The response to TNF blockers depending on their comparator in rheumatoid arthritis clinical trials: the lessebo effect, a meta-analysis.

To compare the effect of the biological reference agents (infliximab, etanercept, adalimumab) in RA in pivotal superiority placebo-controlled trials (reference agent vs placebo) vs their effect in equivalence active comparator-controlled trials (reference agent vs biosimilar). The PubMed, EMBASE and Cochrane databases were searched for randomized, double-blind, controlled trials up to March 2020 comparing a biological reference agent vs placebo or biosimilar. The study assessed the ACR 20/50/70 responses of the reference agent in these groups (Reference-pbo and Reference-bs, respectively). The effect of the reference agent in both groups was estimated with 95% CI, pooled using random-effects models and then compared using a meta-regression model. We included 31 trials. The main characteristics of the population (disease duration and activity, % seropositivity and methotrexate dose) of the population in both groups were similar. The meta-analysis found a better ACR20 response to the biological originator in the Reference-bs group with a global rate of 70% (95% CI, 66, 74) compared with 59% (95% CI, 55, 62) in the reference-pbo group (P =0.001). A significant difference was also found for ACR 50 [44% (95% CI, 39, 50) vs 35% (95% CI, 31, 39), respectively, P <0.01]. The effect of the reference biologic agent was better when compared with an active drug to a placebo. This could be linked to an increased placebo effect in active comparator-controlled studies or a nocebo effect in placebo-controlled studies. This effect can be called the lessebo effect.

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