Purpose: Two studies were conducted to assess the pharmacokinetic (PK) properties and tolerability of edaravone in Japanese subjects with mild to moderate hepatic impairment or normal hepatic functioning (study 1), and in white subjects with severe hepatic impairment compared to subjects with normal hepatic functioning (study 2). Methods: Studies 1 and 2 were multicenter, open-label, single-dose studies that included subjects aged 18-75 years. In study 1, subjects were stratified into 3 different groups of hepatic functioning according to Child-Pugh score: mild hepatic impairment, score 5 or 6 (n = 8); moderate hepatic impairment, score 7-9 (n = 6); or normal hepatic functioning (n = 8). In study 2, subjects had severe hepatic impairment (Child-Pugh score 10-14; n = 6) or normal hepatic functioning (n = 6). In both studies, all subjects were given edaravone 30 mg IV infused over 60 min on the morning of day 1. Blood samples for use in PK analyses were collected from days 1-3. The PK properties (C-max, AUC 0-last, and AUC(0-infinity)) of edaravone and its sulfate conjugate metabolite were measured. Findings: In study 1, the geometric least-squares mean (GLSM) C-max and AUC(0-infinity) of unchanged edaravone were 1.203- and 1.065-fold greater, respectively, in subjects with mild hepatic impairment versus normal hepatic functioning, and were 1.235- and 1.142-fold greater, respectively, in subjects with moderate hepatic impairment versus normal hepatic functioning. In study 2, GLSM C-max and AUC(0-infinity) of unchanged edaravone were 1.203- and 1.190-fold greater, respectively, in subjects with severe hepatic impairment versus normal hepatic functioning. In both studies the AUC 0-last, AUC(0-infinity), unbound AUC from time zero to infinity, and C-max of unchanged edaravone were increased slightly with increases in Child-Pugh classification. No adverse events considered related to edaravone were reported, except for 1 case of sinus bradycardia in a subject with normal hepatic functioning in study 2. The event was moderate in severity, considered as possibly related to edaravone, and resolved during the study. (C) 2020 Elsevier Inc.