• Arnab Mukherjee, Anasuya Hazra, Mike K Smith, Steven W Martin, Diane R Mould, Chinyu Su, and Wojciech Niezychowski.
• Pfizer Inc, Groton, CT, USA.
• Br J Clin Pharmacol. 2018 Jun 1; 84 (6): 1136-1145.

AimsTofacitinib is an oral, small molecule JAK inhibitor being investigated for ulcerative colitis (UC). In a phase 2 dose-ranging study, tofacitinib demonstrated efficacy vs. placebo as UC induction therapy. In this posthoc analysis, we aimed to compare tofacitinib dose and plasma concentration as predictors of efficacy and identify covariates that determined efficacy in patients with UC.MethodsOne- and two-compartment pharmacokinetic models, with first-order absorption and elimination, were evaluated to describe plasma tofacitinib concentration-time data at baseline and week 8. Relationships between tofacitinib exposure (dose, average plasma drug concentration during a dosing interval at steady state [Cav,ss ] and trough plasma concentration at steady state [Ctrough,ss ]) and week 8 efficacy endpoints were characterized using logistic regression analysis. Baseline disease, demographics, prior and concurrent UC treatment were evaluated as covariates.ResultsPlasma tofacitinib concentrations increased proportionately with dose and estimated oral clearance, and Cav,ss values were not significantly different between baseline and week 8. Dose, Cav,ss and Ctrough,ss performed similarly as predictors of efficacy based on statistical criteria for model fit and comparison of model predictions for each endpoint. Individual Cav,ss values were similar between clinical remitters and nonremitters at predicted efficacious doses (10 and 15 mg twice daily). Baseline Mayo score was a significant determinant of efficacy. Predicted differences from placebo in clinical remission at 10 mg twice daily for patients with baseline Mayo score >8 and ≤8 were 39% (95% CI: 7-70) and 21% (-2-50), respectively.ConclusionsExposure-response characterization demonstrated the potential of tofacitinib 10 and 15 mg twice daily as induction therapy for UC without monitoring of plasma drug concentrations for dose optimization.© 2018 The British Pharmacological Society.

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