Comments on the article “Effectiveness and safety of tofacitinib in rheumatoid arthritis: a cohort study”

Excerpt

We read with interest the study published by de Ávila Machado et al. regarding the comparative effectiveness and safety of tofacitinib and non-tumor necrosis factor (TNF) inhibitors among patients with rheumatoid arthritis (RA) [1]. Although the study findings are very interesting, there are several concerns in regard to the study design. First, the study used an exposure definition that caused RA disease severity to be heterogeneous between and within the comparison groups. According to RA treatment guidelines, patients at an early stage of RA are recommended to start a combination of DMARDs, or to initiate TNF inhibitors, or non-TNF inhibitors after the failure of DMARDs monotherapy. On the other hand, patients with an established RA are recommended to use a combination of DMARDs, DMARDs with TNF inhibitors, DMARDs with non-TNF inhibitors, or DMARDs with tofacitinib [2]. Therefore, the exposure definition used in this study may reflect RA patients at different stages of disease severity which has the potential of introducing bias in the observed estimates. …