The effect of methotrexate versus other disease-modifying anti-rheumatic drugs on serum drug levels and clinical response in patients with rheumatoid arthritis treated with tumor necrosis factor inhibitors

To investigate the effect of concomitant conventional synthetic disease-modifying anti-rheumatic drugs (csDMARDs) with adalimumab or infliximab on maintaining serum drug and clinical outcomes after the first year of treatment in patients with rheumatoid arthritis (RA). Second, to assess the influence of methotrexate (MTX) dose on these outcomes. Ninety-two patients with RA starting infliximab ( n = 67) or adalimumab ( n = 25) tumor necrosis factor inhibitor (TNFi) with available drug levels and clinical improvement assessment (European League Against Rheumatism [EULAR] response) after 12 months were included. Patients were grouped according to concomitant csDMARD use: (i) TNFi monotherapy; (ii) TNFi+MTX; (iii) TNFi with csDMARDs other than MTX (TNFi+OD). Patients receiving MTX were also classified by dose as