Chromatographic Characterization of Nasal and Inhalation Drug Products: A Review of Liquid Chromatography Strategies for Formulation Assessment, Particle Size Correlation, and In Vitro Performance Testing.

Liquid chromatography (LC) has become indispensable for characterizing nasal and inhalation drug products, yet a critical gap persists in integrating chromatographic data with particle size metrics and in vitro performance outcomes to predict in vivo behavior. This review highlights recent advances in LC strategies from reversed-phase high-performance liquid chromatography to ultrahigh-performance liquid chromatography-tandem mass spectrometry; across three interconnected domains: formulation physicochemical characterization, aerodynamic particle size distribution determination, and comprehensive in vitro performance testing. We critically evaluated how LC-based quantification enables simultaneous active pharmaceutical ingredient and impurity profiling, dissolution kinetics assessment, and regional deposition mapping, with method validation data demonstrating linearity spanning three to four orders of magnitude and limits of detection as low as 5 pg/mL. Notably, we highlighted the mechanistic discrimination of erosion-vs. diffusion-controlled release enabled by simultaneous active pharmaceutical ingredient-polymer dissolution profiling and established quantitative correlations between particle size and systemic bioavailability. The review identified persistent challenges in biorelevant dissolution standardization and device-formulation interaction modeling while proposing integrated frameworks for bioequivalence prediction. This comprehensive perspective positions LC not merely as an analytical tool but as the central bridge connecting formulation properties, aerosol performance, and therapeutic outcomes, offering actionable insights for regulatory evaluation in respiratory drug delivery.