Association Between Methotrexate Erythrocyte Polyglutamate Concentration and Biological Drug Concentration and Clinical Response in Rheumatoid Arthritis Patients Treated With Subcutaneous Injectable Methotrexate and a First Biological Drug

The combination of methotrexate (MTX) with a biological disease-modifying antirheumatic drugs (bDMARD) is the next step in treatment with MTX monotherapy in rheumatoid arthritis (RA). Estimation of MTX and bDMARD impregnation could be performed with the erythrocyte MTX polyglutamate (MTX-PG) and bDMARD assays before to move to a second bDMARD. In RA patients treated with MTX (prescribed for at least 6 months at a stable dose for at least 3 months) in combination to a first bDMARD (prescribed since at least 3 months), an assay of MTX-PG and bDMARD will be performed in tow subsets of RA according to the level of disease activity. The first subset is active RA defined by a DAS28 (disease activity score 28)>3.2. The second one is RA in clinical remission defined by a DAS28<2.6. The main hypothesis is the association between the low concentration of MTX-PG and the clinical response of RA patients treated with subcutaneous methotrexate injection associated to a first bDMARD. Adherence to MTX will be reviewed by the Compliance Questionnaire Rheumatology (CQR) questionnaire. This assay could be useful to improve MTX management before to move to a second bDMARD.