Risk of Kidney Impairment during Iguratimod Therapy for Rheumatoid Arthritis Patients: The Role of Concomitant Salazosulfapyridine.

Objective Iguratimod (IGU) is a synthetic disease-modifying anti-rheumatic drug that is mainly used in East Asia. Kidney impairment related to IGU may be under-recognized, and its proportion, severity, and risk factors remain unclear. To assess the influence of IGU on the kidney function among rheumatoid arthritis (RA) and to clarify the risk factors associated with kidney impairment. Methods We retrospectively assessed the influence of IGU on the kidney function in patients with RA and identified the risk factors associated with kidney impairment. We enrolled patients with RA who had been treated with IGU. The clinical characteristics, including the estimated glomerular filtration rate (eGFR), were assessed. The difference in eGFR between baseline and after 3 months of treatment (ΔeGFR) was calculated, and kidney impairment was defined as Δ an eGFR ≥15% from baseline. ΔeGFR was defined as the magnitude of decline in eGFR from baseline to the observation time point. A positive ΔeGFR value indicates a reduction in the kidney function. Results Among 108 patients, Δ an eGFR ≥15% was observed in 32 patients (30%). Concomitant use of salazosulfapyridine (SASP) was more frequent in patients with ΔeGFR ≥15% than in those with ΔeGFR <15%. The median ΔeGFR was higher in patients with IGU and concomitant SASP than in those without. SASP use was identified as the only significant risk factor for Δ an eGFR ≥15% in a binomial logistic regression analysis. The same analysis, after propensity score matching, also yielded similar results. Conclusion IGU combined with SASP reduced eGFR more than IGU alone, and SASP was an independent risk factor for ΔeGFR ≥15% among RA patients treated with IGU.