Eradication Therapy against Pseudomonas aeruginosa in Non-Cystic Fibrosis Bronchiectasis

In patients with cystic fibrosis (CF), chronic bronchial Pseudomonas aeruginosa infection is associated with worsening lung function and an increase in morbidity and mortality [1]. Early detection of infection with P. aeruginosa in patients with CF may be important as certain antibiotic treatments have proven useful in preventing or delaying chronic bronchial infection with P. aeruginosa [2]. Although the most effective treatment has yet to be determined, eradication of P. aeruginosa seems more likely using strategies with nebulised antibiotics [3].

Extensive lung disease and severe bronchial obstruction appear to be present on the development of chronic bronchial infection with P. aeruginosa in patients with non-CF bronchiectasis [4]. More hospital admissions [5,6], worse quality of life [5] and a rapid decline in lung function [7] are also more frequent among these patients compared to those with infections with other bacteria. Thus, as occurs in patients with CF, chronic bronchial infection with P. aeruginosa in non-CF is a severe and similar complication. Appropriate antibiotic inhalation therapy for chronic bronchial infection with P. aeruginosa results in a reduction in P. aeruginosa density in sputum and a significant clinical improvement. However, eradication of this microorganism in chronic bronchial infection is not possible [8,9] or very difficult to achieve [10,11,12]. Based on results from CF studies, the British Thoracic Society recommended attempting early eradication of P. aeruginosa with oral ciprofloxacin, and second-line treatment with intravenous or nebulised anti-pseudomonal antibiotics [13]. Nevertheless, to our knowledge no prospective studies have assessed the eradication of P. aeruginosa in non-CF patients after its first isolation in sputum. In fact, recent reviews on inhaled antibiotics for lower airway infections urge to evaluate early eradication of this microorganism in non-CF bronchiectasis [14,15].

The aim of this study was to evaluate the efficacy of a 3-month treatment with nebulised tobramycin following a short course of intravenous antibiotics for the eradication of P. aeruginosa in non-CF bronchiectasis. This prospective study also examines the outcome of this eradication treatment.

A 15-month, single-masked, randomised study was conducted in a tertiary university hospital. Patients were included from March 2006 to March 2009. Thirty-five patients with non-CF bronchiectasis over 18 years of age were recruited after the first isolation of P. aeruginosa in sputum (fig. 1). The diagnosis of bronchiectasis was made by high-resolution chest CT. Sweat tests and blood analyses were negative for the most frequent mutations of CF in Spain [16]. The patients were followed up according to the standard clinical protocol of our institute with analysis of a sputum sample culture approximately every 3 months. The exclusion criteria were: infection with other Gram-negative non-fermenter bacteria, mucoid P. aeruginosa or microorganims resistant to any of the antibiotics used in the study, concomitant use of quinolones, chronic treatment with macrolides, and abnormal kidney and auditory function test results.

When P. aeruginosa was detected, all patients were treated with intravenous ceftazidime and tobramycin for 14 days during the first 4 weeks from initial detection. Tolerance to nebulised tobramycin was tested by hospital pharmacy personnel prior to randomisation which was created by computer-generated random numbers. Treatment assignment was blinded until completion of the study. The patients were instructed as to the preparation and nebulisation technique by the hospital personnel. Following intravenous treatment, one group received 300 mg of nebulised tobramycin (Tobi®), twice daily, for 3 months, while the other group received placebo treatment consisting of a 0.9% sodium chloride solution. A short-acting bronchodilator was administered approximately 1 h before nebulised tobramycin. Inhalation treatment was administered with a jet nebuliser (Pari LC Plus®; Pari, UK) with a high-flow-rate compressor (CR 60; Medic-Aid, UK) which has been demonstrated to be useful for the inhalation of tobramycin (Tobi®) [17]. The guidelines as to the use of nebulisers established by the British Thoracic Society were also met [18]. Both groups were followed up over a 12-month treatment-free period.

During the 3 first months, all patients were controlled monthly and 5, 7, 9, 12 and 15 months thereafter. The number of exacerbations, number of hospital admissions and days of hospitalisation were registered. Supplementary use of oral antibiotics was allowed on the development of an exacerbation, defined as more frequent coughing, greater dyspnoea and an increase in sputum volume and purulence [19]. The decision as to hospital admission was made by a physician from the emergency department who was unaware of the study. Blood and a sputum sample were collected before antibiotic nebulisation at each control as well as in cases of exacerbation or hospital admission. A quantitative bacteriological culture and determination of tobramycin susceptibility were performed. The sputum sample underwent Gram staining [20] and microbiological study. All samples were cultured conventionally in blood agar and McConkey and Saboraud media and semiquantitatively cultured in chocolate agar with a calibrated loop, and more than 10⁶ colony-forming units per millilitre of sample were detected. The microorganisms isolated were identified by standardised or automated means, and the antibiogram was made according to the Kirby-Bauer technique [21]. Forced vital capacity (FVC), forced respiratory volume in the first second (FEV₁) - both performed according to the criteria of the American Thoracic Society [22] - PO₂ and PCO₂ were tested at the beginning and the end of the study. Auditory acuity measures in both ears at frequencies between 500 and 8,000 Hz [23] and St. George's Respiratory Questionnaire [24] were also performed.

For demographic purposes, the results are expressed as means and standard deviations. The paired Student t test was used to compare means (Mann-Whitney U test, when necessary). The χ² test (Fisher's exact test, when appropriate) was used to compare proportions. Statistical analysis was performed using the SPSS software package version 18.0 (SPSS Inc., USA). For single-outcome comparisons, the treatment effect was considered significant with p values ≤0.05.

The study was approved by the institutional Ethics Committee of the Hospital Universitari Vall d'Hebron (Comitè Ètic d'Investigació Clínica; No. 156/2005). Written informed consent was obtained from all the patients included in the study.

The 35 patients included in the study were distributed into two groups, without any statistical difference between them in any of clinical characteristics at the beginning of the study and after the intravenous and before the nebulisation treatment (table 1). Five patients withdrew due to bronchospasm during the first month of the inhaled tobramycin treatment. These patients had a worse - albeit not statistically significant (p = 0.052) - FEV₁ than the remaining 30 study patients (table 2). Two other patients from the placebo group abandoned the study during the first month.

The proportion of patients free of P. aeruginosa in the first month was 90.9% in the tobramycin group and 76.5% in the placebo group; these values were 54.5 and 29.4%, respectively, at the end of the study. Figure 2 shows the statistically significant cumulative rate of colonisation with P. aeruginosa in the two groups (p = 0.048).

The number of exacerbations and the number and days of hospital admissions were significantly lower in the tobramycin than in the placebo group. The period of antibiotic use (oral, parenteral) in days was longer in the placebo group, but without statistical significance (p = 0.052). A global - albeit not statistically significant - trend to improvement was shown in most of the other parameters studied in the tobramycin inhalation group on comparison with the placebo group. Thus, no significant differences were achieved in the mean change from enrolment to the end of the study period in white blood cell count, erythrocyte sedimentation rate, C-reactive protein level, FEV₁, FVC, PO₂ and PCO₂ (table 3) or in the scores on the four scales of the quality-of-life questionnaire (table 4).

Tobramycin-resistant P. aeruginosa was not detected in sputum during the study. However, other opportunistic organisms were identified in sputum cultures of 2 patients in the tobramycin group [Stenotrophomonas maltophilia (1 patient); Achromobacter xylosoxidans and Pseudomonas putida (1 patient)] and in sputum cultures of 6 patients in the placebo group [Pseudomonas fluorescens (1 patient); S. maltophilia (2 patients); Aspergillus spp. and Nocardia spp. (1 patient); S. maltophilia, Aspergillus spp. and Comamonas spp. (1 patient); Achromobacter anthropi and S. maltophilia (1 patient)].

No auditory acuity changes were found in either group. Serum creatinine concentrations remained within the normal range throughout the study period in all patients.

This study was based on the assumption that chronic bronchial infection with P. aeruginosa in non-CF bronchiectasis is preceded by a period of first and intermittent infection similar to what occurs in CF [2], and that this microorganism might be eliminated by appropriate antibiotic treatment. Thus, chronic bronchial infection with P. aeruginosa, one of the most unfavourable events in non-CF bronchiectasis patients [5,6,7], might be avoided or, at least, delayed. To our knowledge, this is the first randomised, placebo-controlled study to provide evidence that early eradication therapy of P. aeruginosa in non-CF bronchiectasis may be effective.

Many therapeutic options in non-CF bronchiectasis have arisen from the management of patients with CF. However, evidence of benefit in the CF population [25] does not always translate into equivalent benefits in the different non-CF bronchiectasis populations [26]. In this study we have shown that 3 months of nebulised tobramycin after 15 days of intravenous tobramycin and ceftazidime is effective in eradicating P. aeruginosa in non-CF bronchiectasis patients after the first isolation of this microorganism in sputum. We did not include patients with mucoid P. aeruginosa, since, in comparison with non-mucoid P. aeruginosa, this phenotype imposes a barrier to antibiotics, reduces the bioactivity of aminoglycosides [27] and is, consequently, associated with a lower percentage of success in eradication treatment [28]. Antibiotic therapy in the present study led to eradication of P. aeruginosa in 90.9% of the patients at the first month, with clearance being maintained in 54.5% of the cases at 15 months. These eradication rates are similar to the 80% initially observed and the 54.2% at 14.3 months in a recent retrospective study with different antibiotic treatment regimes combined with 3 months of nebulised colistin in non-CF bronchiectatic patients [29]. Both in the previous [29] and in our study, numbers dropped off quite quickly at early stages, and then a certain plateau was reached. We do not know if a longer nebulised antibiotic treatment might be helpful to keep the P. aeruginosa eradication reached just after this therapy. Studies on the treatment of initial infection with P. aeruginosa in CF have described differences in the duration of eradication according to the patient selection criteria, treatment regimens and outcome measures [2]. However, long-term eradication rates in this disease [30,31,32,33,34] seem to be greater than those obtained in the patients with non-CF bronchiectasis in our study. Some potential factors may explain the differences in the efficacy of eradicating P. aeruginosa from the airways in these two populations. In non-CF bronchiectatic patients, infection with P. aeruginosa occurs in those with more severe lung disease and bronchial obstruction [4]. Thus, on one hand, greater lung inflammation and/or lung tissue injury may limit the ability to eradicate P. aeruginosa, while, on the other hand, with the presence of greater airway obstruction, the distribution of an aerosolised antibiotic may be reduced and the drug may not be able to reach the site of infection. Moreover, it has been shown that the clearance of tobramycin from the lower airways of younger CF patients may be slower, which could further favour the eradication of P. aeruginosa in this population [35].

Our study demonstrates that antibiotic eradication treatment has a notable clinical impact, with a significant reduction in exacerbations and days and numbers of admissions as well as a trend to improvement in all the other parameters studied being observed in patients receiving this therapy. In contrast, compelling evidence of a clinical benefit in CF with early intervention is very scarce [3], and it has been suggested that young CF patients with early infection with P. aeruginosa often have minimal symptoms and mild lung disease, which may lead to insensitive outcome measures [35].

The timing of the administration of antimicrobial therapy may be critical as there may be a window of opportunity after which antibiotic eradication treatment is no longer successful. Although patients in our study received therapy after the detection of the first positive culture, they may have already been infected prior to the visits carried out every 3 months, thereby delaying the initiation of treatment. Chronic bronchial infection in CF and the presence of chronic P. aeruginosa in sputum specimens have been defined as an increase in specific serum antibodies [36]. The presence of these antibodies has been used to identify individuals with CF who fail to clear P. aeruginosa [37] and even to exclude patients from antibiotic eradication treatment [31]. In non-CF bronchiectasis specific serum antibodies to P. aeruginosa are present, similar to what occurs in patients with CF [6]. Thus, it is reasonable to assume that these antibodies may also be used to better select non-CF bronchiectatic patients who may be candidates for receiving this treatment.

Nebulised tobramycin therapy had to be discontinued due to bronchospasm in 5 patients in whom FEV₁ was especially poor, suggesting that the risk of this complication should be considered in patients with low FEV₁ values [9]. No abnormalities in serum creatinine or audiometry were observed in our study, which supports the high safety margin and absence of nephrotoxicity and ototoxicity in the inhaled antibiotic [7,8,9]. The emergence of tobramycin-resistant P. aeruginosa was not observed, neither was a higher rate of other opportunistic microorganisms in patients treated with tobramycin inhalation solution compared to those receiving placebo. Moreover, our results suggest that nebulised tobramycin could even reduce other opportunistic organisms, since they were detected less often in patients in the tobramycin group than in the placebo group. In fact, Murray et al. [12] showed that long-term nebulised gentamicin in patients chronically infected with P. aeruginosa or other pathogens could be useful for eradicating not only P. aeruginosa but also these other microorganisms.

According to the overall results of our study, and taking in account the significantly lower costs for this treatment compared to those needed to treat chronically infected CF patients [38], eradication treatment for P. aeruginosa in patients with non-CF bronchiectasis may be recommended. The use of additional systemic therapy, as performed in our study, might be justified, since more severe airway obstruction and disease related to non-CF bronchiectasis may not allow inhaled antibiotics to reach all areas, thereby reducing the probability of eradication. Moreover, monotherapy with a nebulised antibiotic has demonstrated a success rate similar to that seen with combination therapy in CF [2], and a 3-month treatment period has also been shown to provide additional benefit to other shorter regimens [39] and may, thus, be suitable for patients with non-CF bronchiectasis. Further studies including a larger number of patients and longer follow-up would most likely improve the results of our study.

The authors wish to thank Rosa Llòria for editorial assistance and manuscript preparation.

EU Clinical Trial Register No. 2005-005820-15.