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Medical Allergic reaction question

  1. Feb 7, 2008 #1
    Is it true that you can only have an allergic reaction to something AFTER the initial exposure?

    For example, the very first time you get exposed to something you could be allergic to, it will do nothing?
     
  2. jcsd
  3. Feb 7, 2008 #2

    Tsu

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    I'm not absolutely sure, I don't believe that that is true. It's a possibility - but not a given. In my job as a Cat Scan Tech., we administer a liquid to patients commonly called 'xray dye'. It is clear liquid that contains iodine and about one in 90,000 people (who have never had the injection) can have a severe anaphylactic reaction to it and most of their body systems shut down immediately. Or they can have numerous exams utilizing this liquid and have absolutley no reaction to it, and then, one day - out of the blue - they have a major reaction to it when administered - even though they've had it before with no problems. Allegric reactions are often random occurances.
     
  4. Feb 8, 2008 #3
    Tus is right, it can be the first time, or the 100th time.
     
  5. Feb 8, 2008 #4

    Moonbear

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    Usually, a first exposure doesn't induce a reaction, or it's only a very mild reaction. A full blown allergic reaction requires a previous exposure. In Tsu's example, one cannot rule out the individual ingredients. For example, x-ray dyes contain commonly used preservatives. Someone may have developed a sensitivity due to previous exposure to the preservative, for example in their cosmetics or detergents.

    The sensitizing agent may not need to be the exact one that someone reacts to either. For example, if someone is allergic to one antibiotic, it is likely they will be allergic to others in the same class.
     
  6. Feb 8, 2008 #5
    I myself, was stung by a hornet when I was 8, and went into a anaphylactoid reaction, An anaphylactoid reaction produces a very similar clinical syndrome but is not immune-mediated. Anaphylactoid and Anaphylaxis are both treated the same way.
    Some drugs and foods ( morphine,shellfish) may cause an anaphylactoid reaction on the first exposure.
    I would think for the majority of the population, it is the act of being sensitized a few times before a allergic reaction occurs. But if either signs of anaphylactoid and anaphylaxis become known, seek help at once.

    A small study from American Academy of Pediatrics
    http://pediatrics.aappublications.org/cgi/content/full/102/1/e6
    Initial reactions usually occurred at home (median age, 24 months for PeaNut and 62 months for Tree, nut) and were considered to result from a first exposure in 72% of cases.
     
    Last edited: Feb 8, 2008
  7. Feb 8, 2008 #6

    Moonbear

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    Here's something else that discusses that, and by chance, they even happen to mention radiologic dyes (x-ray dye) as causative of anaphylactoid reactions.

    http://www.postgradmed.com/issues/2002/05_02/rusznak.htm

    Hmm...this one mentions radiologic contrast dyes too...and some contraindications for their use; Tsu, if you weren't already aware of these, it might be worth looking into further.

    http://www.hon.ch/Library/Theme/Allergy/Glossary/anaphylactoid_reaction.html
     
  8. Feb 8, 2008 #7

    Tsu

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    Thanks MB!!

    Yes, we are all VERY aware of the contraindications for contrast media injections. I just HATE it when my patients try to code out on me!! :biggrin: Actually the crustacean/mussels part is no longer valid. That used to be a red flag when we used the ionic contrasts, but these days it's a moot point. We are more concerned now with renal function and other underlying diseases; diabetes, heart problems (on beta-blockers - as the article mentioned), multiple myeloma... We have a HUGE list of things on our questionaires.
     
  9. Feb 8, 2008 #8

    Moonbear

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    How dare they! :grumpy:
    Thanks for the clarification.

    Oh, and I didn't catch before...hypatia said that anaphylactoid reactions are NOT immune-mediated. They are, but are not allergic reactions...i.e., they are not IgE mediated...at least that seems to be the distinction from what I've gathered in some quick reading, such as from the links above. I had come across some assorted other case reports where they were calling such reactions anaphylactic reactions upon first exposures to some drugs, but within the description of the follow-up testing, those patients did not have any IgE response (which had me baffled until hypatia mentioned the anaphylactoid reactions and I dug into them), so it seems to be a commonly confused term, even within the literature and among medical practitioners. I guess in a clinical setting, since both respond to the same treatment, the nuances of mechanism aren't important, though to an allergist they might be.
     
  10. Feb 8, 2008 #9
    Where have you found that they ARE immune-mediated?

    http://www.anaesthesiajournal.co.uk/article/PIIS147202990700152X/abstract

    3}Anaphylactoid reactions occur through a direct nonimmune-mediated release of mediators from mast cells and/or basophils or result from direct complement activation, but they present with clinical symptoms similar to those of anaphylaxis.
     
    Last edited: Feb 8, 2008
  11. Feb 8, 2008 #10

    Tsu

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    I KNOW!!! Can you believe that!?!? It just wrecks my whole day!!! :grumpy:


    This may help clear up the differences between "anaphylactoid" and "anaphylatic". The uses of either may have been what caused the confusion in the first place, but I think it addresses the OP question best. It's from the drug company Merck from this page:

    http://www.merck.com/mmhe/sec16/ch185/ch185e.html


     
  12. Feb 8, 2008 #11

    Moonbear

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    Here's one example (well, 2 examples, but same author):
    http://www.ncbi.nlm.nih.gov/pubmed/...ez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

    and

    http://www.ncbi.nlm.nih.gov/pubmed/...ez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

    There are some articles by other authors that support this too, basically distinguishing anaphylactic from anaphylactoid by the presence or absence of IgE involvement, but I'm not sure what I can quote of them (they have further restrictions than the usual journals in our library subscription).
     
  13. Feb 9, 2008 #12
    opps posted in wrong thread!
     
    Last edited: Feb 9, 2008
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