- Leukotriene receptor antagonists have become an integral part of asthma treatment as an add-on therapy for patients with moderate disease activity. To determine whether in vivo treatment with montelukast, a leukotriene receptor antagonist, at the recommended therapeutic dose affects neutrophil functions which are essential for host defense. Twenty nonsmoking patients between the ages of 18 and 70 with moderate asthma were recruited to the study. All of them were receiving inhaled corticosteroids for at least 6 months and beta2-agonist as needed. After the 2-week run-in period, in addition to the regular medication, each patient was treated with 10 mg of montelukast for a 6-week period. Pulmonary function test was performed and blood was tested for neutrophil activity twice during the run-in period and twice during the treatment period. Each assay was performed in parallel to a matched control. The 6-week treatment period with montelukast did not significantly affect neutrophil chemotaxis or phagocytosis nor the elevated superoxide production. However, at 2 weeks of treatment some of the patients showed a reduction in neutrophil function. The study demonstrated that the recommended dose of montelukast has no significant effect on peripheral blood neutrophil activities, indicating that montelukast treatment does not induce an inflammatory process and does not interfere with the first line of host defense.