Infliximab trough levels: A comparison between the Quantum Blue Infliximab assay and the established ELISA

BACKGROUND AND AIM

Therapeutic drug monitoring of infliximab (IFX) using the established laboratory-based enzyme-linked immunosorbent assay (ELISA) cannot produce results fast enough to allow IFX dose adjustments prior to each IFX infusion. We investigate the validity of IFX trough levels obtained through the Quantum Blue IFX (QB-IFX) rapid assay compared with the established ELISA.

METHODS

Adult inflammatory bowel disease patients receiving maintenance IFX infusions at Middlemore Hospital and Dunedin Public Hospital were prospectively recruited from July to October 2016. Serum samples were stored at -40 °C until processed using QB-IFX by a clinician at Middlemore Hospital and a research staff at Dunedin Public Hospital strictly following the manufacturers' instructions in an open label fashion.

RESULTS

Forty four inflammatory bowel disease patients were recruited. Median duration of IFX therapy was 21 months (interquartile range: 12-44). Overall, the correlation between ELISA and QB-IFX trough levels was 0.73 (95% confidence interval [CI]: 0.53-0.85). The sensitivity and specificity of a QB-IFX level < 7 in detecting an ELISA level < 7 were 0.79 (95% CI: 0.59-0.92) and 0.75 (95% CI: 0.48-0.93), respectively. Conversely, the sensitivity and specificity of a QB-IFX level < 2 detecting an ELISA level < 2 were 1.00 (95% CI: 0.52, 1.00) and 0.97 (95% CI: 0.85, 1.00), respectively.

CONCLUSION

The QB-IFX had excellent sensitivity and specificity for IFX levels < 2 obtained with the established ELISA. Therefore, QB-IFX could be used for real time dosing decisions when the IFX level is low and dose escalation is required.

Association Between Infliximab Trough Levels and the Occurrence of Paradoxical Manifestations in Patients with Inflammatory Bowel Disease: a Case-Control Study

BACKGROUND AND AIM

Anti-tumour necrosis factor [TNF] agents have dramatically improved the prognosis of inflammatory bowel disease [IBD]. However, despite their good safety profile, use of these agents may lead to paradoxical manifestations involving skin or joints. Pathogenesis of such side effects is poorly understood and may involve anti-TNF pharmacokinetics. The aim of the present study was to look for an association between infliximab trough levels [ITL] and cutaneous [CPM] or rheumatological [RPM] paradoxical manifestations.

METHODS

IBD patients receiving infliximab as maintenance therapy were included in a cross-sectional prospective monocentre study. At inclusion, patients had an ITL measurement [LISA-TRACKER®, Biomedical Diagnostics BMD] and were assessed for paradoxical manifestations: a CPM was defined by new onset or exacerbation of pre-existing psoriasis lesions during IFX therapy, and an RPM by new onset of severe poly-arthralgia during IFX therapy.

RESULTS

Among the 121 patients included [69 female; median age: 38.9 years; 92 with Crohn's disease], 7% had CPM and 8% RPM. Median ITL values were 5.87 [range: 0.52-19.53] µg/ml in patients with CPM and 1.90 [0.00-13.5] µg/ml in those with RPM, as compared respectively with 5.12 [0.00-49.12] µg/ml in patients without CPM [p = 0.56] and 5.57 [0.00-49.12] µg/ml in those without RPM [p = 0.058]. No prognostic factor was associated with CPM. The single factor associated with RPM was elevated antinuclear antibodies.

CONCLUSION

ITL were not elevated in IBD patients developing cutaneous or rheumatological paradoxical manifestations when receiving IFX as maintenance therapy. As suggested by the high level of antinuclear antibodies, RPM could be related to an induced autoimmune disorder.