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

Methotrexate (MTX) is the first-line treatment of rheumatoid arthritis (RA). In case of MTX failure, it is discussed to start a Biologic Disease-modifying Antirheumatic Drug (bDMARDs) according to the latest European recommendations of the EULAR. Before to add a Biologic Disease-modifying Antirheumatic Drug (bDMARDs), an objective estimation of MTX impregnation could be carried out by MTX polyglutamates (MTX-PG). In rheumatoid arthritis patients with active disease estimated by DAS28 (Disease activity Score 28)\> 3.2 insufficiently controlled by MTX subcutaneously and patients in remission obtained with a DAS 28 \<2.6 with methotrexate prescribed since more than 6 months at stable dose for at least 3 months, a concentration of MTX-PG will be achieved.