Intra-tracheal administration to mice by the Penn Century MicroSprayerR Aerosolizer of rhodamine-labeled mhLYS showed that the distribution among lung lobes was asymmetric (rhodamine was always found only in 1 or 2 lobes of the right lung) and heterogeneous suggesting that a poor distribution may have contributed to low safety and efficacy showed by CAMP-RPs. Moreover, we produced NEM whose properties are well suited for the direct administration to bronchi/bronchioles of colistin, a model CAMP. Similarly to the results obtained using the aerosolizer, the distribution by a special insufflator of the fluorescently-labeled CAMP-RP in lung lobes was asymmetric and heterogeneous. Our results suggest that intra-tracheal administration of powders in mice requires further improvement before it is possible to perform a reliable efficacy test in vivo.