What You Need to Know About Biphasic Anaphylaxis

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If you’re an allergy parent (or the friend or family member of someone with severe allergies), you know all about the fear of an anaphylactic reaction.

The racing heart and the difficulty breathing. The tightening of the throat. The itching, swelling, and vomiting. How important it is to have epinephrine with the person at all times.

But have you heard of biphasic anaphylaxis? It’s when a person appears to recover from anaphylaxis and everyone is finally starting to relax, but then they have a second reaction … without being exposed to the allergen again.

biphasic anaphylaxis

Experts say biphasic reactions happen more often than we’d like to believe — possibly involving 15 per cent of children with severe allergic reactions. Sometimes the second reaction is more mild than the first, but other times it’s life-threatening.

After an anaphylactic reaction, a patient is usually under observation at the hospital for 4-6 hours. In a study conducted by the Children’s Hospital of Eastern Ontario, 75 percent of the biphasic reactions occured within six hours of the original reaction.

But biphasic anaphylaxis can also strike long after the initial reaction. Patients have reported a second reaction 10 hours, 26 hours, 40 hours, and even 72 hours after their initial reaction. What if the patient used up all of their auto-injectors during the first reaction, and the second reaction hits before they’ve trekked to the pharmacy for refills?

Some people are more likely to experience biphasic anaphylaxis than others:

  • Children aged 6-9
  • Those who were delayed in getting initial treatment
  • Those who needed more than a single dose of epinephrine during the first reaction
  • Those who have a more severe, life-threatening first reaction
  • Those who take longer to stabilize during the first reaction

The best way to prepare for the possibility of biphasic anaphylaxis is by carefully monitoring your child after an anaphylactic reaction, and making sure you have more epinephrine ready in case of a second reaction.

H/T AllergyHome.org

Heather Laura Clarke, a contributing writer at Scratch or Sniff, lives in Nova Scotia, Canada, with her high-school sweetheart husband, seven-year-old son, and five-year-old daughter. She writes for newspapers and magazines across Canada and the U.S., and blogs about her family life at Heather's Handmade Life. Follow her adventures on Twitter or Instagram.

2 Comments to What You Need to Know About Biphasic Anaphylaxis

  1. Thanks for the post, my son has developed a tree nut allergy and I am trying to understand how all of this works. He had contact with some Nutella on a picnic table and had a reaction. I thought we were going to have to use the EpiPen but I think some of his reaction afterwards was anxiety. I had no idea about a possible second reaction! Thanks for arming me with this information.

    • I didn’t know about second reactions either, Michelle, until a Scratch or Sniff writer mentioned them last week. It’s crazy! I think a lot of parents would relax after the first reaction was under control, and a second would completely catch them off guard. Scary stuff.

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