Treatment of Multiple-Drug-Resistant Gram-Negative Infections
Purpose: The use of colistin for the treatment of infections caused by multiple-drug-resistant (MDR) gram-negative micro-organisms was studied.
Methods: The efficacy of colistin for treating infections caused by MDR gram-negative microorganisms and the development of renal toxicity were studied in hospitalized adult patients in Spain. Patients treated between January 2001 and October 2001 were included.
Results: Over the study period, 71 courses of inhaled colistin, 12 courses of i.v. or intramuscular (i.m.) colistin, and 2 courses of intrathecal colistin were administered to 80 patients. All were infected by MDR organisms: 69 (86%) by Acinetobacter baumannii and 11 (14%) by Pseudomonas aeruginosa. In 41 patients (51%), the episodes were caused by A. baumannii strains susceptible exclusively to colistin. The causative organisms were cleared in 92% of the patients from whom posttreatment repeat specimens were obtained. The in-hospital mortality rate was 18% (14 patients). There were no significant changes in mean serum urea or creatinine concentrations in patients receiving i.v. or i.m. therapy.
Conclusion: Colistin was used in 80 patients infected with A. baumannii or P. aeruginosa and appeared to be efficacious and safe.

The emergence of multiple-drug-resistant (MDR) gram-negative microorganisms, including Pseudomonas aeruginosa and Acinetobacter baumannii, is a major concern worldwide. MDR A. baumannii and P. aeruginosa are important causes of nosocomial infection, and outbreaks of these microorganisms, which are resistant to most available antimicrobial agents, have been reported in burn units, intensive care units (ICUs), cancer centers, and patients with cystic fibrosis. The increased prevalence of these strains has revived interest in the use of colistin as an antibiotic. Although colistin is approved for use in Spain, it is not commercially available and must be obtained from foreign sources.

MDR A. baumannii was responsible for an outbreak of infection in our hospital in 1992, and since then it has continued to be a problem, mainly in the ICUs. Because of the ability of A. baumannii to acquire resistance to multiple antimicrobials, inhaled colistin is now used as an infection-control measure and as empirical treatment when this organism is isolated from tracheobronchial secretions or sputum samples in patients with clinical signs of infection (fever and leukocytosis). The aim of this measure is to avoid the development of pneumonia and spreading of the organism into the bloodstream.

The objective of this study was to study the use of colistin for the treatment of infections caused by MDR gram-negative microorganisms. We collected data on the administration route, causative organisms, and microbiological clearance of the infecting organisms in patients who received colistin therapy. We also determined the frequency of renal toxicity in patients who received colistin by injection.