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Poster presentations: Clinical: Therapy and Observation 2020

P414 Risk factors for the development of anti-drug antibodies to infliximab and adalimumab in Crohn’s disease

E. Khoo1, A. Lord2, K. Hanigan1, A. Croft1, G. Radford-Smith1,2

1Royal Gastroenterology Department, Brisbane and Women’s Hospital, Herston, Australia, 2QIMR Berghofer Medical Research Institute, Gut Health Laboratory, Herston, Australia

Background

Anti-tumor necrosis factor-α (anti-TNFa) therapy have been established as an effective maintenance treatment for complicated Crohn’s Disease (CD). However, the efficacy of Infliximab (IFX) and Adalimumab (ADM) may be affected by low serum levels and/or the presence of anti-drug antibodies (ADA). This reinforces the importance of therapeutic drug monitoring (TDM). We aim to assess the clinical benefit of proactive vs. reactive TDM. Secondly, to assess the impact of TDM on clinical management. Thirdly, to identify risk factors for low serum drug levels and the development of ADA in CD patients.

Methods

This was a single-centred observational cohort study performed at a tertiary hospital, comprising of total 229 CD patients: 142 received IFX and 87 received ADM, who have had a trough drug level, tested using enzyme-linked immunosorbent assay. Demographic and clinical data were retrospectively collected from electronic medical records. Fisher’s Exact Test was used to determine if there are nonrandom associations between variables. A p-value of less than 0.05 was considered statistically significant.

Results

One hundred and fourteen patients (49%) receiving a standard anti-TNFa regimen had subtherapeutic drug levels (67 had IFX < 3 μg/ml and 47 had ADM < 5 μg/ml). Interestingly, almost half of this cohort were asymptomatic. Reactive TDM completed among symptomatic patients have shown to have a statistically significant benefit in detecting subtherapeutic drug level (p = 0.0001). Following these results, only fifty-two patients (46%) had a change of therapy (29 IFX, 25 ADM); while the remaining sixty-two patients (54%) continued the same dosing regimen with only one documented admission within 90-days following the drug level being taken. Eight patients (4%) were found to have positive ADA, all in the presence of subtherapeutic drug levels. Two of these had a subsequent flare of their disease. They were all switched to another class of biologic therapy. Non-smoking status at diagnosis and the concomitant use of immunomodulator were found to have statistically significant associations with a therapeutic drug level (p = 0.0176 and p = 0.0001, respectively). Similarly, both of these risk factors were associated with lower risk of ADA formation (p = 0.0057 and p = 0.0165, respectively).

Conclusion

This study suggests that a large proportion of patients have subtherapeutic drug levels at standard dosing schedules. However, low drug levels do not correlate with a higher risk of complications if patients are in clinical remission. The results of this study also indicate that non-smoking status at diagnosis and the concomitant use of immunomodulator are associated with higher serum drug levels and lower risk of developing anti-drug antibodies.