Xolair, IgE, and the Acute Allergic Response


In my last post, I touched on improvements in treating the severest pediatric asthmatics.  One thing I noticed in reviewing the info for the post was that 10% of the current study patients were on a medication called Xolair.  Xolair, or omalizumab, is a new class of medication that blocks the acute allergic response from occurring.  It is only indicated for use in a very few people: severe asthmatics with allergies and an elevated IgE level.  This is a little complicated, so some background is helpful.

How Xolair works, image courtesy of NEJM

How Xolair works, image courtesy of NEJM

IgE is an antibody.  Antibodies are proteins the immune system makes to help fight off infections.  There are three other main antibodies besides IgE: IgG, IgA, and IgM.  IgE is the allergy antibody.  In the cartoon above, it is represented by the blue Y-shaped figures.  One end of IgE binds to allergens like ragweed pollen or cat dander and the other end binds to cells like the mast cell;.  When two IgE molecules bound to a mast cell also bind to the same allergen they crosslink.  Crosslinking is the signals the mast cell to go to work, which it does by essentially exploding and releasing all kinds of nasty chemicals that make you sneeze, wheeze, and get hives.

Omalizumab is a hybridized, murine, monoclonal antibody directed at the Fc portion of human IgE.  Got it?  In English, that means that omalizumab, the red Y-shape, latches on to the end of IgE that normally touches the mast cell and prevents it from binding to the mast cell.  If IgE can’t bind to the mast cell, then it can’t crosslink and the mast cell is effectively neutralized.  It’s like taking the bullets out of a gun.

Studies looking at omalizumab use in severe asthmatics have shown reduction in medication use, improvement in symptoms, and improvement in quality of life.  In my own experience, the response has been black-and-white.  Some people have made remarkable improvements on omalizumab and some haven’t responded much at all.

Omalizumab is not a cure-all.  It is an injectable medication that has to given every 2-4 weeks.  There are some risks associated with its use as well.  Mostly, it’s incredibly expensive.  A 2007 study gives an average monthly cost of $1300.  I’m conservative about recommending it to people and in the coming healthcare environment, I’m not sure what its fate will be.  That being said, in people with frequent severe exacerbations, ED visits, and/or hospitalizations as well as those on continuous or near continuous oral corticosteroids for asthma, omalizumab can make a huge difference.  If you’re a severe asthmatic, ask your doctor about omalizumab/Xolair.

Dr. O

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