Final answer:
In the event of an anaphylactic reaction, the correct medicine to administer is epinephrine. It acts quickly to mitigate severe symptoms, and following that, antihistamines may be used to manage symptoms.
Step-by-step explanation:
The medicine you should use when someone is having an anaphylactic reaction is epinephrine. This drug is specifically designed to counteract the effects of an anaphylactic reaction, which is a severe and potentially life-threatening allergic reaction. Anaphylaxis can cause a dramatic drop in blood pressure, shortness of breath, and swelling of the tongue and throat. In such cases, the immediate use of an epinephrine autoinjector, commonly referred to by its brand name, EpiPen®, can save a person's life by constricting blood vessels to increase blood pressure, relaxing smooth muscles in the lungs to improve breathing, and reducing airway swelling.
After the initial emergency treatment with epinephrine, patients may receive antihistamines and corticosteroids to manage ongoing symptoms and prevent late-phase reactions. However, it is essential to understand that antihistamines are used for milder allergy symptoms and are not sufficient as a first-line treatment for an anaphylactic reaction. The primary focus in an anaphylactic emergency must be on administering epinephrine as soon as possible.