Toxicology USMLE Step 1 Practice Question

A 23-year-old woman is brought to the emergency department 8 hours after ingesting approximately 30 tablets of acetaminophen 500 mg during an argument with her partner. She reports nausea, vomiting, and mild right upper quadrant discomfort but has no jaundice or altered mental status. Her temperature is 37.1°C, blood pressure is 118/74 mmHg, pulse is 98/min, and respirations are 16/min. Physical examination reveals mild epigastric tenderness without hepatomegaly or asterixis. Laboratory studies show AST 42 U/L, ALT 38 U/L, INR 1.1, serum creatinine 0.9 mg/dL, and a serum acetaminophen concentration that, when plotted on the Rumack-Matthew nomogram, falls above the treatment line in the toxic range. Which of the following is the best next step in management?