Advances in inhalable nano-formulations

Nano-drug delivery systems offer significant benefits, including high specific surface area, structural and functional diversity, and surface modifiability. When formulated as inhalable nano-formulation, these can not only enable precise pulmonary drug delivery but also improve pulmonary bioavailability and enhance thera-peutic efficacy. Currently, there are four types of inhalable nano-formulations for the treatment of respiratory diseases. Inhalable liquid preparations exhibit facile manufactur-ability and broad applicability yet demonstrate compromised stability during aerosolization. Through structure optimization, surface modification, dispersion medium optimization and device improvement, the atomization stability of nano-drug has been enhanced. Pressurized metered-dose inhalers loaded with nano-drugs face technical challenges: conventional propellants may dissolve nano-carriers, whereas co-solvents like ethanol compromise delivery efficiency. Thus, it is necessary to develop novel propellants that provide thermodynamic stability and optimal delivery performance. Nano-drug formulations in dry powder inhalers exhibit relatively favorable physical stability, however, pulmonary delivery efficiency and nanoparticles integrity during processing remain problematic. Pulmonary delivery efficiency can be improved by employing strategies such as blending excipients to promote the re-dispersibility of nanoparticle agglomerates, optimizing the design of microcarrier, and innovating preparation processes. In contrast, soft mist inhalers are an ideal option for pulmonary delivery of nano-drugs owing to their gentle and efficient atomization properties to maintain nano-drug integrity. This review summarizes the inhalable nano-formulations and focuses on challenges and proposed strategies encoun-tered in integrating nano-drug delivery systems and inhalation drug delivery systems. It aims to provide references for the future development of inhalable nano-formulations.