Azithromycin for cystic fibrosis

Active treatment of lung infection is a cornerstone of cystic fibrosis (CF) management 1. Together with attention to nutritional well-being, this strategy has led to considerable improvement in median survival for people with CF over the past 50 yrs 2. However, over the past decade, little in the way of therapeutic advance has been available for the CF team. Recombinant DNAse, and purer formulations of tobramycin have improved the range of aerosolised therapies available 3, 4, but there have been no new anti-pseudomonal antibiotics, and more fundamental therapies, such as ion transport modulation or gene replacement, are yet to prove themselves at clinical trial 5, 6. In this climate, azithromycin has been enthusiastically embraced by many centres across the world as a potentially important and relatively inexpensive treatment for CF lung disease. The present study will critically review evidence from randomised controlled trials (RCTs) and reflect on the role of azithromycin in the management of CF lung disease. Meta-analysis in the current review is from a recent update of a systematic review published on the Cochrane database 7, 8. Investigators gave original data to the present review and are acknowledged for their contribution.

Background

Azithromycin is an azalide antibiotic, which is a subclass ofthe macrolide family 9. It has no direct killing effect against the Gram-negative bacteria, Pseudomonas aeruginosa, but it is active against other Gram-negative bacteria, such as Haemophilus influenzae and Moraxella catarrhalis. It has a similar, though less potent, spectrum of activity as erythromycin against Gram-positive bacteria, such as Streptococci and Staphylococcus aureus. The structure of azithromycin results in a distinct pharmacokinetic profile to other macrolides, such as erythromycin and clarithromycin. Although plasma concentrations are low, azithromycin has good tissue penetration and high concentrations in airway secretions can be achieved. Consequently, a short course of once a day treatment has been advocated for soft tissue and respiratory tract infection. These advantages may be offset by development of resistance in target pathogens because of the widespread use and long tissue half-life of azithromycin 10. A recent report described high nasal carriage rates of S. aureus from students in the USA; a quarter of these isolates were resistant to azithromycin 11. Similar to other macrolides, azithromycin also has a role in treating atypical infections such as Mycoplasma pneumoniae, Lyme disease and Chlamydia pneumoniae.

Early reports of macrolides for cystic fibrosis

In 1994, Hoiby 12 highlighted similarities between CF and diffuse panbronchiolitis, a condition associated with chronic P. aeruginosa lung infection, found principally in the East Asian population. He commented on the improvement that many of these patients had experienced in their respiratory condition following treatment with the macrolide antibiotic, erythromycin, and suggested that macrolide antibiotics might have a role in CF through indirect anti-pseudomonal properties.

The variety of nonantibiotic effects attributed to azithromycin has been extensively reviewed by Bush and Rubin 13. There is good evidence that macrolides modulate inflammatory pathways by suppressing pro-inflammatory cytokines 14. In addition, macrolides may have more wide ranging effects on the innate immune system, modulating neutrophil function, reducing the presentation of adhesion molecules and altering expression of nitric oxide synthases 15–17. Finally, macrolides may have more mechanistic effects, reducing airway mucus production and altering the biofilm phenotype of P. aeruginosa 18, 19.

Does azithromycin work in cystic fibrosis?

Three well-designed RCTs have examined azithromycin versus placebo for CF lung disease 20–22. All employed appropriate treatment allocation and concealment. In total, 286 adults and children (>8 yrs) with CF were included in these trials (table 1⇓). Change in forced expiratory volume in one second (FEV₁) over the course of the study period was the primary outcome measure in each trial, though different methods were used to analyse these data (table 1⇓). Although the three trials examined different time points, and a trial by Equi et al. 20 employed a cross-over design, meta-analysis of relative change in FEV₁ was possible with data at five time points (data from the first arm of the cross-over study were included as the two groups had similar baseline characteristics). Relative change in FEV₁ is calculated as follows: At both 1 and 6 months, the weighted mean difference in relative change of FEV₁ is significantly in favour of azithromycin (table 2⇓; fig. 1⇓). At 6 months, this value was 5.8% (95% confidence interval: 2.4–9.2%). This meta-analysis is consistent with the reported improvements in FEV₁ in each of the trials and provides reassurance of a small but true improvement in FEV₁ with azithromycin. Similar improvements are seen with forced vital capacity (significant at time points 2 months and 6 months). These data suggest a consistent, but small improvement in respiratory function following treatment with azithromycin for a period of 6 months.

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Fig. 1.—

A “forest” plot demonstrating the combined data for relative change in forced expiratory volume in one second from the three randomised controlled trials included in the Cochrane review, “macrolide antibiotics for cystic fibrosis” 8, 20–22. Data are available for five times points (1, 2, 3, 4 and 6 months). The plots show results from individual trials: mean () and 95% confidence interval (95% CI; –––) and combined data (♦). The weighted mean difference consistently favours treatment with azithromycin and is statistically significant at 1 and 6 months. Refer to table 2⇓ for specific data in relation to this figure.

Regarding secondary outcomes that are more relevant to patients, Wolter et al. 20 demonstrated a significant reduction in hospital inpatient days and number of additional courses of i.v. antibiotics in the azithromycin group. These findings were not reproduced in the studies by Equi et al. 21 or Saiman et al. 22. However, Saiman et al. 22 did demonstrate a significant reduction in the number of patients admitted in the azithromycin group (14 out of 97 versus 29 out of 98; p=0.05).

Wolter et al. 20 and Saiman et al. 22 employed validated “Quality of Life” (QoL) questionnaires to monitor for improvement over the trial period. Wolter et al. 20 demonstrated improvement in both groups (RCTs improve your QoL!), although more pronounced in the azithromycin group. Saiman et al. 22 demonstrated a significant improvement in the “physical functioning” component of their questionnaire in the azithromycin group. Equi et al. 21 demonstrated no difference with a visual analogue score (appropriate for children). Overall, the changes in these secondary outcomes were not impressive, and inconsistencies between the studies were found.

Why does it work?

Having noted the significant improvement in respiratory function, it is useful to reflect on the mechanism of action. Does it relate to an indirect anti-pseudomonal or anti-inflammatory effect, or is it simply the result of standard antibiotic properties of azithromycin? Wolter et al. 20 reported a significant effect on the “time trend” of C-reactive protein over the course of the study with a fall in the azithromycin group. However, this systemic measure of inflammation is not a valid predictor of the local inflammatory process in the airways 23. Saiman et al. 22 measured interleukin-8 and neutrophil elastase (both markers of inflammation in CF) in sputum and demonstrated no clinically significant difference between the groups at the end of the study period.

There was no evidence of decreased acquisition of P. aeruginosa in patients treated with azithromycin. In the study by Saiman et al. 22, eight patients had a new acquisition of P. aeruginosa (five in placebo group). There was no significant change in pathogens isolated from respiratory culture in the studies by either Wolter et al. 20 or Equi et al. 21. However, in the study by Saiman et al. 22, 12 patients in the placebo group had recently detected S. aureus compared to two in the azithromycin group (p=0.01). All the trials had relatively high levels of S. aureus isolated in the patients involved. Even if the mechanism of action for azithromycin isanti-pseudomonal, a significant reduction in positive respiratory cultures may not occur, particularly if the action is indirect. However, these data, overall, are not supportive of an anti-inflammatory hypothesis, and data from the study by Saiman et al. 22 suggest that the improvement in respiratory function may relate to the anti-staphylococcal properties of azithromycin.

Azithromycin has received the most attention for CF, although other macrolide antibiotics have been examined in clinical trials. A total of four underpowered trials have examined clarithromycin and have not reported a difference in outcomes (data presented at conferences but not published) 8.

Is azithromycin safe?

There have been no reports of serious adverse events related to azithromycin in any of the trials reported to date; however, the RCT is not the ideal tool for detecting serious, but uncommon, adverse events, and the longest duration of treatment was 6 months. The study by Saiman et al. 22 reported a significant increase in mild adverse effects (wheeze, diarrhoea and nausea) in patients receiving azithromycin. Whilst diarrhoea and nausea are recognised sequelae of macrolide therapy, it is more difficult to explain the increased relative risk (RR) of wheeze in these patients (RR=4.2; 95% confidence interval: 1.46–12.25)) 8. There are no data from the trial by Saiman et al. 22 to suggest an increased incidence of allergic bronchopulmonary aspergillosis, but some attention to this finding is required in future studies. These adverse events are mild and may be self-limiting. However, this increased RR may result in reduced concordance with azithromycin treatment.

Given the unique pharmacology of azithromycin, it is important that careful monitoring and reporting of adverse events is undertaken on patients started on the drug. In a small randomised study assessing different doses of azithromycin, a significant rise in liver enzymes occurred in one patient on 1,000 mg of azithromycin, once a day for 5 days (and smaller rises in two other patients) 24. All returned to normal levels, and ultrasound scans were normal 2 weeks after the dosing period. An isolated rise in liver enzymes in one patient was reported by Equi et al. 21.

What is the correct dose?

There are limited data available as to the correct dosage of azithromycin in CF. The largest of the three RCTs employed a dose of 500 mg given once on a Monday, Wednesday and Friday (dose reduced to 250 mg in patients weighing <40 kg). The studies by Wolter et al. 20 and Equi et al. 21 employed daily dosage regimes with no obvious improvement in outcome compared to the study by Saiman et al. 22. The pharmacokinetic study by Cipolli et al. 24 demonstrated high levels of azithromycin in bronchial secretions 6 days after a 5-day course (either 500 or 1,000 mg), supporting the Saiman et al. 22 study regime of intermittent dosing and raising the possibility that even less frequent administration (i.e. weekly) may be a possible strategy.

When should we prescribe azithromycin for cystic fibrosis?

There is consistent evidence from three well-designed placebo-controlled RCTs of a significant, although small, improvement in respiratory function in CF patients receiving azithromycin for periods of 3–6 months. Should the CF team now prescribe azithromycin for all their patients? The current authors suggest that there are still questions to be answered before adopting this policy, not least regarding dosage. Thereis probably a good argument for reserving azithromycin for patients with chronic P. aeruginosa infection, in whommaintaining respiratory condition has been difficult. Ofconcern in this cohort of patients (many of whom will be on DNAse) is the reported inhibitory effect of macrolides on DNAse activity 25. DNA hydrolysis was significantly reduced in vitro by all macrolides, but most noticeably by azithromycin. The subgroup analysis in the trial by Equi et al. 21 demonstrated an apparent lack of efficacy when participants were on DNAse. The possibility of azithromycin inhibiting DNAse in vivo requires further investigation.

Some participants in the three RCTs (table 1⇑) were not infected with P. aeruginosa. However, at present, it is not clear whether azithromycin improves respiratory condition in suchcases. A further study is planned in the USA examining the question of the use of azithromycin for children with CF without chronic P. aeruginosa infection (personal communication, L. Saiman, Columbia University, New York, NY, USA). In CF centres that advocate anti-staphylococcal prophylaxis (generally in Europe), azithromycin may replace the standard regime (often flucloxacillin or cefradine), as well as offering potential anti-pseudomonal effects. The role of azithromycin as a prophylactic agent in newly diagnosed infants, for example those identified through newborn screening programmes, requires a rigorous multi-centre RCT with clearly defined and relevant outcomes. There is an urgent need for such a study, which must assess increasing resistance patterns to azithromycin, as well as efficacy outcomes.

All patients prescribed azithromycin for medium to long-term periods need to be monitored carefully for adverseeffects. In view of the transient derangement in liver function experienced in the study by Cipolli et al. 24, it would appear prudent to monitor this with an annual liverultrasound scan and twice yearly analysis of serum enzymes. Any adverse effects noted should be reported to the national drug monitoring agency and to the national CF database.

In a barren time for new therapies, azithromycin increases the cystic fibrosis physician's armamentarium and offers a potentially useful therapy to arrest respiratory decline. However, questions remain as to its precise role in the clinic and continued vigilance is required for adverse outcomes.