Outcome measures for clinical trials assessing treatment of cystic fibrosis lung disease.

Cystic fibrosis (CF) is a complex genetic disease characterized by death from loss of lung function. Therapies target pathophysiologic changes associated with pulmonary disease progression. Although therapeutic mechanisms differ, efficacy demonstration is limited to a few accepted outcome measures, each with shortcomings that are becoming more pronounced as CF population health improves. Pulmonary function improvement (as forced expiratory volume in 1 s [FEV1]) and reduction of pulmonary exacerbation risk are commonly used outcomes. Changes in FEV1 decline rate, quality of life, linear growth and/or weight gain are less utilized outcomes. Validated outcomes tend to work best in subjects with more aggressive or advanced lung disease and less so in healthier subjects. Assays of effects on primary therapeutic targets have yet to be validated as surrogate measures of clinical efficacy. As CF population health improves, it will become increasingly difficult to employ current clinical outcome measures to demonstrate efficacy.