*2.2. Data Collection*

All data were retrieved from electronic medical records of Kangwon National University Hospital. Demographic data, including age, gender, concomitant medications (uric acid-lowering agents, colchicine, aspirin, diuretics including furosemide, and thiazide), and comorbidities data (hypertension, diabetes mellitus, CVD, heart failure, dyslipidemia, liver cirrhosis, fatty liver, CKD, and dementia), were collected. Liver disease (as defined as liver cirrhosis or fatty liver) was diagnosed by abdominal ultrasound or abdominal computed tomography. We also collected the following biochemical laboratory data: uric acid, aspartate aminotransferase (AST), alanine aminotransferase (ALT), blood urea nitrogen (BUN), creatinine (Cr), total cholesterol, triglyceride, low-density lipoprotein (LDL) and high-density lipoprotein (HDL), at time of diagnosis. In addition, uric acid, AST, ALT, BUN, and Cr were obtained one and three months after initiating febuxostat.

#### *2.3. Definition of Hepatotoxicity*

Hepatotoxicity was defined as more than three times the upper normal limit when the baseline AST/ALT was normal, and double the baseline AST/ALT when the baseline was abnormally elevated [10].
