Background: Pharmaceutical companies and other trial sponsors must submit certain trial results to ClinicalTrials.gov. The validity of these results is unclear.
Purpose: To validate results posted on ClinicalTrials.gov against publicly available U.S. Food and Drug Administration (FDA) reviews on Drugs@FDA.
Data sources: ClinicalTrials.gov (registry and results database) and Drugs@FDA (medical and statistical reviews).
Study selection: 100 parallel-group, randomized trials for new drug approvals (January 2013 to July 2014) with results posted on ClinicalTrials.gov (15 March 2015).
Data extraction: 2 assessors extracted, and another verified, the trial design, primary and secondary outcomes, adverse events, and deaths.
Results: Most trials were phase 3 (90%), double-blind (92%), and placebo-controlled (73%) and involved 32 drugs from 24 companies. Of 137 primary outcomes identified from ClinicalTrials.gov, 134 (98%) had corresponding data at Drugs@FDA, 130 (95%) had concordant definitions, and 107 (78%) had concordant results. Most differences were nominal (that is, relative difference <10%). Primary outcome results in 14 trials could not be validated. Of 1927 secondary outcomes from ClinicalTrials.gov, Drugs@FDA mentioned 1061 (55%) and included results data for 367 (19%). Of 96 trials with 1 or more serious adverse events in either source, 14 could be compared and 7 had discordant numbers of persons experiencing the adverse events. Of 62 trials with 1 or more deaths in either source, 25 could be compared and 17 were discordant.
Limitation: Unknown generalizability to uncontrolled or crossover trial results.
Conclusion: Primary outcome definitions and results were largely concordant between ClinicalTrials.gov and Drugs@FDA. Half the secondary outcomes, as well as serious events and deaths, could not be validated because Drugs@FDA includes only "key outcomes" for regulatory decision making and frequently includes only adverse event results aggregated across multiple trials.
Primary funding source: National Library of Medicine.