We developed clinical pharmacogenetic index for the prediction of DAS28 after 6 months of MTX monotherapy in Slovenian RA patients consisting of DAS28 at diagnosis, presence of erosions, MTX dose, SLC19A1 rs1051266, SLCO1B1 rs2306283, TYMS rs347430033, and AMPD1 rs17602729. This evidence concerns the gene SLC19A1 and rheumatoid arthritis.