Impact of different infliximab dose regimens on treatment response and drug survival in 462 patients with psoriatic arthritis: results from the nationwide registries DANBIO and ICEBIO

Objective. The aim of this study was to describe dose regimens, dose escalation and clinical outcomes in TNF-alpha inhibitor (TNFi)-naive patients with PsA treated with infliximab in routine rheumatology care. Methods. We conducted an observational cohort study based on the nationwide Danish Rheumatologic Database (DANBIO) and Center for Rheumatology Research (ICEBIO) registries. Stratified by country, characteristics of patients treated with <= 3 mg infliximab/kg body weight, 3-5 mg/kg or >= 5 mg/kg every 8 weeks were described. Outcomes were evaluated by ACR 20%, 50% and 70% (ACR20/50/70) responses and European League Against Rheumatism good response after 6 months, disease activity after 12 months, Kaplan-Meier plots and regression analyses. Results. Four hundred and sixty-two patients (376 Danish, 86 Icelandic) received treatment with infliximab. In Danish patients, the starting dose was <= 3 mg/kg in 110 patients (29%), 3-5mg/kg in 157 (42%), >= 5 mg/kg in 38 (10%) and unregistered in 71 (19%). In Icelandic patients, corresponding numbers were 64 (74%), 17 (27%), 0 (0%) and 5 (6%). Patients with a higher body weight received lower doses per kilogram. Danish patients received higher doses than Icelandic patients at baseline [ median 3.1 (interquartile range 3.0-3.8) vs 2.3 (2.1-2.9) mg/kg, P < 0.05] and after 12 months [ 3.3 (3.0-4.5) vs 2.9 (2.2-3.5) mg/kg, P < 0.0001]. After 12 months, 58% of Danish and 66% of Icelandic patients maintained treatment. Danish patients had shorter drug survival than Icelandic patients (1183 vs 483 days). In univariate analyses stratified by country, time until dose escalation, response rates, drug survival and 1-year's disease activity were independent of starting dose. Drug survival was shorter among patients not receiving concomitant MTX. Conclusion. In clinical practice, > 70% of Icelandic and Danish PsA patients treated with infliximab received sustained doses below the 5 mg/kg every 8 weeks recommended in international guidelines. Lower starting doses did not affect drug survival or response.