Effectiveness of biologic DMARDs in monotherapy versus in combination with synthetic DMARDs in rheumatoid arthritis: data from the Swiss Clinical Quality Management Registry.

Objectives: To determine the frequency of use of biologic DMARDs (bDMARDs) in monotherapy, to describe the baseline characteristics of patients treated with bDMARDs in monotherapy and to compare the effectiveness of bDMARDs in monotherapy with that of bDMARDs in combination with synthetic DMARDs (sDMARDs).
Methods: Using data from the Swiss RA (SCQM-RA) registry, bDMARD treatment courses (TCs) were classified either as monotherapy or as combination therapy, depending on the presence of concomitant sDMARDs. Prescription of bDMARD monotherapy was analysed using logistic regression. bDMARD retention was analysed using Kaplan-Meier and Cox models with the addition of time-varying covariate effects. Evolution of the DAS28 over time was analysed with mixed-effects models for longitudinal data.
Results: A total of 4218 TCs on bDMARDs from 3111 patients were included, of which 1136 TCs (27%) were initiated as monotherapy. bDMARD monotherapy was preferentially prescribed to older, co-morbid patients with longer disease duration, lower BMI, more active disease and more previous bDMARDs. After adjusting for potential confounding factors, drug retention was significantly lower in monotherapy [hazard ratio 1.15 (95% CI: 1.03, 1.30)]. Other factors such as type of bDMARD and calendar year of prescription were associated with a stronger effect on drug retention. Response to treatment in terms of DAS28 evolution was also slightly but significantly less favourable in monotherapy (P = 0.04).
Conclusion: Our data suggest that bDMARD monotherapy is prescribed to more complex cases and is significantly less effective than bDMARD therapy in combination with sDMARDs, but to an extent that is clinically only marginally relevant.
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