Publication and non-publication of drug trial results: a 10-year cohort of trials in Norwegian general practice

OBJECTIVES: Previously, we identified a 10-year cohort of protocols from applications to the Norwegian Medicines Agency 1998-2007, consisting of 196 drug trials in general practice. The aim of this study was to examine whether trial results were published and whether trial funding and conflicts of interest were reported. DESIGN: Cohort study of trials with systematic searches for published results. SETTING: Clinical drug trials in Norwegian general practice. METHODS: We performed systematic literature searches of MEDLINE, Embase and CENTRAL to identify publications originating from each trial using characteristics such as test drug, comparator and patient groups as search terms. When no publication was identified, we contacted trial sponsors for information regarding trial completion and reference to any publications. MAIN OUTCOME MEASURES: We determined the frequency of publication of trial results and trial characteristics associated with publication of results. RESULTS: Of the 196 trials, 5 were never started. Of the remaining 191 trials, 71% had results published in a journal, 11% had results publicly available elsewhere and 18% of trials had no results available. Publication was more common among trials with an active comparator drug (χ(2) test, p=0.040), with a larger number of patients (total sample size≥median, p=0.010) and with a longer trial period (duration≥median, p=0.025). Trial funding was reported in 85% of publications and increased over time, as did reporting of conflicts of interest among authors. Among the 134 main journal articles from the trials, 60% presented statistically significant results for the investigational drug, and the conclusion of the article was favourable towards the test drug in 78% of papers. CONCLUSIONS: We did not identify any journal publication of results for 29% of the general practice drug trials. Trials with an active comparator, larger and longer trials were more likely to be published.