Features and results availability of non-commercial Spanish COVID-19 trials: a systematic review of clinical trial registers and corresponding literature.

Objectives: This study aimed to characterize non-commercial Spanish COVID-19 trials and to determine the availability of results. Differences in outcomes according to the interventions assessed (medicines, non-medicines) will also be determined.

Methods: This systematic review was conducted in March 2024 by searching non-commercial Spanish COVID-19 trials on four registers (EUCTR, Clinical.

Trials: gov, ISRCTN, DRKS) and the WHO ICTRP. Phase-1 medicines trials were excluded. Several variables were retrieved from registers. Publication of main trial results were searched on PubMed, Cochrane COVID-19 Study Register, and Google Scholar. Journals' impact factor and articles' citations on Google Scholar were also registered. Results from medicines and non-medicines trials extracted from registers and articles were compared.

Results: A total of 170 trials (57.1% medicines trials) were identified. These 170 trials were randomized (87.1%), masked (41.8%), or multicenter (39.4%); a total of 15,555 participants were enrolled, mostly in small trials (median, n = 88). Only 8.8% (15/170) of trials posted results on the registers; only 47.6% (81/170) of trials had either published results or posted them on registers. Publications accounted for 92.6% (75/81) of these. Articles were published in 56 different journals, had a median impact factor of 4.4 and a median of 10 citations. Most (58.7%, 44/75) described negative results. There were statistically significant differences (p < 0.001) between medicines and non-medicines trials on timely registration and on being multicenter. This was also the case among published trials with respect to negative results of the primary endpoint.

Conclusion: Although most trials were randomized, a minority were multicenter, large, or masked. Trial results should be posted on the registers to make them accessible to everyone.