Which medication is often used to treat anaphylaxis in a patient?

Epinephrine is the first-line treatment for anaphylaxis, a severe and potentially life-threatening allergic reaction. It works by rapidly reversing the symptoms of anaphylaxis through multiple mechanisms. By stimulating both alpha and beta-adrenergic receptors, epinephrine causes vasoconstriction, which helps to increase blood pressure in patients experiencing hypotension, and bronchodilation, which alleviates respiratory distress due to bronchospasm. Additionally, it reduces vascular permeability, which can help decrease edema and hives.

Other medications listed serve different roles. Antihistamines can help to alleviate some allergic symptoms, but they do not provide the fast-acting treatment necessary for anaphylaxis. While oxygen therapy is crucial in managing respiratory distress, it is not a primary treatment for the anaphylactic reaction itself. Beta-blockers can actually exacerbate the symptoms of anaphylaxis and complicate the treatment, making them an inappropriate choice in this emergency situation. Thus, epinephrine is the critical medication that should be used immediately in cases of anaphylaxis.