The drug of choice for an immediate anaphylactic reaction is which of the following?

• A. Diphenhydramine
• B. Albuterol
• C. Epinephrine
• D. Hydrocortisone

Answer: (C)

In an immediate anaphylactic reaction, the most critical treatment is epinephrine because it acts rapidly on multiple body systems to reverse the life-threatening changes. Epinephrine constricts swollen blood vessels (alpha-1), which reduces airway and tissue edema and raises blood pressure, and it also stimulates the heart (beta-1) to improve perfusion. At the same time, it relaxes bronchial smooth muscle (beta-2), relieving bronchospasm, and it dampens the ongoing release of mediators from mast cells. This combination stops the progression of airway compromise and shock much more effectively and quickly than other drugs.

Antihistamines like diphenhydramine may help with itching or hives but they don’t reverse airway swelling or hypotension fast enough. A bronchodilator such as albuterol can help if bronchospasm is present, but it doesn’t address the vascular collapse or the underlying mediator release. Corticosteroids like hydrocortisone take hours to have an effect and are not useful for the immediate reversal of symptoms.

Administer epinephrine promptly by intramuscular injection (mid-outer thigh). Typical adult dose is 0.3 to 0.5 mg of 1:1000 solution; for children, 0.01 mg/kg up to 0.3 mg per dose, repeating every 5–15 minutes as needed while monitoring the patient. Seek emergency care if symptoms persist or recur.