Context: Concerns about the safety and efficacy of diabetes interventions persist, in part because randomized clinical trials (RCTs) have not measured their effect on patient-important outcomes, ie, death and quality of life (morbidity, pain, function).
Objective: To systematically determine the extent to which ongoing and future RCTs in diabetes will ascertain patient-important outcomes.
Data sources: On November 10, 2007, we searched primary RCT registries ClinicalTrials.gov (http://www.clinicaltrials.gov), International Standard Randomized Controlled Trial Number Register (http://isrctn.org), and Australian New Zealand Clinical Trials Registry (http://www.anzctr.org.au).
Study selection: We identified phase 2 through 4 RCTs enrolling patients with diabetes. Of 2019 RCTs, 1054 proved eligible. We randomly sampled 50% of the eligible RCTs (527 of 1054) and selected 436 registered since registration became mandatory (2004).
Data extraction: Pairs of reviewers working independently collected study characteristics and determined the outcomes measured and their type (physiological outcomes, surrogate outcomes thought to reflect an increased risk for patient-important outcomes, and patient-important outcomes).
Results: Of the 436 registered RCTs included in this analysis, 24 (6%) had not started enrollment, 109 (25%) were actively enrolling, and 303 (69%) had completed enrollment. Primary outcomes were patient-important outcomes in only 78 of 436 RCTs (18%; 95% confidence interval [CI], 14%-22%), physiological and laboratory outcomes in 69 of 436 (16%; 95% CI, 13%-20%), and surrogate outcomes in 268 of 436 (61%; 95% CI, 57%-66%). Patient-important outcomes were reported as primary or secondary outcomes in 201 of 436 (46%; 95% CI, 41%-51%). In multivariate analysis, large trials (odds ratio [OR], 1.10; 95% CI, 1.02-1.19 for every additional 100 patients) and trials of longer duration (OR, 1.03; 95% CI, 1.01-1.06 for every additional 30 days) were more likely while parallel design RCTs (OR, 0.15; 95% CI, 0.05-0.44) and type 2 diabetes trials (OR, 0.23; 95% CI, 0.09-0.61) were less likely to assess patient-important outcomes as a primary outcome.
Conclusion: In this sample of registered ongoing RCTs in diabetes, only 18% included patient-important outcomes as primary outcomes.