A 45-year-old man is having periodontal flap surgery. He has had articaine LA, the team wear nitrile gloves, and the pockets were irrigated with chlorhexidine 0.2 percent. Within 5 minutes he develops flushing, wheeze and a blood pressure of 75/40 mmHg. He has had uneventful articaine injections many times before. Which agent is the most likely trigger?