barriers need to be considered in addition to the thermodynamic driving force when assessing the risk of a salt to undergo conversion to parent free base. Herein, we describe the concurrent application of in situ Raman spectroscopy and pH monitoring to investigate the disproportionation kinetics of three model salts, pioglitazone hydrochloride, sorafenib tosylate, and atazanavir sulfate, in aqueous slurries. We found that even for favorable thermodynamic conditions (i.e., pH ≫ pHmax), disproportionation kinetics of the salts were very different despite each system having a similar pHmax. The importance of free base nucleation kinetics was highlighted by the observation that the disproportionation conversion time in the slurries showed the same trend as the free base nucleation induction time. Pioglitazone hydrochloride, with a free base induction time of <1 min, rapidly converted to the free base in slurry experiments. In contrast, atazanavir sulfate, where the free base induction time was much longer, took several hours to undergo disproportionation in the slurry for pH ≫ pHmax. Additionally, we altered an established thermodynamically based modeling framework to account for kinetic effects (representing the nucleation kinetic barrier) to estimate the solid-state stability of salt formulations. In conclusion, a solution-based thermodynamic model is mechanistically appropriate to predict salt disproportionation in a solid-state formulation, when kinetic barriers are also taken into consideration.

The Effect of In-Situ-Generated Moisture on Disproportionation of Pharmaceutical Salt

Pharmaceutical salts are ubiquitously present in the market given their benefits in optimizing the critical properties of an active pharmaceutical ingredient (API). Achieving these benefits requires careful selection and understanding of the salt form of choice. Stability is especially critical here, as salts are susceptible to disproportionation. Several studies have shown the impact of moisture on disproportionation, with more focus on external humidity (moisture coming from outside the system). This work, on the other hand, is systematically designed to study the impact of moisture generated in situ (moisture produced within the system). To that end, an in-house developed compound 1 was selected as our salt API, and its disproportionation was studied in blends (binary and prototype) with hydrated model excipient─trisodium phosphate dodecahydrate (TSPD). TSPD possesses 12 water molecules, which could get released when triggered with enough energy (confirmed by thermogravimetric analysis and humidity studies). As a control for this study, similar blends were prepared with anhydrous trisodium phosphate (TSP), which has comparable properties to TSPD but lacks water. Overall, significant disproportionation was observed in TSPD blends exposed to 40 °C or 70 °C in a closed system; while no disproportionation was observed when the system was left open due to the escape of the moisture generated in situ. The API also remained intact for the blends with anhydrous TSP, as expected. Meanwhile, stressing at 40 °C/75%RH condition resulted in significant disproportionation for both TSPD and TSP blends due to the exposure to external humidity. Hydrated excipients are normally used in drug development, and this work stresses the need for probing the impact from within the system when such excipients are utilized with salt API. This will help fully unravel the overall effect of moisture on the drug, which is relevant downstream when selecting processing conditions, packaging, and so forth.

A comparison of three crystalline forms of miconazole: solvent-free, ethanol monosolvate and hemihydrate

The crystal structures of miconazole {MIC, C18H14Cl4N2O, systematic name (RS)-1-[2-(2,4-dichlorobenzyloxy)-2-(2,4-dichlorophenyl)ethyl]-1H-imidazole}, its ethanol monosolvate (C18H14Cl4N2O·C2H5OH) and its hemihydrate (C18H14Cl4N2O·0.5H2O) were compared. A detailed comparison of the molecular conformation of the miconazole molecules showed a structural similarity of the solvate forms, whereas the unsolvated form is related to the gas-phase structure. This suggests that the molecular conformation of miconazole is influenced by solvent molecules. The crystal architectures of the considered solvatomorphs are differentiated by the intermolecular interactions formed by ethanol and water molecules. The structural studies are enriched by Hirshfeld surface and energy framework analysis. The pairwise model energies of the dominant contacts were estimated to be in the range 20–70 kJ mol−1. It is interesting that the contribution of dispersive forces predominates over the electrostatic forces.

Detecting and Quantifying Microscale Chemical Reactions in Pharmaceutical Tablets by Stimulated Raman Scattering Microscopy

It has been estimated that approximately 50% of all marketed drug molecules are manufactured and administered in the form of salts, often with the goal of improving solubility, dissolution rate, and efficacy of the drug. However, salt disproportionation during processing or storage is a common adverse effect in these formulations. Due to the heterogeneous nature of solid drug formulations, it is essential to characterize the drug substances noninvasively at micrometer resolution to understand the molecular mechanism of salt disproportionation. However, there is a lack of such capability with current characterization methods. In this study, we demonstrate that stimulated Raman scattering (SRS) microscopy can be used to provide sensitive and quantitative chemical imaging of the salt disproportionation reaction of pioglitazone hydrochloride (PIO-HCl) at a very low drug loading (1% w/w). Our findings illuminate a water mediated pathway of drug disproportionation and highlight the importance of noninvasive chemical imaging in a mechanistic study of solid-state chemical reactions.

Applications of Powder X-Ray Diffraction in Small Molecule Pharmaceuticals: Achievements and Aspirations

Since the discovery of X-ray diffraction and its potential to elucidate crystal symmetry, powder X-ray diffraction has found diverse applications in the field of pharmaceutical sciences. This review summarizes significant achievements of the technique during various stages of dosage form development. Improved understanding of the principle involved and development of automated hardware and reliable software have led to increased instrumental sensitivity and improved data analysis. These advances continue to expand the applications of powder X-ray diffraction to emerging research fields such as amorphous systems, mechanistic understanding of phase transformations, and "Quality by Design" in formulation development.