Comparative Efficacy and Safety of 4 Randomized Regimens to Treat Early Pseudomonas aeruginosa Infection in Children With Cystic Fibrosis FREE

Pseudomonas aeruginosa, the predominant pathogen associated with chronic infection in cystic fibrosis (CF),¹ results in more rapid decline in lung function, increased hospitalization, and decreased survival^2- 3 starting in the first decade of life.^1,4- 16 Several randomized trials^16- 19 and a cohort study²⁰ demonstrated that inhaled antibiotics (colistin or tobramycin) with or without oral fluoroquinolones may result in prolonged eradication of early (nonchronic) P aeruginosa acquisition.^16,21- 22 Although spontaneous clearance may occur in some patients,^18- 19 data suggest that antibiotics might be superior to no treatment.²³ Based on these data, aggressive antibiotic treatment at initial P aeruginosa airway detection has been recommended using a range of antibiotic strategies and treatment duration.^24- 26

It remains unclear whether clearance of P aeruginosa from airway cultures has any impact on other health indicators such as exacerbation of respiratory symptoms (pulmonary exacerbation [PE]²⁷), lung function, hospitalization, and growth.²⁸ While there is potential to benefit from early intervention, concerns remain regarding the risks of long-term antibiotic exposure and selection of resistant bacterial pathogens.²⁹

Quiz Ref IDWe compared the clinical and microbiological effectiveness as well as the safety of 4 antibiotic treatment strategies for newly identified P aeruginosa infection isolated from respiratory cultures in children with CF.³⁰ We hypothesized that more frequent administration and double antibiotic therapy would result in reduced rates of PE and frequency of P aeruginosa– positive respiratory cultures over an 18-month study period. We report herein the results of the largest randomized controlled trial of antibiotic therapies to treat P aeruginosa detection ever conducted in young children with CF.

We conducted a multicenter, randomized trial of young children with CF at the time of new isolation of P aeruginosa in respiratory tract cultures. Eligible participants were recruited at 55 Cystic Fibrosis Foundation–accredited clinical centers throughout the United States (see “EPIC Participating Centers and Investigators” box). The duration of study participation was 18 months. All centers obtained institutional review board approval, and all participants' parent or legal guardian provided informed consent. Details of the study design are presented elsewhere.³⁰

Quiz Ref IDMale and female subjects 1 year or older and 12 years or younger with a diagnosis of CF³¹ with a documented respiratory tract culture positive for P aeruginosa within the 6 months prior to randomization were eligible. New isolation of P aeruginosa was defined as the first lifetime documented respiratory positive culture or as a positive culture after at least a 2-year absence of P aeruginosa growth. Among participants aged 12 to 15 months, at least 1 P aeruginosa– positive respiratory culture since birth was required. No more than 1 course of inhaled or intravenous antipseudomonal therapy was allowed prior to baseline. Additional detailed eligibility criteria have been previously reported.³⁰

Quiz Ref IDParticipants were equally randomized to 1 of 4 antipseudomonal treatment algorithms (eTable 1): (1) scheduled antimicrobial therapy consisting of tobramycin inhalation solution (TIS) combined with oral ciprofloxacin every 3 months (cycled TIS and oral ciprofloxacin); (2) scheduled TIS combined with oral placebo every 3 months (cycled TIS and oral placebo); (3) TIS combined with oral ciprofloxacin only when quarterly respiratory cultures were found positive for P aeruginosa (culture-based TIS and oral ciprofloxacin); and (4) TIS combined with oral placebo only when quarterly respiratory cultures were found positive for P aeruginosa (culture-based TIS and oral placebo). The antimicrobial therapy administered during treatment cycles was open-label TIS (TOBI), 300 mg twice a day for 28 days, and either oral ciprofloxacin (Cipro), 15 to 20 mg/kg/dose up to 750 mg/dose twice a day, or oral placebo for 14 days. A 14-day ciprofloxacin course was chosen to minimize the emergence of P aeruginosa resistance.^32- 33 At the beginning of the study, all participants received an initial treatment cycle according to their assigned group and a second consecutive 28-day course of TIS monotherapy if respiratory cultures sampled during the third week of the first antipseudomonal cycle remained P aeruginosa positive (eTable 1).

Participants had study visits at the time of randomization, 3 weeks later, and then quarterly for a total of 18 months.³⁰ Oropharyngeal swabs, or sputum cultures, if available, were obtained at each study visit. Semiquantitative bacterial cultures were processed at a central microbiology laboratory.³⁴ All P aeruginosa isolates were assessed for mucoid phenotype, and antibiotic susceptibility testing of all CF pathogens was performed.³⁰ Cultures sampled for clinical indications and processed at local laboratories were not included in the evaluation of the microbiological study end points. As part of the physical examination, participants had a standardized musculoskeletal assessment to monitor ciprofloxacin toxic effects. Nutritional assessment included length (children ≤18 months) or height and weight. Spirometry data were collected in subjects 4 years or older who were able to perform the procedure.³⁵ Age-appropriate audiometric testing was performed at 40 selected sites with the capability of performing the testing. Laboratory studies to assess safety included measurement of serum creatinine and serum urea nitrogen levels, liver function, and a complete blood cell count at baseline and every 6 months.

The primary clinical end point was the time to first PE requiring intravenous antibiotics or hospital admission during the 18-month study period. Since there is no validated definition of exacerbation in patients this age, we used an a priori–developed definition.³⁰ The primary microbiological end point was the proportion of P aeruginosa –positive respiratory cultures among all quarterly cultures obtained after the initial treatment cycle.

Secondary clinical efficacy end points included (1) time to PE requiring any (intravenous, inhaled, or oral) antibiotic use or hospitalization, (2) anthropometric measures (linear growth, weight gain), and (3) pulmonary function test results (forced vital capacity, forced expiratory flow, and forced expiratory volume in 1 second). Evaluation of the safety profiles included adverse events, musculoskeletal symptoms, hearing acuity, hematological profile, and renal and liver function. In addition, emergence of antibiotic-resistant P aeruginosa and other significant pathogens was monitored.

The sample size for the clinical efficacy end point (time to first PE requiring intravenous antibiotics or hospitalization) was estimated based on the annual exacerbation event rate reported in the 1985-2000 Cystic Fibrosis Foundation National Patient Registry.³⁰ There was a 50% difference in the annual exacerbation rate between children with new-onset P aeruginosa infection (0.36 per person-year) and children never infected with P aeruginosa (0.18 per person-year). A reduction in the exacerbation rate with more aggressive antibiotic therapy from 0.36 to 0.18 per person-year was assumed to be clinically meaningful. An 18-month study with 300 patients had 80% power to detect at least a 40% reduction in the risk of exacerbation in the cycled group as compared with the culture-based treatment group (primary comparison of interest) at the 2-sided α level of 5%. The design of this study also allowed comparisons between participants who received ciprofloxacin vs those who received placebo. Treatment interaction between cycled therapy and ciprofloxacin was also tested.

The randomization code was developed using a computer random-number generator to assign treatments within permuted blocks of size 12. Randomization assignment was available at the sites via an interactive voice response system with e-mail confirmation of the treatment assignment. Children remained on the same allocation throughout the study.

All study personnel and participants were blinded to oral therapy assignment but not to cycled or culture-based treatment allocation. The core study investigators were blinded to all treatment allocation for the entire study.

The intention-to-treat population was used for the primary efficacy and safety analyses (Figure 1). There was no imputation for missing values in secondary analyses and complete case analysis was performed. The censored failure time for the primary clinical efficacy analysis was the date of PE diagnosis, or the end of follow-up if no PE had occurred.³⁰

Hazard ratios and 95% confidence intervals (CIs) were estimated using Cox proportional hazards regression, with covariate adjustment for baseline age group (1-3, >3-6, and >6 years). The age group–adjusted odds ratios (ORs) of a P aeruginosa– positive culture and 95% CI were estimated using generalized estimating equations with robust variance, specifying a logit link and assuming an independence working correlation structure.³⁰

There was no interaction between cycled therapy and ciprofloxacin for the main study end points. Thus, the 2 main evaluations including cycled vs culture-based therapy and oral ciprofloxacin vs oral placebo are presented.

In secondary analyses, we evaluated time to PE requiring any antibiotics or hospitalization. Differences between groups in the linear rate of change from baseline in height and weight and spirometry results were tested using repeated-measures regression with robust variance estimation, with covariate adjustment for baseline age group.³⁶ Differences in proportions were tested using a 2-sample test of proportions. Adverse events were descriptively summarized using the Medical Dictionary for Regulatory Activities system organ class and preferred term.

For all analyses, a 2-sided significance level of .05 was used without adjustment for multiple comparisons. All analyses were performed using the statistical software SAS version 9.1.3 (SAS Institute Inc, Cary, North Carolina) or R statistical package version 2.9.1 (R Foundation for Statistical Computing, Vienna, Austria).

Enrollment, conduct, and safety outcomes were monitored throughout the study by a Data and Safety Monitoring Board (see “EPIC Participating Centers and Investigators” box), with a formal safety report reviewed every 6 months.

A total of 337 children were screened for inclusion from December 2004 to February 2008 and 304 participants were randomized equally (n = 76) to each of the 4 treatment algorithms, received at least 1 dose of study drug (Figure 1), and were included in the intention-to-treat analysis. The follow-up was completed in June 2009. Over the study period, 3 to 8 participants withdrew from each treatment group (Figure 1). Follow-up visit completion, sample collection, and compliance with study medications were 90% or greater across treatment groups.

Participant baseline characteristics were well balanced across groups, including genotype status (Table 1 and eTable 2). All participants had a P aeruginosa– positive culture within 6 months prior to randomization (week 0), and 46% received antimicrobial therapy during the 6 months preceding enrollment. At the time of randomization, 295 participants had a viable respiratory microbiology culture, with 118 (40%) P aeruginosa positive and 170 (58%) positive for Staphylococcus aureus (Table 1).

Following the first treatment cycle, the cycled and culture-based groups differed in treatment frequency during the study (Figure 2).

Quiz Ref IDOverall, 24 of 152 (16%) in the cycled therapy group and 26 of 152 (17%) in the culture-based group experienced a PE requiring intravenous antibiotics or hospitalization. The hazard ratio (HR) of PE comparing cycled with culture-based therapy was 0.95 (95% CI, 0.54-1.66) (P = .86) (Figure 3A). Twenty-nine of 152 (19%) in the ciprofloxacin group and 21 of 152 (14%) in the placebo group experienced a PE requiring intravenous antibiotics or hospitalization (HR of PE, 1.45; 95% CI, 0.82-2.54; P = .20) (Figure 3B). Overall, the proportion of P aeruginosa– positive cultures was on average less than 20%. No statistically significant differences were seen in the odds of a P aeruginosa– positive culture comparing the cycled vs culture-based group (OR, 0.78; 95% CI, 0.49-1.23; P = .28) (Figure 3C) or the ciprofloxacin vs placebo group (OR, 1.10; 95% CI, 0.71-1.71; P = .67) (Figure 3D).

The primary end points across all 4 treatment groups are in the eFigure.

Seventy of 152 participants (46%) in the cycled therapy group vs 81 of 152 (53%) in the culture-based group experienced a PE requiring any (intravenous, inhaled, or oral) antibiotics or hospitalization (HR, 0.80; 95% CI, 0.58-1.11) (Table 2). Eighty-three of 152 participants (55%) in the ciprofloxacin group vs 68 of 152 participants (45%) in the placebo group experienced a PE requiring any antibiotics or hospitalization (HR, 1.29; 95% CI, 0.94-1.78) (Table 2).

The majority of participants had negative culture results throughout the study (Table 2), and among those who had positive results, the majority had no more than 2 P aeruginosa– positive cultures. The proportion of participants who had negative results at the end of the study in the cycle- and culture-based groups was not different. Emergence of mucoid strains of P aeruginosa appeared in 5 of 136 participants (3.7%) in the cycled arm and 6 of 143 (4.2%) in the culture-based arm and 6 of 141 (4.2%) vs 5 of 138 (3.6%) in the ciprofloxacin and placebo groups, respectively (eTable 3). Overall, the emergence of tobramycin or ciprofloxacin resistance ranged from 0% to 4% across treatment groups without significant differences by treatment (eTable 3). New isolation of other CF pathogens was not different across treatment groups. Although not different between groups, there was a nonnegligible new isolation of Stenotrophomonas maltophilia in 29 of 138 cycled-treated participants (21%) and 26 of 141 culture-based–treated participants (18.4%) and 29 of 137 (21.2%) vs 26 of 142 (18.3%) in the ciprofloxacin vs placebo group, respectively.

Age-adjusted longitudinal regression models for the estimation of the 18-month rate of change in height and weight showed no statistically significant differences between treatments (Table 2). Among participants able to perform spirometry, the 18-month rate of change in forced expiratory volume in 1 second showed no significant differences comparing the cycled (n = 73) vs culture-based (n = 70) groups or between the ciprofloxacin (n = 67) vs placebo (n = 76) groups (Table 2).

No significant differences in the occurrence of adverse events or serious adverse events were identified in the cycled vs culture-based arm (eTable 4), with the exception of participants assigned to oral ciprofloxacin (whether cycled or culture-based therapy), who demonstrated a greater frequency of symptoms of cough. Throughout the study, renal function, liver function, or blood cell counts were not statistically different among treatment groups. Likewise, no statistical differences were seen between groups in results of musculoskeletal examination (n = 304) or audiometric testing (n = 212).

Although several randomized trials demonstrated eradication of P aeruginosa from the respiratory tract of patients with CF who have recently acquired the bacterium,^16- 20 to our knowledge, the current study is the first to compare the effect of different therapeutic approaches. We found no statistically significant difference in terms of a reduction in PEs, growth rate, and pulmonary function between cycled quarterly TIS compared with treatment based on microbiological findings. Additionally, we were unable to detect differences in these clinical outcomes by adding a second antibiotic, oral ciprofloxacin. There was no difference in the proportion of P aeruginosa– positive cultures across the 4 treatment groups by the end of the study.

The study did not focus on a formal economic evaluation of treatment options, patient satisfaction, time spent receiving therapy, and overall burden to the family. However, participants randomized to the cycled therapy treatment arms received, on average, 5 additional 28-day treatment cycles of tobramycin or 280 additional inhalation treatments (15-20 minutes per treatment) over the 18 months compared with the culture-based group. Because there was no significant difference in hospitalizations or other measures of clinical benefit and given the low rates of exacerbations, it would be difficult to justify this additional treatment burden. This observation is supported by recent data suggesting that a single 28-day cycle is as effective as a 56-day cycle in clearing P aeruginosa from the airway, with a median time to recurrence of over 2 years.¹⁶ The present investigation focused extensively on the systematic evaluation of the safety profile of the different regimens and impact on bacterial resistance. The incidence of treatment-emergent resistance of P aeruginosa to tobramycin and ciprofloxacin was low, ranging from 0% to 4%. Because P aeruginosa recurrence was rare, it was not possible to test many isolates for antibiotic susceptibility. Although not different between groups, we observed emergence of a tobramycin-resistant, gram-negative pathogen S maltophilia in up to 20% of study participants. This frequency is concerning, but the clinical significance of this finding and this pathogen is unclear. S maltophilia has been observed in other studies of inhaled antibiotics,³⁷ without suggestion of an accelerated decline in lung function, at least in older patients with CF chronically colonized with P aeruginosa.³⁸ However, a recent study concluded that chronic S maltophilia detection in patients with CF is a risk factor for PEs.³⁹

While not statistically significant, there was a trend toward more respiratory adverse events (increased cough) in participants assigned to receive ciprofloxacin. Considering that this finding was observed in the context of several secondary analyses, additional research is needed to address these potential concerns. Musculoskeletal adverse effects and hearing abnormalities were not increased.

Conduct of a large, randomized therapeutic trial in young children with CF was challenging. First, the duration of treatment and time commitment of families could have affected study attrition and study compliance. Fortunately, the attrition rate was remarkably low (<10%) and compliance with drug administration was excellent (>90%) in all treatment groups, minimizing bias from loss to follow-up or attenuation of effect size. Second, established clinical outcomes used in CF therapeutic trials involving older participants^37,40- 41 cannot be reproducibly collected in young children. For example, only 47% of study children were able to perform pulmonary function testing.³⁵ Thus, forced expiratory volume in 1 second could not be used as a primary end point. In addition, only 6% of children were able to expectorate sputum, which is the optimal measure of lower airway infection.⁴² Thus, oropharyngeal cultures were collected to monitor microbiologic status, a method that is standard clinical practice in asymptomatic patients across the United States.⁴³ We acknowledge that oropharyngeal cultures are a less sensitive measure of lower airway bacterial infection but we could not justify the increased risk or cost of repeated bronchoscopy in this population.⁴⁴

Quiz Ref IDThe trial was conducted at multiple and widespread geographic sites across the United States, with a population enrolled in the study representing approximately 60% of all eligible patients in the United States.⁴⁵ Despite enrolling a large proportion of eligible patients and allowing a long follow-up period, the study might have been unable to detect modest differences between the treatment arms. Nonetheless, this study remains one of the largest trials ever conducted in this young CF population. The rate of hospitalizations for respiratory symptoms was lower (0.17 person-year) than observed in the Cystic Fibrosis Patient Registry (0.36 person-year) during study planning. The lack of a placebo group limits our ability to detect a true effect of the study treatments. Over the past decade, the Cystic Fibrosis Foundation care guidelines have recommended quarterly microbiology cultures for all patients.⁴³ This increased surveillance may have resulted in earlier institution of oral antibiotics for respiratory symptoms, affecting the frequency of respiratory-related hospitalizations. All antibiotic use for acute respiratory symptoms (87%) was higher than intravenous antibiotic (21%) administration, with no difference across groups. Two comparative groups are being analyzed for the primary end points, a historic control of children with CF enrolled in an epidemiology study⁴⁶ from 1990 to 2000 with similar eligibility criteria and a concurrent cohort of patients who became P aeruginosa positive during this trial but chose not to enter the clinical trial.⁴⁷

This report is an important step in understanding the optimal treatment of early P aeruginosa infection in CF. While not definitive regarding which treatment approach is optimal, the results of the trial provide well-controlled data and suggest little difference in clinical impact across treatment regimens. However, further understanding of the long-term clinical impact and safety of early antibiotic treatment will require additional studies. Study participants were enrolled in a 10-year observational study (89% enrolled) to collect long-term microbiologic, pulmonary function, growth, and hospitalization outcomes.

In conclusion, the approach of administering TIS at the time of recently documented isolation of P aeruginosa in the respiratory tract of children with CF resulted in similar success in maintaining participants free from PEs over an 18-month period, compared with a prophylactic antipseudomonal treatment strategy. Therefore, providing treatment based on a cycled, quarterly schedule is not supported by the results of this trial. The addition of oral ciprofloxacin did not confer additional protection with respect to PEs, microbiological eradication, or other clinical outcomes. These data also indicate that young children recently acquiring P aeruginosa have a high likelihood of eradication with antibiotic therapy and a prolonged period until reemergence of the pathogen. Based on these findings, judicious use of TIS with close microbiologic monitoring of airway cultures in young patients with CF recently infected with P aeruginosa is recommended.