In cases of severe allergic reactions, what should be administered immediately if available?

In cases of severe allergic reactions, the immediate administration of epinephrine is critical due to its rapid ability to counteract the life-threatening symptoms of anaphylaxis. Epinephrine works by causing vasoconstriction, which increases blood pressure, and bronchodilation, which improves breathing by relaxing the muscles around the airways. It can quickly reverse symptoms such as swelling, hives, and difficulty breathing, making it essential in emergencies.

While corticosteroids are important in managing allergic reactions over the long term, they do not act swiftly enough to address the acute symptoms of anaphylaxis. Oxygen therapy can be beneficial, especially if the individual is experiencing respiratory distress, but it does not treat the underlying allergic reaction. Similarly, ephedrine can provide relief for some types of allergic reactions but is not the preferred immediate treatment for anaphylaxis. Hence, the use of epinephrine via an EpiPen is the most appropriate and effective response during such emergencies.