P612 Mirikizumab Pharmacokinetics and Exposure - Efficacy Relationships in Patients with Ulcerative Colitis

Friedrich, S.(1);Chua, L.(1);Tuttle, J.L.(2);Feagan, B.G.(3);Sandborn, W.J.(4);

(1)Eli Lilly and Company, Immunology, Indianapolis, United States;(2)Eli Lilly and Company, Lilly Biotechnology Center, San Diego, United States;(3)Western University, Gastroenterology, London- ON, Canada;(4)University of California San Diego, Gastroenterology, La Jolla, United States;


Mirikizumab (miri), a p19-directed IL-23 antibody, demonstrated efficacy in a Phase 2 trial in patients with moderately-to-severely active ulcerative colitis (UC)1 (NCT02589665).  Analyses of the pharmacokinetics (PK) of miri and the relationships between exposure and efficacy at Week 12 are reported.


Patients were randomised to receive IV placebo, miri 50 mg or 200 mg with possibility of exposure-based dose increases, or miri 600 mg every 4 weeks, with efficacy assessment at Week 12.  Serum concentrations of miri were analyzed using population PK methods.  Population models were also used to evaluate the relationships between various clinical efficacy measures at Week 12 and miri exposure. The effects of patient factors on both PK and exposure-efficacy relationships were evaluated.  Model-based and graphical methods were also used to understand the potential for confounded relationships between miri exposure and efficacy.


A systemic clearance of 0.023 L/hr was estimated for miri, similar to estimates in healthy subjects and patients with psoriasis.  Miri exposure increased in a linear manner.  Patients with lower serum albumin concentration or lower body weight tended to have significantly higher clearance or lower volume of distribution, respectively (p<0.01); however, the magnitude of the impact was small and contributed less than 15% to random variability. The model-based exposure-response analyses generally showed that patient factors had a stronger impact on efficacy at Week 12 than miri exposure.  Prior biologic experience and baseline rectal bleeding (RB) score had significant impacts (p<0.01) on the estimated placebo effect and maximal miri treatment effect (Emax), respectively.  In the clinical response model, the estimated placebo response rate was 20 percentage points higher in biologic naïve vs experienced patients.  The estimated response rate at a miri dose of 600mg was 28% higher in patients with a baseline RB≥2.  Inclusion of these factors in the exposure-efficacy models caused the estimated EC50 to drop substantially, suggesting that the post-hoc exposure-efficacy relationships are likely confounded based on these patient factors.  Graphical evaluations also suggested the presence of confounding factors.  


Miri PK in UC patients was consistent with PK observed in healthy subjects and psoriasis patients.  Evaluation of the relationships between miri exposure and efficacy in UC patients accounted for the potential impact of patient factors.  Confounding patient factors may distort the true cause-effect relationship between exposure and efficacy and were carefully considered in support of optimal selection of doses for miri Phase 3 studies.  

1.  Gastroenterology. 2020;158(3):537-549.