Impact of Infliximab Biosimilar (Ixifi®) Trough Levels on Disease Activity and Inflammatory Markers in Iraqi Rheumatoid Arthritis Patients

Background: Rheumatoid arthritis is an autoimmune inflammatory condition that impacts the small and larger joints. Ixifi® is a biosimilar medication derived from infliximab that exclusively targets Tumor Necrosis Factor-α. Serum Ixifi® trough concentration is necessary to manage disease activity in rheumatoid arthritis. Objective: Assess the impact of the Ixifi® trough level on disease activity and inflammatory biomarkers. Methods: A cross-sectional observational study was undertaken at Baghdad Teaching Hospital, involving forty-two patients diagnosed with rheumatoid arthritis according to ACR/EULAR 2010 criteria. After 3 months after initiating therapy with Ixifi®, the serum concentrations of Ixifi®, as well as CDAI, ESR, and CRP biomarkers, were measured. Results: After 3 months of therapy with Ixifi®, the patients in the remission group had a higher concentration of Ixifi® compared to the mild, moderate, and severe disease activity groups. Ixifi® trough level in remission was 5.45 µg/ml, while in mild, moderate, and severe groups, it was 3.575 µg/ml, 2.2 µg/ml, and 0.66 µg/ml, respectively. The CDAI scores were in the severe group (26.0), moderate group (19.0), mild group (7.0), and remission group (2.0). Furthermore, the findings indicate an inverse correlation between the Ixifi® trough level and both ESR and CRP. Conclusions: A drop in Ixifi® levels leads to an increase in disease severity and inflammation, while high concentrations of Ixifi® decrease disease activity, ESR, and CRP.