Treatment of Pseudomonas and Staphylococcus Bronchopulmonary Infection in Patients with Cystic Fibrosis

The optimal antibiotic regimen is unclear in management of pulmonary infections due to pseudomonas and staphylococcus in cystic fibrosis (CF). We systematically searched all the published literature that has considered the evidence for antimicrobial therapies in CF till June 2013. The key findings were as follows: inhaled antipseudomonal antibiotic improves lung function, and probably the safest/most effective therapy; antistaphylococcal antibiotic prophylaxis increases the risk of acquiring P. aeruginosa; azithromycin significantly improves respiratory function after 6 months of treatment; a 28-day treatment with aztreonam or tobramycin significantly improves respiratory symptoms and pulmonary function; aztreonam lysine might be superior to tobramycin inhaled solution in chronic P. aeruginosa infection; oral ciprofloxacin does not produce additional benefit in those with chronic persistent pseudomonas infection but may have a role in early or first infection. As it is difficult to establish a firm recommendation based on the available evidence, the following factors must be considered for the choice of treatment for each patient: antibiotic related (e.g., safety and efficacy and ease of administration/delivery) and patient related (e.g., age, clinical status, prior use of antibiotics, coinfection by other organisms, and associated comorbidities ones).


Background
Cystic fibrosis (CF) is the most frequent life-threatening congenital disease in Caucasians. Airway colonization with pathogens like P. aeruginosa and S. aureus belongs to the primary reasons for premature death in patients with CF and antibiotic treatment is a primary reason for improvement of life expectancy within the last decades in patients treated with aggressive antimicrobial regimes [1]. Thereby, CF patients in middle Europe and the US did not reach school age some decades ago, and now CF patients in these countries survive for about 40 years by mean [1]. Therefore the question to optimize antibiotic treatment is a crucial issue in CF care and, basically, the approach of a survey on evidence based antimicrobial therapy in CF can give some-but possibly limited-answers to this basal question. The objective of this systematic review is to summarize the available evidence on the use of antibiotics for the treatment of patients with CF infected by P. aeruginosa and S. aureus (MSSA, MRSA). We aim to include randomized trials (RCTS) mainly, but if we find no RCT for any of the outcome, we will discuss the observational studies.

cystic fibrosis) AND infection (pseudomonas OR Staphylococcus) AND (clinical trial, randomized controlled trial) AND (pneumonia OR lower respiratory tract infection) AND (child OR children OR infant OR paediatric OR pediatric OR adult).
Two independent reviewers reviewed the search results to identify relevant original human clinical trials. Additional studies were identified through manual searches of reference lists of the originally identified studies as well as reviews on the subject. No language restrictions were applied.

Study Selection.
Trials were selected if they used any route for administration of antibiotics for the eradication, prophylaxis, and/or treatment of either P. aeruginosa and/or S. aureus in patients with CF of any age and both sexes, treatment allocation was randomized or quasirandomized, and there was a control group (placebo or another inhaled antibiotic) and studied clinical (with or without microbiological) parameters. Trials only reporting microbiological parameters were excluded. In case there was no RCT for an important outcome, we considered observational studies if available.

Search Results.
A Cochrane Library (CENTRAL) search using the term "antibiotics" and filter "Record Title" yielded 26 Cochrane Systematic Reviews (CSR) and 1 protocol, 15 other (systematic) reviews, and 124 clinical trials. Simultaneous PUBMED search using the above search terms yielded 178 trials. Hand searching of the bibliography of relevant citations yielded an additional 32 papers that were retrieved and examined.

Results
After applying above exclusion criteria (under study selection), removing the duplicates, and excluding review papers, 208 references were obtained. These were reviewed again in order to determine if they met the selection criteria. One hundred and seventy-four references were discarded: 77 were not randomized/quasirandomized (for an outcome with already existing RCTs), 38 on patients without CF, 21 substudies, 19 pharmacokinetic studies, 12 pharmacodynamic studies, 10 in vitro studies, and 7 pharmacoeconomic studies. Finally, 24 RCTs (P. aeruginosa = 21; S. aureus = 3), and 10 observational studies (P. aeruginosa = 3; S. aureus = 7) were included in the present review. Please also refer to Tables 1-6 for characteristics of the studies and summarization of key results. First, the antibiotic strategy about eradication of first or new airway colonization and treatment of chronically persistent airway colonization with P. aeruginosa will be discussed followed by the strategy for chronic suppressive therapy and eradication of S. aureus (both MSSA and MRSA).

Pseudomonas aeruginosa.
Individuals with cystic fibrosis (CF) whose respiratory tract is colonized with P. aeruginosa have as a group increased pulmonary disease, a more rapid decline in pulmonary function and a decreased survival to adulthood. Studies have shown that antibiotic therapy initiated shortly after a new detection of P. aeruginosa is effective in preventing or delaying the onset of chronic infection. Antibiotics administered via parenteral, inhaled, and oral routes are efficacious; however, the optimal regimen and duration of therapy remain unclear. Inhaled antibiotics are an attractive option, delivering high concentrations of antibiotic directly to the infection site while minimizing systemic exposure. In the present review, we will discuss evidence based antimicrobial therapy of P. aeruginosa in two parts: first part consisting of eradication of first or new air way colonization and the second part consisting of treatment of chronically persistent airway colonization.

Eradication of First or New
Airway Colonization with P. aeruginosa. The effectiveness of the various antibioticregimes in eradicating early P. aeruginosa requires careful evaluation. There are many P. aeruginosa eradication protocols which utilize inhaled/nebulized or intravenous (iv) antipseudomonal antibiotics with or without oral antibiotics. These regimens are discussed below.

Tobramycin (Inhaled) versus Placebo or Other Antibiotics.
A Cochrane review (CR) [36] including 2 RCTs [37,38], and another new RCT [39] were analyzed. Evidence from two trials [37,38] showed treatment of early P. aeruginosa infection with inhaled tobramycin results in microbiological eradication of theorganism from respiratory secretions more often than placebo (OR 0.15 (95% CI 0.03 to 0.65)) and that this effect may persist for up to 12 months. In a recent trial [39], 58 patients with median age of 9 years were randomized to treatment with tobramycin inhalation solution (TIS) for 28 days or inhaled sodium colistimethate (2 × 2 million units/d) plus oral ciprofloxacin (30 mg/kg/day) for 3 months (CC). The authors found no difference, and the two treatment groups resulted in similar eradication success at the end of treatment (80 and 90%, resp.) and similar clinical evolution during the first 2 years of follow-up.
In a cohort study [40], 15 patients (mean age 9 years) inhaled 80 mg tobramycin twice daily (BID) for 12 months. After 1 year, 14/15 was free from P. aeruginosa, and after 2 years, 9/15 had negative serum antibody titers against P. aeruginosa. There was an improvement in lung function noted before the intervention. In another cohort study [41], 36 young children treated with TSI (tobramycin solution for inhalation) 300 mg BID for 28 days or 56 days eradicated P. aeruginosa for up to 3 months after treatment.
There are three new trials [42][43][44] that were not included in the above CR. The ELITE trial [42] included 88 subjects and used microbiological (not clinical) criteria as the primary outcome. The authors found that treatment with TIS for 28 days is an effective and well-tolerated therapy in CF. The larger EPIC study [43] included 304 children. Participants randomized to cycled therapy received TIS for 28 days, with oral ciprofloxacin or oral placebo for 14 days every quarter, while participants randomized to culturebased therapy received the same treatments only during quarters with positive P. aeruginosa cultures. There were no statistically significant differences in exacerbation rates between cycled and culture-based groups (hazard ratio (HR), The Scientific World Journal 3  [44] included 263 subjects to clarify the efficacy of two different eradication treatments, oral ciprofloxacin, and TIS (test treatment), compared with oral ciprofloxacin and inhaled colistin (reference treatment). Hundred five patients were assigned to inhaled colistin/oral ciprofloxacin (arm A) and 118 were assigned to inhaled tobramycin/oral ciprofloxacin (arm B). P. aeruginosa was eradicated in 66 (62.8%) patients in arm A and in 77 (65.2%) in arm B (OR 0.90, 95% CI 0.52 to 1.55). Following treatment, an increase in S. maltophilia was noted (OR 3.97, 95% CI 2.27 to 6.94) with no differences between the two arms (OR 0.89, 95% CI 0.44 to 1.78).

Colistin versus Placebo.
We could identify one study [45]. This cohort study including very few patents ( = 7) with recent P. aeruginosa positive cultures used inhaled Colomycin 500,000 U BID and found a 36% reduction in the culture rate in long term.
The study was carried out over 44 months as only 16% of the treated patients developed chronic P. aeruginosa infection after 3(1/2) years compared with 72% of the control patients.

Ciprofloxacin, Colistin, and Tobramycin versus Control.
Vazquez et al. [50] included 16 patients and used oral ciprofloxacin (30-40 mg/kg/d) for 2 weeks, inhalations of colistin (1 million units), and inhaled tobramycin (100 mg BID) for long term. In follow-up, P. aeruginosa culture was positive in 4.6% of the treatment group compared to 86% of historic control group.

Intravenous (IV) Antibiotics with or without Inhaled and/or Oral Antibiotics.
In a pilot study [51] in 28 patients aged from 2 to 18 years, the authors gave a two-week course of azlocillin (150 mg/kg/d) and tobramycin (10-15 mg/kg/d). The eradication of P. aeruginosa that was achieved in 18 children was only temporary. Samples from only 10 and 5 patients remained negative 3 and 6 months after treatment, respectively. Only 5 children remained free from P. aeruginosa for a prolonged period from 14 to 32 months. Munck et al. [52] initiated treatment with a combination of IV ceftazidime (300 mg/kg/d) or imipenem (75 mg/kg/d) plus tobramycin (7.5 mg/kg/d) for 18-21 days, followed by nebulized colistin (1-3 million units) for >2 months in 19 patients. Initial colonization was eradicated in all patients, but again all reacquired P. aeruginosa within 3-25 months during 3 years of follow-up. Griese et al. [53] included 17 patients and used inhaled tobramycin (80 mg BID) for 4 weeks in <5 yrs and ciprofloxacin plus inhaled colistin (1 million units BID) for 3 weeks in >5 yrs. In some patients, IV ceftazidime and tobramycin were also used. Initial P. aeruginosa colonization was successfully eradicated in 15 of 17 patients for at least two years. Nixon et al. [54] included 24 patients and used IV ticarcillin clavulanate plus tobramycin for 2 weeks, followed by oral ciprofloxacin or inhaled tobramycin for 3 months. Initial P. aeruginosa colonization was successfully eradicated in 25% patients only. Douglas et al. [55] included 26 patients and used IV ticarcillin clavulanate (300 mg/kg/d) or ceftazidime (150 mg/kg/d) plus IV tobramycin (7.5 mg/kg/d) for 2 weeks, followed by oral ciprofloxacin (10 mg/kg BID) and inhaled tobramycin (80 mg/kg BID) for 4 weeks. Initial P. aeruginosa colonization was successfully eradicated in 23 of 26 patients, and 3 of 23 patients developed recurrences after 1 year.

Treatment of Chronically Persistent Airway Colonization
with P. aeruginosa. It has been seen that the long-term effect on the prevalence ofchronic P. aeruginosa infection depends on the rate of acquisition of new infections, the efficiency of the eradication regime, that is, the clearance rate, as well as the time period free of P. aeruginosa after-treatment. Recent data shows that the effects of chronicinfection are more severe in those who acquired it at an earlier age [56]. There are many protocols which utilize inhaled/nebulized or oral or 6 The Scientific World Journal

The Role of Inhaled Antibiotics
A Cochrane review studied the role of inhaled antibiotics for long-term suppression of chronic P. aeruginosa infection [57]. Seventeen trials including 1562 participants compared an inhaled antibiotic with placebo or usual treatment for a period of 1 and 32 months. Lung function (FEV1) was higher and exacerbations were less in the antibiotic-treated group. Resistance to antibiotics and minor side effects were more in the antibiotic-treated group.

Tobramycin Inhaled versus Placebo.
For more details, see Table 2.
The Scientific World Journal 7  [59]. The inclusion criteria were chronic P. aeruginosa infection and FEV1 25-75%. The authors found reduced rate of respiratory events (dyspnea and wheezing) more with FTI than placebo and more with an 80/20 mg dose of FTI than 160/40 mg dose. No clinically significant differences between groups were reported for laboratory values. FTI maintained the substantial improvements in FEV1% predicted and was well tolerated.

Tobramycin versus Colistin.
In a multicenter trial, 115 patients aged ≥6 years were randomised to receive either nebulized tobramycin (TNS) or colistin, BID for 4 weeks [60]. The primary end point was a change in FEV1% predicted. TNS produced a mean 6.7% improvement in lung function ( = 0.006), whilst there was no significant improvement in the colistin-treated patients (mean change 0.37%). In another randomized trial, 380 patients aged ≥6 years were randomised to Colobreathe dry powder for inhalation (CDPI, one capsule containing colistimethate sodium 1 662 500 IU, BID) or three 28-day cycles with BID 300 mg tobramycin (TIS) for 24 weeks [61]. The conclusion was that CDPI demonstrated efficacy by virtue of noninferiority to TIS in lung function after 24 weeks.

Colistin Inhaled versus Placebo.
For more details, see Table 3.

Other Inhaled Antibiotics versus Placebo.
One RCT assessed the efficacy and safety of a novel aerosol formulation of levofloxacin (MP-376, Aeroquin) in 151 patients with CF with chronic P. aeruginosa infection [62]. The participants received one of three doses of MP-376 (120 mg OD, 240 mg OD, 240 mg BID) or placebo for 28 days. The authors found a dose-dependent increase in FEV1, with a difference of 8.7% between the 240 mg BID group and placebo ( = 0.003). Also a significant reduction (61-79%) in the need for other antimicrobials was observed with all MP-376 treatment groups. In a crossover study, the authors included 20 participants 8 The Scientific World Journal of 15-42 years age and administered carbenicillin (1 g) and gentamicin (80 mg) BID for 6 months [63]. Compared to placebo, improvement in lung function (FEV1, FVC, and PEF) was more and exacerbations of infection (courses of IV antibiotics) were less in treatment group. In another crossover study, the authors included 33 participants of 7.8-16 years age, and administered gentamicin (20 mg) BID for 12 months [64]. There was no significant difference in antibiotic usage, days in hospital or clinical symptoms between no treatment and treatment group, but subjects in treatment group with P. aeruginosa in sputum showed significantly less deterioration in lung function over 2 years. Yet, in another crossover design, the authors included 7 participants with mean age of 15.6 years and administered gentamicin (80 mg) TID for 3 months [65]. There was no significant difference in the lung function (FEV1, FVC) between the two groups. A randomized crossover study compared three treatment groups: ceftazidime, gentamicin and carbenicillin, and saline, each given for 4 months [66]. There was significant improvement in the lung function (PEF, FEV1, and FVC) in both the treatment groups compared to the saline group, but there was no difference in the two treatment group.

Oral Fluoroquinolones Compared to Placebo or Other
Antibiotics. In a RCT, 31 participants of ≥18 years of age received ciprofloxacin or placebo for 10 days every 3 months for 1 year [67]. In the treatment group, patients reported a significant improvement in cough and PEF but not in the FEV1 and FVC. Also, there was no reduction in the hospital admissions or the number of courses of IV antibiotics.
In a randomized trial including participants of 8-25 years of age, 21 were randomly assigned to oral ciprofloxacin alone and 23 were randomly assigned to ciprofloxacin plus inhaled amikacin [68]. Continued improvement in clinical symptoms was observed in 14 patients in both treatment groups and the difference was not significant.
In a randomized crossover study 26 adult patients received ciprofloxacin 750 mg BID or ofloxacin 400 mg BID for 14 days, with three months washout period [69]. Treatment with both the drugs was associated with improvement in the clinical score, lung function tests, and inflammatory parameters; no difference between ciprofloxacin and ofloxacin was found.
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In an open prospective clinical trial, the clinical efficacy of the conventional aminoglycoside plus beta-lactam treatment was compared to that of monotherapy with oral quinolones in 26 adult patients [70]. Six two-week courses of antipseudomonas treatment were administered with an interval of approximately three months between treatments. In each patient, two courses of conventional treatment were followed by two courses of quinolone treatment and then by other two courses of conventional treatment. The observed improvements in pulmonary function were somewhat higher when the patients received conventional treatments, and in the most seriously affected patients, conventional treatment was significantly better than quinolone treatment.

Azithromycin Compared to Placebo or Other Antibiotics.
For more details, see Table 4.

Parenteral Antibiotics Compared.
Six children with P. aeruginosa isolated from their respiratory tract completed a randomized crossover study of oral flucloxacillin and nebulized aminoglycoside versus placebo [71]. The patients in the treatment group had higher FEV1 results at the end of the month of active treatment than placebo.
In a prospective multicenter interventional trial of iv meropenem (120 mg/kg/day) or iv ceftazidime (200-400 mg/kg/day), each administered together with iv tobramycin (9-12 mg/kg/day) and 78 patients were included for suppression therapy of chronic P. aeruginosa colonization [72]. Both treatments improved lung function, and no difference between treatment groups was observed.

Staphylococcus aureus.
S. aureus is one of the first microbes and also one of the commonest to infect patients with cystic fibrosis. There has been an increase in the prevalence of colonization/infection with both methicillinsusceptible (MSSA) and methicillin resistant (MRSA) S. aureus over the past decade [73]. Colonization of the anterior nares with S. aureus represents an important risk factor for subsequent infection in both healthy and diseased population, but only few studies have investigated colonization in with CF. In one study, the authors reported a significantly increased prevalence among patients with CF who had not received anti-staphylococcal prophylaxis prior to taking the cultures [74]. Another study using nasal lavage found the presence of identical genotypes in upper and lower airways, which suggests that upper airways play a role as a reservoir of S. aureus (like P. aeruginosa) in CF [75]. In a 2-year cohort study of 100 children with CF, small-colony variants (SCVs) of S. aureus were detected among 24% of participants and were significantly associated with a greater drop in lung function during the study [76]. Other studies have also found SCVs to be associated with higher rates of antimicrobial resistance and more advanced lung disease [77]. We will discuss below the treatment (prophylactic and eradication) strategy for S. aureus.

Methicillin Sensitive S. aureus (MSSA).
The approach for eradication of an initial infection and chronic suppressive treatment are different. In a retrospective cohort study, the authors enrolling 191 patients reported eradication of MSSA in 74% of the subjects after a single course of antistaphylococcal antibiotics [78]. With continuing treatment, only 9% were found to be chronically infected over a sixmonth period, and on further follow-up, only a low level of resistance was found to anti-staphylococcal antibiotics [79]. Based on this, the European CF Consensus group has recommended initial 2-4 weeks of anti-staphylococcal antibiotic with new S. aureus infection [80]. However, the long-term results of such a approach are unknown and warrant further investigation.
Regarding the early chronic suppressive therapy, there have been many studies with variable results. These are summarized in Table 5.
As it can be seen from the table, early chronic suppressive treatment of S. aureus has been associated with an increased infection with P. aeruginosa without any major clinical benefits. Same was the findings by the Cochrane review [81]. Though the US Guidelines do not recommend use of prophylactic anti-staphylococcal antibiotics as the UK and Australian guidelines, however, recommend flucloxacillin prophylaxis starting from the infancy [82].
Like treatment of P. aeruginosa with inhaled antibiotics, few studies have the role of inhaled antibiotics in the chronic treatment of MSSA infection. In one study, 13 patients (3-34 years) with chronic bronchopulmonary infection due to MSSA were treated with nebulized ampicillin (500 mg/12 h in those weighing <40 kg and 1 g/12 h in those >40 kg) over a period from 6 to 45 months (mean, 23 months) [83]. A significant reduction in the consumption of oral antibiotics (from 28 to 7 days/year) and number of hospitalizations (from 4 to 1/year) were observed. No significant differences were found for lung function, although it did not decline during the entire treatment period. Neither there was cocolonization due to P. aeruginosa nor was MSSA eradicated. (MRSA). There are no current guidelines for treatment of MRSA in patients with CF. The prophylactic treatment has its own problem of emergence of antimicrobial resistance without any appreciable long-term effect. The treatment regimen differs depending upon whether outpatient or inpatient therapy is indicated. Drugs used for outpatient therapy include co-trimoxazole, minocycline (in children > 8 years) and linezolid. If inpatient therapy is indicated, then iv vancomycin or teicoplanin are the drugs of choices. Recently, inhaled drugs like tobramycin/fosfomycin and inhaled vancomycin have been tried with some success [84].

Methicillin Resistant S. aureus
Regarding the eradication protocol, there have been few uncontrolled studies done so far. These are summarized in Table 6.
Though the concerns about MRSA and the success with early P. aeruginosa eradication have encouraged several centers to attempt eradication of MRSA, the long-term results are unknown. We need long-term controlled followup studies before any recommendations/guidelines can be made regarding the same.

Discussion
6.1. Key Findings. P. aeruginosa colonisation has a negative effect on lung function in patients with cystic fibrosis (CF). It is rather easy to eradicate the organism in the early stage of colonisation and to maintain a reduced bacterial density during chronic colonisation. For this, intermittent (few monthly) microbiological culture is advisable. Once the organism is isolated, the therapy depends upon presence or absence of symptoms. As a guide, the first isolation of P. aeruginosa without any clinical signs should be treated with oral ciprofloxacin plus inhaled aztreonam (AZLI) or colistin (COL) or tobramycin (TOB) (alternative being iv treatment with or without inhaled antibiotics) [85]. Reviewing the available data on the efficacy and safety of aztreonam (AZLI), colistin (COL), and tobramycin (TOB) administered by inhalation, we have discussed significant differences among these antibiotics. Inhaled antipseudomonal antibiotic treatment improves lung function. However, more evidence, from trials of longer duration, is needed to determine whether this benefit is maintained and to determine the significance of development of antibiotic-resistant organisms. Regarding the maintenance treatment of chronic P. aeruginosa infection/colonization, stable patients >6 years of age should be treated with any one of the inhaled antibiotics. For patients with development of mild symptoms, oral ciprofloxacin, and those with severe symptoms, intravenous antibiotics (preferably in combination) can be added [85]. Patients with highly resistant pathogens detected in sputum cultures may still derive clinical benefits from aerosolized antibiotics. This may be due to the substantial pharmacodynamic benefits of aerosolized antibiotics; that is, high concentrations of drug can be delivered to the site of infection with low risk of toxicity.
S. aureus is one of the earliest bacteria to be detected in infants and children with CF. The rise of MRSA in the last decade has caused a lot of attention to this organism, as the isolation of this organism has been associated with a decline in lung function. Similar to P. aeruginosa, many centers target this organism for aggressive treatment because of the negative impact on CF patients. As we have already discussed, there are many therapeutic options for both MSSA and MRSA. But many questions remain regarding the clinical utility and tradeoffs of prophylactic therapy for MSSA and eradication and treatment for MRSA. We also highlighted paucity of RCTs in the therapy of S. aureus. In order to advance the care of CF patients, controlled clinical trials are needed to find the optimal approach for managing CF patients who are infected with either MSSA or MRSA. But, currently no consensus exists regarding the same.

Limitations.
A number of limitations apply to all the trials (mostly RCTs) included in this overview. First, most of the trials included relatively small numbers of patients, which lack of adequate power to prove the hypothesis (outcome measures). There is a probability of a type II error, simply because of the comparable study sizes and the limited number of studies, therefore population size under review. Second, not all trials are reported on each key outcome and outcomes are not reported in a consistent format.

Direction for Future Research.
As the inflammatory response of airways and the effect of inhaled antibiotics may not be the same in children and adults and many CF patients are surviving beyond adolescence, age-stratified analyses should be performed in future clinical trials. Increased availability of new inhaled antibiotics should also allow comparative trials to be performed between them. Though, assessment of pulmonary function (FEV1) is the common end point in many trials, quality of life (symptom score, medication score, and level of bother) should also bemeasured. Besides the standardtreatment regimen with 28-day on/28-day off cycles of inhaled antibiotics, feasibility of easier delivery schedules (such as 1 or 2 week on/off cycles or once daily dosing) should be investigated [86].

Conclusions
As it is difficult to establish a firm recommendation based on the available evidence, the following factors must be considered for the choice of treatment for each patient: antibiotic related (e.g., safety and efficacy and ease of administration/delivery) and patient related factors (e.g., age, clinical status, prior use of antibiotics, coinfection by other organisms, and associated comorbidities).