Final answer:
Epinephrine should be administered instantly when an anaphylactic reaction occurs to counteract severe allergic reactions and can be delivered using auto-injectors like EpiPens®.
Step-by-step explanation:
Epinephrine, also known as adrenaline, should be administered quickly in the event of anaphylaxis, which is a severe allergic reaction that can be potentially fatal due to a drop in blood pressure and contractions of bronchial smooth muscle. Patients are commonly prescribed auto-injectable epinephrine devices like EpiPens®, which are designed to be used immediately upon exposure to an allergen, such as insect stings or foods like shellfish and peanuts. The correct timeframe for administering epinephrine via an auto-injector like the EpiPen® is instantly after confirmation of an anaphylactic reaction, to counteract the effects before seeking further medical treatment. The use of antihistamines and corticosteroids may follow for several days to prevent late-phase reactions, although their efficacy in this use is based on theoretical considerations and not well studied.