Epinephrine is the only effective treatment for anaphylaxis

There is no substitute for epinephrine, which is the only first-line treatment for anaphylaxis. Neither antihistamines nor glucocorticoids work as quickly as epinephrine, and neither can effectively treat the severe symptoms associated with anaphylaxis.

However, antihistamines such as diphenhydramine (Benadryl) or cetirizine (Zyrtec), glucocorticoids like prednisone, or a combination, may be used in addition to epinephrine in some cases of anaphylaxis, after epinephrine is administered.

Antihistamines can relieve some symptoms of a mild (non-anaphylactic) allergic reaction, such as hives, itching or flushing, usually within an hour or two after they are given. Glucocorticoids take even longer to have an effect, so they are not useful for the treatment of any acute symptoms.

As noted in anaphylaxis practice guidelines published in the Journal of Allergy and Clinical Immunology, neither antihistamines nor glucocorticoids have been shown effective in preventing biphasic anaphylaxis, so they should not be given routinely after immediate allergy symptoms have resolved. However, some patients may benefit from a short course of glucocorticoids, for example if they had severe facial swelling or asthma symptoms related to their anaphylactic reaction.

How to prevent future anaphylactic reactions

Anyone who has had anaphylaxis is at increased risk of experiencing anaphylaxis again. Unless there is minimal risk of re-exposure to the allergen, you should carry an epinephrine autoinjector with you at all times. In addition, you should see an allergist for further evaluation and management, especially if there is any doubt about what triggered your anaphylaxis or whether you may have other allergic triggers. Finally, do your best to completely avoid your allergic trigger, as even small amounts can cause a severe allergic reaction.

(Parul Kothari, M.D., is a contributor to Harvard Heart Publications.)