Background The effects of comedication with conventional synthetic disease modifying antirheumatic drugs (csDMARDs) on TNF inhibitors (TNFi)-retention in spondyloarthritis (SpA), are inconclusive. Results from previous observational studies may have easily led to spurious conclusions, since confounding, especially “confounding by indication”, was not fully addressed.
Objectives To evaluate if comedication with csDMARD influences TNFi-retention in patients with SpA, while performing a comprehensive set of adjustments to best handle confounding.
Methods Patients with SpA (according to their treating rheumatologists) from the Rheumatic Diseases Portuguese Register (Reuma.pt), with first TNFi started between 2001 and 2014 were included in this prospective, multicenter, cohort study. Our main outcome was time to first TNFi discontinuation. Cox-regression was used to estimate the effect of csDMARD comedication on TNFi-retention in two types of models, one including baseline (time-fixed) variables and the other with time-varying variables, including socio-demographic features, measures of disease activity, physical function and co-treatment with other drugs (NSAIDs and oral steroids). To control for possible “confounding by indication”, the effect of csDMARD comedication on TNFi-retention was also tested after propensity score (PS)-adjustment.
Results In total, 954 patients (mean (SD) age 41.5 (12.0) years; 59.6% males; 13.7 (10.4) years of disease duration) were included and 289 (30.3%) discontinued their first TNFi after a median follow-up time of 2.5 years (range: 0.08–13 years). A large proportion of patients were treated with csDMARDs at baseline (389; 41%). Inefficacy was the most common reason for TNFi discontinuation (55.7%), followed by adverse events (31.1%). In the multivariable analysis comedication with csDMARDs had no effect on TNFi-retention, neither in the baseline model (HR: 0.83; 95% CI: 0.59; 1.16) (figure A) nor during follow-up adjusting for time-varying covariates (HR: 1.13; 95% CI: 0.71; 1.80). The effect of csDMARDs remained not statistically significant after PS-adjustment (figure B).
Conclusions Comedication with csDMARDs does not prolong TNFi-retention in SpA patients in clinical practice suggesting no benefit in the concomitant use of these drugs.
Disclosure of Interest None declared
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