Extracted variables included gender, age, race/ethnicity, year of treatment initiation, self-reported alcohol consumption, self-reported history of preexisting liver disease, and serum AST levels at baseline and follow-up at 1 month, 3 months, and 6 months. Age was categorized as 25 to 34 years, 35 to 49 years, and ≥ 50 years. Race/ethnicity was categorized as African American, white, Hispanic, Asian, and unknown. Preexisting liver disease was categorized as hepatitis (A, B, or C), cirrhosis, and other (including neonatal jaundice), trauma (gunshot wound or motor vehicle accident), alcoholism, thrombosis, jaundice, gallstones, and unknown etiology. Alcohol consumption was categorized as none, the equivalent of 1 to 7 drinks (a glass of wine, can of beer, or mixed drink) per week, 8 to 14 drinks per week, and ≥ 15 drinks per week. When alcohol consumption was unavailable, the age/gender/race median consumption was assigned; for all subclasses, this imputed value was none. Sensitivity analysis indicated that results were essentially unchanged when subjects whose alcohol consumption was unavailable were excluded. If baseline AST levels were missing, and follow-up values were recorded, the baseline AST level was assumed to be less than the ULN. If more than one value for serum AST was available for a follow-up visit, the largest value was retained for analysis.