ABCG2 and rheumatoid arthritis: mRNA level of drug transporters ABCC1, ABCC3, and ABCG2 were higher in RA patients with poor response to MTX treatment in comparison to the patients with good response (p = 0.69, p = 0.81, p = 0.74, p = 0.08, p = 0.69, respectively) (Fig. 4).