Population Pharmacokinetic Model of Cabozantinib in Patients with Medullary Thyroid Carcinoma and Its Application to an Exposure-Response Analysis.

BACKGROUND AND OBJECTIVES: Cabozantinib is a tyrosine kinase inhibitor approved in the USA and EU for the treatment of patients with progressive, metastatic medullary thyroid cancer (MTC). The indicated cabozantinib dose is 140 mg/day, with dose modifications allowed for patients who develop adverse events (AEs). The analysis objective was to develop a population pharmacokinetic (PopPK) model in MTC patients and to use the model for exposure-response (ER) analysis of dose modifications. METHODS: A PopPK model for cabozantinib was developed using data from three clinical trials (2079 evaluations from 289 patients), including a randomized, double-blind, placebo-controlled phase III study of patients with progressive, metastatic MTC. The PopPK model predictions [model-predicted steady-state area under the plasma concentration-time curve (AUCss,pred)] were used for an ER analysis of the time to first dose modification. RESULTS: The final PopPK model was a one-compartment model with first-order absorption and first-order elimination. Estimated cabozantinib apparent oral clearance (CL/F) and apparent volume of distribution (V c/F) were 106 L/day [±2.98 % relative standard error (RSE)] (males) and 349 L (±2.73 % RSE), respectively. CL/F was reduced by 22 % (to 83 L/day) in females. Sex and body mass index (BMI) were significant covariates that combined contributed 15 % to the variability in cabozantinib CL/F, but did not warrant dose adjustment. Higher cabozantinib AUCss,pred was correlated to an increased risk of early dose modification and a lower average dose through to Day 85. Early cabozantinib dose modification was not associated with a reduction in progression-free survival (PFS). CONCLUSION: A PopPK model was developed for cabozantinib pharmacokinetics in MTC patients. Higher cabozantinib exposure was associated with earlier first dose modification and a lower average administered dose through to Day 85. Early first dose modification did not appear to impact PFS.