Objectives: A key systematic review (SR) methodology is comprehensive searching. The Drug Effectiveness Review Project (DERP) SRs search US Food and Drug Administration (FDA) documents to identify unpublished evidence. This study evaluates the success of those efforts.
Study design and setting: We examined DERP reports published since 2003 for the use of FDA preapproval and postmarketing documents. We categorized evidence as (1) unique unpublished studies, (2) supplemental unpublished data, or (3) FDA postmarketing data analysis. Three reviewers independently assigned predetermined impact categories (e.g., qualitative or quantitative usage, fills gaps, confirms findings, and alters conclusions), resolving disagreements through consensus.
Results: Among 114 DERP reports, 19% included unpublished studies and/or supplemental data and 10% included postmarketing analyses. From 175 preapproval documents, 14% provided eligible unpublished studies and 4.0% supplemental unpublished data that helped confirm previous findings, identify important harms, and fill gaps in knowledge about understudied subpopulations, outcomes, and comparisons. Report conclusion statements changed in 9 of 33 instances of premarketing documents compared with 4 of 12 postmarketing analyses.
Conclusions: The FDA documents can provide important unpublished evidence for SRs, although in a small proportion of cases. Future research should identify attributes that predict which reviews may benefit most from review of FDA documents.
Keywords: Drug therapy; Food and Drug Administration; Publication bias; Reporting bias; Systematic reviews; Unpublished evidence.
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