THE IMPORTANCE OF THE INITIAL TREATMENT: Many studies have shown excess mortality during acquired pneumonia with mechanical ventilation when the initial antibiotic treatment is inappropriate, even following subsequent adaptation of the latter. EFFICACY OF TREATMENT: From a clinical point of view, since the regression of the various signs appears after varying time lapses, it is not easy to judge within the first three days the efficacy of an antibiotic. From a microbiological point of view, the bacterial concentrations observed at the time of diagnosis decrease within the first two days, when the response to treatment is favorable. PROBLEMS WITH VANCOMYCIN: Treatment of reference in the case of gram+ germ infections, vancomycin currently fails in 40% of MRSA pneumonias acquired under mechanical ventilation. The probable reason for such failure is an insufficient local concentration, which does not exceed the minimal inhibiting concentration (MIC) of the germ. BETWEEN EFFICACY AND TOLERANCE: The increase in the MIC of vancomycin in the serum and the lungs during acute MRSA acquired under mechanical ventilation may provoke problems in tolerance, notably renal.