Anti-drug antibodies in Colombian patients with rheumatoid arthritis treated with Enbrel vs Etanar - Preliminary report.

The present study was undertaken to detect antibodies against etanercept (ETN) in a group of Colombian patients with rheumatoid arthritis (RA) and being treated with Enbrel^® vs. Etanar^®. From these patients with RA, clinical and laboratory data were collected and serum taken for anti-drug antibody (ADAb) analysis. Samples from 32 patients (16 who had been treated with Enbrel^® and 16 with Etanar^®) were analyzed. Positive sera for ADAb were found in six of the 32 subjects (18.7%); five (31.2%) in the Enbrel^® group and one (6.25%) in the Etanar^® group. Patients under treatment with Enbrel^® registered a longer disease duration than patients being treated with Etanar^® (15.4 years vs. 10.98 years, p = 0.175) as well as a longer average treatment with the drug (45.7 vs. 23.9 months, p = 0.052). The percentage of patients with disease activity defined as a disease activity score by C-reactive protein (DAS28-CRP) scores ≥2.3 was higher in those patients with positive sera in the enzyme-linked immunosorbent assay (ELISA) (66.7%) than in those with negative sera (34.6%). A logistic regression test revealed that the higher the DAS28-CRP value, the higher the ELISA absorbance value. The results showed evidence of greater frequency of ADAb in patients treated with ETN than has been reported to date. Greater disease activity was seen in those patients in whose serum ADAb had been detected. Significant differences were found between the positive ELISA for the group of patients treated with Enbrel^® compared to those treated with Etanar^®. Some of the factors that could explain this difference are the length of the treatment time with the drug, the commercial ELISA kit used to detect ADAb, or the immunogenicity itself of each product.