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* From the Division of Respiratory Medicine, Hospital for Sick Children, University of Toronto, Toronto, ON, Canada.
Correspondence to: Allan L. Coates, BEng, MDCM, Division of Respiratory Medicine, Hospital for Sick Children, 555 University Ave, Toronto, ON, Canada M5G IX8; e-mail: allan.coates{at}sickkids.ca
| Abstract |
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Design and methods: A prospective placebo-controlled clinical trial with crossover design was devised using challenge tests with 75 mg colistin in 4 mL saline solution and a placebo solution of the same osmolarity using a breath-enhanced nebulizer for administration. Subjects were recruited as follows: high risk (HR) for bronchospasm due to a personal history of recurrent wheezing, a family history of asthma and/or atopy, or bronchial lability, as demonstrated in pulmonary function tests; or low risk (LR) without these characteristics.
Results: The mean FEV1 (expressed as the mean [± SD] fall from baseline) of the HR group (n = 12) fell 12 ± 9% after placebo was administered, and fell 17 ± 10% after colistin was administered. For the LR group (n = 8), the mean FEV1 fell 9 ± 4% following placebo administration and 13 ± 8% following colistin administration. There was a greater number of subjects in the HR group compared to the LR group, which had a mean fall in FEV1 of
15% (p < 0.01) after inhaling colistin. The differences between placebo and colistin therapy in the LR group were not significant.
Conclusion: The results demonstrated that colistin can cause bronchospasm, particularly in those patients with coexisting CF and asthma.
Key Words: bronchial spasm colistin cystic fibrosis inhaled antibiotics
| Introduction |
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Colistin sulfomethate, a polymyxin E antibiotic, has the potential to be a suitable agent for aerosolization in CF patients due to its high antimicrobial activity against PA, including multiresistant strains.67 Although its use systemically was largely curtailed in the early 1970s because of nephrotoxicity and neurotoxicity,78 there has been increasing interest in aerosol administration. Presently, nebulized colistin is used in many European centers treating CF patients,7 with some studies,4910 but not all,11 showing positive results. One study3 in adult CF patients with panresistant PA who were awaiting lung transplantation suggested the return of sensitivity to tobramycin in PA strains in 100% of patients compared to 30% in control subjects.
Nebulized colistin causes chest tightness and bronchospasm in some patients. This side effect has been demonstrated largely in adult studies of CF patients.1213 A bronchospasm reaction to nebulized solutions of colistin has been attributed to hyper-tonicity and/or to the drug itself. Hypertonic solutions have been shown to produce bronchocon-striction, particularly in patients with hyperreactive airways,1415 and patients receiving hypertonic antibiotic therapy have been shown to have more bronchospasm than those patients receiving antibiotics with lower tonicity.16 The proposed mechanism involves the release of histamine through changes in osmotic loads around mast cells.1215 During the nebulization of an isotonic solution, the tonicity becomes progressively higher as the evaporation of water from nebulized droplets occurs. In a study with adults,12 nebulized colistin produced equal symptoms of chest tightness and magnitude of fall in FEV1 irrespective of the tonicity of the solution. These effects were evident earlier with the use of the hypertonic solution (7.8 min after the onset of nebulization) and were delayed with the use the hypotonic solution (34.2 min after the onset of nebulization). In one study, Cunningham and colleagues17 found a significant fall in FEV1 in response to the inhalation of colistin, which was not either related to IgE levels or associated with the chest discomfort experienced by some patients. These results are hard to interpret in that different nebulizers with different levels of efficiency18 were used, and there was no comparison with placebo inhalation. Furthermore, 95% of their subjects had been regularly receiving inhaled colistin and had clearly demonstrated previously that they had not experienced any major adverse effects. In a study comparing inhaled tobramycin to colistin, Hodson et al11 found a fall in FEV1 in patients receiving both preparations. These results are also difficult to interpret since 85% of their subjects were receiving ß-adrenergic receptor agonists, and no information about the time of administration of the bronchodilators was given. While bronchoconstriction may be blunted by the coadministration of salbutamol, the preservative benzalkonium chloride in the salbutamol (Ventolin; GlaxoSmithKline; Research Triangle Park, NC) respiratory solution interacts with colistin to cause precipitation,19 further complicating the issue. The occurrence of bronchospasm with therapy using an isotonic nebulized colistin solution suggests the possibility of airway reactivity to the colistin molecule itself. This has been supported by an in vitro demonstration of mast cell degranulation caused by colistin.20 If the illustrated benefits outweigh the risks of bronchospasm, aerosolized colistin may be an effective therapeutic agent in the treatment of multiresistant PA infection in children with CF. To date, the magnitude of bronchospasm in children with CF is unknown. In addition, the bronchospasm that may develop in children may be related to the dose of colistin deposited in the lungs or to possible inherent airway hyperreactivity in selected CF patients.
The hypothesis of this study was that bronchospasm occurs following a colistin inhalation challenge in pediatric CF patients compared to challenge with placebo and that the likelihood of bronchospasm is greater in subjects with coexistent indicators of asthma compared to those without a previous personal or family history, or a response to therapy with bronchodilators.
| Materials and Methods |
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All episodes of coughing or wheezing were graded based on a scale of no symptoms to 2+, and oxygen saturation was monitored during nebulization to ensure that it remained at > 93%. In the event of any respiratory embarrassment, the test was to be terminated and the symptoms recorded. Coughing by itself was not a reason for termination, unless the patient was coughing to the extent that nebulization could not be continued without multiple pauses. If the test was terminated prematurely, spirometry was performed as soon as possible after termination to assess the FEV1, and then the patient was treated with salbutamol.
For each patient, the total drug output of the nebulizer was calculated by taking concentrating effects due to evaporative losses into account. The details of these calculation have been described elsewhere.25262728 In order to estimate the expected deposition, device efficiency was estimated from the flow tracings of four CF patients18 breathing through a nebulizer using the output algorithms based on the work by Katz et al,24 and using the method described by Ho and colleagues.18 The mean in vivo efficiency, which was defined as the amount of the drug that is likely to enter the airway and deposit below the cords per breath in relation to the total amount of output of drug per breath, was found to be 59.7%. For the sake of simplicity, the deposition was estimated as the amount that left the nebulizer during each session multiplied by 0.6.
Data analysis of the primary outcome evaluated the number of patients with a significant fall in FEV1 (defined as a decrease of FEV1 from baseline by
15%) in each group and for each solution using paired t tests and
2 analysis. Values are expressed as the mean and SD.
| Results |
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15%, and in the LR group (9 ± 4%; p < 0.001), with 1 of 8 patients having a fall in FEV1 of
15% (Fig 2). The mean fall in FEV1 after the inhalation of colistin was 17 ± 10% for the HR group, with 7 of 12 patients having a fall of
15%, and 13 ± 8% for the LR group, with 4 of 8 having a fall of
15%. The changes in FEV1 postinhalation of placebo vs colistin were significant for the HR group (p < 0.002), but not for the LR group. There was a statistical difference in the response between the HR and LR groups for a fall in FEV1 of
15% post-colistin inhalation (p < 0.01), but not post-placebo inhalation. The largest fall in FEV1 was 29% in the HR group following the inhalation of colistin, which resulted in an FEV1 of 36% predicted. For the HR group, 3 of 12 patients had an FEV1 of < 40% predicted following colistin inhalation, but this did not occur in any of the HR patients after placebo inhalation. In all three patients, the baseline FEV1 was between 45% and 50% predicted. The largest fall in FEV1 for the LR group was 27% following placebo inhalation. In no case did the FEV1 fall to < 40% predicted in the LR group, irrespective of the agent inhaled. The lowest baseline FEV1 in the LR group was 54% predicted, and all others were > 60%.
No serious adverse events occurred during the study, and the test was never terminated before completion. No patient in either group experienced any desaturations following either placebo or colistin inhalation. Wheezing that had not been present preinhalation occurred in four patients postinhalation in the HR group (three recorded as mild, one as 2+), and two in the LR group (recorded as mild and 1+). The wheezing was not related to whether or not the inhalation was of placebo or colistin, nor was it related to the degree of fall in FEV1. In the HR group, four patients experienced 2+ coughing post-placebo inhalation, and two patients were recorded as having 2+ coughing and one as having mild coughing post-colistin inhalation. For the LR group, two patients experienced coughing (1+ and 2+) post-placebo inhalation, and two experienced it post-colistin inhalation (both 1+). None of the coughing episodes were related to the degree of fall in FEV1. Three of four patients in the HR group who complained of mild chest tightness did so after inhaling colistin, whereas with the two patients in the LR group (both of whom experienced mild tightness), one episode occurred after placebo inhalation and the other after colistin inhalation. While 8 of 12 subjects in the HR group met the criteria for salbutamol administration post-colistin inhalation, this was not different from the situation following placebo inhalation (
2 analysis) in which half of the patients met the criteria. Whether or not the bronchoconstriction was caused by placebo or colistin, it was completely reversed by the inhalation of salbutamol. For the LR group, five of eight patients received salbutamol after both placebo and colistin inhalation. Although the fall in FEV1 was less in the LR group, interestingly, it was still slightly but significantly lower than baseline following salbutamol administration in those who had inhaled colistin (72 ± 12% vs 65 ± 13%, respectively; p < 0.05) compared to those who had inhaled placebo (75 ± 12% vs 71 ± 13%, respectively; p < 0.05) [paired t test for both].
For the HR group, the mean postnebulization osmolarity of colistin was 475 ± 24 mosm/L, and of placebo was 511 ± 52 mosm/L. The degree of fall in FEV1 was not related to the increase in osmolarity, nor were these differences significant (p > 0.05). The relatively low rate of output of colistin,24 compared to other medications,18 and the restriction of nebulization to 20 min resulted in a significantly larger mean residual volume in the nebulizer compared to that for placebo (1.59 ± 0.29 vs 0.95 ± 0.16 mL, respectively) with similar results found in the LR group. For the HR group, 48 ± 8% of the colistin left the nebulizer and either entered the patient or impacted on the expiratory filter vs 67 ± 5% for placebo, differences that were highly significant (p < 0.001 [paired t test]). The results were similar in the LR group, 55 ± 13% vs 67 ± 6%, respectively; p < 0.04). In terms of dose of colistin, the estimated mean pulmonary deposition in the HR group was 30.2 ± 2.2% of the charge dose of 75 mg, which did not differ from a mean of 29.9 ± 2.9% seen in the LR group. The calculated expected deposition of colistin did not correlate with the fall in FEV1.
| Discussion |
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The design of this study was intended to give insight into the risk of bronchospasm in two extremes of patients in the CF population as opposed to the risk for the general population as a whole. The number of patients who complained of chest tightness was too small to be able to decide whether this was due to the inhalation of colistin, as it was also observed in both groups following the inhalation of placebo. Similarly, the presence of wheezing postinhalation that was not observed preinhalation occurred in insufficient numbers of patients to allow any conclusion as to whether or not this was related to colistin. In most cases, the degree of bronchoconstriction, even in the HR group, was relatively mild and easily reversed with bronchodilator treatment, but in the case of the LR group bronchoconstriction was not completely reversed. It is possible that the dose of the bronchodilator salbutamol (400 µg) given by metered-dose inhaler and valved holding chamber was too low. On the other hand, the failure to completely reverse the fall in FEV1 occurred in patients in the LR group who had never demonstrated a response to bronchodilators during routine testing. This leads to speculation that the fall in FEV1 in this group could be due in part to factors other than a spasm of the smooth muscle in the airway, such as local irritation, which could conceivably give rise to edema that was unaffected by bronchodilators. For those patients whose prenebulization FEV1 was
50% predicted, a case could be made for pretreatment with bronchodilators prior to the inhalation of colistin.
One limitation of this study is that the general CF population, which frequently includes patients who have at one point demonstrated a response to bronchodilators but have no other markers for increased airway lability, made up only a small portion of the groups studied. Subjects 10 and 12 (Table 2 ) did not have a personal or family history of asthma or atopy, but subject 10 had multiple responses to bronchodilators of > 8% (with the largest being 32%), and subject 12 had two of four responses > 8% (with the largest being 15%). These two subjects met the HR inclusion criteria based on their responses to bronchodilators. Subject 10 had a 34% fall in FEV1 in response to colistin inhalation, while subject 12 had only a 5% fall in FEV1. From the data in the LR group, it could be inferred that many of these patients would be at risk for some degree of bronchospasm following inhalational therapy.
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Bronchoconstriction may be caused by direct chemical stimulation as occurs in a methacholine challenge test, allergy in the airway, irritation from chemicals or fumes, hyperosmolarity in the airway, and from nonspecific causes. Given the degree of response to placebo, the osmolarity of the aerosol toward the end of nebulization may well have played a role in causing bronchoconstriction. As a word of caution, the nebulizer was driven by a compressor and consequently a "wet" gas source. Had it been driven by dry hospital gas (or tanks of compressed air), there would have been much more drying and a greater increase in osmolarity.26 There is a suggestion that colistin may have acted as an irritant, causing increased bronchoconstriction in the HR group. It is unlikely that any of the subjects were allergic to colistin, since none had previously been exposed to the drug.
In conclusion, it is apparent that the inhalation of colistin, because of the drug itself, the tonicity of the airway, or a combination of the two, results in a certain degree of bronchospasm and a fall in FEV1 postinhalation. This occurs whether or not the patient has a coexisting tendency for "asthma" or has no family history for asthma or atopy and no response to bronchodilators. However, the degree of fall in FEV1 appears to be greater in the former, placing them at greater risk for respiratory embarrassment due to the nebulization of colistin. Bronchospasm does respond to therapy with bronchodilators, and pretreatment with these agents could be an option in those patients with advanced lung disease and low baseline spirometry. In other words, colistin-induced bronchospasm, while it does exist, appears to be manageable and does not constitute a reason not to administer colistin by inhalation when medically indicated.
| Footnotes |
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The nebulizers were generously provided by Pari Respiratory Equipment, and the colistin was provided by Parke Davis Canada. The study was supported in part by the Canadian Cystic Fibrosis Foundation, and no author had any financial relationship with either Pari Respiratory Equipment Inc. or Parke Davis Canada.
Received for publication February 6, 2004. Accepted for publication September 15, 2004.
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