Drug levels, anti-drug antibodies, and clinical efficacy of the anti-TNFα biologics in rheumatic diseases.

The objectives of this study are to evaluate the effect of anti-drug antibodies on the clinical efficacy and withdrawal rate of the anti-TNFα biologics in patients with rheumatic diseases. Consecutive patients with rheumatic diseases recently commenced on anti-TNFα biologics were recruited. Serum samples were collected for assay of drug level and antibody titer against the corresponding biologics. Comparison of the clinical efficacy and drug retention rate was performed between patients with and without anti-drug antibodies. Fifty-eight Chinese patients were studied (64 % women; age 47.8 ± 12.9 years; disease duration 6.7 ± 6.4 years). The proportion of patients using infliximab (IFX), adalimumab (ADA), and etanercept (ETN) was 41, 28, and 31 %, respectively. Antibodies against IFX, ADA, and ETN were demonstrated in 12(50 %), 5(31 %) and 0(0 %) patients, respectively. Patients who developed anti-drug antibodies had significantly lower levels of the corresponding drugs (IFX level: 0.004 ± 0.01 vs 3.81 ± 3.49 μg/ml; p = 0.002; ADA level: 0.0 vs 7.6 ± 8.3 μg/ml; p = 0.008). Anti-drug antibody-positive patients had a significantly higher cumulative drug withdrawal rate due to inefficacy (64.7 and 71.8 % vs 10.3 and 10.3 % at month 12 and month 24, respectively; p < 0.001). In rheumatoid arthritis and psoriatic arthritis, non-responders was significantly more frequent in antibody-positive patients (54 vs 13 %; p = 0.01). In spondyloarthritis, the improvement in ankylosing spondylitis disease activity score was significant in patients without antibodies (3.89 ± 0.82 to 2.22 ± 0.86; p = 0.01) but not in those with anti-drug antibodies (3.40 ± 1.67 to 3.23 ± 1.40; p = 0.73). We concluded that the presence of neutralizing antibodies is associated with lower serum levels of the anti-TNFα biologics, leading to lower efficacy and higher withdrawal rate.