**4.2** *In vivo* **efficacy of inhalable phage dry powder**

Pulmonary delivery of dry powder to small animals is challenging as they cannot inhale powder actively. Intratracheal delivery using a dry powder insufflator, either the commercially available Penn-Century models or custom-made insufflators [62], are commonly employed to introduce powders directly into the lungs of the experimental animals. Chang et al. explored the *in vivo* efficacy of phage powder to treat lung infections caused by MDR *P. aeruginosa* in a mice pneumonia model [63]. After challenging the neutropenic mice with intratracheal administration of the bacterial suspension for 2 h, powder of phage PEV20 was administrated use a Penn-Century dry powder insufflator at a concentration of 2 × 107 pfu/mg. A significant bacterial reduction (5.3 log cfu) was noted after 24 h post-infection accompanies with 1 log phage propagation. The successful treatment outcomes and safety profile from this study warrant further investigation to fully evaluate the therapeutic potential of inhaled phage powder in managing lung infections.
