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P301. Infliximab trough levels and anti-infliximab antibodies in rheumatoid arthritis and in IBD patients – A comparison from a single center

A. Nunes1, S. Garces1, A. Vieira1, J. Demangeot2, J. Freitas1

1Hospital Garcia de Orta, Almada, Portugal; 2Instituto Gulbenkian de Ciencia, Lisbon, Portugal

Low trough levels of Infliximab (IFX) and the formation of anti-IFX antibodies are associated with the loss of therapeuthic efficacy. This can happen both in IBD and in Rheumathoid Arthritis (RA) patients.

Aims: To compare the frequency of both anti-IFX antibodies and low trough levels of IFX in two series of patients with RA and IBD.

Methods: Two groups of IBD and RA patients under IFX treatment were compared; previously to the next IFX infusion, the levels of IFX and of antibodies to IFX were measured (bridging solid phase ELISA). Duration of disease, duration of treatment, dosage of infused IFX and use of immunossupression were compared in both series.

Results: 21 RA patients (17 female), median age 59.5 years were compared with 22 IBD patients (13 female), 6 with Ulcerative Colitis and 16 with Crohn's Disease, median age 37.4 years. Duration of disease was not different (9.18 years in RA vs 8.31 years in IBD) and the duration of treatment in years was also comparable (2.40 in RA vs 2.09 in IBD). The dosage of administered IFX per year was higher in IBD (median 36.8 mg/Kg) than in RA (median 19.5 mg/Kg), but there was no difference between the IFX trough levels in both series (RA 4397 mg/L with low values in 7 patients, IBD 5345 mg/L with low values in 5 patients). RA patients were under methotrexate and prednisolone therapy and 12 IBD patients were treated with thiopurines, but the levels of anti IFX antibodies were not different in both groups (RA: 7 pts, mean 7092.5 ng/mL; IBD 4 pts, mean 2523.8 ng/mL).

Conclusion: In a transversal evaluation of these two groups of patients, despite the different diseases, median age and IFX dosages, no significant difference was be found in the IFX trough levels or in the levels of anti IFX antibodies. The real prevalence of antibodies is certainly higher, as many patients with anti IFX antibodies (and loss of response) were actually switched to treatment with alternative anti-TNF therapies.