A 24-year-old woman presents to the emergency department 20 minutes after being stung by a bee. She is flushed, complaining of throat tightness and dizziness. On examination, she is hypotensive at 82/52 mmHg, tachycardic at 120 beats/min and has widespread urticaria with wheeze. You diagnose anaphylaxis. According to Australian anaphylaxis guidelines, what is the most appropriate initial drug treatment?