A 32-year-old man is rescued from a burning warehouse. He is confused, hypotensive and tachypnoeic, with soot on his face but no wheeze. His pulse oximeter reads 100% while receiving oxygen, and there is no obvious external bleeding. Venous blood gas analysis shows a lactate concentration of 14 mmol/L (reference range 0.5–2.2 mmol/L). Which one of the following is the most appropriate antidotal treatment?