Systemic antimicrobial therapy of nosocomial pneumonia: monotherapy versus combination therapy.

The treatment of nosocomial pneumonia is difficult because of the absence of a precise microbial etiology in a sizable fraction of cases and the severity of predisposing conditions in patients who develop these infections. Staphylococcus aureus and aerobic gram-negative rods continue to be the most common isolates in these infections. Therapy of nosocomial pneumonia is often empiric, with initial antimicrobial therapy based upon local experience and sensitivity patterns, immune competence of the patient and disease severity. Combination therapy with an aminoglycoside and a beta-lactam has long been the cornerstone of therapy, and clinical success has been correlated with peak serum bactericidal levels of 1:8 in non-granulocytopenic patients and peak gentamicin and tobramycin levels greater than 8 micrograms/ml. The introduction of new broad-spectrum antibiotics, such as monobactams, third-generation cephalosporins and imipenem, has introduced the possibility of monotherapy for the treatment of nosocomial pneumonia. In general, monotherapy has proven to be a useful alternative to combination therapy, with success rates ranging from 77 to 96%. Development of resistance during therapy, particularly by Pseudomonas, Enterobacter and Serratia spp., remains an unresolved problem.