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1 Depts of Paediatrics, University of Perugia, Perugia, and 2 University of Naples, Naples, Italy.
CORRESPONDENCE: F. M. de Benedictis, Dept of Paediatrics, "G. Salesi" Children's Hospital, Via Corridoni 11, 60123 Ancona, Italy. Fax: 39 715962234. E-mail: debenedictis{at}ao-salesi.marche.it
Keywords: Exercise-induced bronchoconstriction, montelukast, tolerance
Received: February 10, 2006
Accepted April 16, 2006
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ABSTRACT |
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 TOP ABSTRACT PATIENTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Thirty-two asthmatic children (aged 6–12 yrs) were enrolled in a double-blinded, randomised, parallel group design to receive a 4-week treatment with MNT (5 mg chewable tablets administered once daily in the evening) or placebo. Exercise challenge was performed at baseline and after 3, 7 and 28 days of treatment, 20–24 h after dosing.
MNT was significantly more protective than placebo against EIB at each time. The mean percentage drop of forced expiratory volume in one second (FEV1) was 24.6, 13.6, 12.0 and 11.6 for MNT, and 24.4, 22.4, 21.8 and 21.0 for placebo, at baseline and after 3, 7 and 28 days, respectively. For each drug, no significant difference in the percentage drop of FEV1 was found between different days.
Regular treatment with montelukast provided significant protection against exercise-induced bronchoconstriction in asthmatic children over a 4-week period with no tolerance to the bronchoprotective effect.
Exercise-induced bronchoconstriction (EIB) is a common manifestation of asthma in children and can interfere in their daily activities. The pathogenetic mechanism of EIB is not completely clear, but the release of inflammatory mediators from airway mast cells appears likely 1. Although leukotrienes (LTs) have been inconstantly recovered from urine after exercise 2, the evidence for the role of these mediators in EIB derives from the bronchoprotective effect of anti-LT drugs 3.
Montelukast (MNT), a specific antagonist of cysteinyl-leukotriene (Cys-LT) receptors, showed a consistent effect against EIB in children when administered either as a single dose 4, 5 or as regular treatment 6. In adults, a 12-week treatment with MNT attenuated the fall in pulmonary function following exercise with no tolerance to the bronchoprotective effect 7. No study has evaluated the effect over time of regular treatment with MNT in inhibiting EIB in children. The present authors therefore examined the effect of once-daily MNT on EIB at several time-points during a 4-week treatment period.
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PATIENTS AND METHODS |
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At screening, all patients had a forced expiratory volume in one second (FEV1) of at least 75% of predicted and a decrease in FEV1 of at least 12% from the baseline after a standardised exercise challenge. Patients were not eligible for the study if they had been hospitalised for asthma within 3 months, had contracted a respiratory infection in the 4 weeks before the study, or were affected by other chronic respiratory diseases other than asthma. The use of any anti-asthma drug different from short-acting ß2-agonists within 1 month before the study was a reason for exclusion (except for patients already taking inhaled steroids 200–400 µg daily of beclomethasone dipropionate or equivalent, who were allowed to continue this dose unchanged throughout the study). Immunotherapy at a constant dose was permitted. Patients were withdrawn from the study if the treatment was interrupted for >2 consecutive days, if it was not administered in the evening before the exercise test day, if therapy with an excluded medication was initiated, or in the event of worsening asthma that required treatment with systemic steroids.
Study design
This was a multicentre, double-blinded, randomised, parallel-group, placebo-controlled study. After screening, patients were assigned to receive MNT 5 mg chewable tablet (Singulair, Merck, West Point, PA, USA) or matching placebo once daily at 
20:00 h for 4 weeks. Exercise challenge was repeated at 3±1, 7±2, and 28±3 days after starting treatment, 20–24 h after dosing (the through point of the dosing interval). For each patient, every effort was taken to perform the exercise challenge at the same time of the day. Short-acting, inhaled ß2-agonists were withheld for 12 h before each exercise test.
Exercise challenge
The exercise test consisted of a 2-min warm-up and 6-min steady-state running on a treadmill (RAM of 770 Esoate, Padova, Italy) inclined to produce a heart rate of at least 85% of the maximum predicted for age (calculated as 220–age (yrs)) 9. Small adjustments in workload (treadmill speed or grade) were made, if necessary, to achieve targeted hearth rates. Nasal clips were used during the test and heart rate was continuously monitored. Room temperature and relative humidity were measured and recorded. Differences of 1°C in temperature and 5 mg H2O·L-1 of air in humidity on the test days on each patient were considered acceptable 10. At the discretion of the investigator, patients could receive an inhaled ß-agonist for distressing symptoms at any time during or after exercise challenge.
Pulmonary function measurement
Pulmonary function was measured with a standard spirometer (Microlab 3300; MicroMedical Limited, Rochester, UK) according to accepted standards 11. Predicted normal values for spirometry were obtained from the study by Polgar et al. 12. Measurements were performed before each exercise test (pre-exercise value) and then at 1, 5, 10, 15, 30 and 60 min after the end of the exercise. Heart rate was also measured at these time-points. The exercise test was performed only if the pre-exercise FEV1 was 
70% of the mean predicted for the child's height.
The following parameters were calculated from the results of the pulmonary function tests:
Maximum percentage fall in FEV1 = pre-exercise FEV1–lowest post-exercise FEV1/pre-exercise FEV1
Percentage of protection = (Pp–Pt)/Pp
where Pp is the maximum percentage fall in FEV1 after placebo test, and Pt is the maximum percent fall in FEV1 after active treatment. Clinical protection was considered to have been obtained if the percentage fall in FEV1 after exercise with the drug was half or less than half of the percentage fall in FEV1 after the screening test 13. Tolerance was defined as a significant difference from zero in the slope of the time-response profile of the treatment effect with days 3, 7 and 28 for the end-point.
Compliance
Compliance was measured at each visit by counting the number of packages of tablets that were used, divided by the number of packages of tablets that should have been used during the specific time interval. For the purpose of the study, a compliance of 90% was considered acceptable.
Statistical analysis
Tolerance was the primary end-point, and it was assessed by comparing the rate of change over the 28-day treatment period for the end-point by using an ANOVA model that takes into account the variability within and between patients 14. Unpaired t-test was used to compare the maximum decrease of FEV1 after exercise between the study groups. A paired t-test was used to analyse the within-group change of lung function from baseline. A 95% confidence interval (CI) was constructed for the mean difference in the maximum percentage decrease of FEV1 between the MNT and the placebo group. Fisher’s exact test was used to compare the number of patients who had clinical protection 15. The study was designed to have 80% power (for 32 completing patients) to detect a difference between treatment groups of 50% in the fall of FEV1 after exercise, on the assumption that variability was similar to that observed in previous studies 4, 16. Differences were considered significant when p<0.05.
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RESULTS |
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TOPABSTRACTPATIENTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The mean±SD percentage drop in FEV1 was 24.6±12.3, 13.6±12.9, 12.0±9.7, 11.6±11.1 for MNT, and 24.4±7.7, 22.4±6.4, 21.8±7.3, 21.0±5.7 for placebo at screening test and after 3, 7 and 28 days of treatment, respectively (table 2). At screening, there was no difference in the percentage drop of FEV1 between MNT and placebo (p = 0.096; mean difference -0.15; 95% CI -7.87–7.56). Conversely, a significant difference between the two drugs was observed at each time-point after treatment: day 3, p = 0.026 (mean difference 8.81; 95% CI 1.15–16.48; day 7, p = 0.005 (mean difference 9.83; 95% CI 3.21–16.45); and day 28, p = 0.011 (mean difference 9.47; 95% CI 2.37–16.58; fig. 1).
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). There was no difference in lung function changes after exercise between patients who were receiving or not receiving inhaled steroids. Percentage of protection for MNT was 39, 44 and 44% after 3, 7 and 28 days, respectively. Clinical protection was provided in seven out of 15 (46%) versus one out of 15 (6%; p<0.05), 10 out of 15 (66%) versus 0 out of 14 (p<0.005), nine out of 14 (64%) versus one out of 13 (7%; p<0.005) patients treated with MNT or placebo after 3, 7 and 28 days, respectively. No adverse events were seen. Compliance rates ranged 94–100% and were similar across treatment groups.
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DISCUSSION |
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TOPABSTRACTPATIENTS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The protective effect of MNT on EIB is in accordance with the results of previous studies in asthmatic children 4, 5, 6, 17 and further supports the role of Cys-LTs in the pathogenesis of EIB 2, 18. The percentage protection of MNT on EIB after 3 days of treatment was very close to that observed in other exercise studies, after a single dose 5 or two doses 4. Data from the current study therefore confirm that long-term use of MNT is not a prerequisite for its efficacy on EIB. Although intermittent administration of this drug might be beneficial as either first-line or adjunct therapy in individuals in whom EIB is the primary manifestation of asthma 19, anti-inflammatory treatment should be instituted on regular basis.
The current study was the first to evaluate the effect of MNT against EIB at different time-points during regular therapy in children. In adults, 12-week treatment with MNT attenuated the fall in pulmonary function following exercise with no tolerance 7. However, the time effect of MNT during the first 4 weeks of treatment, which may be a window for the onset of early tolerance, has not been formally evaluated. Villaran et al. 20 and Edelman et al. 21 examined the effect of MNT and salmeterol on EIB over an 8-week period. Protection by MNT was evident at day 3 and persisted throughout the whole treatment period without development of tolerance, while the effect of salmeterol appeared to wane over time. Unfortunately, the placebo group was not included in these studies, thus making the conclusions on lack of early tolerance to the bronchoprotective effect of MNT inconsistent.
The present study offers evidence that bronchoprotection induced by MNT is of similar magnitude after 3, 7 and 28 days. The finding that the degree of protection against EIB is not diminished over time differentiates MNT from other anti-asthmatic agents and may result in relevant clinical advantage. Indeed, several studies highlighted that the extent of protection on EIB diminishes with the regular use both for short-acting and long-acting ß2-agonists 22. Furthermore, in a placebo-controlled study of EIB in children, 12-week treatment with inhaled beclomethasone induced tolerance to the bronchoprotective effect 23.
A statistically significant effect of a drug on EIB does not necessarily indicate the effect is clinically important. Therefore, the clinical protection against EIB was also evaluated as an index of good clinical control. This analysis yielded the same results as that of the percentage decrease in FEV1 itself, and corroborates the role of MNT in the prevention of EIB. The rate of nonresponders to MNT varied from 54 to 36% at different times. No conclusions can be drawn about the clinical characteristics of such patients, since the present study was not designed to answer this question. Almost a quarter of the children in the current study were receiving regular treatment with inhaled steroids. These patients showed the same response as those who were not treated with these agents. On this point, it is relevant to note that tolerance to bronchoprotection afforded by anti-asthmatic drugs, such as ß2-agonists, is not prevented by concomitant inhaled steroid therapy 24.
The effect of MNT on baseline FEV1 was not significant in the current study. This finding has been found by other authors 6, 7 and might reflect the characteristics of patients in the current study who had normal lung function in the majority of cases. Some studies showed that MNT manifests a mild bronchodilator activity 25, but the protection against EIB afforded by this drug is independent of lung function values 7, 20. This aspect supports the view that other factors in addition to smooth muscle inhibition play a role in drug-induced protection against exercise. Evaporative water loss from airway mucosa is considered an important mechanism in the pathogenesis of EIB as it may cause a transient change in osmolarity in the epithelial fluid, which subsequently induces the release of inflammatory mediators 26.
No significant difference in the percentage fall of FEV1 after exercise was observed on the screening or placebo days, indicating that subjects remained responsive to exercise throughout the study period. In the placebo group, the fall of FEV1 at different time-points was universally (except for two cases) less than half of the screening value for each patient, thus explaining that exercise-induced reduction in lung function was also reproducible for individuals.
In conclusion, regular once-daily treatment with montelukast does not appear to reduce the protective effect on exercise-induced bronchoconstriction over time and may represent a preferential therapeutic option for chronic treatment of exercise-induced bronchoconstriction in children.
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: montelukast; 
: placebo. #: p = 0.026; ¶: p = 0.005; +: p = 0.011.