A 66-year-old woman with a history of chronic alcohol abuse has had headaches and nausea for the past 4 days. She has become increasingly obtunded. On physical examination, she has right upper quadrant tenderness, tachycardia, tachypnea, and hypotension. Laboratory studies show serum AST of 475 U/L, ALT of 509 U/L, alkaline phosphatase of 23 U/L, total bilirubin of 0.9 mg/dL, albumin of 3.8 g/dL, and total protein of 6.1 g/dL. She is treated with N-acetylcysteine. Which of the following drugs has she most likely ingested in excess?