DOP14 Modelling of the relationship between infliximab exposure, faecal calprotectin, and endoscopic remission in patients with Crohn’s disease

E. Dreesen1, S. Berends2, D. Laharie3, G. D’Haens4, S. Vermeire5, A. Gils1, R. Mathôt2

1Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Leuven, Belgium, 2Department of Hospital Pharmacy, Amsterdam UMC, Amsterdam, The Netherlands, 3Hepato-gastroenterology and Digestive Oncology, Haut-Lévêque Hospital- Bordeaux UMC, Bordeaux, France, 4Department of Gastroenterology and Hepatology, Amsterdam UMC, Amsterdam, The Netherlands, 5Department of Gastroenterology and Hepatology, University Hospitals Leuven, Leuven, Belgium


Less than 50% of patients with Crohn’s disease (CD) starting infliximab (IFX) therapy achieve endoscopic remission (ER). Evidence for the benefits of pharmacokinetic (PK) and pharmacodynamic (PD) monitoring remains scarce. We aimed to develop a population (pop)PK/PD model to characterise the IFX dose-exposure-biomarker-response (faecal calprotectin [fCal] and ER) relationship in patients with CD.


Analyses were performed using data of a phase 4 dose-escalation study (TAILORIX). Patients started standard 5 mg/kg IFX induction therapy at weeks [w]0, 2 and 6. From w14 through w54, the IFX dose could be irreversibly doubled based on one of the three monitoring algorithms.1 Endoscopies were performed at w0, 12 and 54. Three sequential models were developed: A 2-compartment popPK model linking IFX dose to exposure, an indirect response popPK-PD model describing the inhibitory effect of IFX exposure on fCal, and a first-order Markov popPD model linking fCal to transitions between states of ER (CD endoscopic index of severity <3), no ER and dropout (Figure 1). All modelling and simulation were performed using NONMEM 7.4.


The study included 116/122 (95%) patients with CD enrolled in TAILORIX who had ≥1 detectable IFX serum concentration. In the developed models, it was shown that IFX clearance increased with increasing fCal, decreasing albumin, increasing CD activity index and presence of antibodies to IFX (transiently). Baseline fCal increased with increasing CRP and decreasing platelet count. Lower fCal increased probability of attaining ER and decreased probability of losing ER. Probability of dropping out given an earlier state of absence of ER increased with elapsing time. Simulations of 150 000 patients receiving 5, 7.5 or 10 mg/kg IFX (1:1:1) resulted in a flat dose–response curve due to large interindividual variability in PK and PD (Figure 2, top panels). The predicted fraction of patients achieving ER at w12 was 45.1% [30.3–60.5] (median [IQR]) when on 5 mg/kg IFX (~46.4% observed in data). However, simulations of 10 mg/kg IFX induction doses predicted only a slight increase in the fraction of patients achieving ER at w12 to 47.5% [32.0–62.6]. This minor benefit at the population level argues against systematic 10 mg/kg induction dosing in all patients. A similar observation was done during maintenance therapy, where 70.8% [62.6–75.5] of all simulated patients maintained ER at w54 (~72.2% observed in data) (Figure 2, right panels).


Model-informed infliximab dose optimisation towards a predefined fCal concentration—while accounting for PK and PD variability—may improve the effectiveness of infliximab therapy (eg. 64% chance of ER at w12 ~100 μg/g fCal at w6).


D’Haens et al. 2018. Gastroenterology.