This study will take two 9 months periods. Primary analysis will include a one-sided 95% CI for the difference in failure rate in the prednisolone group minus the Montelukast group. Secondary analyses will include repeated measures ANOVA for differences in changes of continuous variables and the Fisher's Exact test for comparison of proportions. An exploratory sub-group logistic regression analysis will be done for examining interaction between the main treatment effect and possible covariates.