Abstract
Objective Methotrexate (MTX) is an anchor drug for most patients with rheumatoid arthritis (RA); its use may be limited depending on renal function. Therefore, this study aimed to examine the discrepancy in the estimated GFR (eGFR) using conventional serum creatinine (Cr)-, cystatin C-, and MTX-associated toxicities in patients with RA.
Methods In total, 436 patients were enrolled, and eGFR was evaluated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation based on both cystatin C and serum Cr levels. The CKD and MTX dosing stages were classified according to eGFR. MTX-associated toxicities were also evaluated.
Results The mean eGFR using CKD-EPI cystatin C (CKD-EPIcys) was 89.44 ml/min/1.73 m2, lower than the eGFR using CKD-EPI creatinine (CKD-EPIcr) of 95.55 ml/min/1.73 m2. After converting eGFR to CKD-EPIcys by CKD-EPIcr, 29.8 % were reclassified to a higher stage according to the Kidney Disease: Improving Global Outcomes (KDIGO) CKD stage. Also, according to the MTX guidelines, 6.3 % of the group with an eGFR > 50 mL/min /1.73 m2 were reclassified to eGFR 10-50 mL/min, requiring dose adjustment. The incidence of MTX-associated toxicities, such as anemia, leukopenia, and nephrotoxicity, was significantly higher in the CKD stage-changed group than in the non-stage-changed group.
Conclusion Our results showed that eGFR based on Cr was overestimated compared with eGFR based on cystatin C. In addition, we demonstrated that MTX-associated toxicities were significantly increased in the group with a changed stage when the eGFR was converted from CKD-EPIcr to CKD-EPIcys.
