A 27 year old woman presents with a widespread itchy erythematous rash and swelling of her lips and tongue 10 minutes after eating peanuts. She is breathless, speaking only in single words, with a respiratory rate of 30 breaths per minute and oxygen saturation 90 percent on air. There is an audible expiratory wheeze and her pulse is 120 beats per minute. Blood pressure is 80 over 50 mmHg. What is the single most appropriate immediate management step?