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* From the Department of Clinical Pharmacology and Therapeutics, Ninewells Hospital and Medical School, University of Dundee, Dundee, Scotland, UK.
Correspondence to: Brian J. Lipworth, MD, Department of Clinical Pharmacology and Therapeutics, Ninewells Hospital and Medical School, University of Dundee, Dundee, Scotland DD1 9SY, UK
| Abstract |
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Design: Placebo-controlled, double-dummy, crossover study.
Setting: Outpatient clinic.
Patients: Twenty patients with persistent asthma not controlled with inhaled corticosteroid therapy.
Interventions: Montelukast, 10 mg once daily, or salmeterol, 50 µg bid, each for 2 weeks with 1-week run-in and washout placebo periods.
Measurements and results: Adenosine monophosphate (AMP) bronchial challenge, blood eosinophil count (EOS), exhaled nitric oxide, and lung function after both placebo periods and after the first and last doses of each active treatment. Patients recorded their domiciliary peak expiratory flow (PEF), asthma symptoms, and rescue bronchodilator requirement (RES) twice daily throughout the study. For the primary end point of the provocative concentration of AMP causing a 20% fall in FEV1, compared to placebo (47.5 ± 13.0 mg/mL), there were significant differences with the first (114.1 ± 36.9 mg/mL) and last (94.2 ± 30.4 mg/mL) doses of montelukast as well as the first (160.1 ± 64.5 mg/mL) but not the last (70.1 ± 23.7 mg/mL) dose of salmeterol. Only montelukast produced significant suppression of the EOS. Neither drug affected exhaled nitric oxide levels. There were significant improvements with the first doses of salmeterol for all parameters of lung function. After 2 weeks of treatment, there were significant improvements with both drugs for RES and morning PEF. There were no significant differences between drugs for any end points except EOS.
Conclusions: Montelukast and salmeterol exhibited significant improvements in asthma control when given as second-line therapy. Montelukast also produced significant effects on AMP challenge and EOS suggesting anti-inflammatory activity.
Key Words: adenosine monophosphate inhaled corticosteroids montelukast nitric oxide salbutamol symptoms
| Introduction |
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Combining a long-acting ß2-agonist with low-dose inhaled corticosteroid has been shown to provide equivalent or superior asthma control than using higher doses of inhaled corticosteroid alone,2 as is reflected in current asthma management guidelines. However, as long-acting ß2-agonists are bronchodilators and act mainly at the bottom of the inflammatory cascade, there are concerns that they may mask underlying inflammation.3 Also, when given on a regular basis, long-acting ß2-agonists have been shown to exhibit tolerance to their bronchoprotective and bronchodilator effects as a result of ß2-adrenoceptor downregulation.4 5 6 7
Leukotriene receptor antagonists are a novel class of therapy available in the management of asthma. They have both anti-inflammatory and bronchodilator activity, although not as great as that of inhaled corticosteroids or long-acting ß2-agonists, respectively.8 They have been shown to have additive clinical effects in patients with severe asthma during tapering step-down with inhaled corticosteroid therapy.9 10 In a multicenter trial11 of patients with persistent asthma, 80% of whom were receiving concomitant inhaled corticosteroids, treatment with salmeterol produced significantly greater improvements than zafirlukast in overall asthma control as assessed by peak flow, asthma symptoms, and albuterol use. This study, however, did not evaluate the effects on bronchial hyperresponsiveness or airway inflammation.
We have previously documented that single doses of montelukast and salmeterol are bronchoprotective against adenosine monophosphate (AMP) bronchial challenge.12 We therefore decided to evaluate the long-term dosing effects of salmeterol and montelukast as second-line treatment in patients whose asthma was not adequately controlled with inhaled corticosteroid as monotherapy. The primary end point was to assess the effects on AMP bronchial challenge, which causes bronchoconstriction indirectly by release of inflammatory mediators from primed mast cells.13 AMP bronchial challenge has been shown to be more sensitive in detecting anti-inflammatory effects than a direct bronchial challenge, such as methacholine, and is probably more clinically relevant.14 We also assessed subgroup inflammatory markers, including exhaled nitric oxide and blood eosinophil count (EOS),15 16 as well as daily symptom control, rescue bronchodilator requirements (RESs), peak expiratory flow (PEF), and lung function.
| Materials and Methods |
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Methods
The study was of a randomized, placebo-controlled, single-blind,
double-dummy, crossover design. Unfortunately, we were unable to obtain
identical placebo tablets; therefore, the study was of a single-blind
design. Patients continued with their usual maintenance dose of
inhaled corticosteroid treatment throughout the study. In addition,
patients were randomized to receive (1) inhaled salmeterol 50 µg
twice daily, plus placebo tablet once daily, or (2) oral montelukast,
10 mg once daily, plus placebo inhaler twice daily. Each
active-treatment phase was for a duration of 2 weeks. Before each
treatment and at crossover, patients had a 1-week treatment period with
placebo inhaler (one inhalation twice daily) and placebo tablets once
daily while continuing with their inhaled corticosteroids. All tablets
were taken at 8 AM, and inhaled medications were taken at 8
AM and 8 PM. Two puffs of inhaled ipratropium
bromide, 40 µg per puff, were used as required for symptomatic relief
purposes as first-line rescue, with inhaled salbutamol as second-line
rescue.
The inhalers and tablets were masked and sealed in envelopes by a pharmacist along with instruction sheets at the beginning of the trial. Before the study and at each visit, subjects were given detailed instruction by a third party in how to use their inhalers. Each subject received a written instruction sheet to follow while taking his or her medication at home, based on the recommended advice of the manufacturers, and a simple tick chart was used as an aide to compliance. Data from patients with > 90% compliance over the study were considered to be evaluable.
Measurements
All laboratory measurements were performed at 8 AM.
Patients attended at the end of the 1-week run-in and crossover washout
placebo periods, and after each 2-week active-treatment period.
Patients also attended after the first dose of active therapy,
ie, 12 h after the first dose of inhaled salmeterol and
24 h after the first dose of oral montelukast.
AMP challenge testing was performed as previously
described,18
between 8 AM and 10
AM, after patients had withheld treatment with their
reliever medication for 12 h. In brief, AMP that had been prepared
fresh daily was administered in doubling cumulative doses given at
5-min intervals until a fall in FEV1
20% was
recorded. The PC20 was calculated using a
computer-assisted curve-fitting package (Biolab Assistant 1.1;
University of Dundee; Dundee, Scotland, UK) and interpolation of the
steep part of the log dose-response curve. A value of 1,600 mg/mL was
assigned if the FEV1 did not fall below 20% of
the baseline value.
Patients underwent measurement of exhaled nitric oxide using an integrated, clinical, real-time, nitric oxide gas analyzer (model LR2000; Logan Research; Rochester, UK) using the procedures described by Kharitonov et al.19 Three measures of nitric oxide were taken, and the results were analyzed as the mean of the three values. Spirometry was performed using a Vitalograph compact spirometer (Vitalograph Ltd; Buckinghamshire, UK).
Airways resistance was measured in a constant-volume, pressure-compensated, whole-body plethysmograph (PK Morgan; Gillingham, Kent, UK). Patients also provided a blood sample for measurement of EOS at 8 AM on arrival to the laboratory on each occasion. EOS was measured using an SE-9000 Hematology Analyzer (Sysmex UK Ltd; Bucks, UK).
Throughout the study, at 8 AM and 10 PM, patients recorded the highest of three measurements of PEF using a Mini-Wright peak flowmeter (Clement Clarke; Essex, UK), with their symptoms of asthma according to a 4-point scale with zero indicating no symptoms and 3 indicating severe symptoms, and their requirement for rescue bronchodilator therapy.
Statistical Analysis
The study was designed with at least 80% power to detect a 1.0
doubling-dose difference (twofold) in PC20 (the
primary end point) for active treatment vs placebo, with the
error
set at 0.05 (two tailed). The data for PC20 were
log transformed in order to normalize their distribution before
analysis. All PC20 data are therefore represented
as geometric mean with the geometric SEM in parenthesis. For all
domiciliary diary data, mean values for the 7-day run-in and washout
placebo periods and for the 2 weeks of each active-treatment period
were analyzed. Overall comparisons for active treatments vs placebo
treatments were made by multifactorial analysis of variance using
subject, treatment, period, and duration of treatment (first dose/last
dose) as factors. This was followed by Bonferroni multiple-range
testing (set at 95% confidence interval [CI]) in order to obviate
multiple pairwise comparisons. Consequently, comparisons are only
denoted as being significant (p < 0.05) or not significant in order
to not confound the
error. The analysis was performed using a
statistical software package (Statgraphics; STSC Software Publishing
Group; Rockville, MD).
| Results |
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| Discussion |
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In the present study, there was no loss of beneficial effects in diurnal asthma control over the 2-week period (Fig 3) , in contrast to marked loss in bronchoprotection against bronchial challenge (Fig 1) . This apparent discrepancy between the comparative effects on bronchial challenge or lung function and diurnal asthma control may be explained by their relative degrees of tolerance, although proper evaluation of bronchodilator tolerance would have required assessment of a salbutamol dose-response curve. Tolerance with long-acting ß2-agonists is recognized to be more pronounced with their bronchoprotective than bronchodilator effects.22 Grove and Lipworth5 showed in a study comparing the effects of salmeterol, 50 µg bid, or placebo in patients receiving inhaled corticosteroids, that although there were improvements in PEF and reductions in rescue bronchodilator therapy, there was only a 0.7-doublingdose residual protection against histamine challenge after 4 weeks. In a study with regular formoterol, 24 µg bid for 2 weeks, in addition to inhaled corticosteroid therapy, there was 0.5-doublingdose protection against methacholine after 2 weeks with sustained improvement in peak flows.4 Similarly, with AMP bronchial challenge, there was an 0.8-fold protection after 1 week of regular formoterol, 24 µg bid.7 The mechanism for this tolerance is thought to occur as a result of ß2-adrenoceptor uncoupling from the stimulatory G protein, internalization of surface receptors, and reduced transcription of receptor messenger RNA.23 24
Our results are consistent with previous studies4 5 with salmeterol and formoterol, where there was a residual degree of trough bronchoprotection with AMP and methacholine between 0.5 doubling doses and 0.8 doubling doses. We deliberately elected to measure trough measurements with both drugs at the end of their usual dosing interval, as this reflects the period when the airways are most susceptible to bronchoconstrictor stimuli.
Leukotriene receptor antagonists have been shown to have bronchoprotective properties with allergen, exercise, and other challenges,8 although there are no previous data regarding their effects on AMP bronchial challenge that is a useful marker of inflammation.13 The bronchoprotective properties of long-acting ß2-agonists on AMP bronchial challenge are partly because of functional antagonism of smooth muscle ß2-adrenoceptors, although there may be a component because of direct inhibition of the mast cell ß2-adrenoceptors.25
There are conflicting data on the effects of leukotriene receptor antagonist, administered as monotherapy, on bronchial hyperreactivity. In a dose-response study for 12 weeks, montelukast had no significant effect on methacholine challenge, compared to placebo.26 In a randomized, double-blind, crossover study, zafirlukast, 20 mg bid, and fluticasone propionate, 100 µg bid, for 2 weeks exhibited 1.7-fold and 2.8-fold protection, respectively, against histamine challenge.27 In a subgroup analysis of a randomized crossover trial, there was 2.4-fold protection against methacholine hyperreactivity after 2 weeks of zafirlukast, 20 mg bid, compared to placebo.28 Two studies with pranlukast have also shown protection against methacholine challenge, which in one study was accompanied by biopsy specimen changes of reduced airway inflammatory cells.29 30
It is possible that the relatively small effect observed in the present study with montelukast may have been because of the relatively short duration of treatment and that it would take longer to achieve a maximal response. It should also be pointed out that underlying bronchial hyperreactivity would have already been blunted by the preexisting inhaled corticosteroid therapy. The importance of assessing bronchial hyperreactivity is reinforced by a study from Sont et al,31 in which it was found that altering steroid therapy according to bronchial hyperreactivity in addition to symptom control and lung function resulted in better asthma control and a reduction in airway inflammation on bronchial biopsy specimens. This, in turn, suggests that using two drugs that have additive effects on airway inflammation (ie, inhaled corticosteroids and leukotriene receptor antagonists) may have beneficial effects on asthma disease activity. This is supported by two separate studies,9 10 in which adding-in montelukast facilitated a lower maintenance dose of inhaled corticosteroids during tapered step-down.
We also assessed asthmatic inflammation by measuring effects on peripheral EOSs and exhaled nitric oxide. The blood eosinophil concentration is considered to be a surrogate marker of asthmatic disease activity,16 with an increase in number because of recruitment from the bone marrow during asthmatic inflammation.32 We found significant reduction in blood eosinophil numbers with montelukast but not with salmeterol, which is in keeping with previous studies.33 34 It may be unfair, however, to compare the effects of a topical drug such as salmeterol and a systemic drug such as montelukast on a systemic marker of disease activity. In this respect, recent data35 have shown that treatment with regular formoterol as monotherapy induced significant reductions in eosinophil numbers in bronchial biopsy specimens. Exhaled nitric oxide is a sensitive marker of airway inflammation, and it therefore may be surprising to find no difference with either treatment when compared to placebo. However, recent data36 have shown that the dose-response curve for exhaled nitric oxide becomes flat after 400 µg/d of inhaled budesonide. As all of our patients were receiving inhaled corticosteroids at a dose > 400 µg/d before the run-in period, exhaled nitric oxide levels would not be expected to significantly change with the addition of second-line treatment.
In conclusion, although we have shown that salmeterol and montelukast are both useful adjunctive therapies for asthma not adequately controlled with inhaled corticosteroids, the addition of montelukast may confer anti-inflammatory effects. Longer-term studies are required to evaluate the effects of salmeterol and montelukast on asthma exacerbation rates when administered as second-line therapy in addition to inhaled corticosteroids.
| Acknowledgements |
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| Footnotes |
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This study was funded by a University of Dundee departmental grant and received no support from the pharmaceutical industry.
Received for publication May 11, 2000. Accepted for publication October 27, 2000.
| References |
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