Combined Conventional Synthetic Disease Modifying Therapy vs. Infliximab for Rheumatoid Arthritis: Emulating a Randomized Trial in Observational Data

Abstract

Observational studies are often considered unreliable for evaluating relative treatment effectiveness, but it has been suggested that following target trial protocols could reduce bias. Using observational data from patients with rheumatoid arthritis (RA) in the Swedish Rheumatology Quality Register (SRQ), between 2006 and 2020, we emulated the protocol of the Swedish Farmacotherapy trial (SWEFOT) and compared the results. SWEFOT was a pragmatic trial nested in SRQ, between 2002 and 2005, where methotrexate (MTX) insufficient responders were randomized to receive additional infliximab or sulfasalazine (SSZ) + hydroxychloroquine (HCQ). Patients with RA initiating infliximab (N = 313) or SSZ + HCQ (N = 196) after MTX were identified in SRQ and the Prescribed Drugs Register, mimicking the SWEFOT eligibility criteria. The primary outcome was the proportion of European Alliance of Associations for Rheumatology (EULAR) good responders at 9 months, classifying patients who discontinued treatment as "nonresponders." Through sensitivity analyses, we assessed the impact of relaxing eligibility criteria. The observed proportions reaching EULAR good response were close to those reported in SWEFOT: 39% (vs. 39% in SWEFOT) for infliximab and 28% (vs. 25%) for SSZ + HCQ. The crude observed response ratio was 1.39 (95% confidence interval (CI) 1.04-1.86), increasing to 1.48 (95% CI 0.98-2.24) after confounding adjustment, compared to 1.59 (95% CI 1.10-2.30) in SWEFOT. Results remained close to SWEFOT when relaxing eligibility criteria until allowing prior disease-modifying anti-rheumatic drug (DMARD) use which reduced the observed difference between treatments. By applying a prespecified trial emulation protocol to observational clinical registry data, we could replicate the results of SWEFOT, favoring infliximab over SSZ + HCQ combination therapy at 9 months.

Reporting of Observational Studies Explicitly Aiming to Emulate Randomized Trials

“…We retrieved 3133 unique records, of which 200 were included in the review (Figure 1). All reasons for excluding records after full-text review are given in eAppendix 6 in Supplement 1.…”

“… The included studies spanned 26 fields of medicine, predominately infectious disease (43 [22%]; 27 [14%] on COVID-19), cardiology (30 [15%]), and oncology (30 [15%]) . One hundred and thirty-one studies (66%)…”

“…One-hundred and fifteen studies (58%) completely reported how the target trial protocol was emulated. Eighty-seven studies (44%) provided both the protocol of the target trial and described how it was emulated (Table 2).…”

“…One-hundred and fifteen studies (58%) completely reported how the target trial protocol was emulated. Eighty-seven studies (44%) provided both the protocol of the target trial and described how it was emulated (Table 2). The following items of the emulation were frequently reported: eligibility criteria (193 [97%]), treatment strategies (191 [96%]), assignment procedures (173 [87%]), primary outcome (196 [98%]), the follow-up period (186 [93%]), a causal contrast (146 [73%], and an analysis plan (194 [97%]) (Table 2).…”

“…Seventy studies (35%) reported in the title that the study aimed to emulate a target trial; 180 (90%) did so in the Methods section. Twenty studies (10%) reported the study was prospectively registered, 16 of these 20 (80%)…”