An 18-year-old woman develops uicaria and wheezing after an injection of intravenous contrast for an abdominal CT scan. Her blood pressure is 120/60 mm Hg, hea rate is 155 beats per minute, and respiratory rate is 30 breaths per minute. Which of the following is the most appropriate immediate therapy?

This patient is having an anaphylactoid reaction with destabilization of the cardiovascular and respiratory systems. Anaphylactoid reactions are most commonly caused by iodinated contrast media, b-lactam antibiotics (eg, penicillin), and Hymenoptera stings. Manifestations of anaphylactoid reactions include both lethal (bronchospasm, laryngospasm, hypotension, dysrhythmia) and nonlethal (pruritus, uicaria, syncope, weakness, seizure) phenomena. Epinephrine is the initial treatment for laryngeal obstruction and bronchospasm, followed by histamine antagonists (H1 and H2 blockers), amino-phylline, and hydrocoisone. Vasopressors and fluid challenges may be given for shock. Conscious patients are usually stabilized with injected or inhaled epinephrine, while unconscious patients and those with refractory hypotension or hypoxia should be intubated.