Background/Purpose To evaluate the Cut-off level of adalimumab (ADL) and the prevalence of antibodies anti-adalimumab (anti-ADL-ab), in patients with psoriatic arthritis (PsA) and ankylosing spondylitis (AS).

Methods

We included  115 test of serum level of ADL and anti-ADL-Ab from 60 consecutives patients, on treatment with ADL at least 6 months, diagnosed of peripheral arthritis PsA (16 test in 10 patients), or AS (99 test in 50 patients). Clinical characteristics, clinical activity index (DAS28-ESR, SDAI, for peripheral PsA; BASDAI and ASDAS for AS, were recorded.

Serum levels of ADL and anti-ADL-Ab was evaluated by an ELISA kit: Promonitor®-ADL and Promonitor®-anti-ADL-Ab (Progenika Biopharma, S.A., a Grifols Company). Cut-off level for serum level of ADL was >0.004 U/mL and for anti-ADL-Ab was >3.5 U/mL. Serum samples were collected before injection of ADL, and stored frozen -80ºC, until analysis. 

Receiver operating characteristics (ROC) analysis was used to obtain a cut-off value for ADL trough levels between RA patients with low disease activity (DAS28 ≤ 3.2) versus those with moderate or high activity (DAS28 > 3.2), and for AS patients, between ASDAS ≤2.1 vs >2.1. 

Results

We enrolled 60 patients, 56% were women, mean age 48±16 years. In 50 (84%) patients with AS, 99 test (86%) for ADL level and anti-ADL-Ab and in 10 patients (16%), diagnosed of PsA, 16 (14%) test was done.

For the whole patients: the average time of treatment was 9.5±9 years and the average time on treatment with ADL 1.7±1.4 years; in 38 (63%), ADL was the first biological drug administered; the mean BMI was 27 and the prevalence of anti-ADL-Ab was 30% (18 patients: 14 -28%- patients with AS and 4 -40%- of patients with PsA).

In patients with anti-ADL-Ab versus patients without ant-ADL-ab, we obtained significantly higher level of ADL (11.5±5.3 vs 0.12 ± 0.2; p<0.0001), less BASDAI response (2.7±1.8 vs 5.5±2.0; p<0.0001), less ASDAS level (1.8±0.6 vs 3.5±2.6; p=0.008) and less time on treatment with ADL (2.2±1.4 vs 0.8±0.4; p<0.0001). Although the 35% patients without anti-ADL-ab was treated with DMARDs and only 10% of patients with anti-ADL-ab, there was not statistical differences (p=0.2). .The cut-off level of ADL in patients with AS to achieve an ASDAS≤2.1 was 5.4 mg/L, with AUC of 82.9% (sensitivity: 91%; specificity: 75%).

Table 1. Characteristics in responders and non-responders patients in relation with ASDAS results.

	Responders (n:42) ASDAS ≤ 2.1	Non-Responders (n:42) ASDAS ≤ 2.1	P
ADL level, mean ± SD	11.0 ±  4.4	1.7 ± 4.1	<0.001
Anti-ADL-ab (%)	2*	71	0.006
BASDAI, mean ± SD	2.5 ± 1.5	5.7 ± 1.8	<0.001
DMARD (%)	40	17	0.4
Time (years) on ADL, mean±SD	1.7±1.2	1.2±1	0,08

(*a patient with a detectable low level of ADL and the anti-ADL-ab was demonstrated using acid dissociation technique).

Conclusion

1.Cut-off level of ADL in patients with AS to achieve an ASDAS≤2.1 was 5.4 mg/L. 2. Prevalence anti-ADL-Ab in AS was 28%. 3. Anti-ADL-ab is correlated significantly with lower level of ADL, BASDAI and ASDAI results and less time on treatment. 4. Patients responders have occasionally anti-ADL-ab, and significantly higher serum concentrations of ADL than non-responders.

This study has a grant from Spanish Society for Rheumatology

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/cut-off-level-of-adalimumab-and-prevalence-of-antibodies-anti-adalimumab-in-patients-with-ankylosing-spondylitis-results-from-a-local-registry/