Inhaled Tobramycin Effectively Reduces FEV^sub 1^ Decline in Cystic: Fibrosis An Instrumental Variables Analysis

This study aims to determine effectiveness of inhaled tobramycin on FEV^sub 1^ decline in patients with chronic P. aeruginosa infections using observational data from the Cystic Fibrosis Foundation Patient Registry. Patient-level tobramycin use was measured at first chronic P. aeruginosa infection. Decline in FEV^sub 1^ 2 years after infection was estimated for patients treated with tobramycin and compared with untreated patients. Multiple linear regressions with confounder adjustment and propensity scores were used to estimate mean FEV^sub 1^ decline for each group. Because care is organized by centers, we used center-specific prescription rates as an instrument to reduce treatment-by-condition bias. Using center-level prescribing rates, instrumental variables analysis showed less FEV1 decline for patients who received tobramycin when first eligible compared with those who did not receive tobramycin.