Introduction Biologic use in the UK is increasing in patients with Crohn's disease (CD). While highly effective at inducing and maintaining remission, secondary loss of response occurs in approximately 15% of patients on maintenance treatment with biologics every year. There is some preliminary evidence that drug levels may play a role in this. However, measurement of anti-TNF levels has not been routinely available in the UK until very recently.
Methods We performed a service evaluation of a CE marked kit measuring serum levels of infliximab (IFX) as well as anti-drug antibodies (BMD, Marne La Vallee, France). Samples were taken immediately prior to infusion of IFX in patients attending for infusions over a 9-week period (March–May 2011). Results were not used in clinical management. A retrospective notes review was undertaken in January 2012 to see how drug levels related to clinical activity and to outcome. Only patients with CD on stable maintenance therapy were included and if repeated samples were taken, only the first measurement was used.
Results 52 samples were taken on 41 patients. Eight were excluded either because they did not have CD or because they were still in the induction phase of treatment. 33 patients (17 male) were, therefore, included in the analysis. Seven had subtherapeutic levels (SL) of IFX (<2 μg/ml). Patients with SL had a higher median Harvey Bradshaw index (HBI) (5 (range 0–7)) and C reactive protein (CRP) (8 (0–50)) at the time the sample was taken than those with therapeutic levels (TL) (HBI (1 (0–8) p=0.03: CRP 0 (0–8) p<0.05). The highest HBI and CRP recorded during subsequent follow-up was also higher in those with SL than TL but not significantly so (HBI SL 4 (2–11) vs TL 2 (0–12): CRP SL 11 (0–56) vs TL 0 (0–21)). Patients with SL were also more likely to require dose escalation of IFX (SL 2/7: TL 0/26 (p<0.04)) and intervention (change of drug therapy or surgical/endoscopic intervention) (SL 3/7: TL 2/27 (p=0.05)).
Conclusion Subtherapeutic IFX levels were associated with increased disease activity defined by biomarkers (CRP) and disease activity scores (HBI). Subtherapeutic levels were also predictive of a worse disease course over the following 6–8 months. Measuring anti-TNF drug levels in patients with IBD is promising and the utility of these tests in every day practice should be investigated further.
Competing interests None declared.