Høiby: Recent advances in the treatment of bacterial infections in CF
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Recent advances in the treatment of Pseudomonas aeruginosa
infections in Cystic Fibrosis
Niels Høiby, MD, Dr. Med. Scient.
Professor and chairman of Department of Clinical Microbiology 9301,
Rigshospitalet & ISIM, University of Copenhagen, Juliane Maries vej 22,
2100 Copenhagen, Denmark
e-mail: hoiby@hoibyniels.dk
Abstract
Chronic Pseudomonas aeruginosa lung infection in CF patients is caused by biofilm
growing mucoid strains. Biofilms can be prevented by early aggressive antibiotic
prophylaxis or therapy and they can be treated by chronic suppressive therapy. New
results indicate that addition of oral ciprofloxacin to inhaled tobramycin may reduce
lung inflammation. Clinical trials with new formulations of old antibiotics for
inhalation therapy (aztreonam lysine) against chronic P. aeruginosa infection
improved patient-reported outcome, lung function, time to acute exacerbations, and
sputum density of P. aeruginosa. Other drugs such as quinolones are currently under
investigations for inhalation therapy. A trial on use of anti-Pseudomonas antibiotics
for long-term prophylaxis showed no effect as regards P. aeruginosa in patients who
were not already infected. Use of azithromycin to treat CF patients P. aeruginosa
infection did not improve lung function.
Introduction
The consequence of the mutations in the CFTR gene is malfunction of the chloride
channel in cystic fibrosis (CF) patients, which leads to decreased volume of the
paraciliary fluid in the lower respiratory tract, and that in turn leads to impaired
mucociliary clearance of inhaled microbes 1. This impairment of the noninflammatory defense mechanism of the respiratory tract leads to early recruitment of
the inflammatory defense mechanisms e.g. PMNs and antibodies 2 3 4. CF patients,
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therefore, from early childhood suffer from recurrent and chronic respiratory tract
infections characterized by PMN inflammation. In spite of the inflammatory response
and intensive antibiotic therapy, however, infections caused by P. aeruginosa, the
Burkholderia cepacia complex (mostly B. multivorans and B. cenocepacia) and
Achromobacter xylosoxidans, persist and lead to respiratory failure and lung
transplantation or death of the patients 5. Several other species including
Staphylococcus. aureus, Haemophilus. influenzae, Stenotrophomonas. maltophilia
and Mycobacteria other than tuberculosis and Aspergillus fumigatus also contribute to
the mortality and morbidity 5.
Adaptive mechanisms of P. aeruginosa exist which explain why this pathogen is able
to survive and persist for several decades in the respiratory tract of CF patients in
spite of the defense mechanisms of the host and intensive antibiotic therapy. P.
aeruginosa is able to survive by switching to the biofilm mode of growth which
provides tolerance to the inflammatory defense mechanism, to the aerobic respiratory
zone and to the conductive zone of the lungs which contain anaerobic sputum, and to
the antibiotic therapy 6 7 8. The biofilm strategy is also used by Burkholderia,
Achromobacter and Stenotrophomonas 9.
Current strategies for management of bacterial infections in cystic fibrosis
The lungs consist of the smaller conductive zone and the larger respiratory zone. The
respiratory zone includes respiratory bronchioles, alveolar ducts and alveolar sacs 10
11
. This part of the lungs has no cilia, no goblet cells and no submucosal glands and
the defense system includes alveolar macrophages and defensins. All the venous
blood of the body passes through the capillaries of the alveoles, which consist of a
nearly continuous sheet of blood and only a very thin barrier is present between the
air and the blood. The smaller conducting zone includes trachea, the bronchi and the
terminal bronchioles. This part of the lungs has cilia, goblet cells and submucal glands
and has a ordinary arterial blood supply from aorta. The mucus is produced in the
respiratory zone and the major defense system is the muco-ciliary escalator 10 and
PMNs recruitted from the respiratory zone 12.
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Nebulised tobramycin and colistin and other antibiotics are widely used to treat P.
aeruginosa lung infection in CF patients. Very high concentrations of these drugs are
obtained in the conductive zone (sputum), whereas very little actually reaches the
respiratory zone, since the measurable concentration in serum, which reflects the
amount in the respiratory zone, is very low 13 14
15 16 17
. On the contrary, when
antibiotics are administred intravenously or orally, very low concentrations are found
in sputum, but high concentrations in the respiratory tissue because the whole dose of
e.g. an intravenous bolus of antibiotics is transported directly by the blood to the
alveolar capillaries before being distributed to the rest of the body 18. Since both the
respiratory and the conductive zones of the lungs are infected with P. aeruginosa,
there is both in vitro and in vivo pharmacokinetic/pharmacodynamic evidence for
using combined systemic and nebulised antibiotics in CF patients 19 20 21. Most of the
research in antibiotic management of bacterial infections in CF is carried out in
intermittently colonized patients to prevent chronic infection or in chronically
infected patients to prevent further tissue damage in the respiratory zone. These
current therapeutic strategies are described in consensus reports 22 23. However, the
burden of treatment for CF patients is large and adherence to therapy may therefore
be difficult so there is a great need for novel therapeutic strategies
Recent trials and results
1. Inhaled medications and inhalation devices
The particle size (1-5µm), the lung dose delivered (3-8% - >50%) and the
administration time (10-20 min to < 2-3 min.) have all improved during recent years
as treatment of lung infections with antibiotics administred by inhalation therapy has
become standard care in CF centers. This important development means that some
antibiotics like colistin, tobramycin and aztreonam can now be inhaled within 2-3
minutes x1-3/day. The development from jet nebulizers to dry-powder inhalers and
pressured metered dose inhalers and the relevant publications are summarized in two
excellent recent surveys 24 25.
2. Inhaled versus systemic antibiotics for early eradication therapy
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Inhaled tobramycin has been shown to transiently clear P. aeruginosa from lower
airways in CF patients but does not markedly reduce lung inflammation, which is a
key factor in disease progression 26. Clinical stable CF children (0.5 – 16 years) with
recent P. aeruginosa infections were therefore randomized to receive 4 weeks of
inhaled tobramycin or two weeks of systemic i.v. ceftazidime and tobramycin. If i.v.
treatment was not possible, oral ciprofloxacin and nebulized tobramycin for 2 weeks
was used alternatively. Bronchoalveolar lavage fluid (BALF) was obtained just before
and 4-6 weeks after treatment. It was considered impossible to blind the study, but
measurement of inflammatory parameters was done blindly. The primary outcome
was change in % PMNs in BALF from the ’worst lobe’ and secondary parameters
were change i total cells, PMNs, cytokines and bacterial quantity. Only 21 of 41
patients agreed to be enrolled and only 15 patients completed the study (6 in the
inhaled group and 9 in the systemic group). The study was therefore underpowered
which explains why most of the results were non-significant. However, median
changes in total cells/ml and in PMNs/ml BALF were substantially greater in the
systemic group than the inhaled group (p<0.01 and p<0.02), and the greatest decrease
was found in the patients treated with both ciprofloxacin and tobramycin, whereas the
inhaled group showed little change. A large multi-center study is therefore still
needed, where oral ciprofloxacin combined with nebulized tobramycin or colistin is
compared with nebulized tobramycin or colistin using the same primary and
secondary parameters 26.
3. Nebulized Aztreonam Lysine for P. aeruginosa infection
Three phase III studies have recently been published. Two were multinational, multicenter, randomized, double-blind, placebo-controlled studies, where a 28-day course
of 75 mg aztreonam lysine given x3/day (AIR-CF1, 164 patients)27 or x2/day and
x3/day (AIR-CF2, 211 patients)28 were compared with placebo as maintenance
treatment for chronic P. aeruginosa infection in moderately-to-severe lung disease
(25%≤FEV1≤75% predicted) where the patients in AIR-CF1 had no recent use of
anti-pseudomonal antibiotics or azithromycin, wheras AIR-CF2 had just completed a
28 days course of tobramycin inhalation. The primary end-point in AIR CF-1 was
patient-reported outcomes using the Cystic Fibrosis Questionaire-Revised Respiratory
Scale (CFQ-R) and in AIR-CF2 the end-point was the time needed for inhaled or i.v.
anti-pseudomonal antibacterials. Both trials are well performed and reached
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conclusive results which can be used in daily treatment of CF patients. AIR-CF1
showed a significant improvement of CFQ-R scores, FEV1 and decrease of P.
aeruginosa density in sputum compared with placebo and AIR-CF2 showed
significant delayed time (21 days) needed for inhaled or systemic anti-pseudomonal
antibiotics and AIR-CF2 showed the same improvement of CFQ-R scores, FEV1 and
P. aeruginosa density as in AIR-CF1. Comparable results were obtained with the
x2/day and x3/day dosing regimes. Adverse events were the same in the placebo arms
and aztreonam arms and consistent with CF lung disease. A transient 4-fold increase
of MICs were found in the aztreonam treated patients. Median sputum concentrations
of aztreonam was 451-677 µg/g sputum and 0.5-0.6 µg/ml serum (AIR-CF1).
The patients enrolled in AIR-CF1 and AIR-CF2 were then followed for 18 months in
the open-labeled AIR-CF3 study (274 patients) where up to 9 repeated 28 days
courses of x2/day (85 patients) and x3/day (189 patients) of aztreonam were given
alternating with 28 days off treatment 29. The endpoint measures were CFQ-R score
and a number of non-respiratory quality of life scores in addition to sputum P.
aeruginosa density and % of days and number of days hospitalized, time to first
respiratory hospitalization and % change in weight and the time to use i.v. antibiotics.
Generally, the results from AIR-CF1 and AIR–CF2 studies were replicated in this
study but the x3/day dosing was significant better than the x2/day dosing in terms of
lung function and respiratory symptoms. Adherence to treatment was 92% in the
x2/day and 88% in the x3/day groups 29.
4. Cycled antibiotic prophylaxis to prevent P. aeruginosa colonization.
Early aggresive eradication of intermittent P. aeruginosa colonization is a treatment
that has to be repeated to keep most of the patients free of chronic P. aeruginosa
infection 30. A triple-blind placebo-controlled randomised 3-year study (65 CF
children) was therefore carried out to investigate whether 3-monthly 3-week
treatments with oral ciprofloxacin and inhaled colistin or both placebo would prevent
initial P. aeruginosa infection 31. The primary outcome was P. aeruginosa infection
and therefore respiratory cultures were obtained every 3 months. The percentage of
cultures containing non-fermenting Gram-negative bacteria other than P. aeruginosa
was significantly higher in the treatment group, which suggests thatthe three-monthly
prophylaxis did not reduce the risk of initial and chronic P. aeruginosa infection.
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5. Effect of azithromycin on pulmonary function in CF patients without P.
aeruginosa infection
Azithromycin is used routinely in the treatment of CF patients with chronic P.
aeruginosa infection since a number of trials both in CF adults and children showed
improvement in lung function 32. The mechanism by which azithromycin works is
thought to be through inhibition of bacterial communication (quorum sensing) and
reduction of inflammation since azithromycin does not inhibit growth of P.
aeruginosa at the concentrations obtainable in vivo. This was the rationale behind a
large (260 patients, 6-18 years) multi-center, randomized, double-blind, placebocontrolled trial where azithromycin (250 mg or 500 mg dependent on body weight
was given every other day to patients who had negative P. aeruginosa cultures for at
least one year. The primary outcome was change in FEV1 33. The outcome was,
however, negative since 24 weeks treatment with azithromycin did not result in
improved pulmonary function although the treated group had reduction in
exacerbations and cough compared with the placebo group. On the other hand,
significantly more macrolide resistant S. aureus and H. influenzae were isolated in the
treated group.
Ongoing studies
At present, there are two multicenter, randomised, double-blind, placebo-controlled
studies focus on prevention of chronic P. aeruginosa infection by early aggressive
eradication.
The American (300 patients, 1-12 years) multicenter EPIC study 34has 4 arms, where
28 days of 4 different treatment inhalation strategies are compared. Two culture-based
therapies 1) Inhaled tobramycin and oral placebo, 2) inhaled tobramycin and 14 days
oral ciprofloxacin, and the two cycled therapies 3) inhaled tobramycin and oral
placebo, and 4) inhaled tobramycin and 14 days oral ciprofloxacin. 1) and 2) are
repeated when quarterly respiratory cultures are found positive for P. aeruginosa and
3) and 4) are followed by 56 days off therapy, for six quarterly cycles. Preliminary
results 35showed no significant differences between the 4 strategies neither with
respect to P. aeruginosa positive cultures nor exacerbations and there was no
concerns of drug toxicity or development of resistance.
The Scandinavian (200 patients) multicenter study compare the standard 3-week
nebulized colistin and oral ciprofloxacin and additional oral azithromycin or placebo
for prevention of chronic P. aeruginosa infection36. This is a culture-based study and
in addition screening of the patients for P. aeruginosa antibodies is used to assure,
that the patients do have chronic infection at the enrollment. The rationale of the study
is the demonstrated quorum sensing inhitory effect of azithromycin which could
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disarm P. aeruginosa and thereby facilitate its early eradication6. The study is
ongoing and no results have been reported.
Hurdles for the future
The major hurdle is the biofilm mode of growth of P. aeruginosa and also
Burkholderia cepacia complex, Achromobacter xylosoxidans and Stenotrophomonas
maltophilia which have become established CF pathogens resistant to eradication
with antibiotics5 9. There are several possiblilities which should be tested in the future
including inhibition of quorum sensing by e.g. garlic37, or break of the biofilm matrix
by alginate lyase, F-actin or DNase 38.
Conclusions
Focusing new formulations of old antibiotics (aztreonam) on chronic P. aeruginosa
infetion has been shown to be effective and a valuable addition to the current strategy
of maintenance treatment of CF patients. Several other drugs such as quinolones are
currently under investigations for inhalation therapy. On the other hand using
antibiotics for long-term prophylaxis does not seem to be valuable as regards P.
aeruginosa and the main indication for azithromycin treatment is still chronic P.
aeruginosa lung infection.
List of abbreviations
CF: Cystic fibrosis
CFTR: cystic fibrosis transmembrane conductance regulator
PMN: Polymorphonuclear leukocytes
i.v.: Intra-venous
BALF: Bronchoalveolar lavage fluid
FEV1: Forced expiratory volume in one second
CFQ-R: Cystic Fibrosis Questionaire-Revised Respiratory Scale
DNase: Desoxy-ribonuclease
Competing interests
None
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