Kinetic Barriers to Disproportionation of Salts of Weakly Basic Drugs

Professor Lynne S. Taylor: Scientist, educator, and adventurer

This special edition of the Journal of Pharmaceutical Sciences is dedicated to Professor Lynne S. Taylor (Retter Distinguished Professor of Pharmacy, Department of Industrial and Molecular Pharmaceutics, Purdue University), to honor her distinguished career as a pharmaceutical scientist and educator. The goal of this commentary is to provide an overview of Professor Taylor's career path, summarize her key research contributions, and provide some insight into her personal and professional contributions as an educator, mentor, wife, mother, friend, and adventurer.

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.

Investigation of the Formaldehyde-Catalyzed NNitrosation of Dialkyl Amines: An Automated Experimental and Kinetic Modelling Study Using Dibutylamine

The potential for drug substances and drug products to contain low levels of N-nitrosamines is of continued interest to the pharmaceutical industry and regulatory authorities. Acid-promoted nitrosation mechanisms in solution have been investigated widely in the literature and are supported by kinetic modelling studies. Carbonyl compounds, particularly formaldehyde, which may be present as impurities in excipients and drug product packaging components or introduced during drug substance manufacturing processes are also known to catalyze nitrosation, but their impact on the risk of N-nitrosamine formation has not been systematically investigated to date. In this study, we experimentally investigated the multivariate impact of formaldehyde, nitrite and pH on N-nitrosation in aqueous solution using dibutylamine as a model amine. We augmented a published kinetic model by adding formaldehyde-catalyzed nitrosation reactions. We validated the new kinetic model vs. the experimental data and then used the model to systematically investigate the impact of formaldehyde levels on N-nitrosamine formation. Simulations of aqueous solution systems show that at low formaldehyde levels the formaldehyde-catalyzed mechanisms are insignificant in comparison to other routes. However, formaldehyde-catalyzed mechanisms can become more significant at neutral and high pH under higher formaldehyde levels. Model-based sensitivity analysis demonstrated that under high nitrite levels and low formaldehyde levels (where the rate of formaldehyde-catalyzed nitrosation is low compared to the acid-promoted pathways) the model can be used with kinetic parameters for model amines in the literature without performing additional experiments to fit amine-specific parameters. For other combinations of reaction parameters containing formaldehyde, the formaldehyde-catalyzed kinetics are non-negligible, and thus it is advised that, under such conditions, additional experiments should be conducted to reliably use the model.