Final answer:
The nurse should immediately administer epinephrine intramuscularly (IM) to a patient presenting with symptoms of anaphylaxis due to a peanut allergy. Epinephrine is essential for rapidly counteracting the severe allergic response, and is the first line of treatment in such emergencies.
Step-by-step explanation:
The nurse should administer epinephrine intramuscularly (IM) first when a patient presents with symptoms of anaphylaxis due to a suspected peanut allergy. Anaphylaxis is a severe allergic reaction that can rapidly become life-threatening, characterized by respiratory distress, a drop in blood pressure, and potential shock.
Epinephrine works swiftly to constrict blood vessels, which increases blood pressure, and it relaxes bronchial smooth muscle to improve breathing. It can also modulate heart rate and reduce airway swelling. Patients with known severe allergies often carry epinephrine auto-injectors, such as EpiPens®, to treat unexpected anaphylactic episodes immediately. In the clinical setting of an ED, the prompt administration of epinephrine is critical for stabilizing the patient's condition.
Antihistamines and corticosteroids are secondary treatments that may be used after the initial administration of epinephrine to manage further immune response and inflammation, although their immediate effectiveness in treating anaphylaxis is less than that of epinephrine.