A 19-year-old man is brought to hospital 90 minutes after swallowing approximately 60 g of paracetamol. He is drowsy, sweaty and vomiting. Arterial blood gas analysis shows pH 7.08, lactate 12 mmol/L (0.5–2.2 mmol/L) and an anion gap of 29 mmol/L; the initial paracetamol concentration is 950 mg/L. Which one of the following is the most appropriate additional treatment, while intravenous N-acetylcysteine is continued?