Background: Idiopathic pulmonary fibrosis (IPF) is a devastating disease, yet validated, reliable criteria for evaluating patient response to therapies in clinical trials are lacking.
Methods: To optimize selection of end point criteria for the study of interferon (IFN)-γ1b in patients with IPF, we retrospectively analyzed the components of the primary efficacy end point used in a large, controlled study of 330 patients for reliability, validity, and sensitivity to treatment effect. The primary end point components were death, disease progression defined as a ≥ 5 mm Hg increase in resting alveolar-arterial oxygen pressure gradient (P[A-a]O2), and disease progression defined as a ≥ 10% decrease in percentage of predicted FVC.
Results: We found that the P(A-a)O2 criterion was not reliable and was not associated with mortality. In contrast, the FVC criterion was reliable and was associated with a 2.4-fold increase in the risk of death. Of the three measures, only mortality was sensitive to a treatment effect of IFN-γ1b. Additionally, the tendency for mortality benefit was observed in nearly all patient subgroups defined by baseline physiology. The effect of IFN-γ1b on mortality was strongest in patients with baseline percentage of predicted FVC ≥ 55% (p = 0.004) or percentage of predicted diffusing capacity of the lung for carbon monoxide ≥ 30% (p = 0.008).
Conclusion: We conclude that mortality is the most inclusive end point for future trials of IFN- γ1b in patients with IPF, and that a > 10% decrement in the percentage of predicted FVC represents a valid measure of disease progression.