Inhaled drug delivery: Past, present, and future

Inhaled drug delivery has been an emerging route for the treatment of lung diseases with clear advantages over oral and intravenous routes. However, the delivery efficacy is affected by multiple physiologic barriers including mechanical clearance, mucociliary clearance, macrophage phagocytosis and exhalation lymphatic transport in the respiratory tract. As such, research emphasis has been placed on the development of optimized carriers that could overcome these physiologic barriers via nebulization. In this review, we provided an overview of inhaled drug delivery methods to highlight non-invasive strategies for the treatment of lung diseases. The potential mechanisms of typical lung diseases and the history and development of pulmonary drug delivery methods are reviewed. Strategies to overcome the challenges of inhaled drug delivery methods are further discussed to highlight the advances made so far. Recent progress made on inhaled drug delivery methods based on various carriers are highlighted for the prospective development of pulmonary drug delivery nanoplatforms. We aim to give a systemic overview of inhaled drug delivery methods to promote the development of aerosolized nanomedicines while enabling functional designs for clinical applications, allowing precise and effective therapies against lung diseases.