Within 5 minutes after a bee sting, a 15-year-old girl suddenly has difficulty breathing, with marked inspiratory stridor from laryngeal edema. She experiences marked urticaria and notes swelling of the hand that was stung. Which of the following is the best pharmacologic agent to treat her signs and symptoms?

Her systemic anaphylactic reaction results from an immediate type I hypersensitivity reaction with antigen triggering mast cell-bound IgE with release of preformed mediators such as histamine. Epinephrine is the fastest acting agent to treat this life-threatening condition. Cyclosporine is used to minimize lymphocyte-mediated transplant rejection. Glucocorticoids can reduce immune inflammatory reactions, although this occurs over days to weeks, not minutes. Methotrexate is useful in the treatment of graft-versus-host disease and for some malignancies. Penicillin is an antibiotic that can induce a type I hypersensitivity reaction in sensitized persons.