Acute Careniche
A 19-year-old woman is brought to the emergency department by her flatmate two hours after swallowing a handful of paracetamol tablets following an argument. She is alert and tearful, and can say only that the box was nearly full. She weighs 55 kg and her observations are normal. The tablets were dispensed to her on a prescription last month; the partly emptied pack and its pharmacy label are in her bag. Her flatmate was at work all day and found her at home this evening. Which one of the following will most reliably establish the largest dose she could have taken?