Systemic drugs-like oral montelukast can reach lower airways, whose inflammation plays a crucial role in the evolution of asthma, while inhaled drugs hardly reach them. The impulse oscillometry (IOS) technique is useful to evaluate both central and peripheral airways function.

To measure the effect of oral montelukast on airways resistance evaluated by oscillometry in children with asthma.

In an open study, respiratory function in 23 children with mild asthma and a positive bronchodilator response was assessed by spirometry and oscillometry. They took oral montelukast during 4 weeks and were again evaluated. As a control group, 23 similar patients with no preventive treatment underwent the same study.

Children on oral montelukast showed improvements (measured in kPasL⁻¹) in all oscillometry parameters: mean 0.20 (22.4%) in total respiratory impedance Zrs5, 0.18 (21.8%) in total airway resistance Rrs5, 0.09 (17.8%) in central airway resistance Rrs20, and 0.09 (28.8%) in distal capacitive reactance Xrs5; the frequency of resonance Fres improved 2.3Hz (8.7%) (  in all cases). No changes were found in the control group. Expiratory flows showed no changes except for a small (0.23Ls⁻¹, 7.4%) but significant worsening of FEF25–75 in the control group.

Montelukast improves central and especially peripheral airways function in the first month of treatment, as evaluated by IOS, a technique based on tidal breathing analysis which is more sensitive than conventional forced spirometry.