Ability of a meta-analysis to prevent redundant research: systematic review of studies on pain from propofol injection

Objective To examine whether, according to the conclusions of a 2000 systematic review with meta-analysis on interventions to prevent pain from propofol injection that provided a research agenda to guide further research on the topic, subsequently published trials were more often optimally blinded, reported on children, and used the most efficacious intervention as comparator; and to check whether the number of new trials published each year had decreased and whether the designs of trials that cited the review differed from those that did not. Study design Systematic review comparing old trials (published before, and included in, the review) with new trials (published afterwards). Data sources Medline, Cochrane, Embase, and bibliographies to January 2013. Eligibility criteria for study selection Randomised studies testing any intervention to prevent pain from propofol injection in humans. Results 136 new trials (19 778 patients) were retrieved. Compared with the 56 old trials (6264 patients), the proportion of optimally blinded trials had increased from 10.7% to 38.2% (difference 27.5%, 95% confidence interval 16.0% to 39.0%, P<0.001), and the proportion of trials that used the most efficacious intervention as comparator had increased from 12.5% to 27.9% (difference 15.4%, 4.0% to 26.9%, P=0.022). The proportion of paediatric trials had increased from 5.4% to 12.5%, although this was not significant (difference 7.1%, -1.0% to 15.2%, P=0.141). The number of new trials published each year was significantly higher (median number/year 12 (range 7-20) v 2.5 (0-9), P<0.001) with no obvious decreasing trend. 72.8% (n=99) of the new trials cited the review, with their designs similar to trials not citing the review. Only 36.0% (n=49) of the new trials were considered clinically relevant since they used the most efficacious intervention as comparator or included a paediatric population. Conclusions The impact of the systematic review on the design of subsequent research was low. There was an improvement in the reporting of optimal blinding procedures and a tendency towards an increase in the proportion of paediatric trials. The most efficacious intervention was more often chosen as comparator but remained marginally used, and the number of trials published per year had not decreased. The use of systematic reviews should be encouraged to inform rational, and thus ethical, trial design and improve the relevance of new research.