No. This is one of the most important things I tell every parent of a child with a severe food allergy at Pratiksha Rainbow Children's Hospital, Guwahati, and I want to be direct about it because the mistake of reaching for an antihistamine instead of an adrenaline auto-injector in anaphylaxis costs lives. Antihistamines are effective medicines for mild allergic reactions. They block histamine, one of the chemicals released by mast cells during an allergic reaction, and they relieve the symptoms that histamine drives: hives, runny nose, itching, and mild swelling. In a mild reaction that stays contained to the skin or nasal passages, antihistamines are the right treatment. In anaphylaxis, they are the wrong treatment, and the delay caused by giving an antihistamine first while anaphylaxis progresses can be fatal. The reason is pharmacological. Anaphylaxis is not driven by histamine alone. During anaphylaxis, mast cells and basophils release a cascade of mediators that includes leukotrienes, prostaglandins, platelet-activating factor, and cytokines, none of which are blocked by antihistamines. These mediators cause the airway to swell and the circulation to collapse simultaneously. An antihistamine does not open a swelling airway. An antihistamine does not raise blood pressure in circulatory collapse. And even for the histamine component, antihistamines take thirty to sixty minutes to reach their peak effect, which is far too slow to prevent the airway closure or cardiovascular collapse of severe anaphylaxis. Adrenaline, given by intramuscular injection, acts within two to three minutes. It constricts the blood vessels and raises blood pressure, relaxes the airway smooth muscle, reduces airway swelling, and inhibits further mediator release. Nothing else does all of this simultaneously. Antihistamines have a role in anaphylaxis management, but only as an adjunct after adrenaline has been given, never as a replacement for it.
Written by Dr. Nayan Mani Deka, MBBS, MD (Paediatrics), Diploma in Allergy and Asthma (CMC Vellore), Certified PALS, APLS, NSSK, Consultant Paediatrician, Asthma Allergy Specialist and Immunotherapist, Pratiksha Rainbow Children's Hospital, VIP Road, Borbari, Guwahati, Assam 781036. Phone: +91 9436732863 / +91 6000714825 / +91 8812866239.
Related reading
Anaphylaxis in Children: How to Recognise It and What to Do in the First Five Minutes
Pediatric Allergy: Focus on Food Allergy and Anaphylaxis
