Which medication is commonly used for severe allergic reactions or anaphylaxis?

Epinephrine is the medication of choice for severe allergic reactions or anaphylaxis because it acts quickly to counteract the life-threatening symptoms associated with anaphylaxis. When administered, epinephrine works by stimulating alpha and beta-adrenergic receptors. This results in several key effects: it causes vasoconstriction, which increases blood pressure; it relaxes bronchial smooth muscle, leading to improved airflow and reduced wheezing or stridor; and it decreases the release of additional mediators from mast cells and basophils, which contribute to the allergic response.

In anaphylaxis, where rapid response is crucial, epinephrine is typically delivered via an intramuscular injection, often in the thigh. Its fast action makes it essential in emergency situations where the airway may be compromised or a patient is in shock due to low blood pressure. Other options, while they may have their uses in allergic reactions, do not provide the rapid reversal of the symptoms seen with epinephrine. For example, antihistamines like Benadryl can help alleviate some symptoms of allergic reactions but do not address the immediate and severe complications of anaphylaxis, such as airway compromise or severe hypotension.