Outcome measures that can evaluate treatment efficacy are important to enhance development of new therapeutic agents for Cystic Fibrosis (CF). We investigated whether the lung clearance index (LCI) measured by multiple breath washout (MBW) can detect a treatment effect of hypertonic saline (HS) inhalation after single dosing within a 24 h period.

In this randomized controlled cross-over trial, CF patients received inhalation of HS and isotonic saline (IS). MBW and spirometry were performed at 5 time points over 24 h. LCI was measured using both a nitrogen washout technique (LCI_N2) and sulfur hexafluoride as a tracer gas (LCI_SF6). The primary endpoint was the change in the LCI_N2 between baseline and 24 h. Secondary endpoints included change in LCI_SF6 and spirometry outcomes.

Twenty-one patients were randomized. Sixteen completed all study visits and all time point measurements. Eighteen patients contributed to the intention to treat analysis. Significant changes were not detected for either LCI or the spirometry outcomes. However, the primary outcome parameter (change in LCI between the baseline visits and 24 h after inhalation) demonstrated a trend towards improved LCI, in the HS treatment arm compared with the IS treatment arm, −0.60 LCI_N2 (SE 0.32), p = 0.08); similar trends were not observed for spirometric measures. The overall effect size of HS was smaller than in previous studies of longer duration.

These data suggest that LCI may potentially be used as an outcome measure in early phase trials with therapeutic agents that have a larger treatment effects than a single inhalation of HS.