1536. Population Pharmacokinetic Analysis of Baloxavir Morboxil, a Cap-Dependent Endonuclease Inhibitor, in Adult and Adolescent Healthy Subjects and Influenza Patients and Exposure-Response Relationships in the Patients at High-Risk of Influenza Complications

BACKGROUND: Baloxavir marboxil is a prodrug of baloxavir acid which is a selective inhibitor of cap-dependent endonuclease. The global Phase 3 study conducted in the influenza patients at high-risk of influenza complications (CAPSTONE-2) enrolled adult and adolescent patients from 2016 to 2018. Baloxavir marboxil demonstrated significantly shorter time to improvement of influenza symptoms (TTIIS) than placebo. The aim of this study was to build a population pharmacokinetic (PK) model of baloxavir acid and to evaluate the exposure-response relationships in high-risk patients. METHODS: The population PK analysis was conducted on the pooled data from 13 clinical studies: 10 phase 1 studies, a phase 2 study, and 2 phase 3 studies. A total of 11846 plasma concentrations from 1827 subjects were used for this analysis. The influence of background characteristics including risk factors of influenza complications was assessed on the PK of baloxavir acid. The individual C(max) and AUC were estimated with an empirical Bayesian approach. Exposure-response analysis was conducted for TTIIS and virus titer in the high-risk patients. RESULTS: A 3-compartment model with first-order absorption and lag time was selected as a structural PK model, and well described the plasma concentrations. The population PK analysis suggested that (1) AUC in non-Asians was 30.7% lower than that in Asians, (2) body weight significantly affected the exposures to baloxavir acid, (3) the exposures in high-risk patients were similar to those in otherwise healthy patients, and (4) no PK differences were identified regarding the risk factors for influenza complications. The exposure-response analyses showed that the body weight-based dose regimen (40 mg for the patients weighing <80 kg and 80 mg for the patients weighing ≥80 kg) shortened TTIIS and reduced virus titer for both type A and B influenza, across the entire range of baloxavir acid exposures observed in CAPSTONE-2 although subject number in the lowest exposure group was limited and it was difficult to discuss the magnitude of the responses accurately. CONCLUSION: The results of the population PK analysis and exposure-response analyses provide useful information for understanding the pharmacokinetic and pharmacodynamic characteristics of baloxavir marboxil. [Image: see text] [Image: see text] [Image: see text] [Image: see text] DISCLOSURES: All authors: No reported disclosures.