Clarithromycin and Levofloxacin are essential antibiotics used to treat bacterial infections such as tuberculosis and pneumonia. Lung surfactants may be used as drug carrier of antibiotics directly into the airways. The phospholipid DPPC is a major lipid in commercial lung surfactants and is used to mimic their surface and mechanical properties so that it is a reasonable model. This proposal intends to investigate the structure of DPPC-antibiotics mixed monolayers in order to understand if they are suitable to be used as drug delivery systems in respiratory medicine. The idea is to use neutron reflectometry (NR) to characterize the density, packing, thickness, surface activity, and molecular area of the film at the air-water interface. Also, NR is a suitable technique for the study of interfacial structure, molecular organization and composition of mixed films.