Lower respiratory tract infections (LRTI) are commonly classified as either bronchitis or pneumonia, and these infections are associated with an extremely high morbidity in the community, as well as a high mortality in those patients that require hospitalisation. Therefore, such infections place a huge burden, both economically and as a user of health services, on the entire health care system. The antibiotic treatment of community-acquired pneumonia caused by gram-negative organisms or staphylococci is controversial, and these organisms may cause one-third of the cases of community-acquired pneumonia. Nosocomial pneumonia is caused even more often by gram-negative bacteria, and as such the development of rational and effective antibiotic therapy to cover these organisms is very important.