Drug delivery in the airways by inhalation can be used for local and/or systemic action, depending on the ability of the aerosolized drug to cross the air-blood barrier. For proteins, this is partly conditioned by the drug's molecular weight, as well as aerosol characteristics. This editorial focuses on protein inhalation for topical delivery purposes. Even though systemic applications (such as insulin inhalation) are not considered herein, it is worth noting that systemic diffusion following topical delivery may happen in some cases, and provide therapeutic benefit (as is the case for granulocyte-macrophage colony-stimulating factor (GM-CSF)).

Bacterial respiratory tract infections (RTIs) are increasingly difficult to treat due to evolving antibiotic resistance. In this context, bacteriophages (or phages) are part of the foreseen alternatives or combination therapies. Delivering phages through the airways seems more relevant to accumulate these natural antibacterial viruses in proximity to their bacterial host, within the infectious site. Areas covered: This review addresses the potential of phage therapy to treat RTIs and discusses preclinical and clinical results of phages administration in this context. Recent phage formulation and aerosolization attempts are also reviewed, raising technical challenges to achieve efficient pulmonary deposition via inhalation. Expert opinion: Overall, the inhalation of phages as antibacterial treatment seems both clinically relevant and technically feasible. Several crucial points still need to be investigated, such as phage product pharmacokinetics and immunogenicity. Furthermore, given phage-specific features, appropriate regulatory and manufacturing guidelines will need to be defined. Finally, randomized controlled clinical trials should be carried out to establish phage therapy's clinical positioning in the antimicrobial arsenal against RTIs.