[Rheumatoid arthritis (RA) disease activity predicts function of ABCB1 (P-gp) and ABCG2 (BCRP1) drug-efflux transporters].

P-gp and BCRP1 are transporter proteins that may confer drug resistance.,To compare P-gp and BCRP1 function in rheumatoid arthritis patients with active and inactive disease and to define their relation with disease activity.,We included 17 active patients paired (age, gender, disease duration) to 17 inactive patients. All had baseline evaluations and 27 had additional six-month follow-up. P-gp and BCRP1 functional activity was measured in peripheral mononuclear cells by flow cytometry. Percentage of lymphocytes able to extrude substrates for P-gp and BCRP1 were recorded in the presence/absence of selective inhibitors. Informed consent was obtained. Descriptive statistics and linear regression model were applied.,Active patients had higher efflux function of both transporters than inactive patients: median (25-75 IQR) P-gp of 7.1% (1.4-29.3) vs. 1.6% (0.7-3.5), p = 0.02 and BCRP1 of 6.2% (1.3-22.4) vs. 1.3% (0.7-2), p = 0.007. At baseline, disease activity was the only predictor of both transporter functions. At follow-up, changes in disease activity correlated with shift in P-gp (r = 0.35, p = 0.07) and BCRP1 (r = 0.33, p=0.09) function.,Patients with active rheumatoid arthritis had a higher efflux function of P-gp and BCRP1 compared to inactive patients. The behavior of P-gp and BCRP1 appeared to be conditioned by disease activity.