A 38-year-old woman with no significant past medical history is brought to the hospital 6 hours after ingesting an unknown quantity of acetaminophen in a suicide attempt. She is alert and oriented, with normal vital signs. Physical examination is unremarkable. Liver function tests show AST 80 U/L, ALT 95 U/L, bilirubin 0.9 mg/dL, and INR 1.1. Serum acetaminophen level is 85 µg/mL (toxic range at 6 hours). You suspect acute hepatocellular injury from acetaminophen toxicity. At this stage (6 hours post-ingestion), the hepatocytes are still in the reversible phase of injury. What is the most appropriate immediate next step in management?