The most appropriate next step in treatment is to administer epinephrine. This patient's hypotension, bronchospasm, and urticaria are characteristic of a severe anaphylactic reaction. Epinephrine is the drug of choice for anaphylaxis, preferably given as an intramuscular injection because of more rapid and consistent absorption compared with subcutaneous injection. Intravenous delivery may be advantageous in patients with compromised muscle perfusion from shock. Food allergies and insect stings are important anaphylaxis triggers, while a medication is the most likely trigger in a hospitalized patient.

Although antihistamines are the most commonly prescribed drug for anaphylaxis, they do not treat the life-threatening manifestations of anaphylaxis such as bronchospasm and hypotension. It is also likely that epinephrine, rather than antihistamines, is the agent responsible for the resolution of urticaria in these patients.

In patients taking β-blocker therapy, glucagon may be an effective treatment for hypotension and bradycardia that is resistant to epinephrine. The inotropic and chronotropic effects of glucagon are not mediated through β-receptors. However, glucagon is a second-line treatment for anaphylaxis, even in patients taking β-blockers.

Methylprednisolone is an adjunctive therapy to prevent delayed or protracted reactions in patients with anaphylaxis. However, the drug takes several hours to take effect and therefore is not useful for rapidly reversing the life-threatening manifestations of anaphylaxis. A recent systematic review did not discover any randomized controlled trials that confirmed the effectiveness of glucocorticoids in the treatment of anaphylaxis.