Grøn KL, et al. - Whether the nationwide Danish guidelines regarding rheumatoid arthritis patients initiating biological treatment (bDMARDs) could be perceived as a surrogate randomization tool where calendar time rather than patient-specific factors defined choice of bDMARD, was investigated in this observational cohort study emulating a randomized trial (intention-to-treat). As per guidelines, certolizumab pegol (year: 2013-2014, recommended compliance: 80%); abatacept(2014-2015, 80%); biosimilar infliximab(CT-P13) (2015-2016, 50%) were the mandatory drugs for bio-naïve patients who had received concomitant methotrexate. Researchers focused on compliance to guidelines (supporting the assumption of surrogate randomization) as well as on comparing efficacy of certolizumab pegol, abatacept and CT-P13 in patients treated according to guidelines. Findings revealed high compliance to guidelines (70%/65%/59%). For DAS28 remission, the adjusted odds ratios at 6 and 12 months for abatacept were 0.96 and 0.74 and for CT-P13 were 1.38 and 0.96, when compared with certolizumab. Head-to-head comparison of certolizumab pegol, abatacept and CT-P13 was allowed by the surrogate randomization procedure. Despite the estimated efficacy being somewhat different across drugs, wide confidence intervals were reported and statistical significance was not reached.