Prolonged efficiency of secondary prophylaxis with colistin aerosols for respiratory infection due to Pseudomonas aeruginosa in patients infected with human immunodeficiency virus

Pseudomonas aeruginosa: Infections, Animal Modeling, and Therapeutics

Pseudomonas aeruginosa is an important Gram-negative opportunistic pathogen which causes many severe acute and chronic infections with high morbidity, and mortality rates as high as 40%. What makes P. aeruginosa a particularly challenging pathogen is its high intrinsic and acquired resistance to many of the available antibiotics. In this review, we review the important acute and chronic infections caused by this pathogen. We next discuss various animal models which have been developed to evaluate P. aeruginosa pathogenesis and assess therapeutics against this pathogen. Next, we review current treatments (antibiotics and vaccines) and provide an overview of their efficacies and their limitations. Finally, we highlight exciting literature on novel antibiotic-free strategies to control P. aeruginosa infections.

Inhaled Antibiotics for Gram-Negative Respiratory Infections

Gram-negative organisms comprise a large portion of the pathogens responsible for lower respiratory tract infections, especially those that are nosocomially acquired, and the rate of antibiotic resistance among these organisms continues to rise. Systemically administered antibiotics used to treat these infections often have poor penetration into the lung parenchyma and narrow therapeutic windows between efficacy and toxicity. The use of inhaled antibiotics allows for maximization of target site concentrations and optimization of pharmacokinetic/pharmacodynamic indices while minimizing systemic exposure and toxicity. This review is a comprehensive discussion of formulation and drug delivery aspects, in vitro and microbiological considerations, pharmacokinetics, and clinical outcomes with inhaled antibiotics as they apply to disease states other than cystic fibrosis. In reviewing the literature surrounding the use of inhaled antibiotics, we also highlight the complexities related to this route of administration and the shortcomings in the available evidence. The lack of novel anti-Gram-negative antibiotics in the developmental pipeline will encourage the innovative use of our existing agents, and the inhaled route is one that deserves to be further studied and adopted in the clinical arena.

A retrospective study on the effects of colistin therapy in children with multidrug-resistant Gram-negative bacterial pathogens: impact of HIV status on outcome

BACKGROUND

Nosocomially acquired multidrug-resistant (MDR) Gram-negative bacteria are important contributors to paediatric intensive care unit (PICU) mortality and morbidity, with limited treatment options.

AIM

To investigate the outcomes of all children treated with colistin for infection with MDR Gram-negative bacteria while admitted to PICU.

METHODS

Retrospective observational study of 19 months. Primary endpoints were all-cause intensive care unit mortality and safety. Secondary endpoints evaluated clinical and microbiological outcomes. Cases were stratified according to HIV status.

RESULTS

Twenty-seven children received 30 colistin courses during the study period. Eight patients (29.6%) were HIV infected, six (22.2%) were HIV uninfected but exposed, and 11 (40.7%) were HIV uninfected and unexposed. Common MDR Gram-negative bacteria cultured were: Acinetobacter species (n=22, 81.5%), Pseudomonas aeruginosa (n=11, 40.7%) and Klebsiella pneumoniae (n=7, 25.9%). Mortality was 37%, with no significant difference between HIV strata. No adverse drug reactions were noted. A composite clinical improvement was noted in 16 courses (53.3%) of colistin. Only 30% of colistin courses used in HIV-infected children resulted in an improved clinical assessment as compared with 83.3% of courses in HIV-uninfected/unexposed children (p=0.04). In HIV-infected children, five of 10 (50%) courses of colistin showed bacteriological clearance compared to the HIV uninfected/unexposed group where all cases showed bacterial eradication (p=0.02).

CONCLUSIONS

HIV-infected children had poorer clinical and bacteriological responses to colistin treatment than HIV uninfected/unexposed. These results require confirmation with prospective studies to determine whether findings are due to poor microbial response, immunodeficiency or repeated reinfections.

Salvage treatment of pneumonia and initial treatment of tracheobronchitis caused by multidrug-resistant Gram-negative bacilli with inhaled polymyxin B

Systemic colistin has shown efficacy against multidrug-resistant Pseudomonas aeruginosa and Acinetobacter spp., but it has presented poor results in pneumonia. Aerosolized polymyxin in cystic fibrosis patients has had good results. In this study, inhaled polymyxin B was used to treat respiratory infections by multidrug-resistant Gram-negative bacilli (MR-GNBs). Nineteen patients were treated with inhaled polymyxin B: 14 pneumonia, most of which had previously failed treatment with intravenous polymyxin B, and 5 tracheobronchitis. Inhaled polymyxin B was given at the dose of 500,000 IU twice a day after an aerosolized beta(2)-agonist. In pneumonia, inhaled and intravenous polymyxin B was given together. Median age was 69 years; 89% were in the intensive care unit. Sixteen infections (84%) were caused by P. aeruginosa. Klebsiella pneumoniae, Alcaligenes xylosoxidans, and Burkholderia sp. caused one infection each. In the 14 pneumonia cases, median of previous use of intravenous polymyxin B was 20 days (range, 0-32). Inhaled polymyxin B was used for a mean of 14 days (range, 4-25). Cure occurred in 10 (53%) patients, improvement in 8 (42%), and failure in 1. Nine patients died during hospitalization (all with pneumonia). Adverse events occurred in 4 patients without interruption of inhalation. This is the largest report using inhaled polymyxin B to treat nosocomial pneumonia by MR-GNB that had failed intravenous polymyxin B. It was also effective alone in P. aeruginosa tracheobronchitis.

Aerosolized colistin for the treatment of nosocomial pneumonia due to multidrug-resistant Gram-negative bacteria in patients without cystic fibrosis

INTRODUCTION

The clinical and economic consequences of the emergence of multidrug-resistant Gram-negative bacteria in the intensive care unit (ICU) setting, combined with the high mortality rate among patients with nosocomial pneumonia, have stimulated a search for alternative therapeutic options to treat such infections. The use of adjunctive therapy with aerosolized colistin represents one of these. There is extensive experience with use of aerosolized colistin by patients with cystic fibrosis, but there is a lack of data regarding the use of aerosolized colistin in patients without cystic fibrosis.

METHODS

We conducted the present study to assess the safety and effectiveness of aerosolized colistin as an adjunct to intravenous antimicrobial therapy for treatment of Gram-negative nosocomial pneumonia. We retrospectively reviewed the medical records of patients hospitalized in a 450-bed tertiary care hospital during the period from October 2000 to January 2004, and who received aerosolized colistin as adjunctive therapy for multidrug-resistant pneumonia.

RESULTS

Eight patients received aerosolized colistin. All patients had been admitted to the ICU, with mean Acute Physiological and Chronic Health Evaluation II scores on the day of ICU admission and on day 1 of aerosolized colistin administration of 14.6 and 17.1, respectively. Six of the eight patients had ventilator-associated pneumonia. The responsible pathogens were Acinetobacter baumannii (in seven out of eight cases) and Pseudomonas aeruginosa (in one out of eight cases) strains. Half of the isolated pathogens were sensitive only to colistin. The daily dose of aerosolized colistin ranged from 1.5 to 6 million IU (divided into three or four doses), and the mean duration of administration was 10.5 days. Seven out of eight patients received concomitant intravenous treatment with colistin or other antimicrobial agents. The pneumonia was observed to respond to treatment in seven out of eight patients (four were cured and three improved [they were transferred to another facility]). One patient deteriorated and died from septic shock and multiple organ failure. Aerosolized colistin was well tolerated by all patients; no bronchoconstriction or chest tightness was reported.

CONCLUSION

Aerosolized colistin may be a beneficial adjunctive treatment in the management of nosocomial pneumonia (ventilator associated or not) due to multidrug-resistant Gram-negative bacteria.

Treatment of nosocomial pneumonia and tracheobronchitis caused by multidrug-resistant Pseudomonas aeruginosa with aerosolized colistin

Gram-negative bacilli including multidrug-resistant (MDR) Pseudomonas aeruginosa are responsible for a significant proportion of episodes of nosocomial pneumonia. Since the development of new antibiotics with activity against gram-negative organisms has not kept pace with the increase in prevalence of MDR pathogens, there has been renewed interest in antimicrobial agents that had previously been used but had been abandoned because of toxic side effects. This report describes three patients with nosocomial pneumonia or tracheobronchitis due to multiresistant strains of P. aeruginosa for whom aerosolized colistin proved beneficial as supplemental therapy. Aerosolized colistin merits further consideration as a therapeutic intervention for patients with pulmonary infections due to MDR P. aeruginosa.