FDA's Flexibility in Subpart H Approvals: Assessing Quantum of Effectiveness Evidence.

This article examines the strength of scientific and clinical evidence for FDA's nineteen non-AIDS, non-cancer Subpart H approval determinations over the Accelerated Approval program's twenty-four year existence. The authors researched the bases for FDA's determinations when an unvalidated surrogate or intermediate clinical endpoint is "reasonably likely to predict clinical benefit." The four key factors set forth in FDA's "Guidance for Industry, Expedited Programs for Serious Conditions - Drugs and Biologics" were applied to past Subpart H approvals. For the nineteen precedents, the authors found wide variances between the quantum and quality of evidence on each of the four factors, indicating that a lack of evidence on any single factor was not disqualifying in and of itself. The results of this study, therefore, show that FDA exercises extraordinarily more regulatory flexibility than either FDA's foundational statutes or even FDA' s most recent 2014 Expedited Programs Guidance explicitly express. Given recent legislative exhortations and the increasing promise of personalized medicine and translational sciences, the authors conclude that Subpart H should be further explored and utilized. The authors provide a detailed analysis of the orecedents established in the nineteen approvals.